Bonding Conduits

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wireddd

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Had a rough in inspection on a pipe run of (4)- 3 inch conduits going thru two 24x36 pullboxes. All fittings were compression on a indoor installation.
In the pull boxes we used 3 inch grounding bushings with lugs on top of the locknuts and tied everything together with #4 solid copper. #4 went thru each lug from one side of box to the other stopping in between to attach to a lug on the box. One continuous piece of copper. Inspector said it was not correct, didn't like it and wouldn't say what should be changed.
Blueprint called for grounding bushings and #4. Didn't specify stranded or solid. Our intent was to provide complete bonding of all pieces together.
This is a sub-feed run, not a service entrance.
Normally in the bottom of service gear one piece of number 6 is used to loop all conduits and then tie to the ground bar but this isn't service entrance.

Any thoughts?
 
I would make the inspector show you what code is in violation and why their department authorized plans and won't accept the work when done as shown
 
What voltage ? Were there any concentric or eccentric knockouts ? What ampacity circuits ?
 
Bonding Conduits

Voltage is 120/208 three phase 4 wire. These were solid 16ga pull boxes which we punched our own 3" KO's We went thru the extra step of bonding all this together, not that it was on the prints. This is a 1200 amp sub-feed from one part of the building to another. Prints only showed grounding bushing bushings and #4 at start of conduit run. Because we had to add 2 pull boxes we added the bonding at these points.
As far as having the inspector explain the violation, probably not possible as thou shall not question authority having jurisdiction.
 
With that voltage and punched knockouts, bonding of the conduits should not normally be required.
If bonding was needed, 250.102(D) would require the jumper to be a minimum of 3/0 Cu for a 1200 amp feeder.
In cases like yours, if bonding is done, it is not unusual for an inspector to required it to be bonded per 250.102.

If is somewhat similar to installing an undersized equipment grouding conductor in a 250.118 recognized conduit system.

If you are going to bond, bond per Code is the thinking.
 
By the NEC the bonding bushings are not required at all so the inspector won't find a specific code article that has been violated, but you said this a 1200 amp feeder which makes the #4 too small.
 
infinity said:
By the NEC the bonding bushings are not required at all so the inspector won't find a specific code article that has been violated, but you said this a 1200 amp feeder which makes the #4 too small.
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And that is a violation. While bonding isn't required, bonding is not prohibited. Even extraneous bonding must be compliant. :eek:hmy:
 
infinity said:
Is that necessary? I'm pretty sure that standard locknuts required by UL to cut the paint as part of their listing.
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If that is true, then it would not be necessary. Can you cite that UL requirement?

petersonra said:
What provision of the code requires this?
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This one...

250.12 Clean Surfaces. Nonconductive coatings (such as
paint, lacquer, and enamel) on equipment to be grounded shall
be removed from threads and other contact surfaces to ensure
good electrical continuity or be connected by means of fittings
designed so as to make such removal unnecessary.
Click to expand...
 
I know that is required by UL when reducing washers are incorporated:
The following information comes from UL 514B;
8.34 Reducing washers resistance test
8.34.1 ? reducing washers shall be assembled to threaded conduit and unpainted steel plates as illustrated in Figure 16, and then subjected to the resistance test described in Clause 8.9. As a result of the test, the voltage drop shall not be greater than 10 millivolts. The samples shall then comply with the current test described in Clause 8.10.

I was not aware it was required on standard locknuts.
 
This is from Mike Holt, not sure where he got this info but I thought that I read somewhere that the requirement for the locknuts came from UL.

PART V. BONDING
Sections
250.96 Bonding Other Enclosures.
(A) Maintaining Effective Ground-Fault Current Path. All metal parts intended to serve as the effective ground-fault current path, such as raceways, cables, equipment, and enclosures must be bonded together to ensure they have the capacity to conduct safely any fault current likely to be imposed on them [110.10, 250.4(A)(5), and Note to Table 250.122].


Author?s Comment: Bonding jumpers are required around reducing washers (donuts) because they do not provide an effective ground-fault current path [250.4(A)(5)]. Figure 250?136​
Nonconductive coatings such as paint, lacquer, and enamel on equipment must be removed to ensure an effective ground-fault current path, or the termination fittings must be designed so as to make such removal unnecessary [250.12].

Author?s Comment: The practice of driving a locknut tight with a screwdriver and pliers is considered sufficient in removing paint and other nonconductive finishes to ensure an effective ground-fault current path.
​
(B) Isolated Ground Circuit. A metal raceway containing circuit conductors for sensitive electronic equipment can be electrically isolated from the sensitive equipment it supplies by a nonmetallic raceway fitting located at the equipment. However, the metal raceway must contain an insulated equipment grounding (bonding) conductor to provide the effective ground-fault current path to the power source in accordance with 250.145(D). Figure 250?137
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infinity said:
This is from Mike Holt, not sure where he got this info but I thought that I read somewhere that the requirement for the locknuts came from UL.
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From what I can gather through non-exhaustive 'net research, UL did a test early in the 90's with grounding listed fittings (standard 514B, category DWTT...?) installed through punched KOs in a typical painted enclosure and issued a report. I'm guessing such fittings passed their test because authoritative figures reference the report for their claims. However, as I understand it, UL does not "officially" take this position nor are locknuts required to provide adequate contact on painted surfaces. As such, as always, approval is subject to AHJ discretion.
 
Smart $ said:
From what I can gather through non-exhaustive 'net research, UL did a test early in the 90's with grounding listed fittings (standard 514B, category DWTT...?) installed through punched KOs in a typical painted enclosure and issued a report. I'm guessing such fittings passed their test because authoritative figures reference the report for their claims. However, as I understand it, UL does not "officially" take this position nor are locknuts required to provide adequate contact on painted surfaces. As such, as always, approval is subject to AHJ discretion.
Click to expand...

Having said that I think that one would be hard pressed to find an inspector who would make you remove all of the paint before installing a locknut.
 
infinity said:
Having said that I think that one would be hard pressed to find an inspector who would make you remove all of the paint before installing a locknut.
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Probably so... but finding one that does will certainly alter an otherwise great day.

FWIW, I have seen metal connectors with locknuts that are UL listed, but not to UL 514B, so be cautious.
 
Bonding Conduits

It is interesting to note that if you buy a UL approved grounding bushing made by Crouse Hinds it only comes with a lug rated up to 1/0 nothing larger.
If you change this lug to a 3/0 one to accept the so called 3/0 required by the code then you have voided the UL listing on the grounding bushing.
Guess maybe the code allows you to clip off a few strands to fit the lug.
It would be nice if everyone would get their act together and make products that comply.
And it is certainly be difficult to bend 3/0 cable into lugs that are about five inches apart. Kind of silly to expect that you will have good solid contact at the lug.
A #14 wire will explode at about 400 amps dead short. A 3/0 is probably around 9000 amps or more. If your overcurrent device with ground fault and instantaneous trip doesn't go by then, it would be kiss your equipment goodbye anyway.
 
Smart $ said:
If that is true, then it would not be necessary. Can you cite that UL requirement?


This one...
250.12 Clean Surfaces. Nonconductive coatings (such as
paint, lacquer, and enamel) on equipment to be grounded shall
be removed from threads and other contact surfaces to ensure
good electrical continuity or be connected by means of fittings
designed so as to make such removal unnecessary.
Click to expand...

I think most locknuts are designed to make such removal unnecessary.
 
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