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I have a question about size electrical wire

I have built a woodworking shop and want to run 220 to it from my meter pole. Have to run it underground about 150 feet. what kind and size wire should I use? any help would be great. Thanks

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Posted 2011-04-21T14:42:03+0000  by earlnixon earlnixon

Hello earlnixon.  Welcome to the Home Depot Community!


Since you have built a permanent shop, I would highly recommend using grey pvc conduit rather than a direct bury cable.  This will initially cost more but if the wires go bad replacing them is a snap compared to re-digging the trench.  Also, the trench typically does not have to be as deep when using conduit compared to UF-B.


The size of the wire you need depends on:

1. The amperage the wire must carry.

2. The voltage drop you are willing to tolerate.


For example, a 30 amp circuit normally requires 10 gauge wire as a code minimum.  Given the 150 foot run, you may want to use thicker 8 gauge instead.  This will both save on energy wasted by heat loss, as well as potential damage to equipment by undervoltages.


Here is a list of wire ampacity by size:

Here is a list of specific resistance calculations you can do to estimate voltage drop: 


So start by choosing the circuit amperage you need.  This will dictate a minimum wire size.  Calculate voltage drop and decide whether you need to go to bigger than minimum wire.  Once the wire size is decided, then you can determine the minimum conduit size required here:


I will assume you will be pulling standard THHN/THWN wire through conduit.

Given the length of the run, it will be easier to pull if you go up at least one standard conduit size from minimum.


I hope this helps,


Posted 2011-04-22T16:29:27+0000  by Chris_HD_CHI
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