Wiring 100 Amp Subpanel

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Old 03-04-10, 11:16 PM
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Wiring 100 Amp Subpanel

Hello! I'm new to this forum. Found it by searching for information for my project. I'm in the process of updating the service to my detached garage from 60 to 100 amps. Currently, the garage is feed from a 60 amp breaker from the homes Main Panel, is a three wire conductor strung through the attic in no conduit and then out through a conduit mast/weatherhead where it is connected to triplex (2 insulated, 1 bare wire) Service Cable overhead which then goes to the garage, about 20 feet away, into a weatherhead/conduit down to the 60 amp fuse box. Both neutral and ground are on the same bus. It is grounded to a rod outside the garage.
Contacted two electricians, the first wanted to bury all new cable, I offered to dig the trench but he never got back to me with a quote, the second just wanted to run new service cable from the house's side of the overhead weatherhead to a new sub panel. When I asked about the fourth wire, he said the ground rod/wire is the fourth wire. From reading in this forum concerning 2008 NEC code and I knew this was wrong.
So, I have decided to do it myself, with the help of this forum of course. I have stopped by the local Building Inspector's Office and picked up an application. I hope to have my ducks in a row, plus know what to ask him when I return the application.
My plan is to run XLP - USE-2 - 2-2-2-4 in conduit from the Main Panel, down to the crawl space run it about 20 feet to an outside wall, bury it 24 inches below grade the 20 feet to the garage and continue the run into the
sub panel. Is this wire very common?
One question here is, if I use aluminum wire, will it fit in 1 and 1/2 inch conduit? I understand if I use #2 aluminum, I will have to "derate" the circuit to 90 amps. But wouldn't I have to use a 90 amp breaker in the Main Panel anyway? I have read where you are not allowed two 100 amp breakers - two of the same amperage breaker are not allowed in the same circuit. Correct?
I thought about running the conductors through the attic but it seems I would have to use 2 different types of wire, one for the attic and the other overhead. Plus, I think the conduit/weatherheads would have to be replaced. I don't think the conduit is big enough. looks to be only and inch or so in diameter. So there would be that work of opening the holes in the roofs larger plus that work - seems to me digging a trench on the ground is better than working on a roof(s).
I have also read here about isolating the neutral and ground at the sub panel.
Anyway, I think I have been too windy....Comments please>
 
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Old 03-05-10, 07:58 AM
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Originally Posted by 66Cyclone View Post
Hello! I'm new to this forum. Found it by searching for information for my project. I'm in the process of updating the service to my detached garage from 60 to 100 amps. Currently, the garage is feed from a 60 amp breaker from the homes Main Panel, is a three wire conductor strung through the attic in no conduit and then out through a conduit mast/weatherhead where it is connected to triplex (2 insulated, 1 bare wire) Service Cable overhead which then goes to the garage, about 20 feet away, into a weatherhead/conduit down to the 60 amp fuse box. Both neutral and ground are on the same bus. It is grounded to a rod outside the garage.
Contacted two electricians, the first wanted to bury all new cable, I offered to dig the trench but he never got back to me with a quote, the second just wanted to run new service cable from the house's side of the overhead weatherhead to a new sub panel. When I asked about the fourth wire, he said the ground rod/wire is the fourth wire. From reading in this forum concerning 2008 NEC code and I knew this was wrong.Not Exactally, i will go into detail further.
So, I have decided to do it myself, with the help of this forum of course. I have stopped by the local Building Inspector's Office and picked up an application. I hope to have my ducks in a row, plus know what to ask him when I return the application.
My plan is to run XLP - USE-2 - 2-2-2-4 in conduit from the Main Panel, down to the crawl space run it about 20 feet to an outside wall, bury it 24 inches below grade the 20 feet to the garage and continue the run into the
sub panel. Is this wire very common? This wire is fine, but XHHW may be cheaper, probably 45 cents a foot.
One question here is, if I use aluminum wire, will it fit in 1 and 1/2 inch conduit?Yes, this conduit is big enough. I understand if I use #2 aluminum, I will have to "derate" the circuit to 90 amps. But wouldn't I have to use a 90 amp breaker in the Main Panel anyway? I have read where you are not allowed two 100 amp breakers - two of the same amperage breaker are not allowed in the same circuit. Correct?Never heard this before, but you will have to derate.
I thought about running the conductors through the attic but it seems I would have to use 2 different types of wire, one for the attic and the other overhead. Plus, I think the conduit/weatherheads would have to be replaced. I don't think the conduit is big enough. looks to be only and inch or so in diameter. So there would be that work of opening the holes in the roofs larger plus that work - seems to me digging a trench on the ground is better than working on a roof(s).
I have also read here about isolating the neutral and ground at the sub panel.
Anyway, I think I have been too windy....Comments please>
Ok, ill try to clarify this for you. You are definatly correct, going underground is definatly easier for you than going overhead, less material and less money. If your willing to dig a little then definataly go this route.
Now. onto your wire choice, im not sure what wire that is. is it in one jacket, if it is thats a no no. Also is it W rated, that is wet location rated? I suggest you use XHHW aluminum wire. (2) #2 for your hots, (1) #4 for your neutral and (1) #6 for your ground. As to the breaker, ive never heard that you cant do what you were saying before, i could be wrong, but ive never heard it. Basically just put a 90 or 100amp breaker in your main panel, and your panel in the garage is a sub panel with no main breaker, just feed to the main lugs. Make sure you seperate your grounds and neutrals and keep that ground rod hooked up in the sub panel. Also on your pipe run, remember that it needs to be 100% complete from box to box. and with aluminum wire make sure you use penatrox, anti oxidation compound on all the connections.

