electrical wiring faq was a question about vac outlet wiring since electrical wiring questions do turn up from time to time on sci electronics and the answers aren t always apparent even to those skilled in electronics i am hijacking the following faq and posting a copy here i ve asked the writers to cross post to sci electronics in the future jeh cmkrnl com x news cmkrnl news answers newsgroups misc consumers house rec woodworking news answers misc answers rec answers subject electrical wiring faq message id wirefaq ecicrl from clewis ferret ocunix on ca chris lewis date apr gmt reply to wirefaq ferret ocunix on ca wiring faq commentary reception followup to poster expires may gmt organization elegant communications inc ottawa canada summary a series of questions and answers about house wiring supersedes wirefaq ecicrl lines archive name electrical wiring last modified sun feb est frequently asked questions on electrical wiring steven bellovin smb ulysses att com chris lewis clewis ferret ocunix on ca comments to automatic if you reply to this article wirefaq ferret ocunix on ca this faq is formatted as a digest most news readers can skip from one question to the next by pressing g answers to many other topics related to houses can be obtained from the misc consumers house archive send an empty piece of mail to house archive dg rtp dg com for information changes to previous issue marked with in left column watch particularly for new in the questions list for new or substantively changed answers note that this is now a registered faq cross posted to news answers and should appear in the faq list of lists subject questions answered in this faq introduction disclaimers what is the nec where can i get a copy what is the cec where can i get a copy can i do my own wiring extra pointers what do i need in the way of tools what is ul listing what is csa approval are there any cheaper easier to read books on wiring inspections how and what why should i get my wiring inspected my house doesn t meet some of these rules and regulations a word on voltages what does an electrical service look like what is a circuit grounding versus grounded versus neutral what does a fuse or breaker do what are the differences breakers can t i use fuses what size wire should i use where do these numbers come from what does mean what is a wirenut marrette marr connector how are they used what is a gfi gfci where should gfcis be used where shouldn t i use a gfci what is the difference between a gfci outlet and a gfci breaker what s the purpose of the ground prong on an outlet then why is one prong wider than the other polarization what kind of outlets do i need in a kitchen where must outlets and switches be in bathrooms what is romex nm nmd what is bx when should i use each should i use plastic or metal boxes junction box positioning can i install a replacement fixture what does it mean when the lights brighten when a motor starts what is phase power should i use it can i get it in my house is it better to run motors at or what is this nonsense about hp on v a circuits how do i convert two prong receptacles to three prong are you sure about gfcis and ungrounded outlets should the test button work how should i wire my shop underground wiring aluminum wiring i m buying a house what should i do what is this weird stuff old style wiring where do i buy stuff subject introduction disclaimers although we ve done a fair bit of wiring we are not electricians and we cannot be responsible for what you do if you re at all uncertain about what is correct or safe don t do it contact someone qualified a licensed electrician or your local electrical inspector electricity is no joke mistakes can result in shocks fires or electrocution furthermore our discussion is based on the u s national electrical code nec and the canadian electrical code cec to the best of our abilities we have confirmed every detail with the electrical code but we don t quote sections simply to keep this thing readable if you think we re wrong we invite you to correct us but please quote references the nec and the cec do not in and of themselves have the force of law many municipalities adopt it en toto others however do not check your with your local building department and provincial hydro inspection offices in canada to find out what applies in your area also your local electrical utility may also have special requirements for electrical service installation bear in mind too that we say here applies primarily to ordinary single family residences multi family dwellings mobile homes commercial establishments etc are sometimes governed by different rules also note that contrary to popular belief in the u s and in some parts of canada canada is not a wholly owned subsidiary of the u s consequently the nec does not apply in canada lots of things are the same including voltages line frequencies and the laws of physics but there are a number of crucial differences in the regulations where we can we ve noted them flagging the relevant passages with nec or cec remember that the cec and nec are minimal standards it is often smart to go beyond their minimal requirements subject what is the nec where can i get a copy the nec is a model electrical code devised and published by the national fire protection association an insurance industry group it s revised every three years the version has been released you can buy a copy at a decent bookstore or by calling them directly at the code exists in several versions there s the full text which is fairly incomprehensible there s an abridged edition which has only the sections likely to apply to most houses and there s the nec handbook which contains the authorized commentary on the code as well as the full text that s the recommended version unfortunately there s no handbook for the abridged edition and the full handbook is expensive us plus shipping and handling subject what is the cec where can i get a copy the canadian standards association is an organization made up of various government agencies power utilities insurance companies electrical manufacturers and other organizations the csa publishes csa standard c which is updated every two or three years each province adopts with some amendments this standard and publishes a province specific code book since each province publishes its own slightly modified standard it would be somewhat confusing to obtain the csa standard itself in this faq cec really means the appropriate provincial standard in particular this faq is derived from the ontario hydro electrical safety code th edition which is in turn based on csa c th edition while differences exist between the provinces an attempt has been made to avoid specific to ontario detail the appropriate provincial code can be obtained from electrical inspection offices of your provincial power authority in ontario it s ontario hydro the ontario hydro book isn t overly fat it s about c and includes mailed updates i hear that these standards are somewhat easier to read than the equivalent nec publications don t bother asking in quebec diy wiring is banned throughout the province subject can i do my own wiring extra pointers in most places homeowners are allowed to do their own wiring in some they re not check with your local electrical inspector most places won t permit you to do wiring on other s homes for money without a license nor are you permitted to do wiring in commercial buildings multiple dwellings eg duplexes are usually considered semi commercial or commercial however many jurisdictions will permit you to work on semi commercial wiring if you re supervised by a licensed electrician if you can find one willing to supervise if you do your own wiring an important point do it neat and well what you really want to aim for is a better job than an electrician will do after all it s your own home and it s you or your family that might get killed if you make a mistake an electrician has time pressures has the skills and knows the tricks of the trade to do a fast safe job in this faq we ve consciously given a few recommendations that are in excess of code because we feel that it s reasonable and will impress the inspector the inspector will know that you re an amateur you have to earn his trust the best way