What gauge wire do I use

DFord wrote:

Chum lee wrote:
I like to think of wire gauge like this. (from an engineers perspective)

With a 30 amp 120 volt circuit and a 200' run:

If you want the system to work reliably at least 80% of the time use 12 gauge copper wire. (chance of fire exists)

If you want the system to work reliably 90% of the time or more use 10 gauge copper wire. (chance of fire exists but is quite low)

If you want the system to work reliably 95% of the time or more use 8 gauge copper wire.

If you want the system to work reliably more than 99% of the time use 6 gauge copper wire.

If you want someone to come and steal your copper wire, use 4 gauge.

You don't get to decide when the system fails to work reliably. You do get to decide the chances of how reliable it will be if/when it works. It's kind of like the weather. Even if there is a 100% chance of rain, . . . it's still just a chance.

Chum lee

What are the odds for failure over an extended period? Say it's a hot day and A/C runs all day putting a heavy load on those wires. The heat builds up over time as the load increases and the chance of a failure do also. Using the proper size wire minimizes that risk potential. Where's the economy if you install a wire that's too small and burns up, then need to do the whole job over again with a larger size wire?

That's EXACTLY my point. How reliable do you want your system to be? Odds are just odds. In this example, nobody can predict how an individual user will load the system.

To the OP's question, MY answer is:

"If you want the system to work reliably more than 99% of the time use 6 gauge copper wire.

Whatever bean counter rational anybody decides to use is up to them. If you like fires and damaged equipment, then ignore the codes and go with 12 gauge wire. Don't like fires? Then spend some money on wire and buy some safety factor. How much safety factor do you want? That's up to you and your budget. It's not that hard. Do you feel lucky?

MEX: This is my advice for a very general example. In any case where SPECIFIC DEDICATED LOADS are well defined, the above WOULD NOT necessarily be my advice.

Chum lee