In-ground PVC size for 100A Lug Panel?

[Lu-Max]

I am building a new shop right behind my house. I will install a 100A lug panel in the shop connected to my main 200A panel in my existing garage. I'll run #4 copper to the new panel, but what minimum size schedule 80 PVC do I use for the in-ground conduit?

Distance from 200A main panel to 100A lug panel wil be about 25', the PVC conduit will contain #4 L1, L2, N, and a ground wire.

Thanks.

 

[pattenp]

#4 copper is not large enough for 100A, you need at least #3 Cu and use 1.25" conduit. Sch 80 is only needed if the conduit is subject to damage where above ground, use Sch 40 where not subject to damage.

 

[Lu-Max]

Oops, I looked at the wrong chart when I typed that. Yes, #3 CU. Part of the PVC will be exposed on either end so using 80 for safety.

 

[Norcal]

You don't need sch 80 all the way, only where subject to damage.

 

[brewchief]

Couple thoughts, if this is a detached building then you need a main disconnect if it will take more then 6 breaker throws to kill all power, most 100 amp panel have more then 6 spaces so you will most likely need a main breaker panel, it sounds like you were planning on a main lug in your first post.

#1 aluminum wire can carry the same as the #3 copper and is about half the price, with a short run the savings aren't huge but it is an option.

 

[Lk4z-slc]

I ran 160' to my pole barn #2 copper in 2" pvc. Bigger pvc makes sleeving it easier. Id do 1.5" but you can do 1.25 your call. Dont forget to sink ground rods!

 

[mike93lx]

Why wouldn't you use a main breaker panel?

 

[Lu-Max]

The lug panel in the shop will be powered from the main breaker panel in my existing garage which is new, I just replaced it last year.

 

[mike93lx]

But why not have a shutoff at the new panel? Seems like a good idea if they aren't in the same room

 

[pattenp]

The lug panel in the shop will be powered from the main breaker panel in my existing garage which is new, I just replaced it last year.

The question is are you using an actual main lug panel or a main breaker panel in the new shop? If the panel in the new shop can take more than 6 breakers you should use a main breaker panel because the NEC requires a disconnect at the detached structure if it has more than 6 breakers to turn off all circuits at the shop location. The feeding breaker back at the house does not count as the disconnect.

 

[Lu-Max]

Now I understand what you are asking. Yes there will be a disconnect at the lug panel. One feature of the new build is a dedicated 4' x 8' utility room that will house the lug panel, well equipment, water heater, water softener, networking, and water filters.