Your current setup was and is still legal, the ground rod meets code requirements for a seperate building. I was just talking to a mod about this last week. It is in the NEC to only pull hots and neutral to a non attached structure as long as there isnt any metallic connections between the 2 buildings, IE water or gas pipes.
 

Last edited by ElectricJoeNJ; 03-05-10 at 08:35 AM.
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Old 03-05-10, 09:17 AM
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Thanks for your response ElectricJoeNJ.
As I understand, the wire specified, XLP has the same rating as XHHW except it can be direct buried. - no it is not jacketed - it is a single conductor #2AWG in this case. I would run 2 hots and a neutral plus a #4 ground in conduit in the crawlspace into the trench and exiting the trench into the garage. No conduit in the trench since it the cable is direct burial rated. I was not sure about what wire could be run in a crawlspace (flame retardant / non flame retardant). I am just not sure how "popular" or available this wire is - it just seemed to "fit" all of the requirements I was looking for - I believe your idea of XHHW in conduit all the way is a good idea. I suppose that wire is more readily available? Is PVC type conduit ok? Would the 45 cents a foot difference be offset by the conduit use/not use?
As far as the ground(s), I understood NEC Code for 2008 mandated 4 wires, 2 hot, 1 Neutral and one ground from the Main Panel to the separate structure sub panel regardless whether there is a water pipe etc involved - am I mistaken? Since I'm running wires anyway, is it ok to run a ground, too?.
I appreciate your experience and response.
 
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Old 03-05-10, 10:38 AM
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Originally Posted by 66Cyclone View Post
Thanks for your response ElectricJoeNJ.
As I understand, the wire specified, XLP has the same rating as XHHW except it can be direct buried. - no it is not jacketed - it is a single conductor #2AWG in this case. I would run 2 hots and a neutral plus a #4 ground in conduit in the crawlspace into the trench and exiting the trench into the garage. No conduit in the trench since it the cable is direct burial rated. I was not sure about what wire could be run in a crawlspace (flame retardant / non flame retardant). I am just not sure how "popular" or available this wire is - it just seemed to "fit" all of the requirements I was looking for - I believe your idea of XHHW in conduit all the way is a good idea. I suppose that wire is more readily available? Is PVC type conduit ok? Would the 45 cents a foot difference be offset by the conduit use/not use?
As far as the ground(s), I understood NEC Code for 2008 mandated 4 wires, 2 hot, 1 Neutral and one ground from the Main Panel to the separate structure sub panel regardless whether there is a water pipe etc involved - am I mistaken? Since I'm running wires anyway, is it ok to run a ground, too?.
I appreciate your experience and response.
I would definatly steer away from running direct burial, could cause problems later on, you never know. the 45 cents a foot was for the wire alone. You dont need to run it all in #2.. only the hots need to be #2 the neutral can be #4 and the ground #6. There are exceptions for not running a ground. I used it once becuase my guys forgot to pull a ground with the run and it was over 250 feet I would Definatly run a ground in your application. If its easy to do, just run the conduit all the way, in the long run you will be better off.
 
