DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (http://www.diychatroom.com/)
-   Electrical (http://www.diychatroom.com/f18/)
-   -   EMT fill - 2 x 3/4" or 1x 1"? (http://www.diychatroom.com/f18/emt-fill-2-x-3-4-1x-1-a-2405/)

IvoryRing 05-03-2006 08:20 AM

EMT fill - 2 x 3/4" or 1x 1"?
 
I'm running power in my 'garage' (which is really going to get turned into a workshop, wood & metal, rarely with a car actually in it)... due to several factors, I'm going to surface mount rather than run behind the sheetrock.

1.) Is there any code problem with running Romex inside EMT? (rather than THHN)

2.) At each power point, I'm running 2 GFCI 20A circuits (each via 12/2 wg), to a 4" square box (to end up with two duplexes side by side, one on circuit A and the other on circuit B), and a 240 20A (via 12/3 wg) to a second 4" square. Am I better off running 2x 3/4" EMT (one for the 12/3 and a second with two 12/2), or 1x 1" EMT (with all 3 cables, and a nipple between the two squares)? I've only got two 90 degree bends, so I'm going to use preformed elbows rather than bending the EMT, so as to avoid buying a bending head.

3.) The 240 I'm running just to be prepared for the future, not because I have any 240 equipment yet. Does normal shop equipment come like a dryer or range, where you have to supply your own cord anyway?

Speedy Petey 05-03-2006 03:20 PM

1) Without going into the arguments regarding this, bottom line is don't do it!
The legality is questionable. Conduit fill is a real issue. Adding circuits is annoying at best, impossible at worst.
And it is simply poor workmanship.

2) Use all 1/2", and use THHN conductors. You do NOT need "12/3" for a 240v circuit. NO neutral is required so you would be running wire for no reason. Regardless, if you use individual conductors you can add what you need later. I would run the pipe and boxes now but not pull any wire until you know your loads.
240v means nothing without knowing the amperage of the equipment you re feeding.

3) Typically tools and equipmment have cords already installed.

IvoryRing 05-03-2006 05:12 PM

Thanks for the feedback Speedy. Would you use 2 seperate 1/2" EMTs, one for the 120, one for the 240? Do you typically leave pull tape/string at install, or just stuff a fish down the EMT when adding conductors later in this situation?

Sparky Joe 05-03-2006 06:27 PM

I'd say use 3/4, 2 if you like though with the number of wires you mentioned its not necessary. In my opinion 1/2 inch looks cheesy exposed and the cost difference is minimal.
I would use the thhn probably costs less and by code you don't need a ground, though its good practice to pull one anyway. And for the 2 duplexes you need only one neutral given that the 2 hot wires are on different phases, if not then you need a neutral with each. So I think you could save more money with thhn than with romex.
And pulling in a string is a good idea if you plan on expanding, just saves work later.

Speedy Petey 05-03-2006 06:52 PM

1/2" looks "cheesy" exposed. Hmmm, there's one I've never heard before.

1/2" is perfectly fine for this application, and I think you are fine with one. With plans for more circuits later you might want to run 3/4", or a second conduit.
3 wires for the 120v circuits, 2 wires for the 240v, and a ground. Six #12 in a 1/2" is well under fill limitis and easy to pull, especially with only one 90.

I don't like pull strings. Leave it out and snake the new circuits in later. You can likely even just push them in.

Sparky Joe 05-03-2006 10:42 PM

Well its your call, I've always thought 3/4 looked more substantial but perhaps i'm fruity for noticing how things look, and of course there's always the capacity issue with going with the minimum.

Speedy Petey 05-04-2006 05:23 AM

I will say, commercially I rarely use 1/2" other than to feed individual devices, but in a home I think it looks "less induatrial", and there is not much need for more. Other than for larger condcutors.

IvoryRing 05-04-2006 10:48 AM

Thanks to both of you for your suggestions and ideas - I think at this point I'm going to run just one 3/4 - the following conductors: 12 green for EGC for all outlets and bonding boxes and EMT, 12 red & 12 black for the 240, 12 black and 12 white for GFCI circuit A, 12 red and 12 white for GFCI circuit B. Seperate neutrals for the two 120v circuits as they are on GFCI breakers.

I'm not particuarly concerned about cheesy/industial appearance - this is a shop anyway, so it isn't going to look 'nice' no matter what. I'm thinking the 3/4 simply for future capacity. As it stands now, I'll have 7x 12ga conductors in the EMT - how close can I get before 'conduit fill' becomes an issue? And when do I have to derate? Should I be pulling 10ga instead of 12ga now for that reason?

Edit to change 'grounds' to 'neutrals'...

Sparky Joe 05-04-2006 06:42 PM

So it sounds like you own a code book(EGC). in the annex in the back for EMT it says you can put 13 #12's in a 3/4 (7 for 1/2) and thats only counting "current carrying conductors" which means grounds don't count, but from experience you'll have a hard time getting more than 10 wires total in there.
From Table 310.15(B)(2)(a) for 4-6 conductors(not grounds) you have to derate to 80% of the capacity, for 7-9 70% capacity, for 10-20 50% capacity, then Table 310.16 says a #12 thhn can carry 30 amps, so for what you are initially pulling, 6 current carrying conductors you've only derated to 24 amps. Even if you pulled a neutral to your 240 you'd be at 70% which is 21 amps.
Sounds like you got a pretty good understanding of what you're doing, so I'm sure you'll do fine.
Oh and be sure to use "industrial" raised covers(the kind that bolt directly to your receptacle and to your 4sq box) not the plastic, or steel, wall plate type.

Speedy Petey 05-04-2006 07:17 PM

Joe, I'm not sure which table you'r using in Annex C, but for #12 THHN in EMT conduit it is nine for 1/2" and sixteen for 3/4". Also conduit fill is based on total conductors, not just CCC (current carrying conductors).

For derating we use CCC's. Also, a neutral of a 120/240v circuit is not counted in derating since it only carries the current imbalance {310.15(B)(4)}

Sparky Joe 05-04-2006 09:34 PM

I do stand corrected on both points, it seems I was looking at ENT, how do you stand on the general workmanship points?

Speedy Petey 05-05-2006 05:23 AM

Quote:

Originally Posted by Sparky Joe
........, how do you stand on the general workmanship points?

Not sure what you mean. :confused:

IvoryRing 05-05-2006 10:51 AM

I do have a copy of '05 NEC, along with the McGraw handbook, and a handful of other books, but I'm sure it's no surprise that it isn't always simple to figure out where to look, and getting feedback from real people is very useful.

Joe - your comment on 'industrial' covers - are those the ones marked 'Exposed' on the box at HD? Aside from 'rounded corners so I won't snag myself', is there some other (either code or just common experience) reason to go with those?


All times are GMT -5. The time now is 04:05 AM.


Copyright 2003-2014 Escalate Media LP. All Rights Reserved