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If you are replacing an old cooktop then you will first have to remove it. Turn off the power to this cooktop at the fuse box. Remove any caulking or attachments on the cooktop. Disconnect the wiring, remembering how the old cooktop is wired, and lift the cooktop out of the opening.  You must be absolutely certain that the power is turned off to your cooktop. You can use a circuit tester to double check by touching one lead on the circuit tester to any wire that is not green or white and the other lead to a white or green (ground) wire. If the light comes on, it means the power is still on. Make sure you remember how the old wiring was connected because the new wiring will connect in the same way. You can even label wires and take a picture of the wiring before removal to help you remember. Get someone to help you lift the cooktop out of its location because they can be quite heavy. Ideally you should have at least 30 inches (76 cm) of clearance above the cooktop and 1-2 feet (30-60 cm) of clearance on the sides. You must also check that there is enough space below the cooktop for your desired model. Check the manufacturer’s instructions for specific requirements for your cooktop. Most cooktops will require a 240 VAC junction box. If you are replacing a cooktop then you probably will already have this installed.  If there is no junction box then you should hire a professional to install one for you. You must also check that the old cooktop has the same amperage as the new cooktop or else the wiring may need to be performed by a professional. Many old cooktops have only a 30-amp circuit while modern cooktops often have a 40-amp or 50-amp circuit. If you have removed a previously installed cooktop then there should already be a hole so you must check the dimensions of the new cooktop to see if it will fit. Measure the length and width of the cooktop and subtract ½ - 1 inch (1.25-2.5 cm) from each side to account for the lip that will overlap the countertop. The hole needs to be the size of the cooktop minus the ½ to 1 inch for the lip. If there is no hole currently or if the hole is too small then you will need to cut a hole or make it larger. If the hole is too big then you can screw shims (long flat metal pieces) into the sides around the opening.  You may need to remove tile around the area before cutting through the counter with a saw. You will need a wet saw to cut through a granite countertop. Alternatively hire a professional for this job because granite can be difficult to cut cleanly. You should also seal the stone before placing the cooktop into its location. Your cooktop may have removable burners, screens or other parts that can be set aside for now. You should also remove any packaging that may be around the cooktop. These hold the cooktop in place. You should hang them from the upper edge of the cutout and then secure them with screws. If you have a granite counter then you should secure the spring clips using double-sided adhesive tape rather than screws. Lower the new cooktop into the opening, making sure to draw the wires through the opening first. Press down until it clicks into place in the spring clips. If you had to remove tile then you will have to reinstall the tiles to lay flush with the edges of the cooktop before laying it into place. You may need to wait for 24 hours for the tiles to set before putting the cooktop into place. The power must still be  off when you do this to prevent injury and shocks. Connect the wires of the cooktop to their corresponding wire in the power supply.  The red and black wires (can also be other colors) are the hot wires which carry electricity to the appliance. Connect the red and black wires on the cooktop to the red and black wires in the power supply box. The white wire is the neutral wire, which completes the circuit. The white wire on the cooktop will connect to the white wire in the power supply. The green wire is the ground wire, which grounds the circuit. Connect the green wire on the cooktop to the green wire in the power supply. Connect all wires together using a wire nut, which is like a little cap. Line up the wires next to each other and then twist the wires around each other. Screw the wire nut onto the twisted wires. The wire nut protects them from touching other bare wires, preventing potential fires. Put back any burners, screens or other removable parts. Flip the breaker back on and turn on the cooktop to check that everything is working well.

Summary:
Remove the old cooktop if there is one. Make sure there is enough clearance around your chosen location. Check that the appropriate junction box exists in your desired location. Measure the dimensions of the cooktop and make sure it will fit if there is an existing hole. Alter the hole in the countertop to fit the cooktop. Detach any removable pieces on your cooktop to make it easier to set in place. Install the spring clips. Lower the new cooktop into place. Connect the wires of the new cooktop to the power supply. Install the removable pieces of your cooktop. Turn the power back on and test the cooktop.