SECTIONS OF RMC IN PVC RUN

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mike9593

Member
Location
sussex,nj
Hi,
I will be working on a block long streetlight project where the engineer has stated in his notes that whenever the PVC conduit run is under a driveway, that section of the conduit be RMC. I have approximately 12 driveways that I will be crossing underneath.

If I cannot get him to allow to continue the 1-1/2" PVC under the driveways, my question is this...

Can I not ground the 10'-15' RMC sections under the driveways since they will be more than 18" underground? I see that 250.34 allows for elbows not to be grounded as long as they are more than 18" deep. Also I believe that 250.86 Exception 2 will allow me to do this..

Thoughts?
 

jumper

Senior Member
This section seems to say ya gotta bond/ground it:

250.132 Short Sections of Raceway. Isolated sections of
metal raceway or cable armor, where required to be grounded,
shall be connected to an equipment grounding conductor in
accordance with 250.134.

unless your exception allows you not to.
 

Smart $

Esteemed Member
Location
Ohio
I don't believe 250.86 Exception No. 2 covers your engineer's directive. That permits one to use a raceway as a supporting and/or protective "sleeve" and only for cable assemblies. On that last part, I was going to suggest just running your PVC unbroken through a 2-1/2 RMC "sleeve".. but PVC wiring method doesn't qualify as a cable assembly.

It's a shame 250.68 Exception No. 3 only covers elbows.

Get back with your project's engineer and ask him how you are supposed to ground the RMC???

You could run a bonding jumper alongside the run and bond each section of RMC, but you would still be violating the required connection to circuit EGC.
 

Carultch

Senior Member
Location
Massachusetts
Hi,
I will be working on a block long streetlight project where the engineer has stated in his notes that whenever the PVC conduit run is under a driveway, that section of the conduit be RMC. I have approximately 12 driveways that I will be crossing underneath.

If I cannot get him to allow to continue the 1-1/2" PVC under the driveways, my question is this...

Can I not ground the 10'-15' RMC sections under the driveways since they will be more than 18" underground? I see that 250.34 allows for elbows not to be grounded as long as they are more than 18" deep. Also I believe that 250.86 Exception 2 will allow me to do this..

Thoughts?

I recommend asking him about using Schedule 80 PVC, where under a driveway. That's what I would spec, if it were my recommendation. It is permitted in most locations where RMC would be required, except with the locations where subject to vehicular impact ("severe" physical damage). And underground is not subject to vehicular impact.

250.80 has an exception that allows you to not ground isolated metal elbows, provided that every metal atom has a minimum 18" cover. So in most applications, where you'd use steel sweeps, most sweeps coincide with a riser that would also be metal. And that riser would get grounded to the equipment. BUT, when you have a subterranean sweep in the middle of the run, you can use a steel sweep, completely buried with 18", and forget about grounding it. The reason why you would run steel sweeps, is to reduce raceway damage due to side wall pressure of pulling.

250.80 does specifically say elbows, so the wording as written doesn't permit you to forget about grounding isolated straight sections of underground RMC. Even though the electrical Physics is the same as an isolated buried metal elbow.

If you have to ground your underground RMC, you can use a direct burial U-bolt, and a direct-burial rated additional EGC running along with the raceway. And terminte that to the EGC system, as soon as practical.
Alternatively, you can end the metal conduit in the nearest handhole, with a bonding bushing. And thus attach the EGC to its lug.
 
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Smart $

Esteemed Member
Location
Ohio
...If you have to ground your underground RMC, you can use a direct burial U-bolt, and a direct-burial rated additional EGC running along with the raceway. And terminte that to the EGC system, as soon as practical.
I direct you to 250.134(B), and then ask you to elaborate on your position as a result.

Alternatively, you can end the metal conduit in the nearest handhole, with a bonding bushing. And thus attach the EGC to its lug.
For all the trouble it is going to be switching from PVC to RMC and back, the engineer just needs to forget about the PVC and run RMC all the way...


...or take the SCH80 PVC route. He can use additional protection techniques, such as encasing in a sand-cement slurry, or even concrete if he wants.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I tend to agree with Smart. The engineer needs to be talked out of his desire to over engineer this thing. Switching between conduit types is silly.

I will disagree on the need for any extra protection if the entire run is PVC. There is no need for any extra protection for PVC underground under a driveway, no reason to even suggest it.
 

jap

Senior Member
Occupation
Electrician
This section seems to say ya gotta bond/ground it:



unless your exception allows you not to.

What code section requires the isolated sections of underground rigid to be bonded to the equipment grounding conductor?

JAP>
 

Carultch

Senior Member
Location
Massachusetts
What code section requires the isolated sections of underground rigid to be bonded to the equipment grounding conductor?

JAP>

Any piece of metal that doesn't intentionally carry current, needs to be electrically continuous with the EGC system. It is the exception, when you don't need to do this.
 

electricman2

Senior Member
Location
North Carolina
Occupation
Retired Electrical Contractor
It really doesn't matter anyway. In a few years the RMC will be reduced to rust and you will end up with direct buried conductors:(
 

Carultch

Senior Member
Location
Massachusetts
Doesn't this installation (street lighting) fall under the NESC, not the NEC?

I think it depends on whether it is customer-owned lighting circuits (probably governed by the NEC), or utility-owned lighting circuits (probably governed by the NESC).

Customer-owned circuits could be the same light fixtures used for street area lighting, except with the application of lighting parking lots or private roads.
 

Carultch

Senior Member
Location
Massachusetts
It really doesn't matter anyway. In a few years the RMC will be reduced to rust and you will end up with direct buried conductors:(

Then what the heck is the Zinc finish for? I thought the hot dip galvanizing was an integral part of RMC, so that it curtails corrosion, with the zinc coating forming a sacrificial oxide barrier that protects the steel core.
 

paul

Senior Member
Location
Snohomish, WA
What makes you say that?

I know its possible that it can be under the NESC... but more likely that it is not, IMO.

If it's controlled by the utility, ie. no meter, then it most likely falls under the NESC. This is one of those grey areas where both can cover it. Tom Baker should be able to chime in and give a more definitive answer.
 
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