<h1>Safety is not the same as legality</h1>
<p>Something might be perfectly safe, but it doesn't make it legal to do or allowed to use. Parking your car over double-yellow lines is one example that is perfectly safe but violates the traffic codes.</p>
<p>Any 3D printed box would violate for example <a href="https://app.leg.wa.gov/wac/default.aspx?cite=296-46B-300" rel="nofollow noreferrer">WAC 296-46B-300</a>, as it isn't in compliance with NEC Class 3 Standard.</p>
<blockquote>
<p>(1) Cables and raceways for power limited, NEC Class 2 and Class 3 conductors must be installed in compliance with Chapter 3 NEC unless other methods are specifically required elsewhere in the NEC, chapter 19.28 RCW, or this chapter.</p>
</blockquote>
<p>The NEC is also known as NFPA 70, and availeable at the Website of the <a href="https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards?mode=code&amp;code=70&amp;tab=editions" rel="nofollow noreferrer">National Fire Protection Agency</a>. You will need to look in Article 725.3 for the exact, current specifications that a cable box would need to follow.</p>
<blockquote>
<p><strong>725.3 Other Articles.</strong> Circuits and equipment shall comply with the articles or sections listed in 725.3(A) through (N). Only those sections of Article 300 referenced in this article shall apply to Class 1, Class 2, and Class 3 circuits.</p>
</blockquote>
<p><em>Also</em> note, that mains wire work is usually regulated in how it has to be done and you might (in some areas) not even be allowed to do it yourself! Even if you may do it, it might be inadvisable to do so due to insurance reasons: non-professional wiring or non-standard parts can be usually excluded from coverage.</p>

CC BY-SA 4.0
2022-02-23T18:21:07.607Z
In the US, homeowners are _generally_ allowed (regulations vary by locale) to do electrical work on their own homes. Most importantly, if there's a fire and the insurance company discovers your 3D-printed electrical box, they'll have grounds for denying your claim.
FreeMan
CC BY-SA 4.0
2020-01-21T20:36:14.920Z
2022-02-23T20:46:30.330Z
2022-02-23T20:46:30.330Z
Trish
<p>I haven't tested the commercial "blue boxes" used to hold 120/240&nbsp;V electrical outlets, switches, and splices to see how they behave when heated.  As such, this argument is based on intuition, which is intrinsically flawed as a logic device.  Never-the-less, I think the no extruded molten plastic (FFF) 3D printing filament will work.</p>

<p>The purpose of the junction box is to contain an overheating connection or switch and prevent it from causing a fire in the wall.  Any FFF filament will have a melting point below the ignition point of wood, and would therefore flow away from the overheating point.  It seems that any thermoplastic with a "normal" melting point would have this problem.</p>

<p>You might look at UV polymerized printing resins, such as are used in the Stratasys Objet, Form Labs, and Prusa SL1.  These printing processes aren't constrained to use plastics that can be melted or heat softened.  Because the polymerization can involve more aggressive crosslinking (polymerization) that FFF materials, they have the potential to be good for a higher temperature.  </p>

<p>As an example of a high-temperature, non-melting plastic which could perhaps have an analogue in SLS resin, polyester "casting compound" is cross linked by a methyl-ethyl-ketone-peroxide catalyst to form clear solid.  24 hours after the polymerization starts, the solid does not melt under the influence of a hot air gun.  I tried to melt it and it would not melt.  It slightly softened, but the plastic cup I had cast it in was dripping away -- but the polyester was not melting.</p>

<p>I looked through the Stratasys materials and Form Labs materials and did not see a much higher temperature material.</p>

CC BY-SA 4.0
2022-02-23T18:24:01.483Z
Underwriters Laboratory, Inc (UL) or other NRTLs fully test all boxes (plastic and metal) for fire containment. A box won't get certified if it doesn't meet standards. Even if you print your own box out of the exact same plastic that a UL listed box is made of, it won't come with UL certification, and your insurance company could have grounds for denying your claim if/when they find it.
FreeMan
CC BY-SA 4.0
2022-02-23T23:02:52.530Z
Agreed.  I should have pointed out that, as the manufacturer of the boxes, the OP would need to obtain certifications for use in the intended applications.
cmm
CC BY-SA 4.0
2020-01-21T20:34:56.053Z
2020-01-21T20:34:56.053Z
cmm
<p>Which type of filament material(s) is safe to use as an in-wall box for regular, 120v wiring? For instance, an electrical outlet box.</p>

