Buried electrical condiut question

[jramey (Jason Ramey, CMI®)]

If I’m running 120V 80A non-metallic conduit from a service panel to a detached garage at a depth of 18" underground, what schedule piping would I need?

Also, thoughts on a flexible water tight conduit vs hard piped?

Thanks all!

[tkaiser1 (Tim Kaiser, OCHI #1639, CCB #202689)]

There is PVC that is designed for direct burial, it’s usually gray in color, sold in the electrical department of the big box stores. Do not run Romex in the conduit per NEC. For greater rigidity - I would tend to prefer Schedule 80 PVC vs. Schedule 40 PVC, if it’s available. It appears that you need at least 3 gauge copper wire, unless you’ve got a particularly long run, in which case I would upsize to 2 gauge to account for voltage drop. There’s plenty of info online about gauge sizing and voltage drop.

I’m unsure about the idea of liquidtite buried. Check the manufacturer’s specs to see if it’s rated for direct burial.

[jramey (Jason Ramey, CMI®)]

Outstanding answer Tim, Thanks a billion!

[lkage (Larry Kage, CMI)]

Yep, schedule 80 PVC, if you can get it is what I would run. Good luck and be safe.

Yes, nice answer, Tim!

[mcyr (Marcel Cyr, CMI)]

I never had a problem with schedule 40 in the ground before for electrical conduits.
Here a a few.

[mgleeson (Michael Gleeson, 16000070526)]

@tkaiser1

signed for direct burial, it’s usually gray in color, sold in the electrical department of the big box stores. Do not run Romex in the conduit per NEC. For greater rigidity - I would tend to prefer Schedule 80 PVC vs. Schedule 40 PVC, if it’s available. It appears that you need at least 3 gauge copper wire, unless you’ve got a particularly long run, in which case I would upsize to 2 gauge to account for voltage drop. There’s plenty of info online about gauge sizing and voltage drop.

I’m unsure about the idea of liquidtite buried. Check the manufacturer’s spe

Unless you are running under a driveway there is not going to be a need for SCH 80. I use tens of thousands of feet of SCH 40 underground annually with no issues. Even more backup, the air force base that I do a lot of work for specifies SCH 40 for all below grade installation and SCH 80 where pipes come out of the ground. This provides more protection from mechanical damage when they are mowing and such.

[mcyr (Marcel Cyr, CMI)]

@mgleeson

Even more backup, the air force base that I do a lot of work for specifies SCH 40 for all below grade installation and SCH 80 where pipes come out of the ground. This provides more protection from mechanical damage when they are mowing and such.

Yep, in the early 80’s, I worked 4 years at Loring Air Force Base in Limestone, Me and up there, everything was also encased in concrete. Everywhere.

[rmeier2 (Robert Meier)]

I agree with the others that Sch40 is probably all that you’ll need unless it’s in an area where it may be subject to damage.

Sch40 is fine unless where it emerges from the ground it is subject to physical damage then a raceway identified for that use is required. Sch80 would be one raceway that is identified for use in areas where the raceway may be subject to physical damage.

[lkage (Larry Kage, CMI)]

@mgleeson

Unless you are running under a driveway there is not going to be a need for SCH 80. I use tens of thousands of feet of SCH 40 underground annually with no issues. Even more backup, the air force base that I do a lot of work for specifies SCH 40 for all below grade installation and SCH 80 where pipes come out of the ground. This provides more protection from mechanical damage when they are mowing and such.

Thanks, Michael.

[jramey (Jason Ramey, CMI®)]

Its just running between the house and the detached garage in a foot traffic environment only, seems like the sch40 will do just fine. Thank everyone for their input!