250.97 Bonding for over 250 volts

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I have four sets of 3c 350kcmil w/EGC feeding a 1200 amperes 480 volt panel. The wiring method is MCHL. These cables originate from a transformer outside and enter a modular constructed building erected with exposed steel including the floor. The cables terminate into TMC cable connectors and Myers hubs that are installed in the module floor deck plate approximately 18 inches below the 480 panel. The panel sits on the steel floor which has an opening in it to allow the conductors to pass through a chase into the enclosure. The design engineers detail suggests bonding the hubs with one #6 awg green insulated conductor from hub to hub then land the tail to a stainless steel bolt welded in the steel chase plate. Then run a 2/0 bare from the bolt into the panel and attach to the panel ground bus. in addition the design engineers suggest installing a #2 green insulated conductor from the enclosure (can) via bolt through to the module electrode connected to the verticle support mounts at the module base. This is a non hazardous classification.

250.97 Bonding for over 250 volts refers to 250.92 (B) except for (B1) tells us that we have to bond these hubs. 250.102(C) states to use table 250.66. 250.102(C2) size for parallel conductor installations in two or more raceways states to use Table 250.66 and looking at note 3 I would need to add four 350kcmil. 4X 350=1400kcmil then multiply 1,400.000 X .125 = 175 kcmil which is a 4/0. The #6 awg and the 2/0 in the design would appear to be undersized.

An RFI was written and a response stated the the grounding type Myers hubs are UL listed for up to a #6 awg and that Table 250.122 is the table to be using for the 2/0.

A 1200 amperes OCPD is downstream these feeders and if it was upstream then a 1200 amperes OCPD would require a minimum 3/0.

Do I need to get my head examined?
 

ActionDave

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I have four sets of 3c 350kcmil w/EGC feeding a 1200 amperes 480 volt panel. The wiring method is MCHL. These cables originate from a transformer outside ....
Who owns the transformer? Where is the service point? Service disconnect?

250.97 Bonding for over 250 volts refers to 250.92 (B) except for (B1) tells us that we have to bond these hubs. 250.102(C) states to use table 250.66. 250.102(C2) size for parallel conductor installations in two or more raceways states to use Table 250.66 and looking at note 3 I would need to add four 350kcmil. 4X 350=1400kcmil then multiply 1,400.000 X .125 = 175 kcmil which is a 4/0. The #6 awg and the 2/0 in the design would appear to be undersized.
Got to answer above question first.


An RFI was written and a response stated the the grounding type Myers hubs are UL listed for up to a #6 awg and that Table 250.122 is the table to be using for the 2/0.
Well that's just wrong.


A 1200 amperes OCPD is downstream these feeders and if it was upstream then a 1200 amperes OCPD would require a minimum 3/0.
What feeders? Are we talking about feeders or service conductors? Everything you talked about in the previous paragraphs and the code sections cited deal with service bonding.


Do I need to get my head examined?
We all do.
 

augie47

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I would agree that the#6s were too small.
Note 250.102(C)(2)allows an alternative for individual jumpers to each bushing.
 

ActionDave

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The Transformer is owned by the same oil company that owns the 480 panel. The service point would be at the transformer. The main for the feeders is in the panel.
Still don't have a real clear picture of what's going on, but I'll try and keep the conversation gloing. Others will chime in. Do you have a service at all? Is there a power company involved?

Anything on the load side of the service disconnect that is used for equipment grounding is sized using 250.122. Anything on the line side, there is no equipment grounding, everything is bonded to the neutral/grounded and is sized off 250.66.
 
I meant no I do not think mike is my coworker. The detail he submitted is similar but not the same engineer. To answer action Dave's question. There is a Large generator that runs to 13.8kv switch gear and from the switch gear to a transformer then from the transformer to the 1200 amperes 480 volt panel. Each of these are in seperate buildings. Please re-read the first post so we do not get side tracked. I am simply looking for conformation that my feeder raceway and fittings are to be bonded using supply side bonding jumper rules. Because the feeders are over 250 volts the NEC refers us to use the rules in 250.92. I do not think that the Myers hub can be used in this application.
 

