ECN Forum Forums General Topics of the Trade General Discussion Area Residental homerun

As DougW stated, I use deep 4X4s with 3/4" EMT for home runs. I don't get the BIG waste of money. They're 72 cents each.

Dave

Around Chicago you have to use emt and metal boxes for residental.

Yeah but it takes alot longer to rough a house in with pipe than with romex AND plastic is alot cheaper too. I don't think I have ever seen a house roughed in with emt. Why would you (unless it is some local ordinance or something like someone said).

It's not as if you can (legally, by code) pull more than 3 current carrying conductors in a pipe; so what benefit is there to piping it in? None that I can see (unless it's required for some strange reason in your area). If I have more than 3 current carrying conductors in that pipe, my 12's become 14's and my 14's become 16's after you derate. You'd have to pull #10's (THHN). It's a waste of time and material --- MONEY!
Unless, like I said, you have no choice.

You can put 9 THHN, 14 or 12 AWG current carrying conductors in a raceway before derating becomes an issue.

310.16 shows 14 AWG THHN rated 25 amps

Table 310.15(B)(2)(a) shows a 70% downward adjustment for 7 to 9 current carrying conductors

25 amps x .7 = 17.5 amps

The 14 AWG is still OK for a 15 amp breaker.

For 12 AWG

310.16 shows 12 AWG THHN rated 30 amps

30 amps x .7 = 21 amps.

The 12 AWG is still OK for a 20 amp breaker.

There are areas that must use EMT for residential.

For derating purposes you can use the 90 C column of 310.16 if you use THHN.

It isn't required by local code, but I routinely run home runs in my custom homes in EMT to the attic and basement/crawl. I terminate in 12x12x6 pull boxes and run an empty conduit for future expansion. The branch circuits are in RX with the HR stubbed to the crawl/basement/attic for connection in a pullbox.

You can do the same for NM. Article 334.112 requires 90 degree wire and 334.80 allows the 90 degree part of table 310.16 to be used for derating purposes.
This works for 4 NM cables pulled into bored holes also.

You cannot pull 9 #12's in a conduit without derating! I certainly never would and I couldn't get away with it around here either!

The only time I recall EVER putting more than 3 current carrying wires in a single conduit (usually you do not have to count your neutral) was at a bank, but it wasn't a homerun. It had a a bunch of switch-legs for "open" & "closed" signs in it and some travellers and I think the feed. In this case you can load it up because half of the wires will always be non-current carrying.

I gotta go make some $$$.

Again: the NEC is a MINIMUM standard. I NEVER run multi-wire BC's; every hot gets itself a neutral, whether it is in pipe or not. Of course, the service also gets a full sized neutral and I balance the perceived loads. It's amazing how many problems this solves.
But, I'll get back to you on this issue later. Gotsta run.

And if you really want to use pipe then why not PVC?

Later...

Hi,
If you have two double pole GFI breakers one 20A and one 30A going to a single enclosure would you run one or two pipes?

-regards

mustang

CJS,
Correct, but the derating doesn't change anything. Table 310.16(B)(2)(a) requires a 70% adjustment factor for 7 to 9 current carrying conductors in a raceway or cable. The ampacity of #14 THHN is 25 amps and #12 is 30 amps. The adjusted ampacities for these conductors with 9 current carrying conductors in a race way is 17.5 amps for the #14 and 21 amps for the #12. The maximum permitted overcurrent protection per 240.4(D) is 15 amps for the #14 and 20 amps for #12, so for all practical purposes, there is no derating under these conditions.
As far as using conduit, I see no real advantage of PVC over NM, but I believe that the use of EMT is a safety improvement over both PVC and NM.
Don