of doing this is to spend your time doing as neat a job as possible don t cut corners exceed specifications otherwise the inspector may get extremely picky and fault you on the slightest transgressions don t try to hide anything from the inspector use the proper tools ie don t use a bread knife to strip wires or twist wires with your fingers the inspector won t like it and the results won t be that safe and it takes longer and you re more likely to stick a hunk of ga wire through your hand that way don t handle house wire when it s very cold eg below c or f thermoplastic house wire particularly older types become very brittle subject what do i need in the way of tools first there s the obvious a hammer a drill a few screwdrivers both straight and phillips head if you re lucky enough to live in canada or find a source of csa approved devices you need robertson square recess screwdrivers and instead of phillips for drilling a few holes a or spade bit and or electric drill will do if you re doing a lot or are working with elderly lumber we recommend a drill right angle drills are wonderful can be rented and or screw point auger drill bits these bits pull you through so they re much faster and less fatiguing even in year old hardwood timbers screw driver bits are useful for drills expecially if you install your electrical boxes using screws drywall screws work well for stripping wire use a real wire stripper not a knife or ordinary wire cutters don t buy the k mart combo stripper crimper and bottle opener types you should expect to pay to for a good plier type pair it will have sized stripping holes and won t nick or grab the wire it should be easy to strip wire with it one model has a small hole in the blade for forming exact wire loops for screw terminals there are fancier types autostrip cut but they generally aren t necessary and pros usually don t use them a pair of diagonal side cutter pliers are useful for clipping ends in constricted places don t use these for stripping wire you will need linesman pliers for twisting wires for wire nuts you should have a pair of needle nose pliers for fiddling inside boxes and closing loops but it s better to form wire loops with a loop former hole on your wire stripper more accurate if you re using non metallic cable get a cable stripper for removing the sheath or do what some pros do they nick the end of the sheath grab the ground wire with a pair of pliers and simply rip the sheath back using the ground wire as a zipper and cut the sheath off you shouldn t try to strip the sheath with a knife point because it s too easy to slash the insulation on the conductors apparently stanley utility knives fitted with linoleum cutters hooked blades can be used to strip sheath but there is still the possibility that you ll gouge the conductors for any substantial amount of work with armored cable it s well worth your while to invest in a rotary cable splitter us hack saws are tricky to use without cutting into the wire or the insulation three prong outlet testers are a quick check for properly wired outlets about multimeters tell you more but are a lot more expensive and probably not worth it for most people a simple voltage sensor which can detect potential through an insulated wire not supplying any devices is extremely helpful they cost about us at radio shack you should have a voltage detector to check that the wires are dead before doing work on them neon bulb version are cheap and work well if you get more serious a audible alarm type is good for tracing circuits without a helper though i ve been known to lock the drill on and hit breakers until the scream stops for running wires through existing walls you need fish tape often two tapes are needed though sometimes a bent hanger or a length of thin chain will suffice fish tapes can be rented electrical tape lots of it seriously a good and competent wiring job will need very little tape the tape is useful for wrapping dicy insulation in repair work another use is to wrap around the body of outlets and switches to cover the termination screws i don t do this but drywall contractors prefer it to prevent explosions when the drywall knife collides with a live outlet that has no cover plate subject what is ul listing the ul stands for underwriters laboratory it used to be an insurance industry organization but now it is independent and non profit it tests electrical components and equipment for potential hazards when something is ul listed that means that the ul has tested the device and it meets their requirements for safety ie fire or shock hazard it doesn t necessarily mean that the device actually does what it s supposed to just that it probably won t kill you the ul does not have power of law in the u s you are permitted to buy and install non ul listed devices however insurance policies sometimes have clauses in them that will limit their liability in case of a claim made in response to the failure of a non ul listed device furthermore in many situations the nec will require that a wiring component used for a specific purpose is ul listed for that purpose indirectly this means that certain parts of your wiring must be ul listed before an inspector will approve it and or occupancy permits issued subject what is csa approval every electrical device or component must be certified by the canadian standards association before it can be sold in canada implicit in this is that all wiring must be done with csa approved materials they perform testing similar to the ul a bit more stringent except that csa approval is required by law again like the ul if a fire was caused by non csa approved equipment your insurance company may not have to pay the claim in canada there is a branch organization of the ul called ulc ul of canada ulc does not have power of law and seems to be more a liason group between the csa and insurance companies subject are there any cheaper easier to read books on wiring usa the following three books were suggested by our readers residential wiring by jeff markell craftsman books carlsbad ca for isbn practical electrical wiring residential farm and industrial based on the national electrical code ansi nfpa herbert p richter and w creighton schwan mcgraw hill book co wiring simplified h p richter and w c schwan park publishing co try to make sure that the book is based on the latest nec revision which is currently canada p s knight authors and publishes a book called electrical code simplified there appears to be a version published specific to each province and is very tied into the appropriate provincial code it focuses on residential wiring and is indispensible for canadian diy ers it is better to get this book than the cec unless you do a lot of wiring or answer questions on the net it is updated each time the provincial codes are this book is available at all diy and hardware stores for less than c subject inspections how and what why should i get my wiring inspected most jurisdictions require that you obtain a permit and inspections of any wiring that is done amongst other more mundane bureaucratic reasons like insurance companies not liking to have to pay claims a permit and inspections provides some assurance that you your family your neighbors or subsequent owners of your home don t get killed or lose their homes one night due to a sloppy wiring job most jurisdictions have the power to order you to vacate your home or order you to tear out any wiring done without a permit california for instance is particularly nasty about this if fire starts in your home and un inspected wiring is at fault insurance companies will often refuse to pay the damage claims in general the process goes like this you apply to your local inspections office or building department for a permit you should have a sketch or detailed drawing of what you plan on doing this is a good time to ask questions on any things you re not sure of if you re doing major work they may impose special conditions on you require loading calculations and ask other questions at this point they will tell you which inspections you will need if you re installing a main panel you will need to have the panel and service connections inspected before your power utility will provide a connection this is sometimes done