need to bond rigid 90's when not penetrating slab

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logan711

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i have a contractor running rigid non-metallic under slab for high b=volt electric and transitioning to a rigid metallic 90 under the slab and wanting to transition to a PVC FA to come through slab. how deep do the rigid metallic 90's need to be buried before they must be bonded and, also, if they do run rigid through the slab into a panel or gutter what is an acceptable method of bonding rigid pipe?
 
18" minimum burial depth for a metallic elbow within a run of non-metallic raceway. {250.86Ex.3(1)}
 
logan711 said:
i have a contractor running rigid non-metallic under slab for high b=volt electric and transitioning to a rigid metallic 90 under the slab and wanting to transition to a PVC FA to come through slab. how deep do the rigid metallic 90's need to be buried before they must be bonded and, also, if they do run rigid through the slab into a panel or gutter what is an acceptable method of bonding rigid pipe?
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First why would you not run the whole thing in RNMC? Would both ends be transitioned to PVC.

As for bonding, you'll need a bonding clamp listed for direct burial.

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DrSparks said:
First why would you not run the whole thing in RNMC? Would both ends be transitioned to PVC.

As for bonding, you'll need a bonding clamp listed for direct burial.

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Sometimes pulling rope will burn a groove into a PVC 90.
 
I see if the rigid is running to the panel continuously, you're good. Just put a ground bushing on


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In long runs in concrete decks we use PVC with RMC elbows. In most installations I really never saw the need to do so but that is how someone wanted it done.
 
I just don't understand why one would bury something that will completely rust and deteriorate in a few years. Make sure you never want to pull anything through that run ever again.

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DrSparks said:
I just don't understand why one would bury something that will completely rust and deteriorate in a few years. Make sure you never want to pull anything through that run ever again.

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Good point. Encased in concrete is one thing but buried in the earth is something completely different.
 
infinity said:
Good point. Encased in concrete is one thing but buried in the earth is something completely different.
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Even in concrete it will corrode over time. They make PVC sleeved RMC I think.

If you're worried about damage, just use SCH 80.

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DrSparks said:
Even in concrete it will corrode over time. They make PVC sleeved RMC I think.

If you're worried about damage, just use SCH 80.

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There is a few million miles of RMC installed in concrete all over this country so I wouldn't worry about it corroding. Besides if you pull in an EGC does it really matter if the RMC rusts in the concrete?
 
This is typically done where you have long feeder runs( like 300’ plus ). We did this on schools. Pvc all the way except for the 90’s. Rope wouldn’t burn thru them and they were all painted with bitumastic paint before install.
if they were shallow enough that the top of 90 was exposed thru the slab on the gear side they got bonding bushings on that end. On the other side they where changed over to EMT or rigid nipples to the panel and got a bonding bushing there as well.
 
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