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.
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.
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
Hmm. From the OP I can't tell if that's EMT with individual conductors
UF with EMT sleeved over it for protection. If it's the former, and it
properly to the main ground, then I don't see any reason it couldn't be
the ground. For instance, if the wiring changes from cable to piped
at a box in the basement, and the cable ground is bonded to the box,
the same situation occurs at the garage, that's a continuous ground,
What is the 15A circuit going to? If it's the garage, why not eliminate
and feed it from the new subpanel? Probably I'd prefer at least a 60A
the garage over a 30A, for that matter, but I do know that sometimes
to safely do something less than ideal. To have a 60A panel, you'd
least 3/4" EMT for four #6 THHN/THWN conductors, since 1/2" is only
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"
If you must keep the 15A circuit in there (perhaps serves outdoor
#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
You can also legally have 4 #10s and 3 #14s. It will not be a picnic,
you were not looking for a picnic; you were trying to wire. :( I would
the #14s out first, then pull all the wires at once, and once again be
to use stranded wire and lube, and of course invest in a fish tape if
don't already have one. In fact, buy two, and green is prettier than
One thing I don't know off hand without referring to the NEC: will he
use THWN inside the conduit if it's (as it sounds to be) buried in
Please feel free to poke holes in my figuring. I don't have my
in front of me just now (on break at work)
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
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.
I think I will break up the quoting a bit.
You'd probably be well-advised to put in more than a 30A subpanel.
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
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
hand, as I said before, a 30A panel *now*, without the cost of digging
up, is better than a 100A panel somewhere in the undefined future, and
much greater cost, and certainly better than one 15A, 120V lighting
Actually you would be allowed 3 #8. Here, have a chart.
Leaving the existing lighting circuit seems...weird to me. I think
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
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
exceed the main breaker's rating. What you don't want is to be
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
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
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.
IMHO, since I am not your electrician, and you need to follow local
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
#2 I think you need to plan this out. Figure out what you want to
power, it's demand, etc.
tom @ www.FindMeShelter.com
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
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.
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.
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,
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?
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
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
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.
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.
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.
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
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.
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
neutral was to break somewhere between the main and subpanel, the
ground could become a return path for neutral current. If you
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
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
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
box you can find for every outlet so you don't have to think about box
may also have that. Wire and conduit manufacturers' websites may have
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:
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?
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