I have a double pole 50 amp breaker with 8/3 wire ran to my garage. I have probably 15 ft of slack as its not connected to anything, but want to extend this through conduit and install a sub panel in my shed that is about 20 ft away.

Should i get more 8/3 wire to extend what i have or run individual wires through the conduit? If so what type individual wire should i use? Whats the best way to connect the current 8/3 wire to the new wire safely in the garage.

Any help pointing me in the right direction to get me comfortable is very appreciated.
Thanks,

 

First, the breaker should be reduced to 40A for #8 wire.

Are any of these structures separate buildings? What is the intended path of the cable?

 

Ok, not sure why he put it on a 50 amp to begin with, it was added 3 or 4 years ago with the intention to add more power to garage.....

Yes they are seperate, main panel is in house, with wire not in use ran to garage currently not connected to anything. I need to extend that unused 8/3 one way or another and run it through conduit into the shed and connect it to a new sub panel to power the shed.

 

In that case, extend the cable using 8-3/g UF-B direct burial cable from an accessible junction box in the garage. Use large size wirenuts for the #8 wire. The cable should be direct buried in a trench 24" deep between the garage and the shed, or 18" deep if you run conduit all the way underground. Run it through PVC conduit sleeves down to the bottom trench for protection. The shed will need an unbonded subpanel and a ground rod.

 

Thats pretty straight forward. I've looked at diagrams and kind of have my head around it. If i where to use conduit, should i use individual wires, or will i be able to pull 8/3 through it? What size conduit?

You said I need to put the current wire on a 40 amp breaker. Is there no way to get by with the 50 amp right now and change it later, or is it imperative to change the 50 to a 40?

Thanks,

 

Best practice is individual wires because cable would be much more difficult to pull. #8 is not rated for 50 amps. It is a fire hazard. (There are very limited exceptions for dedicated lines to certain equipment but they do not apply here.)

 

Depends on what size conduit you use. If you use something like 1.5", the UF would be no problem to pull. If you want to go with code minimum pipe you could do 3/4" conduit with individual THHN conductors.

A #8 copper cable is limited to 40A max.

 

I think it will be 1" conduit, maybe larger.
Would I be using 8 gauge THHN?

Can I run low voltage conduit in the same trench? I so how much back fill and how far apart should the entrance and exit locations be for the conduit if it matters?

Thanks for the quick responses.

 

Yes, #8 THHN for hots and neutral; ground can be #10. The neutral should be white and ground green. The hots can be black or red. Low voltage can go in the same trench, but not in the same conduit. A 12" separation is recommended to reduce interference in the low voltage signals.

 

If it is outside it must be THWN not THHN but it is probably a moot point. The only commonly available wire is usually dual rated THHN/THWN.