by the local power authority rather than the usual inspectors after installing the boxes and wiring but before the insulation walls go up you will need a rough in inspection after the walls are up and the wiring is complete you will need a final inspection subject my house doesn t meet some of these rules and regulations do i have to upgrade in general there is no requirement to upgrade older dwellings though there are some exceptions ie smoke detectors in some cases however any new work must be done according to the latest electrical code also if you do major work you may be required to upgrade certain existing portions or all of your system check with your local electrical inspector subject a word on voltages one thing where things might get a bit confusing is the different numbers people bandy about for the voltage of a circuit one person might talk about v another v or another v these are all in fact exactly the same thing in north america the utility companies are required to supply a split phase volt feed to your house this works out as two v legs additionally since there are resistive voltage drops in the house wiring it s not unreasonable to find v has dropped to v or v has dropped to v by the time the power reaches a wall outlet especially at the end of an extension cord or long circuit run for a number of reasons some historical some simple personal orneryness different people choose call them by slightly different numbers this faq has chosen to be consistent with calling them v and v except when actually saying what the measured voltage will be confusing a bit just ignore it one thing that might make this a little more understandable is that the nameplates on equipment ofen show the lower ie v instead of v value what this implies is that the device is designed to operate properly when the voltage drops that low v is not the same as v v is the voltage between phases of a phase y circuit that is v from neutral to any hot v is the voltage between phases of a phase y circuit that s v from hot to neutral in keeping with v versus v strangeness motors intended to run on v three phase are often labelled as v subject what does an electrical service look like there are logically four wires involved with supplying the main panel with power three of them will come from the utility pole and a fourth bare wire comes from elsewhere the bare wire is connected to one or more long metal bars pounded into the ground or to a wire buried in the foundation or sometimes to the water supply pipe has to be metal continuous to where the main water pipe entering the house watch out for galvanic action conductivity breaks often between copper and iron pipe this is the grounding conductor it is there to make sure that the third prong on your outlets is connected to ground this wire normally carries no current one of the other wires will be white or black with white or yellow stripes or sometimes simply black it is the neutral wire it is connected to the centre tap cec center tap in the nec of the distribution transformer supplying the power it is connected to the grounding conductor in only one place often inside the panel the neutral and ground should not be connected anywhere else otherwise weird and or dangerous things may happen furthermore there should only be one grounding system in a home some codes require more than one grounding electrode these will be connected together or connected to the neutral at a common point still one grounding system adding additional grounding electrodes connected to other portions of the house wiring is unsafe and contrary to code if you add a subpanel the ground and neutral are usually brought as separate conductors from the main panel and are not connected together in the subpanel ie still only one neutral ground connection however in some situations certain categories of separate buildings you actually do have to provide a second grounding electrode consult your inspector the other two wires will usually be black and are the hot wires they are attached to the distribution transformer as well the two black wires are degrees out of phase with each other this means if you connect something to both hot wires the voltage will be volts if you connect something to the white and either of the two blacks you will get v some panels seem to only have three wires coming into them this is either because the neutral and ground are connected together at a different point eg the meter or pole and one wire is doing dual duty as both neutral and ground or in some rare occasions the service has only one hot wire v only service subject what is a circuit inside the panel connections are made to the incoming wires these connections are then used to supply power to selected portions of the home there are three different combinations one hot one neutral and ground v circuit two hots no neutral and ground v circuit two hots neutral and ground v circuit neutral and or two v circuits with a common neutral is used for most circuits supplying receptacles and lighting within your house is usually used for supplying power to major appliances such as stoves and dryers they often have need for both v and v or for bringing several circuits from the panel box to a distribution point is usually for special v motor circuits electric heaters or air conditioners note in the us the nec frequently permits a circuit similar to be used for stoves and dryers namely that there are two hot wires and a wire that does dual duty as neutral and ground and is connected to the frame as well as providing the neutral for v purposes three prong plugs instead of four only for stoves dryers connected to the main panel when connected to most sub panels prong plugs and receptacles are required in our not so humble opinion this is crazy but the nfpa claims that this practice was re evaluated for the nec and found to be safe check your local codes or inquire as to local practice there are restrictions on when this is permissible is usually wired with three conductor wire black for hot white for neutral and bare for grounding and have one hot wire coloured red the other black a bare wire for grounding and in a white wire for neutral you will sometimes see wired with just a black white and ground wire since the white is hot in this case both the nec and cec requires that the white wire be permanently marked at the ends to indicate that it is a live wire usually done with paint nail polish or sometimes electrical tape each circuit is attached to the main wires coming into the panel through a circuit breaker or fuse there are in a few locales circuits that look like or except that they have two bare ground wires some places require this for hot tubs and the like one ground is frame ground the other attaches to the motor this may or may not be an alternative to gfci protection subject grounding versus grounded versus neutral according to the terminology in the cec and nec the grounding conductor is for the safety ground i e the green or bare wire the word neutral is reserved for the white when you have a circuit with more than one hot wire since the white wire is connected to neutral and the grounding conductor inside the panel the proper term is grounded conductor however the potential confusion between grounded conductor and grounding conductor can lead to potentially lethal mistakes you should never use the bare wire as a grounded conductor or white wire as the grounding conductor even though they are connected together in the panel but not in subpanels subpanels are fed neutral and ground separately from the main panel usually in the trade and in common usage the word neutral is used for grounded conductor this faq uses neutral simply to avoid potential confusion we recommend that you use neutral too thus the white wire is always except in some light switch applications neutral not ground subject what does a fuse or breaker do what are the differences fuses and circuit breakers are designed to interrupt the power to a circuit when the current flow exceeds safe levels for example if your toaster shorts out a fuse or breaker should trip protecting the wiring in the walls from melting as such fuses and breakers are primarily intended to protect the wiring ul or csa approval supposedly indicates that