PVC to RMC - Bonding?

[graham85]

Good Afternoon all,

I have a quick question about grounding/bonding. I am proposing an u/g PVC run but have to change to RMC for a short run and then back to PVC.

My queston is: Do I have to specify the grounding conductor in the PVC be bonded to the RMC conduit or can the grounding conductor be run through the RMC as well?

 

[earlydean]

Re: PVC to RMC - Bonding?

If the whole run is below 18 inches UG, then it does not require grounding.

 

[graham85]

Re: PVC to RMC - Bonding?

The section that is RMC will be only 6 inches below. Is there a section in the NEC that specifies this?

Thank you for your reply.

 

[earlydean]

Re: PVC to RMC - Bonding?

see 300.10 exc. 1, which allows short sections exemption from being bonded.

 

[earlydean]

Re: PVC to RMC - Bonding?

see also Table 300.5 for minimum burial depth, and 300.5 (D)(1), for 'emerging from grade' protection.

 

[don_resqcapt19]

Re: PVC to RMC - Bonding?

In my opinion, 300.10 does not apply to this installation. The exception to 300.10 applies to short isolated sections of raceway used to protect cables and does not apply to complete raceway systems. This appears to be a complete raceway system using two types of raceway. You are required to bond the metallic raceway unless you meet one of the exceptions to 250.86.
Don

 

[graham85]

Re: PVC to RMC - Bonding?

Earl,

That was exactly what I was looking for. Thank you for your quick responses.

Keith

 

[earlydean]

Re: PVC to RMC - Bonding?

300.10 and 300.12 both mention short sections of raceway to provide support OR protection. Isn't that what the section of RMC is for, PROTECTION?

 

[graham85]

Re: PVC to RMC - Bonding?

Don & Earl,

Thank you both for pointing me in right directions. You were right Don, I don't think 300.10 applied and we can't meet 250.86's exceptions. It looks like I might have to modify the design some using Table 300.5. I might put in a 2" pad and put the PVC 12" deep for that section. Thanks again for your help.

Keith

 

[earlydean]

Re: PVC to RMC - Bonding?

Exception #2 of 250.86 says the same thing too.

 

[graham85]

Re: PVC to RMC - Bonding?

Guys,

Here is a little more background.

We need to put the conduit higher for a 25' section because we do not have the depth to put the PVC 18" deep. Because we only have 6-12 inches of depth we were going to use RMC for that section because of Table 300.5. It is part of the overall raceway but it is for the protection of the conductors. So therefore maybe 300.10 does apply as well as 250.86 exception #2.

what do you think?

Keith

 

[websparky]

Re: PVC to RMC - Bonding?

Just my opinion;

It seems if you use 250.86, it would not be within the intent of the code because it is part of a raceway used for conductors as opposed to a protective sleeve for a cable.

My suggestion;

Use RMC the entire length.

 

[don_resqcapt19]

Re: PVC to RMC - Bonding?

In my opinion, the exceptions that talk about "short sections" do not apply to a raceway system. They only apply to short sections of raceway that are used for cable protection. By a raceway system, I mean a raceway or combination of raceways that are continuous between pull points.
Don

 

[spsnyder]

Re: PVC to RMC - Bonding?

I think that Don et al are correct. Seems to me that you should either run RMC the whole way or PVC the whole way and add 4" of concrete above the conduit in the area of concern. How far is the entire run?

 

[earlydean]

Re: PVC to RMC - Bonding?

I disagree. A short section of RMC in the middle of a run of PVC does not need to be bonded, and would be difficult to bond without installing a j-box. What is the danger from this UG section of conduit? If there is a fault in this section, what is the difference than if it were direct burial?

 

[Guest]

Re: PVC to RMC - Bonding?

Does the bonding requirement for this short section or RMC change if the EGC is bare vs. insulated? My recollection is that the bonding requirement varies based on the EGC.

 

[don_resqcapt19]

Re: PVC to RMC - Bonding?

Earl,
If it is not bonded then there is no fault clearing path. It could produce a hazardous step potential on the surface of the earth above the conduit. The code does permit an unbonded metallic elbow to be used, but only if it is covered by at least 18" of earth at the point closest to the service. Exception #2 does not apply to short sections of complete raceway systems. This is made clear by the very fact that there is an Exception #3 to 250.86. If Exception #2 applies to short sections of complete raceway systems, there would be no reason for Exception #3 to be in the code. Also see comment 5-35 in the 92 TCD (Technical Committee Documentation, now known as the Report On Comments). This comment is on the proposal that resulted in what is now Exception #3 to 250.86. CMP 5 stated; "It is not the panel's intent to permit ungrounded straight sections of metal conduit in underground nonmetallic conduit installations.
Don

 

[earlydean]

Re: PVC to RMC - Bonding?

I sure would have been happier if CMP 5 had included that comment in the exception! Anyway, thank you Don for clearing this up.

Exactly how does one go about bonding a short section of RMC in the middle of a run of RNC? Are there any fittings, other than the junction box? A Quazite UG splice box, with the EGC bonded to a grounding bushing would do the trick. But is there a less expensive way?

 

[tommy]

Re: PVC to RMC - Bonding?

If you were to run all pvc. Could'nt you just sleeve the pvc with the RMC. Just for protection.

 

[pierre]

Re: PVC to RMC - Bonding?

The raceway 'system' protects conductors. Short sections of raceway protect conductors, and are permited to not be grounded.
The raceway system even if of different types of raceways is required to be grounded.

Why would this make a difference if not grounded?
Since this is only 6 inches deep, and a ground fault were to occur in the metallic section of conduit, there would be a step potential in the earth surrounding the conduit and a potential shock hazard. That potential is enough for me

Pierre