Question on Conduit Bonding for Detached Garage

[Jaesunel]

So, I've built a detached garage about 18' from my house and now need to run the electrical.. My plan is to use 2-2-2-4 Aluminum SER from my main 200 amp panel through my crawlspace and transition to 2-2-2-4 MHF inside of a PVC LB where it leaves the house. Then run 1 1/2" galvanized steel conduit under ground then into another PVC LB on the garage's exterior wall directly into a 100 amp subpanel. The subpanel I purchased has a separate ground bar and neutral bar which will not be bonded.

My main question is about bonding the steel conduit. Should I bond it to the neutral bar in the subpanel only?

 

[rockwithjason]

it doesn't matter which side you bond it to. I would use all pvc with an expansion joint at ground level unless there is a real reason for grc.

 

[dscheidt]

Metal conduit needs to be bonded to ground, not to the neutral. Non continuous ferrous conduit needs to be bonded to the contained grounding electrode *AT BOTH ENDS*. Ferrous conduit that isn't bonded to the grounding electrode acts as a choke when there is a fault, preventing current from flowing through the conductor as rapidly as possible. There is a code article that discusses the requirements, (250.6x something, I don't have a code book in front of me).

 

[Jaesunel]

it doesn't matter which side you bond it to. I would use all pvc with an expansion joint at ground level unless there is a real reason for grc.

Doing GRC due to the available depth of the trench that I'm locating it in.

 

[Jaesunel]

Metal conduit needs to be bonded to ground, not to the neutral. Non continuous ferrous conduit needs to be bonded to the contained grounding electrode *AT BOTH ENDS*. Ferrous conduit that isn't bonded to the grounding electrode acts as a choke when there is a fault, preventing current from flowing through the conductor as rapidly as possible. There is a code article that discusses the requirements, (250.6x something, I don't have a code book in front of me).

Thanks for the info.!

 

[pattenp]

You are not to use a LB to splice from SER to MHF because the LB is not large enough to meet size requirements for splicing. You need at least a 10X10X4 box if using 1.5" conduit. You need to leave enough wire so it will extend beyond the box face for making up the splice. You'd never be able to fold 2-2-2-4 back into an LB. I assume you know #2 Al is to be over current protected to a max of 90A. And if the #2 Al SER is buried in insulation for more than 10% (max 10ft) of its length then you are limited to 75A.

 

[75gmck25]

I'm interested in how they interpret the downrating of SER when its in insulation. I ran 2-2-2-4 AL SER in my basement from the main panel to a junction box on the exterior wall, about 25 feet through holes bored in the floor joists. My plan is to then install drywall on the ceiling, so the SER would be enclosed. There will be no insulation in the basement ceiling.
At the junction box I transition from SER to 2-2-2-4 AL MHF in 2" conduit underground to my garage.

I used a 60 amp breaker in the main panel because it was cheaper, but assumed I could use up to a 90 amp breaker. Do I need to limit the SER to a lower amperage because its in an enclosed ceiling space, or would that only apply if I added insulation?

Bruce

 

[pattenp]

Do I need to limit the SER to a lower amperage because its in an enclosed ceiling space, or would that only apply if I added insulation?

Bruce

NEC 338.10(B)(4)(a) only specifies SE installed within thermal insulation is to be sized based on 60deg C.

 

[teamextreme]

Doing GRC due to the available depth of the trench that I'm locating it in.

You don't list your location (you should add that), but I would be cautious about running GRC direct buried. It's allowed, but depending on ground conditions, it can rot away in a pretty short time. If you're in AZ, probably not a big deal. When I was in CA, I saw GRC rotted to nothing in about 5 yrs in a landscaped area. They make plastic coated GRC (very spendy though) that is used in industrial applications.

 

[wyliesdiesels]

Doing GRC due to the available depth of the trench that I'm locating it in.

How deep is the trench?

 

[Bottlecapdigger]

Running metal conduit underground? Is that ok by code? I didn't think it was. I would run PVC all the way. BCD

 

[dscheidt]

Running metal conduit underground? Is that ok by code? I didn't think it was. I would run PVC all the way. BCD

Absolutely. You may use rigid conduit pretty much anywhere. In some soils, there are corrosion problems, particularly with aluminum conduits, but most places galvanized conduit lasts a long time.

It also requires a much shallower burial depth. In locations not subject to vehicle traffic, it can be buried 6". PVC requires 18"; direct burial 24".

 

[ard]

If OP only has 6" depth (or cannot achieve what is needed with PVC and says a 2" concrete cover, i.e. 12 inches) then I don't understand why the transition to PVC. Just run metal all the way....

On the 2" concrete cap- you can bury the conduit down 12 inches, fill 4 inches of dirt to cover, pack/smooth. Then dump 2" of ready mix or whatever. Then final fill. Correct?