the equipment itself won t cause a fire fuses contain a narrow strip of metal which is designed to melt safely when the current exceeds the rated value thereby interrupting the power to the circuit fuses trip relatively fast which can sometimes be a problem with motors which have large startup current surges for motor circuits you can use a time delay fuse one brand is fusetron which will avoid tripping on momentary overloads a fusetron looks like a spring loaded fuse a fuse can only trip once then it must be replaced breakers are fairly complicated mechanical devices they usually consist of one spring loaded contact which is latched into position against another contact when the current flow through the device exceeds the rated value a bimetallic strip heats up and bends by bending it trips the latch and the spring pulls the contacts apart circuit breakers behave similarly to fusetrons that is they tend to take longer to trip at moderate overloads than ordinary fuses with high overloads they trip quickly breakers can be reset a finite number of times each time they trip or are thrown when the circuit is in use some arcing takes place which damages the contacts thus breakers should not be used in place of switches unless they are specially listed for the purpose neither fuses nor breakers limit the current per se a dead short on a circuit can cause hundreds or sometimes even thousands of amperes to flow for a short period of time which can often cause severe damage subject breakers can t i use fuses statistics show that fuse panels have a significantly higher risk of causing a fire than breaker panels this is usually due to the fuse being loosely screwed in or the contacts corroding and heating up over time or the wrong size fuse being installed or the proverbial replace the fuse with a penny trick since breakers are more permanently installed and have better connection mechanisms the risk of fire is considerably less fuses are prone to explode under extremely high overload when a fuse explodes the metallic vapor cloud becomes a conducting path result from complete meltdown of the electrical panel melted service wiring through fires in the electrical distribution transformer and having your house burn down breakers don t do this many jurisdictions particularly in canada no longer permit fuse panels in new installations the nec does permit new fuse panels in some rare circumstances requiring the special inserts to key the fuseholder to specific size fuses some devices notably certain large air conditioners require fuse protection in addition to the breaker at the panel the fuse is there to protect the motor windings from overload check the labeling on the unit this is usually only on large permanently installed motors the installation instructions will tell you if you need one subject what size wire should i use for a amp circuit use gauge wire for a amp circuit you can use gauge wire in most locales for a long run though you should use the next larger size wire to avoid voltage drops gauge is only slightly more expensive than gauge though it s stiffer and harder to work with here s a quick table for normal situations go up a size for more than foot runs when the cable is in conduit or ganged with other wires in a place where they can t dissipate heat easily gauge amps we don t list bigger sizes because it starts getting very dependent on the application and precise wire type subject where do these numbers come from there are two considerations voltage drop and heat buildup the smaller the wire is the higher the resistance is when the resistance is higher the wire heats up more and there is more voltage drop in the wiring the former is why you need higher temperature insulation and or bigger wires for use in conduit the latter is why you should use larger wire for long runs neither effect is very significant over very short distances there are some very specific exceptions where use of smaller wire is allowed the obvious one is the line cord on most lamps don t try this unless you re certain that your use fits one of those exceptions you can never go wrong by using larger wire subject what does mean this is used to describe the size and quantity of conductors in a cable the first number specifies the gauge the second the number of current carrying conductors in the wire but remember there s usually an extra ground wire means gauge two insulated current carrying wires plus bare ground wire usually has a black white and bare ground wire sometimes the white is red instead for v circuits without neutral in the latter case the sheath is usually red too wire usually has a black red white and bare ground wire usually carrying v with neutral subject what is a wirenut marrette marr connector how are they used a wire nut is a cone shaped threaded plastic thingummy that s used to connect wires together marrette or marr connector are trade names you ll usually use a lot of them in diy wiring in essence you strip the end of the wires about an inch twist them together then twist the wirenut on though some wirenuts advertise that you don t need to twist the wire do it anyways it s more mechanically and electrically secure there are many different sizes of wire nut you should check that the wire nut you re using is the correct size for the quantity and sizes of wire you re connecting together don t just gimble the wires together with a pair of pliers or your fingers use a pair of blunt nose linesman pliers and carefully twist the wires tightly and neatly sometimes it s a good idea to trim the resulting end to make sure it goes in the wirenut properly some people wrap the open end of the wirenut with electrical tape this is probably not a good idea the inspector may tear it off during an inspection it s usually done because a bit of bare wire is exposed outside the wire nut instead of taping it the connection should be redone subject what is a gfi gfci a gfci is a ground fault circuit interrupter it measures the current current flowing through the hot wire and the neutral wire if they differ by more than a few milliamps the presumption is that current is leaking to ground via some other path this may be because of a short circuit to the chassis of an appliance or to the ground lead or through a person any of these situations is hazardous so the gfci trips breaking the circuit gfcis do not protect against all kinds of electric shocks if for example you simultaneously touched the hot and neutral leads of a circuit and no part of you was grounded a gfci wouldn t help all of the current that passed from the hot lead into you would return via the neutral lead keeping the gfci happy the two pairs of connections on a gfci outlet are not symmetric one is labeled load the other line the incoming power feed must be connected to the line side or the outlet will not be protected the load side can be used to protect all devices downstream from it thus a whole string of outlets can be covered by a single gfci outlet subject where should gfcis be used the nec mandates gfcis for v a or a single phase outlets in bathrooms kitchens within of the sink garages unfinished basements or crawl spaces outdoors near a pool or just about anywhere else where you re likely to encounter water or dampness there are exceptions for inaccessible outlets those dedicated to appliances occupying fixed space typically refrigerators and freezers and for sump pumps and laundry appliances the cec does not mandate as many gfcis in particular there is no requirement to protect kitchen outlets or most garage or basement outlets basement outlets must be protected if you have a dirt floor garage outlets if they re near the door to outside bathrooms and most exterior outlets must have gfcis even if you are not required to have gfci protection you may want to consider installing it anyway unless you need a gfci breaker see below the cost is low in the u s gfci outlets can cost as little as us costs are a bit higher in canada c evaluate your own risk factors does your finished basement ever get wet do you have small children do you use your garage outlets to power outdoor tools does water or melted snow ever puddle inside your garage subject where shouldn t i use a gfci gfcis are generally not used on circuits that a don t