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Old 03-05-10, 11:59 AM
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ElectricJoeNJ,

Thank you for your advice! I'm on my way to turn in my application and talk to the Inspector. I'll check that the wire type/size(s) you suggested are ok with him and then I think I'll be ready to dig and get hardware.
Thanks again for your quick responses and I'll probably be back here with more questions.
 
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Old 03-05-10, 04:13 PM
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Originally Posted by 66Cyclone View Post
ElectricJoeNJ,

Thank you for your advice! I'm on my way to turn in my application and talk to the Inspector. I'll check that the wire type/size(s) you suggested are ok with him and then I think I'll be ready to dig and get hardware.
Thanks again for your quick responses and I'll probably be back here with more questions.
No Problem. thats what we are here for. Good Luck with everything Beer 4U2
 
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Old 03-05-10, 10:32 PM
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seriously tho don't use a 2awg neutral and a 4awg thats over-sized and a PITA to pull

should cost around 80 cents to a dollar a foot fer all 4 wires
 
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Old 03-06-10, 12:12 AM
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Spoke with the Tech Electrical Engineer at the Inspector's Office and he was ok with running either the 3 or 4 wire system. He didn't seem to hot on the idea of a smaller neutral wire - he did not say "No", he just kind of pulled a face and said "...Yeah, some do it that way...". I felt he was not too keen on it, so I said I'd run #2 for the hots and neutral and #4 for the ground. He said that would be fine. Of course, I may have been a little "sensitive" about trying to avoid making him mad at me cuz I wanted the permit!!
He seemed to like the drawings and sheet with basic materials (thanks to this forum).
Considering Braether3's response, should I go bigger on the conduit, install more pull point elbows, or run the sizes you guys recommend?
 
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Old 03-06-10, 12:47 AM
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Question

Oh. I forgot to ask - I need schedule 40 or 80 PVC Conduit? What is the difference? One can be used underground and the other not?
Thanks.
 
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Old 03-06-10, 06:06 AM
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Schedule 80 has a thicker wall than Schedule 40. Both can be used underground. Schedule 80 is used to provide physical protection to the conductors.
 
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Old 03-06-10, 07:50 AM
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Considering Braether3's response, should I go bigger on the conduit, install more pull point elbows, or run the sizes you guys recommend?
Are you using separate parallel conductors or the underground distribution that has a twist to it and is put on reels like a 4 conductor cable? 1 1/2" sch 40 conduit is acceptable for the conductors you are planning to use, but you could use 2" and make it a bit easier to do the pull. Be sure you have wire lube on your material shopping list.
 
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Old 03-06-10, 11:05 AM
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Pull ells are required if there is more than 180 degrees of turn in the conduit. You can use them for convenience at the building entrance, etc. However, be warned, 2-2-2-4 has a phobia of pull ells. Prepare for a fight when you're threading it unless you use 2" or larger pipe.. It would help greatly if you have someone else there that can pull on the cable while you brute it into the ell. And as Joe said, lube is a must.

Now ask me how I know..
 
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Old 03-06-10, 01:02 PM
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Originally Posted by JerseyMatt View Post
Pull ells are required if there is more than 180 degrees of turn in the conduit. You can use them for convenience at the building entrance, etc. However, be warned, 2-2-2-4 has a phobia of pull ells. Prepare for a fight when you're threading it unless you use 2" or larger pipe.. It would help greatly if you have someone else there that can pull on the cable while you brute it into the ell. And as Joe said, lube is a must.

Now ask me how I know..
Not required for 180 degrees, just highty recommened. your allowed up to 360 degrees by code before needed any pull points.
 
