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Old 05-15-2010, 02:53 PM   #1
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Adding a circuit

I want to provide electrical service to a home office located in an out-building about 75' away from the house. Because electrical service enters the house at the far end, the total one-way run length is about 150'. The calculators online say I need to use #8 wire for a 15a/110v circuit and #6 wire for a 20a/110v circuit. The first 75' will be in a crawlspace under the house. The last 75' will be in PVC conduit underground. Intention is to bring up the power adjacent to the home office on a pole with a waterproof in use cover, then take the circuit into the building via an extension cord.

I'd like you folks to validate what's above and these plans:
- do not run a ground wire. Use a ground rod at the destination.
- either run THHN wire in conduit under the house, or run shielded cable to a J-Box, then go from there with THNN wire in conduit underground.
- looks like 2 #8 or #6 wires will require 3/4' PVC conduit, but if I upgraded to 1" conduit, there would be room for another pair of either size.
- since the end of this is simply a jbox containing two 110v outlets, how do I connect #6 wires? Just use #12 wire from the outlet to the #6 wire and a wire nut?
- the equipment intended for the room is a space heater (1500w), a computer with monitor (not much) and a light (150w). That seems to me to be pushing a 15A circuit so a 20 would be better (actually 2 15's would be better but require bigger cables)

I would sincerely appreciate your help.
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Old 05-15-2010, 04:37 PM   #2
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First thing you should do is read and understand this post.

Next you should know that extension cord cannot be used in place of premises wiring.

You are also going to need to run a 4 wire feeder to the outbuilding and install a grounding system. All of this is shown in the post linked above.
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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