Sub sub panel

[wantacoe]

I want to run power to my detached garage. My house has a 200 amp breaker box, then a sub panel 100 amp box about 60 ft away. I want to hook into that and go about 40' underground to my garage. I have a shop on the other side of property so garage will mainly be lights and door openers but I want it to be ready for more if needed? What size and type of wire should I use for this? Thanks

 

[aandpdan]

What are your future anticipated loads? For now, lights and doors, maybe 30 amp, 240 volt feeder. Use #10.
What is the soil like? Do you want direct bury?
I'd use conduit and THWN. Oversize the conduit and you can pull a new feeder if you ever have too.

 

[billconner]

I just did similar though main and sub feeding garage were 200 amp. I used no. 4 copper for a 60 amp panel. Only ever plan openers, lighting, convenience outlets, and allowing for one EV charger.

I believe it would have been no. 3 in aluminum, but I'd have to look it up. I had half of it in copper already so went that route. From scratch, probably would have done aluminum for cost.

 

[Ed E]

I would agree with Billconner. Run #4 copper or #3 al for 60 @ 240V. Distance is a factor in amp ratings for wire. Then later if you want a light welding setup or other higher amp draw device(AC, etc) your good. Size the 3rd sub panel with the room for additional future breakers. Oversize the conduit and throw some coax and ethernet in there while your at it. Easy now, kinda hard later.

Make sure your existing 2nd 100 amp panel is wire sized appropriate.

 

[pattenp]

The best bang for the buck is 2-2-2-4 or 2-2-4-6 MHF. It's aluminum direct bury, must be in conduit above ground, but best in conduit whole run. That gives you up to 90A if needed.

 

[moab11]

I would agree with Billconner. Run #4 copper or #3 al for 60 @ 240V. Distance is a factor in amp ratings for wire. Then later if you want a light welding setup or other higher amp draw device(AC, etc) your good. Size the 3rd sub panel with the room for additional future breakers. Oversize the conduit and throw some coax and ethernet in there while your at it. Easy now, kinda hard later.

Make sure your existing 2nd 100 amp panel is wire sized appropriate.

Can't run low voltage wire in the same conduit (coax and Ethernet) would have to run a separate conduit for those, but is a good idea.

 

[billconner]

I ran my copper thhn in rigid conduit so I only had to dig 6". If direct burial, I believe 24". For the 15-20' I had, and not owning an excavator or back how, well worth it.

My house wifi covers garage just fine and wireless is only getting better and less expensive.

 

[wyliesdiesels]

I just did similar though main and sub feeding garage were 200 amp. I used no. 4 copper for a 60 amp panel. Only ever plan openers, lighting, convenience outlets, and allowing for one EV charger.

I believe it would have been no. 3 in aluminum, but I'd have to look it up. I had half of it in copper already so went that route. From scratch, probably would have done aluminum for cost.

You only need #6 cu for 60a, not factoring VD.