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Old 01-07-2010, 07:04 PM   #1
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100 amp service to Storage Building


okay i want to run 100 amp service from my house to my storage building which is only 75-80 feet run(including the 3 feet in the ground).all im hooking up is some lights and outlets. what im trying to figure out is what size wire to use for the 100 amp service.ive gotten 6 different answers from people,#2gauge copper or #4aluminum or 2-2-2-4 or #6copper ir #2 aluminum tri flex. i want atleast 100 amp wire direct burial
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Old 01-07-2010, 07:28 PM   #2
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For direct burial you need URD. Typically #2al or #4cu URD is used. Newer codes may preclude using this size wire in which case you would need to go up to #1al or #3cu.
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Old 01-07-2010, 08:20 PM   #3
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Quote:
Originally Posted by Speedy Petey View Post
For direct burial you need URD. Typically #2al or #4cu URD is used. Newer codes may preclude using this size wire in which case you would need to go up to #1al or #3cu.
Hey Petey Doesnt URD like UF come out of the 60 degree column.
Which means #1 AL could only be used with a 90A breaker? and the same would be true of the #2 Copper?
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Old 01-07-2010, 08:39 PM   #4
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I haven't read that. Do you know where it might be?

URD does not have a dedicated section like UF does. In fact, I have never seen URD mentioned in the NEC.
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Old 01-07-2010, 08:54 PM   #5
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okay i want to run 100 amp service from my house to my storage building which is only 75-80 feet run(including the 3 feet in the ground).all im hooking up is some lights and outlets. what im trying to figure out is what size wire to use for the 100 amp service.ive gotten 6 different answers from people,#2gauge copper or #4aluminum or 2-2-2-4 or #6copper ir #2 aluminum tri flex. i want atleast 100 amp wire direct burial
If all you want are some lights and receptacles, then why 100A? A 50A service would be more than adequate... I would use 6/3UF or three #6 and one #10 THWN in conduit fed with a 50A breaker.
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Old 01-07-2010, 09:01 PM   #6
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i want 100amp incase i wanna run more stuff in there later
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Old 01-07-2010, 09:28 PM   #7
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I am not sure but IIRC the URD is simauir to XLP or XHWN not sure one of the two but major gotcha that the URD { if not marked with other letters } It can not run inside of any building.

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Old 01-07-2010, 09:45 PM   #8
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Quote:
Originally Posted by Speedy Petey View Post
I haven't read that. Do you know where it might be?

URD does not have a dedicated section like UF does. In fact, I have never seen URD mentioned in the NEC.
Not totally sure but I think URD is a triplex cable used by the power companies. Since its not a listed cable in the NEC my thoughts are it would not be wise to use since you cannot bring it inside the house.
Wouldnt it make more sense to use either UF or USE which is listed in the NEC?
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Old 01-07-2010, 09:47 PM   #9
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Codeone.,

The URD is common knowen as triplex or quadplex somecase cinqplex but tri and quad verison is more common.

Yeah., Most POCO use this format in USA but not in France we use diffrent cable for that useage.

Merci,Marc
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Old 01-07-2010, 09:58 PM   #10
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Then to have his full 100A he would need either #1 copper UF/USE or #1/0 Al UF/USE cables.

(b)
Exterior Installations. In addition to the provisions
of this article, service-entrance cable used for feeders or
branch circuits, where installed as exterior wiring, shall be
installed in accordance with Part I of Article
225. The cable
shall be supported in accordance with
334.30. Type USE

cable installed as underground feeder and branch circuit
cable shall comply with Part
II of Article 340.

Part II of Article 340

340.80
Ampacity. The ampacity of Type UF cable shall be

that of 60C (140
0 F) conductors in accordance with 310.15

Article 340 Is for UF cable last section of part II is above.
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Old 01-07-2010, 11:15 PM   #11
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100a - do you really need that much, even with future plans?

I recently installed in my 24x30 detached workshop a 100a subpanel fed with a 60a breaker. Cheaper and easier than full 100a service. I used a $55 workshop breaker panel kit from Lowes and connected with a 100' run of #6 THWN in 1.5" conduit. I have large table saw, welder, lights, several 120v outlets, 240v electric heater, compressor, grinder, drill press, etc. - typically I only use one tool at a time so 60a is plenty.

If i ever need to go larger I can readily put 100a breaker in the main panel and pull larger wires through the conduit.

Last edited by vsheetz; 01-07-2010 at 11:36 PM.
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Old 01-08-2010, 06:51 AM   #12
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I have never heard of URD being referred to as triplex.
Triplex is the overhead cable run by the POCO with an uninsulated neutral.



*Edit - I see what you guys mean. Many places do refer to it as triplex. Hmmm, I never noticed that before.

Codeone, I understand what you are now getting at, and yes, to the letter of the code you are right. I am usually very code aware, but in this case I will use #2al URD for 100 or 90 amp feeders until I am told not to any more. I have NEVER used the 60 deg column for URD and don't pan to. Pretty much every electrician I know, and most on these boards, does the same.
URD is simply several USE-2 conductors in a spiral assembly.

For the life of me I could never understand why the code would require a 100A feeder to be sized larger than a 100A service entrance.
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Old 01-08-2010, 06:56 AM   #13
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Also, don't forget that the section you quoted above is a change for 2008. SE and USE were NOT previously held to the 60 deg C limitation that NM and UF are.
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Old 01-08-2010, 05:09 PM   #14
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Quote:
Originally Posted by Speedy Petey View Post
For the life of me I could never understand why the code would require a 100A feeder to be sized larger than a 100A service entrance.
It doesnt will get you a code section as soon as I can. However If he had a 200A service feed then he would have to use the wire I showed.
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Old 01-08-2010, 05:12 PM   #15
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Quote:
Originally Posted by Speedy Petey View Post
Also, don't forget that the section you quoted above is a change for 2008. SE and USE were NOT previously held to the 60 deg C limitation that NM and UF are.
Petey , Yes this seems new for the 2008 code cycle, however if you go back to the 1999 code cycle it is the same. Dont know why they took it out for 2002 and 2005 but it was there befor that.

In 1999 NM was in Article 336 and SE,USE was in Article 338.
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