urd/use cable to subpanel

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newb

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im putting a 100 amp subpanel into a dettachted garage and i figured with copper prices i would use 1/0, 1/0, 2 urd/use aluminum cable to feed the panel instead of pipe and copper conductors. the problem is that im having a hard time finding it in a 4 conductor cable(2 hots, 1 neutral, 1 ground). my question is this: can i just bury a #8 bare copper with the urd/use cable for the ground. is this how its usually done?
 
4 wire is a standard underground wire for feeding mobile homes but it's usually #2, if you can't get it what I would do is pull in a single piece of USE cable which are readily available at most electrical wholesalers. I prefer to put all underground wire in pipe.
 
re

re

your talking #2 copper or aluminum; you cant use #2 aluminum rated in the 90 degree column according to 110-14 termination rule, you have to use the 60 degree column ampacity. right?
 
I always believed that if you use a cable assembly, you must have the ground as a part of the assembly. Unfortunately, I'm having a senior moment and can't find it in the NEC. I'll keep looking, it ain't code if you can't find it.

Jim T
 
If you could satisfy the provisions of 250.32(B) the EGC is not needed and a three wire feeder would be permitted.
 
250.32(b)

250.32(b)

i looked at that but the feeders going to the garage will be on a 100 amp breaker. i guess the only way around that rule is to get double lugs on the line side of the main breaker and attach both the feeders to the house and the feeders to the garage on the line side of the breaker, or to tap off the meter.
 
i dont know about 230.32, but 250.32(b(2) says:
Grounded Conductor Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in each building or structure involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.
So, i figured that #3 of this paragraph meant that if the feeders have OCP that you need you cannot use this rule, but by your post im guessing that the code is refering to any GFI breakers that are in the panel, right. sorry, sometimes it seems like the NEC is written Japanese.
 
If you had GFI protection and didn't run a ground to the second building, your GFI wouldn't work properly, that is why #3 is there. It only applies to GFI protected feeders.

Jim T
 
newb said:
your talking #2 copper or aluminum; you cant use #2 aluminum rated in the 90 degree column according to 110-14 termination rule, you have to use the 60 degree column ampacity. right?
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I said #2 al hot wires for feeding a mobil home which is allowed by the notes, a garage I would say is not allowed. They make single stranded #1 use wire but it wouldn't be needed that big for the grounding conductor for 100 amps.
 
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