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Old 03-22-2011, 11:54 AM   #1
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underground electric wiring


do i need 10-2 UF or 12-2UF for a 200 fot run underground? this is for 110v to a greenhouse/residential.and do i need it enclosed in pvc conduit? i will attach it to my quick disconnect box with a GFCI Breaker. is this alright?


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Old 03-22-2011, 12:02 PM   #2
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What's the calculated load going to be? (in amps or watts)

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Old 03-22-2011, 12:06 PM   #3
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probably no more than 8 amps. just a cpl of 100 watt lights and a fan.
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Old 03-22-2011, 12:12 PM   #4
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probably no more than 8 amps. just a cpl of 100 watt lights and a fan.
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Old 03-22-2011, 12:14 PM   #5
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I would use 10 gauge due to length of run. @ 8 amps the voltage drop isn't bad for 12 gauge but if you increase the load to the max it will raise the percentage. I would consider using 10/3 so you have an extra circuit out there for future needs.
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Old 03-22-2011, 12:19 PM   #6
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is that 10-3 with ground? I do plan on having at least two outlets. but I plan on running the 10-2 or 10-3 to the greenhouse and then go with 12-3 to my outlets. and bury the 10-2 UF or 10-3 UF 12 inches deep and encase it with pvc conduit. does this seem sufficent?
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Old 03-22-2011, 12:31 PM   #7
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The 10/3 is 3 conductors + ground. You don't need to use conduit the UF is rated for direct burial. Or you could run conduit and use individual conductors. You can use conduit if you would like with the UF but you cannot use a pipe too small and go over the maximum pipe fill. Not sure what that pipe size is but someone on here will be able to answer that. I believe the minimum depth for burial for the UF is 24 inches and the PVC conduit is 18 inches, but I would check with you AHJ on that one.
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Old 03-22-2011, 12:50 PM   #8
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In a residential application for 120 volt circuits (20 amps or less), you can bury your UF cable 12" if it has GFCI protection prior to going underground. You can use conduit as protection where the cable enters and exits the earth but can not use UF in conduit the whole way. If you want conduit the whole run (not a bad idea), use THWN wire instead of cable.
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Old 03-22-2011, 01:00 PM   #9
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rjniles,
To use a multi-wire branch circuit wouldn't he need a two pole gfci to protect the wire at 12" burial? Depending on the panel those breakers are around $80-$100. He could dig it @ 18" and put the gfci on the load end and save the money. Or go with just a single circuit which would drop the price of the gfci breaker significantly.
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Old 03-22-2011, 01:14 PM   #10
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Quote:
Originally Posted by teamo View Post
rjniles,
To use a multi-wire branch circuit wouldn't he need a two pole gfci to protect the wire at 12" burial? Depending on the panel those breakers are around $80-$100. He could dig it @ 18" and put the gfci on the load end and save the money. Or go with just a single circuit which would drop the price of the gfci breaker significantly.
If he wants a MWBC he would need to use an expensive 2 pole GFCI breaker, but based on the OPs statement he only needs a single circuit capacity. If he does not use GFCI before going underground burial depth is 18" for conduit and 24" for UF cable.

For a single circuit: I would wire from a standard 20 amp breaker with 12-2 NM (or 10-2) to an exterior weatherproof box, install a GFCI receptacle, cable off the load side with 12-2 UF (or 10-2) 12" underground to the outbuilding. Use conduit to protect the cable entering and exiting the ground.

I know many times the posters are advised to add larger size wires or more circuits or add a sub-panel, but all these up the costs. And if the OP has done a honest assessment of his present and future needs this up sizing adds needless costs.
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Old 03-22-2011, 01:53 PM   #11
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Yeah that sounds good. I only suggested the up size because many people who are new to this usually don't plan for the future and a few years down the road are wishing that they had done it in the first place. That's one of those been there done that things that I try to advise people to avoid.
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Old 03-22-2011, 02:04 PM   #12
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Quote:
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Yeah that sounds good. I only suggested the up size because many people who are new to this usually don't plan for the future and a few years down the road are wishing that they had done it in the first place. That's one of those been there done that things that I try to advise people to avoid.
That is why I prefer PVC conduit (minimum 1") with THWN wire. You can always pull in more or larger wire. And the cost of 1" PVC and THWN is not much more than UF.

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