<p>In case it matters, location is the state of Washington, USA.</p>

CC BY-SA 4.0
2020-01-21T18:59:59.880Z
safe, or legal? you would have to get your boxes tested and approved by an underwriting lab in order to legally use them in-wall. I don't think you can (realistically for most) even DIY the plate covers, much less the boxes. On the practical side, filament that doesn't sustain a flame or emit toxic smoke when burned would be wise.
dandavis
CC BY-SA 4.0
2020-01-21T19:24:57.917Z
I'd concur with @dandavis on this. Something to consider, though, is it really worth your time/effort to print something which is readily available and for the most part, rather cheap to just buy on the economy? (Lowe's is showing it available for $.32/ea) You can get contractor packs from Lowe's/Home Depot real easy/cheap. Printing a single box would cost you hours of time. If that doesn't dissuade you, standard wall boxes are made of PVC ... I don't know if that's available in a filament, though.
Pᴀᴜʟsᴛᴇʀ2
CC BY-SA 4.0
2020-01-21T19:26:55.857Z
[A link in case you care.](https://www.lowes.com/pd/CARLON-1-Gang-Blue-Plastic-New-Work-Standard-Switch-Outlet-Wall-Electrical-Box/1000108303)
Pᴀᴜʟsᴛᴇʀ2
CC BY-SA 4.0
2020-01-21T19:54:24.930Z
Thanks for the input, but the outlet box was simply an example. There are use-cases in building a custom, in-wall gang box that is not commercially available. It's hardly ever cheaper to 3D print something when there is already a commercially available product.

My understanding, in terms of safety, is that it must not catch fire or emit smoke/embers in the event that there is an electrical fire. To @dandavis's point, probably why you would need it tested and approved. But, my question still remains, what 3D printing material would be suitable for such an application?
tbm0115
CC BY-SA 4.0
2022-02-23T18:19:48.987Z
If you need to make a gang box that's big enough that it doesn't exist, use a metal box designed to be built up into whatever size you need. Something like a Raco #519. The sides unscrew and you can put together as many as you want until you run out of room in the stud bay.
FreeMan
<print-material><safety><legal>
What filament material is safe to use as in-wall housing (US)?
tbm0115
# What filament material is safe to use as in-wall housing (US)?

(Asked by: username_0 on 2020-01-21)

Which type of filament material(s) is safe to use as an in-wall box for regular, 120v wiring? For instance, an electrical outlet box.

In case it matters, location is the state of Washington, USA.

**Tags:** print-material, safety, legal

> **Comments:**
> **username_1**: safe, or legal? you would have to get your boxes tested and approved by an underwriting lab in order to legally use them in-wall. I don't think you can (realistically for most) even DIY the plate covers, much less the boxes. On the practical side, filament that doesn't sustain a flame or emit toxic smoke when burned would be wise.  
> **username_2**: I'd concur with @username_1 on this. Something to consider, though, is it really worth your time/effort to print something which is readily available and for the most part, rather cheap to just buy on the economy? (Lowe's is showing it available for $.32/ea) You can get contractor packs from Lowe's/Home Depot real easy/cheap. Printing a single box would cost you hours of time. If that doesn't dissuade you, standard wall boxes are made of PVC ... I don't know if that's available in a filament, though.  
> **username_2**: [A link in case you care.](https://www.lowes.com/pd/CARLON-1-Gang-Blue-Plastic-New-Work-Standard-Switch-Outlet-Wall-Electrical-Box/1000108303)  
> **username_0**: Thanks for the input, but the outlet box was simply an example. There are use-cases in building a custom, in-wall gang box that is not commercially available. It's hardly ever cheaper to 3D print something when there is already a commercially available product.  My understanding, in terms of safety, is that it must not catch fire or emit smoke/embers in the event that there is an electrical fire. To @username_1's point, probably why you would need it tested and approved. But, my question still remains, what 3D printing material would be suitable for such an application?  
> **username_3**: If you need to make a gang box that's big enough that it doesn't exist, use a metal box designed to be built up into whatever size you need. Something like a Raco #519. The sides unscrew and you can put together as many as you want until you run out of room in the stud bay.  

