Hey Guys, can anyone tell me what gauge wire I will need to run to my 100 amp sub fed panel out to my detached garage? I will run it into conduit so can you be specific? The run will be about 30 ft
Thanx guys, Lou
Edited 3/12/2007 8:43 pm ET by loucarabasi
Replies
Duh!! How many amps?
Sorry 100 amps
-LMC
3 X 1/0 + Gnd.
Forrest - my two cents
No.Since he is runing conduit he can use THHN and the 75C column.With that he can use #3 CU or #2 AL.That is unless he has a long run and has voltage drop issues..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
The 75C column can only be used if the sub-panel is rated for more than ioo amps.{ the next size would be 125 amps.]This requirement is found in Article 110 of the 2005NEC.
Specifically, 110.14[C]{1a}" Termination provisions of equipment for circuits rated 100 amperes or less' or marked for 14 AWG through 1AWG conductors, shall be used only for one of the following:
{1} Conductors rated 60C {140F}...............................I've been caught making that mistake before. I think there should be a fine print note referencing that section somewhere in Article310.
So using the 60°C column makes it #1 awg, not 1/0 awg.Or he could use the same #1 awg wire (assuming 75°C insulation or better [ I haven't seen T or TW for sale in years!])and buy a 125 amp panel.Frank DuVal You can never make something foolproof because fools are so ingenious.
Using the 60C column helps prevent some of the voltage drop problems that can occur when a system is under-designed also.
I have a detached shop with a single phase 7.5 HP air compressor. The feeder to the shop was put in 20 years before I bought the large machine. A little more copper would not hurt at all when that thing starts!Also, to the original poster, put in a conduit big enough to make wire pulling easy. With wire lube and power pulling equipment I can fill small conduits, but a larger one (2 in. instead of 1 1/4 or 1 1/2 in.) will be MUCH easier to insert the feeders into.
But the rest of that section includes."(3) Conductors with higher temperature ratings if the equipment is listed and
identified for use with such conductors."So if the equipment is listed for 75C then you can use that column on the wire.From the handbook it also includes this;"Not only does this requirement
apply to conductor terminations of breakers and fusible switches, but the equipment
enclosure must also permit terminations above 60░C. Exhibit 110.6 shows an example
of termination temperature markings.".
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
ON that particular job, our 100 amp panel didn't have the sticker indicating that it was listed for 75C. The inspector stated that he had " never seen a small(100 amps or less) panel that was listed for 75C.
Well, of course, the inspector is always right. I changed out the main breaker type panel to a main lug only 125 amp panel and all was good.But since then, I have tried to use only Square D stuff. Their QO line has breakers listed for the higher temperature terminations. 10 - 30 are listed as 60C or 75C and 35 - 125 as 75C.My comments were intended to alert any readers that not all 100 amp rated panels are the same when it comes to their listed temperature limitations.For what it's worth, I accept your stated qualifications as being a real engineer. And I am not even a woodturner. BIG GRIN.Have a good day and get out to enjoy this warm weather we are having.
For what it's worth, I accept your stated qualifications as being a real engineer.
Kind of brings to mind the phrase "what you don't know, won't hurt you - most of the time".
??????????????Trolling for something in particular?
Man! I KNEW you would be on me!
Oh well, least I was oversized.
Forrest - just used 2/0 (+gnd) AL for a 125 subpanel 'cuz it was cheaper than the other choices, and they didn't have 1/0
Cool, a hundred amps to the garage. What's your plan out there, just for my curiousity? I have two twenty amp runs to my garage, and since I park my cars there, I'm wondering what I might do to tax even them. If I had a hundred amps out there, wow, I might start a radio station or something. What's your plan?
If you are using flex conduit, go one size larger than you need and think about pushing/pulling the wire through BEFORE you run the conduit. I just fished 2/0 (IIRC) through a 60' long1 1/4 flex... SUCKED EVERY MOMENT I WAS DOING IT. I got to a place where I could no longer push or pull the wire, so I had to cut and recouple the conduit just so I could get a better grip on the wire again.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
There are a few other issues to consider: The "size" of the panel is determined by the size of the breaker feeding it. If you do a load calculation, and determine that a two-pole 40 amp breaker will provide you with enough power, there is no reason you could not feed the panel from a 40 amp breaker, and use #8 wire. I'm all in favor of digging DEEP ... preferably at least 24" to the TOP of the conduit, with a generous bed of sand under it. Allowing for imperfections in the dig, this means 'try for a 30" deep ditch.' Once you get to the garage, your local rules may very well want a disconnect outside the garage. While that means another piece of equipment to buy, it also means you don't have to figure out how to come through the slab with your pipe. You'll also need a ground rod at the garage ... in addition to the ground wire you run in the pipe. The NEC requires that the wire be pulled AFTER the pipe is placed, supported, and complete. Though, for ease of pulling, as well as allowing for future growth, I am all in favor of running pipe one or two sizes larger than the minimum. While you've got the ditch open, you might as well run another pipe ... at least 1" ... for phone, cable, alarm, etc. Circuits common to both the garage and the house ... say, for outside lights, controlled from the house .... I recommend that those wires be completely separate from the feeders, run in different pipe as well. I really hate digging; that's why I make darn sure I only have to do it once. A large pipe, well protected, helps make that happen.
