Subpanel wiring

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I'm wondering about putting a subpanel in my garage.
Right now there's only 1/2" EMT under about a 10 ft run of concrete and one 15 amp circuit.
Question 1. Would it be legal to run three #10 wires for a subpanel fed from a 30 amp breaker and leave the #14 for the 15 amp circuit? If that conduit is continuous will that be fairly easy to pull through? Can I ground through the EMT? I've heard this might lower the allowable number of wires in the conduit.
Question 2. Once I have that subpanel, is there any limit to the number of circuits that can be split from it if none of them are over 30 amps? eg. could I have a 30 amp 220V and a 20 amp 110V?
Thanks for any help you can provide.
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I recently pulled 3 10 ga wires through 1/2 EMT and it was far from a walk in the park. And that was out in the open pulling one section at a time then joining the sections. Not bad on the straight parts, but a bear through the 90s. I wasn't using stranded wire so that would help. I don't think it would have been possible with small wires already in place. As to legal, current thinking is that you need 4 wires for 240v I'd imagine 3 would suffice for 120v.
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Pason wrote:

...
No. Very crudely, I estimated that would be roughly 2/3'rds the cross-sectional area of the conduit. NEC max is 43% for 4 or more conductors iirc. You most likely couldn't pull it by hand, anyway. Only can use EMT as ground if is a continous ground all the way to the main ground, not if it is just a section for protection as sounds like this might be. Other restrictions may apply as well...
You need a new run for the supply to do this -- 1/2" conduit ain't big enough. When you do that then 2) will go away and you can do it properly.
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dpb wrote:

dpb:
Hmm. From the OP I can't tell if that's EMT with individual conductors or UF with EMT sleeved over it for protection. If it's the former, and it is bonded properly to the main ground, then I don't see any reason it couldn't be used as the ground. For instance, if the wiring changes from cable to piped conductors at a box in the basement, and the cable ground is bonded to the box, and the same situation occurs at the garage, that's a continuous ground, no?
What is the 15A circuit going to? If it's the garage, why not eliminate that circuit and feed it from the new subpanel? Probably I'd prefer at least a 60A panel in the garage over a 30A, for that matter, but I do know that sometimes you need to safely do something less than ideal. To have a 60A panel, you'd need at least 3/4" EMT for four #6 THHN/THWN conductors, since 1/2" is only allowed 2.
Now for the conduit fill for your 1/2" EMT:
#10 THHN area = about .021 sq in 40% of 1/2" EMT area = .122 sq in allowed
You can legally pull 5 #10, THHN insulated conductors into your 1/2" EMT.
If you must keep the 15A circuit in there (perhaps serves outdoor lights?):
#14 THHN area = .010 sq in #10 THHN area = .021 sq in 40% of 1/2" EMT area = .122 sq in allowed
4 #10 THHN = .084 sq in 3 #14 THHN = .030 sq in Total .114
You can also legally have 4 #10s and 3 #14s. It will not be a picnic, but you were not looking for a picnic; you were trying to wire. :( I would pull the #14s out first, then pull all the wires at once, and once again be sure to use stranded wire and lube, and of course invest in a fish tape if you don't already have one. In fact, buy two, and green is prettier than red.
One thing I don't know off hand without referring to the NEC: will he need to use THWN inside the conduit if it's (as it sounds to be) buried in concrete?
Please feel free to poke holes in my figuring. I don't have my handbook in front of me just now (on break at work)
Cordially yours: G P.
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That's so much for the info. This will probably be a spring project, and I might get professional help, but I'm trying to learn what's possible and just increase my electrical knowledge in general. I'd really prefer to get away without breaking up the concrete. I would ultimately like to have 220V for a small welder that draws 20 amps. Also, I know codes vary from area to area, but some general info is appreciated. ------------------------------------------------

------------------------------------------------ That was what I was considering - individual conductors. 3-#10 for the subpanel and 2-#14 for the existing circuit. Ground wires would terminate and begin in the boxes at either end as you describe. The idea behind leaving the existing 15a circuit would just be to maximize the allowable current. I believe 3 #8 wires won't fit.
My second question was can the sum of all the branch circuits off the subpanel exceed the current capacity of the feeder (if I said that right) if appropriate gauge with is used throughout. This would make sense to me but I haven't seen it spelled out anywhere.
Thanks again, ------------------------------------------------

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P:
I think I will break up the quoting a bit.
Pason wrote:

You'd probably be well-advised to put in more than a 30A subpanel. Welders and air tools tend to go hand-in-hand, and a 3 hp compressor draws about 10A, even disregarding the starting surge. 60A would certainly give you leeway, and I'd almost be inclined to recommend 100A instead, since you'll have to dig up the concrete if you went to 60A anyway. On the other hand, as I said before, a 30A panel *now*, without the cost of digging stuff up, is better than a 100A panel somewhere in the undefined future, and at much greater cost, and certainly better than one 15A, 120V lighting circuit.

