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Nords
Apprentice Appliantologist
| Joined: | Mon May 5th, 2008 |
| Location: | Oahu, Hawaii USA |
| Posts: | 1 |
| Flavorite Brew: | Guinness, what else?!? |
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Posted: Sat May 10th, 2008 23:56 |
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I seem to have found a circuit breaker that, when it's open, grounds both the hot and neutral wires.
Our rental house is 30 years old and in reasonably good shape. We've never had a problem with the circuit breakers or the receptacles. When the magnetron in the 16-year-old combination gas stove/microwave died last week, we bought a new gas stove and a separate microwave. Since the new microwave is separate, it needs its own receptacle. It's mounted over the stove (under a wall cabinet) so we ran its cord up through the bottom of the cabinet to add a receptacle in the back of the cabinet.
The stove receptacle is probably 30 years old and looks like it's made out of brown Bakelite. It's labeled 120v/15A and one of its holes is able to accept both "regular" 120v plugs as well as a plug with one blade (the neutral wire) rotated 90 degrees. (The old gas stove had a matching plug.) I checked that the receptacle indeed had 120v on the hot plug and zero on neutral & ground. Then I opened the circuit breaker and pulled out the receptacle. I fished a new wire down behind the wall from the cabinet and pulled it into the stove's receptacle box. Since the stove receptacle already had another receptacle daisy-chained to it, I pigtailed the new wires into one pair of other wires with wirenuts.
I stuffed everything back into the receptacle box and (before shutting the circuit breaker) checked the connections: everything was grounded. Zero ohms resistance. I made sure no wiring was touching in the stove's receptacle box. Still grounded. I pulled all the wires off the receptacle and learned that one pair of hot/neutral wires was still grounded. I pulled another foot of that grounded wire out of the box and it was fine-- no cuts or cracks or any visible problems. Nothing changed when I flexed the wiring-- solidly grounded.
None of the wires are labeled but by now I was pretty sure that the pair of grounded wires was connected to the (open) circuit breaker. I capped them off and shut the breaker. It shut just fine and stayed shut. I checked voltages and had 120v on the hot wire with no voltage on neutral or ground.
I finished wiring in the microwave receptacle and everything works fine. The tenants are happy. Life seems good, but I don't understand how the circuit breaker works.
I thought that a fault in a typical household circuit breaker would just pop open its contacts and leave the load-side wiring ungrounded, not grounded. But the circuit breaker whose load wires I was measuring would have to shut by somehow breaking the ground between the load's hot/neutral wires before making contact with the line-side voltage, and that would mean an extra set of contacts or poles. Grounding when opening seems overly safe, but I don't design circuit breakers and I don't know all the codes.
I can't remember ever working on load-side wiring that was totally grounded when its breaker was open. Is this a standard design that I've never noticed before, a design just for 120v stove receptacles, or a problem?
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Eventually I'll put something witty here.
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RegUS_PatOff
Fellow, Academy of Sublime Masters of Appliantology
| Joined: | Sat Sep 24th, 2005 |
| Location: | Milwaukee, Wisconsin USA |
| Posts: | 1541 |
| Flavorite Brew: | A & W |
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Posted: Sun May 11th, 2008 02:09 |
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circuit breakers don't normally have a connection to ground, unless it's a GFI, but I don't think they would use the ground connection for that purpose.
What scale is your ohm-meter on when measuring that, the lowest scale i.e. 100 OHMS ?
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RegUS_PatOff http://www.youtube.com/watch?v=oPAY2LsKVEw
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Cactus Bob
Master Appliantologist
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Posted: Sun May 11th, 2008 03:20 |
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I BET YOU HAVE PUSH-MATIC BREAKERS ! . or something odd like that , some main breakers will do that too . i ran into this in my own home when i installed my auto-switching ,auto starting generator . it nearly blew the main breaker out of my box , when i replaced it the new one smoked even through it was turned off to the grid . i ended up replaceing the main box that used MODERN breakers .......... youll be fine .. i think this FETURE gorunds your wireing when power is off , protecting from lighting .
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