pose a safety risk and b are used to power equipment that must run unattended for long periods of time refrigerators freezers and sump pumps are good examples the rationale is that gfcis are sometimes prone to nuisance trips some people claim that the inductive delay in motor windings can cause a momentary current imbalance tripping the gfci note though that most gfci trips are real if you re getting a lot of trips for no apparent reason you d be well advised to check your wiring before deciding that the gfci is broken or useless subject what is the difference between a gfci outlet and a gfci breaker for most situations you can use either a gfci outlet as the first device on the circuit or you can install a breaker with a built in gfci the former is generally preferred since gfci breakers are quite expensive for example an ordinary ge breaker costs us the gfci model costs us there is one major exception if you need to protect a multi wire branch circuit two or more circuits sharing a common neutral wire such as a canadian style kitchen circuit you ll need a multi pole gfci breaker unfortunately these are expensive the cost can range into the hundreds of dollars depending on what brand of panel box you have but if you must protect such a circuit say for a pool heater you have no choice one more caveat gfci outlets are bulky you may want to use an oversize box when installing them on second thought use large actually deep boxes everywhere you ll thank yourself for it incidentally if you re installing a gfci to ensure that one specific outlet is protected such as a bathroom you don t really have to go to all of the trouble to find the first outlet in the circuit you could simply find the first outlet in the bathroom and not gfci anything upstream of it but protecting the whole circuit is preferred when you install a gfci it s a good idea to use the little ground fault protected stickers that come with it and mark the outlets downstream of the gfci you can figure out which outlets are downstream simply by tripping the gfci with the test button and see which outlets are dead subject what s the purpose of the ground prong on an outlet then apart from their use in electronics which we won t comment on and for certain fluorescent lights they won t turn on without a good ground connection they re intended to guard against insulation failures within the device generally the case of the appliance is connected to the ground lead if there s an insulation failure that shorts the hot lead to the case the ground lead conducts the electricity away safely and possibly trips the circuit breaker in the process if the case is not grounded and such a short occurs the case is live and if you touch it while you re grounded you ll get zapped of course if the circuit is gfci protected it will be a very tiny zap which is why you can use gfcis to replace ungrounded outlets both nec and cec there are some appliances that should never be grounded in particular that applies to toasters and anything else with exposed conductors consider if you touch the heating electrode in a toaster and you re not grounded nothing will happen if you re slightly grounded you ll get a small shock the resistance will be too high but if the case were grounded and you were holding it you d be the perfect path to ground subject why is one prong wider than the other polarization nowadays many two prong devices have one prong wider than the other this is so that the device could rely not guaranteed on one specific wire being neutral and the other hot this is particularly advantageous in light fixtures where the the shell should neutral safety or other devices which want to have an approximate ground reference ie some radios most prong extension cords have wide prongs too this requires that you wire your outlets and plugs the right way around you want the wide prong to be neutral and the narrow one hot most outlets have a darker metal for the hot screw and lighter coloured screw for the neutral if not you can usually figure out which is which by which prong the terminating screw connects to subject what kind of outlets do i need in a kitchen the nec requires at least two amp small appliance circuits for kitchens the cec requires split duplex receptacles outlets must be installed such that no point is more than nec mm cec from an outlet every counter wider than nec or mm cec must have at least one outlet the circuit these outlets are on may not feed any outlets except in the kitchen pantry or dining room furthermore these circuits are in addition to any required for refrigerators stoves microwaves lighting etc non dedicated outlets within of a sink must be protected by a gfci nec only split duplex receptacles are fed with a v circuit the tab is broken on the hot side of the outlet and one hot goes to the upper outlet and the other hot goes to the lower outlet the neutral connects to both outlets through one screw when carrying through to another outlet the neutral must be pigtailed such that removing the outlet or having the neutral connection fall off doesn t cause the neutral to disconnect from downstream outlets subject where must outlets and switches be in bathrooms there must be at least one outlet in each bathroom adjacent to the sink in addition to any outlet that may be incorporated in the light fixture all such outlets must be gfci protected subject what is romex nm nmd what is bx when should i use each romex is a brand name for a type of plastic insulated wire sometimes called non metallic sheath the formal name is nm this is suitable for use in dry protected areas ie inside stud walls on the sides of joists etc that are not subject to mechanical damage or excessive heat most newer homes are wired almost exclusively with nm wire there are several different categories of nm cable bx cable technically known as armored cable or ac has a flexible aluminum or steel sheath over the conductors and is fairly resistant to damage teck cable is ac with an additional external thermoplastic sheath protection for cable in concealed locations where nm or ac cable is run through studs joists or similar wooden members the outer surface of the cable must be kept at least mm cec nec from the edges of the wooden members or the cable should be protected from mechanical injury this latter protection can take the form of metal plates such as spare outlet box ends or conduit note inspector permitted practise in canada suggests that armored cable or flexible conduit can be used as the mechanical protection but this is technically illegal additional protection recommendations these are rules in the canadian codes they are reasonable answers to the vague references to exposed to mechanical damage in both the nec and cec nm cable should be protected against mechanical damage where it passes through floors or on the surface of walls in exposed locations under feet from the floor ie use ac instead flexible conduit wooden guards etc where cable is suspended as in connections to furnaces or water heaters the wire should be protected canadian practise is usually to install a junction or outlet box on the wall and use a short length of ac cable or nm cable in flexible conduit to jump to the appliance stapling nm to a piece of lumber is also sometimes used where nm cable is run in close proximity to heating ducts or pipe heat transfer should be minimized by means of a mm air space or suitable insulation material a wad of fiberglass nm cable shall be supported within mm of every box or fitting and at intervals of no more than m holes in joists or studs are considered supports some slack in the cable should be provided adjacent to each box while fishing cable is technically in violation it is permitted where proper support is impractical conductor nm cable should never be stapled on edge knight also insists on only one cable per staple referring to the workmanship clause but this seems more honoured in the breach cable should never be buried in plaster cement or similar finish cable should be protected where it runs behind baseboards cable may not be run on the upper edge of ceiling joists or the lower edges of rafters where the headroom is more than m whenever bx cable is terminated at a box with a clamp small plastic bushings must be inserted