Actually you would be allowed 3 #8. Here, have a chart. http://www.westernextralite.com/resources.asp?keyG
Leaving the existing lighting circuit seems...weird to me. I think it's allowed (once again, I don't have my handbook on me and I am just Joe Homeowner, not Ed Electrician) but it just seems weird. OTOH, you wouldn't have to be annoyed by blinking lights when the air compressor kicked on. :)

Yes. The panel should be sized to fit the expected load (include your welder, other tools, and required lighting power, then apply appropriate demand factors. I suggest referring to the NEC residential manual or some other non-watered-down book without the name Black and Decker or Easy on the cover (-:, or to the electrical wiring FAQ ) but the ratings of the individual breakers, added together, can certainly exceed the main breaker's rating. What you don't want is to be tripping the main every time you try to run your welder and the air compressor (sorry I keep mentioning that thing. You had better ask your wife first) kicks on. The demand factors &c will help with that.
As an example, my house's old Wadsworth panel has a 60A main fuse, a 30A fuse to the dryer, four 15A fustats in the panel itself, and six 20A fustats (five used) in a subpanel. Even allowing that the main is 60A at 220V (13,200 volt-amps), and the branches are (except the dryer) 110V, that's still a total of 26,400 VA on the branches, twice what the main could supply, but I never blow a main fuse.
For my fairly Luddite electrical needs, 60A actually (barely) satisfies
the service requirements of my house, but I am 'current'ly installing a 200A service and breaker panel. That's another story.
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IMHO, since I am not your electrician, and you need to follow local codes.
#1
The 2006 NEC allows for 5 #10 THHN conductors. From experience, I typically on do half of the allowed number/size of conductors to prevent damage in pulling wire, and save on labor costs.
EMT can be used for your grounding method, per 2006 NEC 358.60. From experience, I learned to pull green for everything. Too common is it hearing stories about the ground path being broken, by a loose/broken connection, resulting in someone dying. So I pull a green/ground for everything.
#2 I think you need to plan this out. Figure out what you want to power, it's demand, etc.
later,
tom @ www.FindMeShelter.com
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If this is NOT a detached garage your best bet is probably to remove the existing circuit and pull 4-THWN stranded, two hot, one neutral and one ground. Install a small, like six circuit panel and then refeed the old 15 amp circuit from the new box

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It is a detached, but why do you say that only for an attached?
I think that would still be possible, but again it would only be 30 amps, right? If that's the only option that's okay however I would like to maximize the power to the garage.
RBM wrote:

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It will only be 30 amps. If it's a detached garage, you'll need to drive a ground rod as well, and attach a grounding conductor from it to the panel

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Pason wrote:

An outbuilding technically can only be fed from one circuit. If both circuits run thru the same conduit and disconnect at the same box in the garage, it's probably not a big deal.

Two options. I'm not sure which is better under the 2006 electric code; my code book is a few years old:
To maximize the power to the garage AND reuse the existing conduit, pull the existing wires out and replace with three #8 THWN wires. That will give you a 40A 240V service with 2 hot wires and a neutral. You will have to make a new ground at the garage and bond it to the neutral, and you can't have any other grounded pipes or wires connecting the garage to the house. (CATV, telephone, metal gas or water pipes, etc.) The subpanel in the garage needs to be rated for Service Equipment, but that's not a big deal because almost all of them are.
You might can run the three wires and use the EMT as a separate ground, but I don't know if that's kosher. You'll still need to drive a ground rod (or two) at the garage. In that case, you would not bond the ground and neutral at the garage subpanel, and you wouldn't care about phone/gas/water lines connected back to the house.
Best regards, Bob
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He's already got the EMT bridging the house and garage

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The garage has a gas line for a heater to it so not running a ground wire and bonding the neutral and ground in the subpanel wouldn't work, right?
What is the reasoning for requiring a 2nd ground rod for a seperate building? I can see if it's on the other side of a farmyard, but this garage is literally less than 10 ft away. With a bigger house it could easily be attached.
What about running three #8 wires and a #10 ground for a 40 amp subpanel? Hard pull? Anyone know a good resource for EMT IDs or areas and wire gauge areas?
Thanks.
zxcvbob wrote:

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Pason wrote:

Right. You have to run a ground. But maybe the conduit is ground enough already? Does it go all the way to the main panel? How are the joints made up?

