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Posted By: ShockMe77 Device Removal - 03/09/06 01:35 AM
We had a brief discussion in my alternating current principles class last night. The instructor was convinced that all grounded conductors at a receptacle location had to be pigtailed in order to not break the grounded path. Obviously, that's the best way to do the wiring at the receptacles, but is it necessary by the NEC? I only see this rule applying to multiwire installations where breaking the neutral could do serious damage to an appliance (like a PLASMA TELEVISION) if ever broken.

Comments?
Posted By: resqcapt19 Re: Device Removal - 03/09/06 02:15 AM
You are correct. The rule in 300.13(B) only applies to the grounded conductor of a multiwire branch circuit.
Don
Posted By: watersparkfalls Re: Device Removal - 03/09/06 03:35 AM
hey shock,
how would you do it without a pigtail?
put "two" wires under one recepticle ground screw?
if so; where is the ul listing for this type of device?
we all agree that the ground is the most important conductor and a pig tail would be the only way.

h20
Posted By: Tiger Re: Device Removal - 03/09/06 03:43 AM
The grounded conductor is the white/neutral

Dave
Posted By: watersparkfalls Re: Device Removal - 03/09/06 08:53 AM
opps "ed" not "ing"
my mistake....
then i agree, no pigtail required by nec.
not sure about damage to equipment since the "grounding" would still be there.
on a multiwire you open neut at homerun and you put 240 across the circuits and this is never good. although power tools run really fast for a little while yuk yuk.

h20
Posted By: tmegger64 Re: Device Removal - 03/13/06 09:30 AM
Good Morning

What about 250.148(B)?

Tom
Posted By: tmegger64 Re: Device Removal - 03/13/06 09:33 AM
opps same thing with grounded and grounding, got to wake up this am sorry

Tom
Posted By: Larry Fine Re: Device Removal - 03/13/06 02:04 PM
The reason a device-dependent neutral path matters on multi-wire circuits is that, when handle-tied breakers are not used, one circuit can be deenergized to be worked on, but another sharing the same neutral can still be hot, making the load side of an opened neutral connection hot.
Posted By: ShockMe77 Re: Device Removal - 03/14/06 01:42 PM
Larry, and isn't it true that if the grounded splice comes apart, one leg of the multiwire branch circuit will carry a higher voltage than the other ungrounded conductor? I seem to recall seeing/ reading this in one of my trade books somewhere. Could you explain why this happens?
Posted By: George Little Re: Device Removal - 03/14/06 02:15 PM
At the risk of insulting everyone's intelligence on this forum I explain it this way- If you have a multi-wire branch circuit consisting of two ungrounded conductors and one grounded conductor, the loads of each of the ungrounded conductors are using the single grounded conductor for a return to the transformer. Should the grounded conductor be interrupted and the is no return to the transformer via the grounded conductor then the return path is through the other ungrounded conductor and any load on that other ungrounded conductor path, This could and probably would create a problem if the total current flow exceeded the limit of one of the components in this new found path back to the transformer. Example a 10a. load on one ungrounded conductor and a 1a. load on the other conductor now become a total load of 11a. and the 1a. load (100w. bulb for instance) would not tolerate the flow of 11a. and the bulb would burn out.
Posted By: ShockMe77 Re: Device Removal - 03/14/06 04:55 PM
That is an excellent explanation.
Posted By: n1ist Re: Device Removal - 03/15/06 01:22 AM
Not quite. Using ohm's law, at 110V, the 10A load has 11 ohms resistance. The 1A load has 110 ohms resistance. Assuming the resistance doesn't change (not true with light bulbs since the resistance depends on temperature and therefore power...), if the neutral opens,
we now have 110 ohms in series with 11 ohms
(121 ohms) across 220V. In that case the current in either is 1.82A. The 10A load will see 18.2 volts across it and the 1A load will see 182V across it, until it blows.

/mike
Posted By: George Little Re: Device Removal - 03/16/06 02:56 AM
n1ist-You are correct with your math approach but the end result would be the same. You'd burn out something- what ever was the weakest point.
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