in the end of the cable to prevent the clamps forcing the sharp ends of the armor through the insulation bx is sometimes a good idea in a work shop unless covered by solid wall coverings in places where damage is more likely like on the back wall of a garage you may be required to use conduit a ul or csa approved metal pipe you use various types of fittings to join the pipe or provide entrance exit for the wire service entrances frequently use a plastic conduit in damp places eg buried wiring to outdoor lighting you will need special wire eg cec nmw nec uf nmw looks like very heavy duty nmd you will usually need short lengths of conduit where the wire enters exits the ground see underground wiring section thermoplastic sheath wire such as nm nmw etc should not be exposed to direct sunlight unless explicitly approved for that purpose many electrical codes do not permit the routing of wire through furnace ducts including cold air return plenums constructed by metal sheeting enclosing joist spaces the reason for this is that if there s a fire the ducting will spread toxic gasses from burning insulation very rapidly through the building teflon insulated wire is permitted in plenums in many areas canada appears to use similar wire designations to the us except that canadian wire designations usually include the temperature rating in celsius eg ac versus ac in the us nm b is degrees celcius note local codes vary this is one of the items that changes most often eg chicago codes require conduit everywhere there are very different requirements for mobile homes check your local codes especially if you re doing anything that s the slightest out of the ordinary wire selection table incomplete the real tables are enormous uncommon wire types or applications omitted condition type cec nec exposed concealed dry plastic nmd nm armor ac ac teck exposed concealed damp plastic nmd nmc armor acwu teck exposed concealed wet plastic nmwu armor acwu teck exposed to weather plastic nmwu tw etc armor teck direct earth burial plastic nmwu uf service entrance rwu twu armor ra teck acwu nmwu not for service entrance subject should i use plastic or metal boxes the nec permits use of plastic boxes with non metallic cable only the reasoning is simple with armored cable the box itself provides ground conductor continuity u s plastic boxes don t use metal cable clamps the cec is slightly different the cec never permits cable armor as a grounding conductor however you must still provide ground continuity for metallic sheath the cec also requires grounding of any metal cable clamps on plastic boxes the advantage of plastic boxes is comparatively minor even for non metallic sheathed cable you can avoid making one ground connection and they sometimes cost a little less on the other hand plastic boxes are more vulnerable to impacts for exposed or shop wiring metal boxes are probably better subject junction box positioning a junction box is a box used only for connecting wires together junction boxes must be located in such a way that they re accessible later ie not buried under plaster excessive use of junction boxes is often a sign of sloppy installation and inspectors may get nasty subject can i install a replacement light fixture in general one can replace fixtures freely subject to a few caveats first of course one should check the amperage rating of the circuit if your heart is set on installing half a dozen watt floodlights you may need to run a new wire back to the panel box but there are some more subtle constraints as well for example older house wiring doesn t have high temperature insulation the excess heat generated by a ceiling mounted lamp can and will cause the insulation to deteriorate and crack with obvious bad results some newer fixtures are specifically marked for high temperature wire only you may find in fact that your ceiling wiring already has this problem in which case replacing any devices is a real adventure other concerns include providing a suitable ground for some fluorescent fixtures and making sure that the ceiling box and its mounting are strong enough to support the weight of a heavy chandelier or ceiling fan you may need to install a new box specifically listed for this purpose a x across the ceiling joists makes a good support metal brackets are also available that can be fished into ceilings thru the junction box hole and mounted between the joists there are special rules for recessed light fixtures such as pot lamps or heat lamps when these are installed in insulated ceilings they can present a very substantial fire hazard the cec provides for the installation of pot lamps in insulated ceilings provided that the fixture is boxed in a coffin usually x x made by making a pair of joists high and covering with plywood that doesn t have any insulation yes that s feet long nec rules are somewhat less stringent they require at least clearance between the fixture and any sort of thermal insulation the rules also say that one should not obstruct free air movement which means that a cec style coffin might be worthwhile presumably that s up to the local inspector the cec doesn t actually mandate the coffin per se this seems to be an inspector requirement to make absolutely certain that the fixture can t get accidentally buried in insulation ie if you have insulation blown in later there are now fixtures that contain integral thermal cutouts and fairly large cases that can be buried directly in insulation they are usually limited to watt bulbs and are unfortunately somewhat more expensive than the older types before you use them you should ensure that they have explicit ul or csa approval for such uses follow the installation instructions carefully the prescribed location for the sensor can vary there does not yet appear to be a heat lamp fixture that is approved for use in insulation the coffin appears the only legal approach subject what does it mean when the lights brighten when a motor starts this usually means that the neutral wire in the panel is loose depending on the load balance one hot wire may end up being more than v and the other less than v with respect to ground this is a very hazardous situation it can destroy your electronic equipment possibly start fires and in some situations electrocute you ie some us jurisdictions require the stove frame connected to neutral if this happens contact your electrical authority immediately and have them come and check out the problem note a brief second brightening is sometimes normal with lighting and motors on the same v with neutral circuit a loose main panel neutral will usually show increased brightness far longer than one second in case of doubt get help subject what is phase power should i use it can i get it in my house three phase power has three hot wires degrees out of phase with each other these are usually used for large motors because it is more efficient provides a bit more starting torque and because the motors are simpler and hence cheaper you re most likely to encounter a phase circuit that shows volts between any hot and ground and volts between any two hots the latter shows the difference between a normal v v common neutral circuit which is volts between the two hots there are phase circuits with different voltages bringing in a phase feed to your house is usually ridiculously expensive or impossible if the equipment you want to run has a standard motor mount it is much cheaper to buy a new v or v motor for it in some cases it is possible to run phase equipment on ordinary power if you have a capacitor start unit or use a larger motor as a auto generator these are tricky but are a good solution if the motor is non standard size or too expensive or too big to replace the taunton press book the small shop has an article on how to do this if you must note that you lose any possible electrical efficiency by using such a converter the laws of thermodynamics guarantee that subject is it better to run motors at or theoretically it doesn t make any difference however there is a difference is the amount of power lost in the supply wiring all things being equal a v motor will lose times less power in the house wiring than a v motor this also means that the startup surge loss will be less and the motor will get