Need help 220 cooktop with downdraft & old wiring

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  #1  
Old 01-28-20, 01:17 PM
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Need help 220 cooktop with downdraft & old wiring

I wired the new cooktop just like the old cooktop, but I would like a little advice as I don't know who installed the old one.

I have a 220v/30a with 3 wires: bare ground, black (hot) and white (hot).

The new cooktop has 4 wires: white, black, red and bare ground.

I have it installed and it's working fine as follows:
Cooktop Red to incoming White
Cooktop Black to incoming Black
Cooktop Ground to incoming Ground
Cooktop White to incoming Ground

The Cooktop White to incoming Ground was required for the blower/downdraft to work.

As mentioned, this is working and installed as the old one. But that doesn't mean it's right!

Thanks in advance!
 
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Old 01-28-20, 02:05 PM
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Dangerous install. You can not use the ground as a neutral .
You need to replace the three wire cable with a four wire cable.
 
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Old 01-28-20, 03:50 PM
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Thank you! It evidently has been that way for a long time. But it just didn't seem right, glad I asked!

Are you talking about an adaptor or running new wires, etc? Thanks again.
 
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Old 01-28-20, 06:18 PM
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It may have been just fine before if your previous unit did not require a neutral. Now that you need a neutral the only way to get the fourth wire is a new cable.
 
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Old 01-28-20, 06:25 PM
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Older stoves had only 2 hots and a bare ground. The frame of the stove was bonded so actually the ground became the neutral. The plug was referred to as an ungrounded plug. The old plug was a NEMA 10-30, or 10-50. The newer plug is a 14-30 or 14-50. So most likely the wiring is correct for the original cooktop at the time it was wired. Look closely at the instructions as it may show an option for three wire connections. If it has no instructions for three wire connection you will need to replace the three wire circuit with a four wire circuit. There is no adapter to use.
 

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Old 01-28-20, 08:59 PM
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This is a cook top not a stove. Many of them are only 240 volt. This one is 120/240 because it has a fan in it.
 
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Old 01-29-20, 08:04 AM
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This is a cook top not a stove. Many of them are only 240 volt. This one is 120/240 because it has a fan in it.
I know it is not a stove. I was using a stove as an example because the cooktop being installed is 120/240. Some cooktops that are 120/240 have instructions where they can be wired to an existing 3 wire circuit just as a newer 4 wire stove can be placed on a 3 wire circuit when bonded at the frame per the manufacturer instructions.
 
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Old 01-29-20, 10:19 AM
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It is the flip of a coin.

If an appliance comes wired for 120/240 operation it should be required to be on a four wire circuit.
Allowing it to be converted to three wire operation is wrong regardless of the manufacturers instructions.
 
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Old 01-30-20, 09:59 AM
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Some cooktops that are 120/240 have instructions where they can be wired to an existing 3 wire circuit just as a newer 4 wire stove can be placed on a 3 wire circuit when bonded at the frame per the manufacturer instructions.
But the "Existing 3-Wire Circuit" had to be 3 insulated wires such as 8-3 plain NM or 6-3 plain NM. The only exception was when SEU cable was used and the stranded bare neutral conductor was also used as ground. Bare grounding conductors in older NM cable were never approved to be used as a neutral conductor.
 
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Old 01-30-20, 12:32 PM
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I would run a new 4 wire cable to it.
 
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Old 01-30-20, 12:36 PM
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But the "Existing 3-Wire Circuit" had to be 3 insulated wires such as 8-3 plain NM or 6-3 plain NM. The only exception was when SEU cable was used and the stranded bare neutral conductor was also used as ground. Bare grounding conductors in older NM cable were never approved to be used as a neutral conductor.
Good that you pointed that out. I'm use to mainly seeing SE cable used for the stove feeder in older homes and didn't even think about it.
 
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