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Replacing a 3 wire cooktop with 4 wire cooktop

12K views 9 replies 4 participants last post by  Atani 
#1 ·
Hi experts. I'm replacing an older 3-wire cooktop (red, black, bare-metal) with a newer one that has a four wire (red, black, white, green) connection. The wall box has three wires (red, black, white). The installation instructions state:

Frame grounded by connection of grounding lead to neutral lead. If used in a mobile home or if local codes do not permit grounding tfhrough neutral, open connection and use grounding lead to ground unit in accordance with local codes. Connect neutral lead to branch circuit neutral conductor in usual manner.
Attach flexible conduit to the junction box.
CAUTION: To reduce the risk of electic shock and fire, do not use a flexible power supply cord.
Connect the cooktop lead wires to the junction box supply wires in proper phase:
black (L1) to black
red (L2) to red
white wire to neutral
green wire to ground
And the label on the back of the new cooktop states: "For use on 3 wire, 120V/208V - 120V/240V system. 3 wire; 1 phase; 60 Hz" This is a Bosch model NET9652UC which is a hardly-used give-away :thumbup:.

Since the first sentence of the instructions says "Frame grounded by connection of grounding lead to neutral lead." can I connect the new white (neutral) and green (ground) wires coming from the cooktop to the white (neutral) wire in the wall box?

I can't find anything in the local code that would no permit grounding through the neutral but I'm not an electrician and might be missing something (2010 California Electrical Code Title 24 Sec 3).

I've been reading other similar questions and their answers and it also sounds like there might be an issue with the circuit being compatible with 240V appliances but not necessarily with this 120V/240V - can anyone tell from the wall box wiring whether that's the case?

I've attached pictures of the old wires, new wires, and wall box wires.

Much gratitude!
 

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#2 ·
Because the old circuit has an insulated white wire you can use this for the new appliance. There is a grandfather in the code that allows it to be used as both the neutral and ground.

You will connect black to black, red to red, and both the green and white of the appliance to the white in the box.
 
#4 ·
Thanks, Speedy.

I don't have a wire gauge but going by drill bit size they wires (not including their sheath) are definitely larger than a 1/8" bit and look a lot closer to a 5/32" bit. 6 gauge?

They're on one or two 40A breakers. The reason I'm unsure is this: I have among the other breakers two 40A breakers that are paired together. These are labelled as "Dryer" but shutting them off cuts power to the cooktop. Immediately above them is a 20A breaker that's labelled "Upper laundry" and if I shut off both the paired 40A breakers and this 20A, then power is cut to the clothes dryer (it won't start and there's no signal on the non-contact voltage tester). If, however, the paired 40A are off and the 20A is on the dryer won't turn on but the voltage test shows that the dryer wire is "hot". I suspect the previous owner used one of the paired 40A breakers along with the independent 20A breaker for the dryer, and those should be paired instead of the two 40A, if that's possible. I'm not sure.

The load of the replacement cooktop, as listed on the label on its back, is 120V-208V 7200W and 120V-240V 9600W. I can't find any mention of amps.
 

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#7 ·
Actually, as long as a household cooking appliance is 12kW or under it can be used on a 40A circuit. So yes, you are fine.

Did you say giveaway in the OP??? Nice score!
 
#8 ·
As soon I read the giveaway part that guy is pretty lucky got a very nice one as long there is no damage on anything.

Those type of glass toppers are not cheap I just have installed yesterday for my customer that cost little over 850 Euros ( big arse size )

Merci,
Marc
 
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