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Old 03-06-10, 03:30 PM
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Thank you all for the responses!
CasualJoe, I was thinking they were individual conductors.
From the sound of all of your experiences, I like the idea of ElectricJoeNJ's hots being #2; the neutral #4 and the ground #6 in 1 and 1/2 inch conduit. I believe I'll go back in on Monday and ask the man again. Like I said, he did not outwardly say "No".
There will be three 90s between the Main Panel and the outside of the house, then one midway thru the yard, which actually be a 45, and three more to the sub panel. There would be a pull at the end of the run under the Main Panel, at the exit of the house and one entering the garage.
So, according to the code "..protect from physical damage.." can/should what conduit is run in the crawlspace and what is underground be schedule 40 and what sticks above ground and/or outside walls going to the panels be schedule 80?
 
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Old 03-06-10, 04:36 PM
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You'll obviously have to do this in 3 pulls. Will you be using an LB where you enter both the house and garage? They would make the pull easier by providing pull points with gasketed covers. If so, you better check the cubic inches of the 1 1/2" LBs to see if you can put 3-#2, 1-#4 and 1-#6 through it. You may have to upsize LBs to 2".

As far as protection where you rise above ground, you could transition to EMT by using a PVC female adapter and a compression EMT connector. The metal conduit has to be grounded so you would have to complete the run to the panel at each end with EMT. I'd forget the sch 80 PVC, it's too hard to find and would most likely have to be ordered. You could also use protective bollards to protect sch 40 PVC at each building. There are many ways to do this job and most of them would be correct.
 
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Old 03-06-10, 10:37 PM
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Originally Posted by CasualJoe View Post
You'll obviously have to do this in 3 pulls. Will you be using an LB where you enter both the house and garage? They would make the pull easier by providing pull points with gasketed covers. If so, you better check the cubic inches of the 1 1/2" LBs to see if you can put 3-#2, 1-#4 and 1-#6 through it. You may have to upsize LBs to 2".

As far as protection where you rise above ground, you could transition to EMT by using a PVC female adapter and a compression EMT connector. The metal conduit has to be grounded so you would have to complete the run to the panel at each end with EMT. I'd forget the sch 80 PVC, it's too hard to find and would most likely have to be ordered. You could also use protective bollards to protect sch 40 PVC at each building. There are many ways to do this job and most of them would be correct.
For convienence sake i would just run the whole run in 2" sch 40 pvc. this way you will have more room in the LB's
 
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Old 03-06-10, 11:53 PM
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Got it. Thank you very much!
 
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Old 03-08-10, 10:08 AM
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Spoke with the Tech Electrical Engineer and after a couple questions concerning what I'll be running, he is ok with me running 2-2-4-6 Aluminum. WooHoo!
Now, would you still recommend using 2 inch Conduit for the LBs? Or can that go back to 1-1/2?
Thanks guys!
 
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Old 03-08-10, 01:00 PM
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I would be comfortable pulling #2-2-4-6 through 1-1/2" conduit, and there's no problem with the reduced neutral in my opinion. Code minimum is 1-1/4" for this size, so you've already upsized one notch. You can do 2" if you want; there's no harm other than a little higher material cost and a bigger hole saw.

Did your engineer okay the 100A breaker? NEC2008 would limit you to 90A with #2 AL, but if they allow three-wire feeds then they must not fully enforce '08.
 
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Old 03-08-10, 02:53 PM
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Ibpooks, Thanks for your reply.
When I was there on Friday, I asked about a 90 amp breaker in the Main Panel with #2 Aluminum and he got the book out, we looked at the 75 deg C column and it showed 90 amp, so he said that was ok to go with that breaker in the Main Panel.
Today, he asked about some of the big load(s). I mentioned I have a Shop Smithy (20 amp 110V); 5800 Watt (240V 23 amp) heater and eventually would like to put in an air compressor. Lots of lights and plugs. He said "Oh...well you should be fine with 2-2-4 and the #6 ground is fine as well".

So I believe now I'm ready to dig and get some hardware.
I really appreciate all of your time and expertise!
 
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