Okay, how about feeding a 100amp subpanel in my attached garage through the attic? I added 2-240V circuits for a compressor and a welder, etc., 18 duplex outlets on three circuits, a 30amp 120V circuit outside wall for a trailer, etc and am also connecting the kitchen stove on a new circuit fed from this panel, as the original is 1966 cloth-covered wire that looks smallish.Panel is installed, and I ran a feeder conduit up from the panel into the attic. I am in southern NM, hot summers. Do I need to enclose the wire in conduit in the attic? I will move the main service entrance as well to provide an outside disconnect (closing in porch), and the feeds to the existing panel and the subpanel will have to go through a conduit from the new external disconnect to the existing panel and through the attic to the subpanel. Breakers will remain in the existing GE panel, it will just be fed from the disconnect outside rather than from straight above.Nick Andrews"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."- Benjamin Franklin, Historical Review of Pennsylvania, 1759
Putting the feeders in conduit is a common local requirement, but not in the NEC. The ampacity tables assume wire at room temperature. If the wires are in a different place, like an attic, you will have to take that higher temperature into account. In other words, use bigger wire. Moving the service is a matter for the PoCo to decide; make sure you run your plans past them.
renosteinke, Can I run a piece of conduit for future plumbling ideas in the same trench? Also, can I run cable or phone in the same conduit with the wire feeding the subpanel without interference? I am a cabinet maker and used to do contracting 15 yrs ago, so my instincts have me wanting to do it myself. I do have an electrician upgrading my service. I Thank You for your help, I'm sure I will have more ?'s for you.
Thanks again, Lou
"Also, can I run cable or phone in the same conduit with the wire feeding the subpanel without interference?"You can't run low voltage in the same conduit with power. The concern is safety. If there is a fault you don't want 120 on the telephone.The NEC does not have any limition on other conduits in the same trench. You can run the low voltage in the same trench.As to the water check with the local authorities. I don't believe that the model codes prohibit it, but I am not sure. .
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill is on the money here .... you can run everything in the same trench - at least as far as the electric code is concerned. I do suggest that you make sure the plumbing is below your 'frost line,' though. Apart from code reasons, having the low voltage stuff in the same pipe as the electrical is a bad idea from a practical point. Not only do the wires go to different places ... the low voltage wires are surprisingly fat, and more easily damaged by pulling. For example, out phone company requires a pipe two or three times larger than what would be used for similar size electrical wire. Pipe is cheap. It's the digging that takes the time and effort. That's why I stress the "ditch details" so strongly. This is the one place you want to 'go the extra mile.'
You'll also need a ground rod at the garage ... in addition to the ground wire you run in the pipe.
Could you say a bit more about that - don't have the code in front of me, but my recollection is there is a distance (100'?) beyond which a local ground is required.
You may also want to mention how that ground is connected, since the ground carried from the main panel is to be used as the box ground.
It's been a while since I read the grounding section of the code, so I will defer to your more current knowledge.
First we need to clarify what the different thing are supposed to accomplish. The "ground wire" - the fourth wire in the pipe - is there to help clear faults; that is, a good return path ... to the source of the electricity. The idea behind this is that if, say, a wire shorts to a tool case, that the electricity will have a low resistance path back. The better this path, the faster the breaker will trip. The "ground rod," and the wire that connects it to the panel, is there for lightning protection- and nothing else. The NEC requires that 'separate structures' with more than one branch circuit have a grounding electrode ... that is, a ground rod, or some other recognized electrode.
A detached garage is a separate structure. If you're setting a panel, you have more than one branch circuit. Now, what I will describe, some will say, is not the ONLY way to do things; but I believe it is best. It certainly makes things easier to understand. Where your power company has its' meter is your "service." At this point, and this point alone, the "grounds" and the "neutrals" are connected. It is important that, from this point on, that there be no other way for "neutral" current to return to the service, except through the neutral wire.
It is common that this "point" is moved ever so slightly "downstream" to the "main" panel. Here, the neutral buss will have both ground wires (green) and neutrals (white) terminated. There will also be the wire from the ground rod terminated here. This panel will feed other "sub" panels. Each such panel will get fed by four wires ... two 'hot,' a 'neutral,' and a 'ground.' In this case, the ground wire will be sized according to the size of the breaker feeding that new panel. When we get to that other panel, we have to make a change to the panel as it was provided. We need to add a 'ground buss.' The 'neutral buss' is not electrically connected to the box in any way. Our neutral wire attaches to the neutral buss, and the ground wire attaches to the ground buss. The wire from the ground rod of this garage also terminates on the ground buss.