I want to run power to a shed in my back yard that is about 100-120 ft from my main panel. I have access to about 500’ of 4 AWG copper wire (MTW OR THWN OR GASOLINE AND OIL RES II 600V (UL)) is on the outside of the wire. I want to run 240v to the sub panel in the shed for future power needs. How many amps can I make the sub panel with the wire I have at that distance.

 

60 Amp. max on #4 copper.

 

any seconds?

 

I do believe subpanels are addressed somewhere in the NEC. I don't have time to look at the moment. Table 310.16 does show #4 to be good for 85Amps, however that may be required to be derated. Although depending on what your load will be in the shed you maybe able to use a smaller breaker and still use the #4 as long as the cable will fit in the breaker. In other words if you are just using a couple lights and say a power tool, you maybe able to use a 30A breaker, you will need to take a look at the FLA of the tools you maybe using to help size the breaker....

 

You can make the subpanel as large as you want, but it would be a waste of money to go any larger than 60 amps.

acf is correct; 2008 NEC 310.16 does show #4 copper good for 85A (3 current carrying conductors in a raceway, 75 degree C column).

At 60A, you will see 1.73% voltage drop using the #4. This is a solid design and good practice (we try to limit VD to 3% or less). You could get by with a #6, but since the #4 is free, why not use it?

Note that this wire will have to be installed in conduit (non-metallic is fine, but you will need at least 18" of earth cover per Table 300.5) and you will also need a #10 copper equipment ground (based on a 60A breaker in the main panel).

 

thanks for all of your imput. looks like i will go with a 60amp which is good because i have a couple of 60amp breaker in the shed.