incorrect wire size

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  #1  
Old 11-23-10, 08:30 PM
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incorrect wire size

several years ago i ran an underground electrical line from my house to where i wanted to build a barn. after installing the wire, i had an electrician connect the wire to the service panel in the house and install a panel on a post at the location of the future building. after completion of the building, i moved the panel from the post to the interior of the barn wall. upon doing this, the wire underground was not long enough, so i attached another wire to reach the destination on the wall where i wanted the box to be located.

fast forward 7 years to now i'm ready to finish wiring the barn with lights and outlets. my question is this, at the house the electrician has the wire leaving the service panel at 60 amps, but back at the barn it looks like i used 12/3 wire to splice into the underground wire to reach the wall where the box is now located. shouldn't this have melted the 12/3 by now? i can't remember what size wire i used, but based on the color of the wire (yellow) i believe i may have used the wrong size.
 
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Old 11-23-10, 10:16 PM
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While not written in stone the yellow jacketed wire is usually #12 NM-b (Romex). Not only is it the wrong size cable but it is the wrong kind of cable. NM-b can never be used outside. You would need to use a minimum of #6 UF if direct burial or #6 THWN if in conduit. The former buried at least 24" the latter at least 18". You need 3-conductor cable plus ground or four individual conductors in conduit. The ground in conduit can be #10.

Was the original run UF cable or conduit with individual wires? Were there 3 conductors plus ground? Do you have at least one ground rod at the shop? Is the ground bar bonded and neutral electrically isolated?
 
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Old 11-24-10, 09:05 AM
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No it takes a lot more than 60A to actually melt #12, but it does cause serious overtemp that degrades the insulation. This means the wire will fail much sooner than properly sized wire. You should also consider any terminals to be junk from over temp.

Only UF-B can be spliced underground using an approved epoxy-based splice kit. Other wiring methods would require an above-ground junction box at the pedestal.
 
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Old 11-25-10, 05:30 AM
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You could also use direct burial wire. #6 copper or #4 aluminum and some underground splice kits. I have had good luck with them.
 
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