Question on home wiring

[John Grabowski]

Does NEC require a de-rating for the neutral wire current?

If you have 20 Amp breaker on phase A and a 20 Amp breaker on phase B and both phases share a neutral, you would think that the max current the neutral could ever see is 20 Amps, but that is wrong. Due to power factor issues there can be more than 20 Amps flowing through the common neutral wire.

I don't think this will be a problem for the OP in his garage but it was a problem in large office buildings with large numbers of early PCs. I am curious if the NEC codes address this question?

*The code does address nonlinear loads, but I forget specifically in what chapters. Article 210.4 does mention them as a FPN.

[terry]

Quote: "I'm not an electrician but as I understand it if one breaker is shut off the neutral can still carry current if the other breaker is on".

Suggestion: You use a double pole breaker. This disconnects 'both' the hots associated with that Edison circuit and its' single neutral. This is how they are wired in our house.

The two hots are the two 'legs' (sometimes and often incorrectly called 'phases') of the supply. The 'plus and minus' ** 115 volts, usually being the two ends of the single phase 230 volt centre tapped output winding of the local distribution transformer.

** Being AC this + and - business is, strictly speaking, incorrect. But have found it a way of explaining three wire (and ground of course) 115/230 volt systems business to certain people (usually my neighbours!) who don't understand electricity very well. Certainly not those here present of course.

[clare]

By code all the wires will need to be "tagged" - all neutrals white, all lines black (or possibly red) - at BOTH ends.

[clare]

Residential electricians deal with black, white, red and green. ( or shades there-of) So grey and mauve could be black and red?

[terry]

Agree. But have met electricians who know all about current practice of how to wire, how much slack, frequency of stapling etc. etc. but haven't got a clue about the ratio between RMS and peak voltage, or why phase to phase voltage is different from phase to neutral voltage, for example in 3 phase service in a supermarket lighting sytem and have no idea how a GFI works.

[gfretwell]

Grounds have to be green, green with a yellow stripe or bare Neutrals have to be gray or white. No other colors are specified and a "hot" can use anything else. In a commercial installation you might see 10 or more colors for the hots.

[clare]

And they need to know this theory to effectivey and safely wire a house? Residential electricians do not need to know 3 phase. And they need to know how to wire a FFI, but do not need to know the nuts and bolts of how it works.

That's why there are different licences - a lot of industrial electricians would have a heck of a time wiring a house. No conduit? No BX? The wires go THROUGH the 2X4 studs? No raceways?

How the heck am I supposed to rout the wires?

[bafenator]

That is what I have previously done, 6-gauge to a subpanel. Initially, I only brought out two 120V circuits for outlets, and a

220V circuit for lighting. But, it's getting *really* cold, and a friend will be working in there with me. With multiple lathes, halogen work lights, and space heaters working at the same time, it was time for more outlets.

Now, with 6 20-amp circuits for 120V outlets, I'm more than set. If I needed more than that, I'd need a bigger run to the subpanel - and since I only have a 100A service on the house, pulling more than 50 amps just to the garage wouldn't be that good of an idea.

Doing one splice in each box with the 10-gauge wasn't bad at all. Everything went quite well, with no surprises.

[bud--]

And it is inconceivable a licensed electrician, residential or other, wouldn't know that.