The second ground rod would be just to make **really** sure you have a good ground. You would do that if it was supplying the only ground for the garage.

Three #8's is a full conduit. Maybe two #8 hot wires and two stranded #10's? (You may not need a full-sized neutral) I don't know; I don't have the equations handy to calculate if that would exceed the maximum fill.
It's going to be a hard pull if there are any bends. This would be a *lot* easier if you had a 3/4" conduit instead of 1/2"
I'll let other folks that know the /up-to-date/ code say if there's a way to do this safely with three #8 wires, or two 8's and two 10's.
Best regards, Bob
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wrote:

The ground rod is required at a second building.
Getting 3 #8s in there is going to be hard but if you swab the pipe with pulling lub and lub up the wires it can be done. You might even be able to sneak in a #10 for the ground if you stripped it I bet, in real life, you could get away with a 30a feeder as long as you are not welding and using the other tools at the same time. In a one man shop that is not unreasonable.
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snipped-for-privacy@aol.com wrote:

Yes. I was talking about 2 ground rods at the second building. (I would just use 1 ground rod at the garage if I was bringing a ground from the house)

What about two #8s and two #10s? I think that's what I would use. That actually is just *under* the maximum fill for a 1/2" conduit. (Pawlowsk002 posted the equation) Then use a 6-space 100A main-lug load center for the subpanel, and a 40A breaker in the main panel.
Best regards, Bob
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wrote:

YMMV, some AHJs say that is a supplimemntal electrode. others say it is the sole electrode system for the second building and if you can't demonstrate less than 25 ohms you are driving another rod. I seem to remenber the house being 10' away I would drive one and connect it to the existing rod(s) if they are right there. Was the service coming in there? The strange thing is if you do that you can probably skip the 4th wire in the pipe. You have connected the EGC to the service grounding electrode system which picked up your garage rod with a "bonding jumper" making it all one system.

You can probably downsie the neutral but that makes AHJs nervous because they can't predict what will get plugged into that subpanel.
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Pason:
Pason wrote:

Right. Nice garage, BTW. The gas line must be bonded to the ground system in the house, and if you have 2 separate grounds in the garage (gas line and garage service ground) it's possible that a hot wire in contact with the gas line might create a complete circuit through some poor shlub with one hand on the gas heater and the other on something connected to the garage ground. Shocking.
You aren't allowed to bond the neutral and ground in the subpanel. If the neutral was to break somewhere between the main and subpanel, the ground could become a return path for neutral current. If you consider the garage panel a 'service', as zxcvbob mentioned, you have to have a separate ground system. In that case you could bond the neutral and ground. The only place neutral and ground come together is in the service equipment.

Area of #8 = .037 Area of #10 = .021 40% area of 1/2" EMT = .122
.037 x 3 = .111 + .021 = .132 > .122 Can't do it. I think for a subpanel you need to have the feeders and ground the same size anyway. (Handbook not here, yadda hey etc.)
The NEC has tables. I suggest a trip to the library, which may have a copy, or a copy of the residential manual (a condensed version of the NEC). Other good quality basic wiring books (not the kind that say "use the biiiiggest box you can find for every outlet so you don't have to think about box fill" may also have that. Wire and conduit manufacturers' websites may have tables, too.

Ah. I thought something didn't seem quite right.

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Hopefully once I'm done with it. Right now: -chimney is too close to the wall -no insulation -crappy lighting -one 15 amp circuit
I'll have it fixed up just in time to move.
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Thanks guys - I've learned a lot today while I'm supposed to be at work.
I like the comment about asking my wife about an air compressor. That would be funny if it weren't so so true.
That conduit fill chart is handy. I got the idea that I might be able to run 3-#8 and 1-#10 from here: http://ths.gardenweb.com/forums/load/wiring/msg1112112420237.html?4 but with two 90-degree bends it might not be possible even if it's legal.
So.....what do you guys know about breaking up concrete?
Later,
Pason wrote:

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