Multi-wire circuits for basement shop


Old 09-17-04, 03:40 PM
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Multi-wire circuits for basement shop

Before I state my questions, let me first say how impressed I am with this site. I'm sure glad I stumbled upon it. I am running two 20 amp circuits into my basement workshop. I plan to have have four separate outlet locations. At each location, I'll have two duplex receptacles, one for each circuit. I had originally planned to connect the feed-in to the neutral screw of one receptacle, connect the feed-out to the neutral screw of the other receptacle, and connect the remaining neutral screws on each receptacle together with a short piece of white 12 AWG wire. I'm an electrical engineer and I looked at all kinds of phase angle differences between the loads in each receptacle and convinced myself that this should be okay from a current-carrying point of view. However, I got the sense that it would not conform to Code when I read a note in the Black and Decker "The Complete Guide to Home Wiring" that neutrals had to be pigtailed and not routed through the receptacles. After wading through many of the posts on this site, I 've learned that the reason for this is that the failure of a device in the circuit should not cause an interruption in the neutral path. I look at the side of a receptacle and wonder how on earth that solid metal bridge between the screws could fail without openning a breaker. Personally, I would be much more dubious of reliably joining four 12 AWG wires (Feed-in, Feed-out, and pigtails to each receptacle) and the extra congestion it will cause, even in a large workbox. Wire nuts will always concern me, particularly those that claim you do not have to twist the wires together first. But I will use the pigtails, if that is what the code requires. Is there any other problem with having outlets from two different branch circuits in the same box (assuming it is sized properly for the number of wires)?

Second Question: When I look at the weatherhead, I see two 8 AWG(!?!) wires coming from the connecting to two 1/0 wires running down to my service panel. I have what I believe is reffered to as 200 amp service ( a main dual 100 amp breaker) so the 1/0 seems about right for 100 amps in each leg. But 8 AWG? And what about a neutral connection? Is it coming in through the ground? I don't there is room in the service panel for any kind of transformer that could generate the neutral and have sufficiently low impedance.
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Old 09-17-04, 03:59 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Let me see if I can address your questions/concerns without adding to the confusion.

The reason that neutrals must be pigtailed is to prevent an unsafe situation from developing. That much you know from reading. However, they are not so much worrying about the connection between the halves of the duplex receptacle failing as they are about one of the wires coming loose or the receptacle being removed.

The issue is that if you remove the receptacle (to replace it, for example), you break the neutral. If you forget to hook it back up properly you may not notice the problem unless you test each and every receptacle on the circuit, especially the ones downstream from the receptacle you replaced. The downstream receptacles will have no neutral, and you will end up with more than 120 on one side and less than 120 on the other, depending on what you actually plug into the receptacles.

If you use pigtails, you will not be disturbing the downstream neutral when you disconnect the neutral from the receptacle being replaced.

I hope I have made some sense with that.

As for your incoming service, the neutral comes from the power company. The neutral cannot be fabricated from the ground or from a transformer. Look again, there are three wires there. As for the size, the power company has different standards to follow. I'm not sure what they are, but they are quite different from what you and have to follow.
Old 09-17-04, 06:45 PM
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Join Date: Dec 2001
Location: New York
Posts: 1,365
If you have a 2-pole 100A main breaker, you then have a 100A service. It is referred to as a 100A service. I 100A service is typically provided with #4 awg copper or #2awg AL phase conductors. A 200A service gets at least 2/0CU or 4/0AL.

As a side note, 1/0awg is smaller than 2/0awg. Which in turn of course 2/0awg is smaller than 4/0awg.

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