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I had a new cooktop installed but it does not work. The unit replaced an old one and was simply plugged into the existing outlet. After checking the basics (no tripped breakers, etc), I whipped out the old multimeter and measure the voltage difference between each input. The results were surprising:

h1 - h2 = 240  (correct)
h1 - N  = 0    (should be 120)
h2 - N  = 240  (should be 120)
h1 - G  = 120  (correct)
h2 - G  = 120  (correct)
N  - G  = 120  (should be 0)

h1 = Hot 1
h2 = Hot 2
N = Neutral
G = Ground
(Parenthesis are what I expected to measure)

I'm obviously mis-wired, but which wires are in error?

Freedom_Ben
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3 Answers3

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I would open up the receptacle box if possible to see what's going on, but the only way I can think that these readings would be plausible would be if the outlet neutral is not connected to a neutral conductor going back to the panel but is instead shorted to H1. That would produce the readings you've recorded. And if your old stove didn't use the neutral conductor, it would work fine.

Hank
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  • Interesting. I tracked down the old stove plug and popped it open. Sure enough the neutral prong is not used, just h1, h2, and ground. _mind blown_ – Freedom_Ben May 24 '16 at 04:12
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    Well if that's what they're doing, they should be using a NEMA 6. Are you *sure* that third wire is ground and not neutral? Because there was an older plug called NEMA 10 which had neutral and no ground. Either way, the temptation is to link neutral and ground, which is bad news. But it's a lot easier to fix missing ground than missing neutral - run a separate ground vs. replace the entire cable run. – Harper - Reinstate Monica May 24 '16 at 17:24
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Something is terribly, shockingly awry here. The only way you can get these measurements is if the line marked H1 and the line marked N are shorted together -- but normally, that'd trip the breaker. So, either you have an open neutral somewhere upstream of what's shorting H1 to N, or worse yet, you have a circuit breaker that is managing to not trip when faced with a bolted fault, and said fault has somehow not BBQed your house.

ThreePhaseEel
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I would take a hard look at the receptacle wiring. It's possible you formerly had a NEMA 10 at that location (hot-hot-neutral) and someone hacked in a NEMA 14 improperly. Or you could have some other defect in the connection there. Or possibly back at the panel. It just needs a good general going-through - de-energize the circuit, take it all apart and see what you see.

If you have only hot-hot-neutral wires and want ground also, you are allowed to route the ground on a different path, and you can buy ground wire separately, so it's easier to retrofit than you might think.

Harper - Reinstate Monica
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