I’m going to check with the Inspector, but for now how many #12 wires can I run in ½” pipe?
I’m going to check with the Inspector, but for now how many #12 wires can I run in ½” pipe?
It depends what kind of pipe you are using. Is it EMT or PVC? Also what kind or wire are you using? Is it THHN? You shouldn't try to run romex through conduit somyou need to use individual wires. Appendix C of the NEC will give you the answers, but if the number is less than 7 you will be fine. Good luck I hope this helps.
Matt, thank you. It is EMT and THHN.
If, by "pipe", you mean EMT, you can run (9) #12 THHN/THWN conductors. That's from Table C1 in Annex C of the NEC.
I think maybe you could get one wife in 1/2" conduit. But wouldn't that be a serious event? ...oh wait... you said "wires"... that is a different subject. Jury, please disreguard the previous statement.
Originally Posted by Paul Simmel
Depending on your run, I would consider upsizing to 3/4 even if the code/inspector says it will fit. If you go through a couple of bends, you can get jamming of the wires. Happened to me running my subpanel.
EE friend of mine said there's a calc for jamming somewhere in the codes. Will tell you if there's a problem based on conduit/wire size and degrees of bend in each pull.
If it's a straight pull, then forget everything I said!
Cheap insurance.... instead of bends, install 'pull boxes' to make adding a new circuit much easier. You'll thank me in a few years.
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Something I forgot to post last night and is sort of referred to in Russ' post - derating based on the number of conductors you pull.
When you have conductors "bundled" for more than 24", you need to derate the ampacity (current-carrying capacity) of the conductors based on table 310.15(B)(a). 4-6 conductors means derating to 80%, 7-9 conductors means derating to 70%.
If you're running 1/2" EMT and want to pull (3) 20-amp 120v or 240v-only circuits, you're OK. If you wanted to pull (2) 120/240v circuits where you ran a neutral with the 240v circuit so you could pull a 120v off - that'd be fine also.
If you ran (4) 20-amp 120v circuits and used the conduit as your equipment grounding conductor, you'd have a problem.
I also agree with the other posts about running 3/4" conduit. It doesn't cost that much more and will make the pulling a lot easier.
Conduit is cheap, so if you have the room, add an extra run or two. I ran three separate 1/2" conduits approximately 40 ft from the circuit panel to the basement. I was able to pull two pairs of 12aug THHN per pipe with a 1/4" snake with no problems.
A flute without holes, is not a flute. A donut without a hole, is a Danish.
I appreciate the info! (Another question at bottom)
I know the Topic/question is dumb… I had all of last night off to think about today’s work and the conduit-fill was an important consideration for planning today’s work… and the help was very well taken. (I just couldn’t remember how many wires for ½)
The shop/garage is the first phase of the electrical work I will be doing for new construction. Garage is a 100 amp sub-panel (neutral only back to main panel aside from 1" tightly connected EMT).
I have many pull boxes between rather short runs all over. Everything is ½ EMT thus far.
I was afraid of a bottle neck at the beginning of the run. But I think I’ll be ok.
Thus far, within two ½” 10’ runs before breaking up and distributing to their respective locations, I’d like to feed the following:
a)Ceiling lighting (1 circuit)
b)10 Wall outlets (2 circuits)
c)3 garage door openers, outside lamps (1 circuit)
d)Furnace (1 circuit)
e)Hard-wired compressor (3-wire 220, 1 circuit)
If I ran separate neutrals for each circuit, I’d have 13 total wires to split between the two ½ feed lines.
If I shared ceiling lighting/wall outlets, garage openers/wall outlets with common neutrals, then I’d have it down to 11 wires.
Two part question please?
Re the above, sharing neutrals should be every other circuit, right?
From my current sub-panel… (neutral back to main panel – no grounding outside the 1” EMT)… regarding approximately 4 yet to be run 20 amp, 220 circuits, is it safe/code to share every other (in my case) neutral (third wire)? In my last shop, all my 220 third wires were commonly grounded to the conduit – no neutrals.
Not sure about code, but if you share neutrals, you better be darn sure they are on opposite phases for 120v and still only do it for 2 circuits. Should be able to share a GROUND, but not neutrals without thinking about it.
