subpanels and grounding

[brianlanning]

(a slight followup first for those of you who were reading my subpanel thread a few days ago)

I decided not to use the 100amp box. I found a proper 12 postion subpanel at the borg. I've already started the install. I'm using

3/4" emt with #6 wire, 60 amp breaker in the main box, a 75' run, all indoors.

Originally, I was going to run four wires through the 3/4" pipe (red, white, black, and green). The electrical guy at home depot said that if you're using emt, you don't need the separate ground wire since the boxes are grounded together through the emt. Does this sound right? So far, I've run the other three. It's a bit of a long run so I'd rather not do the fourth wire.

brian

[Art Greenberg]

Are you certain you won't exceed the fill limit (or need to derate the conductors) on the conduit with three current-carrying #6 conductors?

Check the NEC. I think you need the ground wire. And bonding at both ends of the conduit.

[Jim]

No, but it does sound like you should let someone who knows what he is doing (such as an electrician) do the job. Jim

[Doug Miller]

If you're using THHN or THWN conductors, that's ok. If TW, THW, RHW, or RHH, you have a code violation already. They're probably THHN, but you oughta check just to make sure. It's stamped on the insulation.

The NEC _explicitly_permits_ the use of EMT as an equipment grounding conductor. [Article 250-91(b)]

[htroberts]

Even if the EMT is allowed to be the grounding conductor, I'd run a copper wire anyway, especially for a circuit feeding a subpanel.

[brianlanning]

I believe it's THHN. He had a code book there and looked up the types, gauge, and conduit sizes on the spot.

Thanks, this is what I was looking for.

brian

[brianlanning]

Those sizes came from a NEC code book they had there in the store.

brian

[LRod]

There is one other thing to consider and that is three 6s in 3/4" conduit, even thought permitted, can be a tough pull (especially over

75'. Can it hurt you to put in 1" instead? You'll probably have to use preformed elbows.

[Lew Hodgett]

Nice try but no cigar.

Not in my world anyway.

Lew

[Scott Lurndal]

And what world is that? See the NEC. EMT is explicitly allowed as the grounding conductor. BX and armoured cable are explicitly disallowed (as of 1999?).

If I were doing it, using the EMT as the grounding means, I'd use compression fittings rather than setscrew.

scott

[Mike M]

[brianlanning]

It was tough. I finished it last night. I used 90 degree fittings also which made it that much worse. Half way through the project, I started threading sections of emt as I assembled them. That made the job a lot easier. I didn't look at the price for 1" conduit. I know the 1 1/4" conduit I would have used for the #3 100amp wire was $15 for an 8' segment. That was three times more than the $5 for the 3/4". So I went with the 60 amp parts. If I had to do it again, I would buy the pipe bender. That tool would probably have been cheaper than the cost of all the fittings and it would have made pulling the wire easier.

brian

LRod wrote:

[Doug Miller]

Threading EMT is _explicitly_forbidden_ by the NEC.

[Dave Hinz]

I didn't know you _could_ thread EMT, even if not forbidden from doing so?

(side note: just how many groups do we cross paths in, Doug?)

[Doug Miller]

I didn't either, actually.... not sure why anyone would try, since the walls are so thin. But it's there in the Code.

At least two besides this one, I think. :-)

[Art Greenberg]

I *think* he meant as in "threading a needle". Rather than pull the wires through a fully assembled conduit run, he's pushing the conduit sections onto the cable, one at a time.

At least, that's what I think he meant.

[LRod]

I took it that way, too.

[brianlanning]

oops, I mean pushing wire throught he conduit, not cutting threads in the ends.

brian

[Scott Lurndal]

I suspect he meant that he was pulling the wire through the sections as they were assembled. There isn't enough steel in EMT to thread....

scott

[ATP*]

Never use the minimum conduit size allowed by the NEC. It's not worth it. Also consider using boxes as pull points when you change direction and at reasonable intervals.