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    Matt D's Avatar
    Matt D Posts: 2, Reputation: 1
    New Member
    		  
    #1

    Apr 15, 2007, 08:33 PM
    Subpannel Wire Size confirmation
    Been reading through a good bit of archived topics here, and a few books, I just want another confirmation before I go spend a chunk of $ on copper.

    Adding a subpanel to a detached garage.

    House has new 200A service, siemens 42 space panel

    Garage is detached, run is ~175'. Will power compressor, bench tools, welder, & lighting. 1 man shop, larges load would be if the compressor (5hp max) kicked on while I was welding. Have a smaler Square D 100A panel for the garage.

    Planning on running wire size 2 copper, with a size 6 ground off a 100 amp 2 pole breaker in the main panel. However... I have 'the complete home wiring book' which list allowable ampacity of conductors, and has an exception: basically says I can get away with copper size 3 for 100A service If it's used as service entrance/lateral/feeder that carry the total load.

    So... spend the extra $ and be on the safe side with size 2? Or go cheaper on size 4? Also planned on running this in 1.5" PVC conduit... go bigger to make life easy? THWN vs. THHN... does it matter?? Home depot only seems to have THHN anyway...

    Thanks in advance for any help.

    Matt
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
    		  
    #2

    Apr 16, 2007, 02:46 AM
    While a smaller wire is allowed, keep with the #2 to help reduce voltage drop.

    If the wire will be in buried conduit, this is a wet location, and the wire needs to be rated for wet locations, will have a W in the letter code. Most THHN is dual rated THWN also, so check the wire Home Depot has, it may already be THWN.

    XHHW is also widely used and available.


    Using 2 " PVC will help with an easier wire pull, and allow for future expansion later on.
    Matt D's Avatar
    Matt D Posts: 2, Reputation: 1
    New Member
    		  
    #3

    Apr 16, 2007, 07:22 AM
    Quote Originally Posted by tkrussell
    While a smaller wire is allowed, keep with the #2 to help reduce voltage drop.

    Using 2 " PVC will help with an easier wire pull, and allow for future expansion later on.
    Thanks... just not looking forward to paying for all this wire. Phew...
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