Same goes for 220v, if the equipment needs a NEUTRAL (like a lot of stoves), it better be a separate wire, not grounded to the conduit. If it's just truly a ground, then you might be alright. If it was me, I'd still run a separate ground wire to the box, and pigtail it to the outlet box.
Paul, my quick recommendation would be keep it simple, upsize the conduit as needed, and run a separate neutral for each circuit. If you're convinced, you can stop reading now.
If you want the long version:
Sharing a neutral between two 120V circuits (a "multiwire branch circuit" in NEC-speak) requires that the two circuits be fed from the opposite hot legs of the service (i.e., 240V will be present between the hots). If this is done correctly, the out-of-phase neutral currents will cancel, and the neutral wire will not be overloaded. Get it wrong, and the currents will summate, potentially putting 40A through a 12 ga wire. Very bad.Originally Posted by Paul Simmel
In most panels, adjacent breakers (not "every other" breaker) are on opposite legs. However, this may vary by manufacturer. You need to be 100% sure.
Having said that, my strong preference is to avoid multiwire branch circuits. The reasons I don't like them are:
1. As described above, it's easy to miswire this kind of circuit. This mistake could easily go undetected, as both circuits will appear to work properly, until an overloaded neutral melts or starts a fire.
2. Even if it's done right the first time, subsequent wiring changes could result in a dangerous condition.
3. A neutral fault in a multiwire branch circuit can be disastrous (i.e., 240V applied to a 120V load).
4. Multiwire branch circuits don't allow downstream GFCI protection.
In my non-professional opinion, there are just too many drawbacks to justify the small savings in materials.
I think you guys are absolutely correct. I’m going to keep it simple and not share neutrals. I am going to run the appropriate sized conduits as needed and sleep at night.
Now that I think about it, another reason for keeping everything separate is to avoid a hot (A) circuit when the breaker is off, if (B) circuit energizes (pulling through the common neutral)? The only safe way to work on either (A) or (B) would be to turn off both breakers. I might remember this, or I’d alternate red and black hots all the way down, but for someone down the line it could be dangerous.
(Please correct me if I am wrong on that.)
Also, and I forget this sometimes, a major factor in running EMT is to have the ability to pull additional lines in the future, so some larger conduit or extra runs t leaves room. I think I will run some empty chases to strategic locations as well.
Thanks very much for the conversation. It is of tremendous value to me.
The NEC requires common disconnect for all hots on a single device [210.4(B)], but not on shared circuits. How's that for partially protecting things.
To explain further, I "split-wired on a multi-wire circuit" a large room in our addition. There is a huge wall that could be a place where you might want to put a big entertainment center. I ran 20 amp circuits and did a multi-wire circuit (shared neutral), using 12-3 Romex. There is nothing in the code that requires use of a 2-pole breaker for the multi-wire circuit. I also split-wired the receptacles, so each outlet on any given receptacle is fed from a different hot leg. That way you effectively have 40 amps worth of power available through each duplex receptacle. Because both circuits are tied to a single yoke, I had to use a 2-pole breaker (or handle ties) so shutting off 1 circuit would shut off both.
For shop wiring in conduit, I'd definitely run separate neutrals.
In terms of running extra large conduit so you can pull lots of extra conductors - that's not going to help. You will run into the derating issue. For example, let's say you ran 3/4" EMT because it would allow you to pull up to (16) #12 conductors. You decide to run (5) 120v circuits through it. That means you'd have (10) current-carrying conductors - (5) hot and (5) neutrals, plus 1 equipment grounding conductor. Sounds good - right? Based on the derating table 310.15.B(2)(a), you'd have to derate the ampacity of your conductors by 50%. That means, to run 20 amp circuits, you'd need to pull #8 conductors for your 20 amp circuit - you couldn't pull #12 anymore.
If you're running 20 amp circuits, you can fit a max of (3) 20-amp circuits with separate neutrals running on #12 THHN/THWN in a single conduit before you have to upsize your conductors to #10.
Last edited by Rob Russell; 11-10-2006 at 6:06 PM.
Paul, your instincts are correct. If the neutral is carrying current, it can become a hazard. The NEC sort-of addresses this by requiring that shared neutrals be pigtailed.Originally Posted by Paul Simmel