---

## 2 answers

### Answer by username_4 on 2020-01-21. Score: 4 | Accepted answer

# Safety is not the same as legality

Something might be perfectly safe, but it doesn't make it legal to do or allowed to use. Parking your car over double-yellow lines is one example that is perfectly safe but violates the traffic codes.

Any 3D printed box would violate for example [WAC 296-46B-300](https://app.leg.wa.gov/wac/default.aspx?cite=296-46B-300), as it isn't in compliance with NEC Class 3 Standard.

> (1) Cables and raceways for power limited, NEC Class 2 and Class 3 conductors must be installed in compliance with Chapter 3 NEC unless other methods are specifically required elsewhere in the NEC, chapter 19.28 RCW, or this chapter.

The NEC is also known as NFPA 70, and availeable at the Website of the [National Fire Protection Agency](https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards?mode=code&code=70&tab=editions). You will need to look in Article 725.3 for the exact, current specifications that a cable box would need to follow.

> **725.3 Other Articles.** Circuits and equipment shall comply with the articles or sections listed in 725.3(A) through (N). Only those sections of Article 300 referenced in this article shall apply to Class 1, Class 2, and Class 3 circuits.

*Also* note, that mains wire work is usually regulated in how it has to be done and you might (in some areas) not even be allowed to do it yourself! Even if you may do it, it might be inadvisable to do so due to insurance reasons: non-professional wiring or non-standard parts can be usually excluded from coverage.

> **Comments:**
> **username_3**: In the US, homeowners are _generally_ allowed (regulations vary by locale) to do electrical work on their own homes. Most importantly, if there's a fire and the insurance company discovers your 3D-printed electrical box, they'll have grounds for denying your claim.  

---

### Answer by username_5 on 2020-01-21. Score: 0

I haven't tested the commercial "blue boxes" used to hold 120/240 V electrical outlets, switches, and splices to see how they behave when heated. As such, this argument is based on intuition, which is intrinsically flawed as a logic device. Never-the-less, I think the no extruded molten plastic (FFF) 3D printing filament will work.

The purpose of the junction box is to contain an overheating connection or switch and prevent it from causing a fire in the wall. Any FFF filament will have a melting point below the ignition point of wood, and would therefore flow away from the overheating point. It seems that any thermoplastic with a "normal" melting point would have this problem.

You might look at UV polymerized printing resins, such as are used in the Stratasys Objet, Form Labs, and Prusa SL1. These printing processes aren't constrained to use plastics that can be melted or heat softened. Because the polymerization can involve more aggressive crosslinking (polymerization) that FFF materials, they have the potential to be good for a higher temperature.

As an example of a high-temperature, non-melting plastic which could perhaps have an analogue in SLS resin, polyester "casting compound" is cross linked by a methyl-ethyl-ketone-peroxide catalyst to form clear solid. 24 hours after the polymerization starts, the solid does not melt under the influence of a hot air gun. I tried to melt it and it would not melt. It slightly softened, but the plastic cup I had cast it in was dripping away -- but the polyester was not melting.

I looked through the Stratasys materials and Form Labs materials and did not see a much higher temperature material.

> **Comments:**
> **username_3**: Underwriters Laboratory, Inc (UL) or other NRTLs fully test all boxes (plastic and metal) for fire containment. A box won't get certified if it doesn't meet standards. Even if you print your own box out of the exact same plastic that a UL listed box is made of, it won't come with UL certification, and your insurance company could have grounds for denying your claim if/when they find it.  
> **username_5**: Agreed.  I should have pointed out that, as the manufacturer of the boxes, the OP would need to obtain certifications for use in the intended applications.  

---

