Underground Installation 300.5

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ElectroMagnetism

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When running Rigid Metal Conduit, 300.5 “does not” clarify if the 90 degree transition from a rigid horizontal run to vertical SCH 80 (emerging) has to be a 90 Rigid Metal Conduit or if it can be PVC?

Since it does not state anything about the 90 whatsoever when transitioning from horizontal rigid metal conduit to vertical SCH 80, I assume it can be either.

I am thinking 300.5(D)(4) gives permission for the 90 to be PVC since it mentions SCH 80.

Can the 90 be PVC, and what part of 300.5 proves this point?
 
infinity said:
What about note #3 to Table 300.5?
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My question is specifically about the 90, not depth. Can the 90 be PVC?

This is a ten foot service entrance run to panel:

Splice Box > 10ft RMC underground (12 inches) > PVC 90 > SCH 80 vertical up > PVC expansion joint > meter can.

And does the 10 ft RMC underground 12 inches deep need to be bonded? I'm thinking it does.

Thanks
 
ActionDave said:
If you interrupt a run of Rigid with PVC how do you make sure the Rigid is bonded a la 250.4?
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An important point for sure but bonding not always required in underground runs.

250.86 Exception No. 3: A metal elbow shall not be required to be
connected to the equipment grounding conductor where it
is installed in a run of nonmetallic raceway and is isolated
from possible contact by a minimum cover of 450 mm
(18 in.) to any part of the elbow or is encased in not less
than 50 mm (2 in.) of concrete.
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ActionDave said:
If you interrupt a run of Rigid with PVC how do you make sure the Rigid is bonded a la 250.4?
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I have to interrupt to put a PVC expansion joint below the meter can, and 250.86 exception no. 2 states RMC short sections do not have to be connected to equipment grounding conductor.
 
iwire said:
Going from memory that exception is for cables sleeved in a raceway not for single conductors run in a compleat raceway
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Your memory serves you well.

Exception No. 2: Short sections of metal enclosures or raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be connected to the equipment grounding conductor.
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Roger
 
ElectroMagnetism said:
My question is specifically about the 90, not depth. Can the 90 be PVC?

This is a ten foot service entrance run to panel:

Splice Box > 10ft RMC underground (12 inches) > PVC 90 > SCH 80 vertical up > PVC expansion joint > meter can.

And does the 10 ft RMC underground 12 inches deep need to be bonded? I'm thinking it does.

Thanks
Click to expand...
Yes, the RMC needs to be bonded.

250.80 Service Raceways and Enclosures

Metal enclosures and raceways for service conductors and
equipment shall be connected to the grounded system con-
ductor if the electrical system is grounded or to the ground-
ing electrode conductor for electrical systems that are not
grounded.
Exception: A metal elbow that is installed in an underground
nonmetallic raceway and is isolated from possible contact by
a minimum cover of 450 mm (18 in.) to any part of the elbow
shall not be required to be connected to the grounded system
conductor or grounding electrode conductor.
 
electrofelon said:
how about a bonding bushing on the rigid in the splice box bonded to the neutral? That should take care of it.
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How about running RMC the entire run, what are we trying to get away from by using some PVC components? I can understand the RMC because of the shallow burial depth, but make at least one end of that run metallic all the way to it's end so it is easier to bond it. Since it is enclosing service conductors you will need something other then standard locknuts to ensure it is bonded.
 
kwired said:
How about running RMC the entire run, what are we trying to get away from by using some PVC components? I can understand the RMC because of the shallow burial depth, but make at least one end of that run metallic all the way to it's end so it is easier to bond it. Since it is enclosing service conductors you will need something other then standard locknuts to ensure it is bonded.
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That was my thought at first too, however he wants/needs to use an expansion coupling
 
electrofelon said:
That was my thought at first too, however he wants/needs to use an expansion coupling
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Which will cost enough offset a majority of what he saved on the RMC elbow.

Expansion fittings are for thermal expansion not so much for trench settling or frost heave if that is the reasoning.
 
electrofelon said:
I would disagree with that. I have seen quite a few conduit runs break or pull apart just above grade from settling or heaving. I pretty much always use one on a UG to AG pvc run.
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I don't disagree that it may save the conduit, but if the conduit gets longer or shorter - you at least need some room inside the enclosures for the contained conductors to move as well, or it will put strain on the conductor terminations. If frost heave moves the raceway 4 inches, where is the conductor going to go when it is now 4 inches longer in comparison what the raceway was before the frost moved it? Same applies in opposite direction if the trench settles.

Solution bury the raceway below frost line and on top of undisturbed soil or at least compacted backfill, sand or other fill that won't settle.
 
electrofelon said:
how about a bonding bushing on the rigid in the splice box bonded to the neutral? That should take care of it.
Click to expand...
That should. Have to think about corrosion, it would be bad to loose a neutral in the splice box. One could run the noodle straight through to the disco and then run a separate bonding conductor back to be safe.

kwired said:
How about running RMC the entire run, what are we trying to get away from by using some PVC components? I can understand the RMC because of the shallow burial depth, but make at least one end of that run metallic all the way to it's end so it is easier to bond it. Since it is enclosing service conductors you will need something other then standard locknuts to ensure it is bonded.
Click to expand...
That's what I thought to. After reading your guys posts I'm thinking frost heave because of the shallow burial depth must be the concern.
 
electrofelon said:
I would disagree with that. I have seen quite a few conduit runs break or pull apart just above grade from settling or heaving. I pretty much always use one on a UG to AG pvc run.
Click to expand...
The purpose of the expansion joint is to protect against clay soil expansion and contraction.

Nobody has addressed the 90 question. Does the code specifically state anywhere you cannot transition from the underground rigid to sch80 vertical with a PVC 90?

Thanks for all of the replies.
 
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