to speed quicker and in some circumstances the smaller power loss will lead to longer motor life this is usually irrelevant unless the supply wires are more than feet long subject what is this nonsense about hp on v a circuits it is a universal physical law that hp is equal to watts given heating loss power factor and other inefficiencies it is usually best to consider hp is going to need watts a v a circuit can only deliver watts to a motor so it cannot possibly be more than approximately hp given rational efficiency factors hp is more like it some equipment manufacturers sears in particular most router manufacturers in general advertise a hp rating that is far in excess of what is possible they are giving you a stall horsepower or similar that means the power is measured when the motor is just about to stop turning because of the load what they don t mention is that if you kept it in that condition for more than a few seconds hopefully your breaker will trip otherwise the motor will melt it s drawing far more current than it can continuously when comparing motors compare the continuous horsepower this should be on the motor nameplate if you can t find that figure check the amperage rating which is always present subject how do i convert two prong receptacles to three prong older homes frequently have two prong receptacles instead of the more modern three these receptacles have no safety ground and the cabling usually has no ground wire neither the nec or cec permits installing new prong receptacles anymore there are several different approaches to solving this if the wiring is done through conduit or bx and the conduit is continuous back to the panel you can connect the third prong of a new receptacle to the receptacle box nec mainly cec frowns on this practise if there is a copper cold water pipe going nearby and it s continuous to the main house ground point you can run a conductor to it from the third prong run a ground conductor back to the main panel easiest install a gfci receptacle the ground lug should not be connected to anything but the gfci protection itself will serve instead the gfci will also protect downstream possibly also two prong outlets if you do this to protect downstream outlets the grounds must not be connected together since it wouldn t be connected to a real ground a wiring fault could energize the cases of prong devices connected to other outlets be sure though that there aren t indirect ground plug connections such as via the sheath on bx cable the cec permits you to replace a two prong receptacle with a three prong if you fill the u ground with a non conducting goop like caulking compound this is not permitted in the nec subject are you sure about gfcis and ungrounded outlets should the test button work we re sure about what the nec and cec say remember though that your local codes may vary as for the test button there s a resistor connecting the load side of the hot wire to the line side of the neutral wire when you press the test button current through this resistor shows up as an imbalance and trips the gfci this is a simple passive and reliable test and doesn t require a real ground to work if your gfci does not trip when you press the test button it is very probably defective or miswired again if the test button doesn t work something s broken and potentially dangerous the problem should be corrected immediately the instructions that come with some gfcis specify that the ground wire must be connected we do not know why they say this the causes may be as mundane as an old instruction sheet or with the formalities of ul or csa listing perhaps the device was never tested without the ground wire being connected on the other hand ul or csa approval should only have been granted if the device behaves properly in all listed applications including ungrounded outlet replacement one of us called leviton their gfcis are labeled for installation on grounded circuits only the technician was surprised to see that he agreed that the nec does not require it and promised to investigate subject how should i wire my shop as with any other kind of wiring you need enough power for all devices that will be on simultaneously the code specifies that you should stay under of the nominal capacity of the circuit for typical home shop use this means one circuit for the major power tools and possibly one for a dust collector or shop vac use at least gauge wire many power tools have big motors with a big start up surge if you can use amp breakers nec though cec requires standard a receptacles which means you d have to replug all your equipment lights should either be on a circuit of their own and not shared with circuits in the rest of the house or be on at least two separate circuits the idea is that you want to avoid a situation where a blade is still spinning at several thousand rpm while you re groping in the dark for the off switch do install lots of outlets it s easier to install them in the beginning when you don t have to cut into an existing cable it s useful if at least two circuits are accessible at each point so you can run a shop vac or a compressor at the same time as the tool you really want but use metal boxes and plates and maybe even metal sheathed cable you may have objects flying around at high speeds if something goes a bit wrong note that some jurisdictions have a no horizontal wiring rule in workshops or other unfinished areas that are used for working what this means is that all wiring must be run along structural members ie stapled to studs other possible shop circuits include heater circuits v circuits for some large tools and air compressor circuits don t overload circuits and don t use extension cords if you can help it unless they re rated for high currents a coiled extension cord is not as safe as a straight length of wire of the same gauge also the insulation won t withstand as much heat and heat dissipation is the critical issue if your shop is located at some remove from your main panel you should probably install a subpanel and derive your shop wiring from it if you have young children you may want to equip this panel with a cut off switch and possibly a lock if you want to install individual switches to safe particular circuits make sure you get ones rated high enough for example ordinary light switches are not safely able to handle the start up surge generated by a table saw buy horsepower rated switches instead finally note that most home shops are in garages or unfinished basements hence the nec requirements for gfcis apply and even if you know that you d never use one of your shop outlets to run a lawn mower the next owner of your house might have a different idea note fine woodworking magazine often carries articles on shop wiring april is one place to start subject underground wiring you will need to prepare a trench to specifications use special wire protect the wire with conduit or special plastic tubing and possibly lumber don t use creosoted lumber it rots thermoplastic insulation and acts as a catalyst in the corrosion of lead the transition from in house to underground wire is generally via conduit all outdoor boxes must be specifically listed for the purpose and contain the appropriate gaskets fittings etc if the location of the box is subject to immersion in water a more serious style of water proof box is needed and of course don t forget the gfcis the required depths and other details vary from jurisdiction to jurisdiction so we suggest you consult your inspector about your specific situation a hint buy a roll of bright yellow tape that says buried power line and bury it a few inches above where the wire has been placed subject aluminum wiring during the s aluminum instead of copper wiring became quite popular and was extensively used since that time aluminum wiring has been implicated in a number of house fires and most jurisdictions no longer permit it in new installations we recommend even if you re allowed to that do not use it for new wiring but don t panic if your house has aluminum wiring aluminum wiring when properly installed can be just as safe as copper aluminum wiring is however very unforgiving of improper installation we will cover a bit of the theory behind potential problems and what you