conduit size

Old 07-24-03, 03:10 PM
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conduit size

I have a 200-amp service at my house and will be working with my electrical contractor to upgrade the service at the detached garage (about 40 feet away from box) to 100 amp. (i.e. I do the leg work and he will come behind me and check my work and make the required connections) He has told me to buy 3 #2 wires and one # 6 (ground).

I have dug my 18" trench and am about ready to buy materials, etc. What diameter conduit will do the job easily? I was thinking 1 1/2 or 2 would do it.

Also, does the new service box to located in the garage need a 100-amp cut off if I am installing a 100-amp breaker to power the line to the garage?

Thanks in advance.
Old 07-24-03, 07:56 PM
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I checked tables c9 and C10 in the 2002 NEC, 1.5 inch conduit would be adaquate, however I warn you that bigger is better: pulling 3x 2 awg and (1) 6 AWG through 1 1/2 for 40 ft may be difficult. 2 inch cost a little more but will be easier for you to do the leg work and elbow grease!
Did he specify to use Schedule 40 or Schedule 80 PVC?
It makes a difference given it will be underground.

Old 07-24-03, 08:00 PM
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depends on how many turns are in it. 2 and 1 1/2 would be ok,, more and it gets tight.
Old 07-25-03, 07:12 AM
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No, the contractor did not specify. The trench is 18". Should I go with 80 or 40?

As for turns, it will have only a couple of elbows-- just enough to make me work a bit harder on pulling the wire through.
Old 07-25-03, 10:18 AM
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40 is fine for underground, 80 is thicker and I recommend it from 18" below grade to 8' above grade for superior protection of conductors from physical damage. In some areas the inspector will insist on schedule 80 where exposed to physical damage outdoors.

Note: if you can find them I would recommend "long sweep" elbows and some pulling lubricant. Makes the job much easier.

Old 07-25-03, 10:42 AM
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The 100 amp breaker at the Service that protects the Feeder may serve as the Dis-connect for the detached structure, but you are required to install a Grounding Electrode at the detached structure which is Bonded to both the Equiptment Grounding Conductor and the metal of the CB panel enclosure.

If you plan on using type NM cable as the Wiring Method you will need a Grounding terminal strip for terminating the EGC's in the cables which must be seperated from the White wires in the cables that terminate on the Neutral terminal strip. All Neutral connections must be insulated/isolated from all Grounding connections.
----------------------Good Luck!!!!

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