can do to make your wiring safe the main problem with aluminum wiring is a phenomenon known as cold creep when aluminum wiring warms up it expands when it cools down it contracts unlike copper when aluminum goes through a number of warm cool cycles it loses a bit of tightness each time to make the problem worse aluminum oxidises or corrodes when in contact with certain types of metal so the resistance of the connection goes up which causes it to heat up and corrode oxidize still more eventually the wire may start getting very hot melt the insulation or fixture it s attached to and possibly even cause a fire since people usually encounter aluminum wiring when they move into a house built during the s we will cover basic points of safe aluminum wiring we suggest that if you re considering purchasing a home with aluminum wiring or have discovered it later that you hire a licensed electrician or inspector to check over the wiring for the following things fixtures eg outlets and switches directly attached to aluminum wiring should be rated for it the device will be stamped with al cu or co alr the latter supersedes the former but both are safe these fixtures are somewhat more expensive than the ordinary ones wires should be properly connected at least way around the screw in a clockwise direction connections should be tight while repeated tightening of the screws can make the problem worse during the inspection it would pay off to snug up each connection note that aluminum wiring is still often used for the main service entrance cable it should be inspected push in terminals are an extreme hazard with aluminum wire any connections using push in terminals should be redone with the proper screw connections immediately there should be no signs of overheating darkened connections melted insulation or baked fixtures any such damage should be repaired connections between aluminum and copper wire need to be handled specially current canadian codes require that the wire nut used must be specially marked for connecting aluminum to copper the nec requires that the wire be connected together using special crimp devices with an anti oxidant grease the tools and materials for the latter are quite expensive not practical to do it yourself unless you can rent the tool any non rated receptacle can be connected to aluminum wiring by means of a short copper pigtail see above shows reasonable workmanship neat wiring properly stripped not nicked wire etc if when considering purchasing a home an inspection of the wiring shows no problems or only one or two we believe that you can consider the wiring safe if there are signs of problems in many places we suggest you look elsewhere if the wrong receptacles are used you can replace them with the proper type or use pigtails having this professionally done can range from to per receptacle switch you can do this yourself too subject i m buying a house what should i do congratulations but it s generally a good idea to hire an inspector to look through the house for hidden gotchas not just for wiring but plumbing and structural as well if an inspection of the wiring shows no problems or only one or two minor ones we believe that you can consider the wiring safe after any minor problems are fixed if there are signs of problems in many places we suggest you look elsewhere here s some hints on what to look for obvious non code wiring can include zip cord wiring either concealed or nailed to walls hot wiring on the identified neutral conductor without proper marking ungrounded grounding outlets except when downstream of a gfci splices hanging in mid air other than proper knob and tube switched neutrals unsecured romex swinging about like grapevines certain wiring practises that are actually to code or were at one time sometimes reveal diy wiring that may have hidden violations switches that seem to control nothing abandoned perhaps not properly terminated wiring a wall switch that shuts off a group of lights that are separately controlled by other wall switches except when it s really convenient switches and outlets in bizarre locations great numbers of junction boxes without outlets or lamps junction boxes with great numbers of wires going into them wiring that passes through a closet instead of a wall or ceiling backwrapped grounding wires subject what is this weird stuff old style wiring in the years since edison invented electricity several different wiring styles have come and gone when you buy an older home you may encounter some of this stuff this section describes the old methods and some of their idiosyncrasies the oldest wiring system you re likely to encounter is called knob and tube k t it is made up of individual conductors with a cloth insulation the wires are run along side structural members eg joists or studs using ceramic stand offs knobs wire is run through structural members using ceramic tubes connections were made by twisting the wire together soldering and wrapping with tape since the hot and neutral were run separately the wiring tends to be rather confusing a neutral often runs down the centre of each room with taps off to each fixture the hot wire tended to run from one fixture to the next in some cases k t isn t colour coded so the neutral is often the same colour as the hot wires you ll see k t in homes built as late as the s comments on k t the people installing k t were pretty paranoid about electricity so the workmanship tends to be pretty good the wire insulation and insulators tend to stand up very well most k t i ve seen for example is in quite good condition no grounding grounding is usually difficult to install boxes are small receptacle replacement particularly with gfci can be difficult no bushing on boxes either so wiring changes need special attention to box entry sometimes the neutral isn t balanced very well between separately hot circuits so it is sometimes possible to overload the neutral without exceeding the fusing on any circuit building code does not permit insulation in walls that contain k t connection to existing k t from new circuits can be tricky consult your inspector modern wiring practise requires considerably more outlets to be installed than k t systems did since k t tends to be in pretty decent condition it generally isn t necessary to replace it simply because it s k t what you should watch out for is renovations that have interfered with it and be cautious about circuit loading in many cases it s perfectly reasonable to leave existing k t alone and add new fixtures on new circuits using modern techniques after k t they invented multi conductor cable the first type you will see is roughly a cloth and varnish insulation it looks much like the romex cable of the last decade or two this stuff was used in the s and s again no grounding conductor it was installed much like modern wiring its major drawback is that this type of insulation embrittles we ve seen whole systems where the insulation would fracture and fall off at a touch bx cable of the same vintage has similar problems this stuff is very fragile and becomes rather hazardous if the wires become bare this wiring should be left untouched as much as possible whenever an opportunity arises replace it a simple receptacle or switch replacement can turn into a several hour long frustrating fight with electrical tape or heat shrink tubing after this wiring technique the more modern romex was invented it s almost a asphalt impregnated cloth often a bit sticky this stuff stands up reasonably well and doesn t present a hazard and is reasonably easy to work with it does not need to be replaced it should be considered as safe as the modern stuff thermoplastic insulation wire just don t abuse it too much subject where do i buy stuff try to find a proper electrical supply outlet near you their prices will often be considerably better than chain hardware stores or diy centres have better quality materials have wider variety including the odd stuff and have people behind the counter that know what you re talking about cultivate friendly knowledgeable sales people they ll give you much valuable information chris lewis clewis ferret ocunix on ca phone canada psroff info psroff request ferret ocunix on ca ferret list ferret request ferret ocunix on ca