ActionDave

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...I am simply looking for conformation that my feeder raceway and fittings are to be bonded using supply side bonding jumper rules. Because the feeders are over 250 volts the NEC refers us to use the rules in 250.92. I do not think that the Myers hub can be used in this application.
The #6 and 2/0 in the design are too small but, you would only have to refer back to 250.92 if you did not meet the criteria in the exceptions of 250.97.
 

Smart $

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no and I dont think you can instal a myers hub in 1/2 plate. too thick. would have to go with a bulk head style hub.
Who said anything about 1/2" plate?

I meant no I do not think mike is my coworker. The detail he submitted is similar but not the same engineer. To answer action Dave's question. There is a Large generator that runs to 13.8kv switch gear and from the switch gear to a transformer then from the transformer to the 1200 amperes 480 volt panel. Each of these are in seperate buildings. Please re-read the first post so we do not get side tracked. I am simply looking for conformation that my feeder raceway and fittings are to be bonded using supply side bonding jumper rules. Because the feeders are over 250 volts the NEC refers us to use the rules in 250.92. I do not think that the Myers hub can be used in this application.
As I mentioned in the linked thread, a hub is listed for use with RMC/IMC... not a connector.

Also mentioned in that other thread, a bonding locknut eliminates the need for a bonding jumper to the connectors... but the mounting plate must be bonded.
 
Well we finally got the Technical authority to see that the 2/0 is undersized and that they are on the supply side of the disconnecting means so supply side rules would are applicable. As for the Myers hubs they will remain and remain with the #6 awg wire. I think the Myers hubs technically are not required to be bonded as per 250.97 exceptions 1 through 4 have been met,(the hubs provide a good enough ground and are listed for that however, if they are bonded it doesn't hurt so why not use the largest size the UL listing allows considering the size of the feeders. The oil companies are not afraid to use a little over kill in there design specs.

Thank you once again for the education assistance! :cool:
 

augie47

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It sounds a bit like a case of "my mind is made up so don't bother me with facts" which is fine but since you mentioned "Listing" numerous times in your quote, there are a couple of things you might give some thought:
If "listing" is important, as Smart$ pointed out, I believe that Myers Hubs are only listed for use with threaded conduit and, if I recall correctly, the only hubs listed for grounding in for 250.92 are those listed by UL per Listing "KDER" which are the ones with ground lugs and then only if the bonding jumpers are sized correctly.
 

augie47

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Smart $

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That's a good link but I can't say i have a 100% understanding. From my research, which may be flawed, I am of the opinion that for 250.92 applications, hubs must be KDER listed and the only one that are have the grounding lug. Others with only the DWTT are not listed for 250.92 applications.
Is that your read ?
For the most part, I'll say you are correct... but I've not done an exhaustive research to determine whether other types of hubs are KDER listed. Then there's the possibility of using a DWTT-only hub and substitute a KDER-listed bonding locknut.

And FWIW not all bonding locknuts are KDER listed. For example, OZ Gedney Type 1 are DWTT while Type 101 are KDER.

http://www.emersonindustrial.com/en...c_locknuts/OZG_Rigid-Conduit-IMC-Locknuts.pdf

Type 1: http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073985908&sequence=1

Type 101: http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073988940&sequence=1

The hardest part of the determination is none of the manufacturers state the UL Category in their documentation. We are relegated to looking up the part certification.
 
I would like to say that it is not my mind that is made up and I came to this site to get the facts for sure. You have to understand that I am not the design engineer nor do I design the specifications that usually meet NEC rules or beyond however if I feel that there is a code violation I am entitled to submit my concern to the authority. The specifications and details that are written for these projects are done my engineering teams that usually go beyond what NEC requires. The best practices for the oil companies here in Alaska are a process that has been developed over many years by many people much like the way the NEC is developed. Sometimes there is a error much like this one and what gets changed is usually very little. The Myers hubs with a tmc connector is not a concern of there's I can assure you as for there must be a couple million Myers hubs with connectors on the north slope oil fields. I am satisfied with the change in size of the bonding jumper from a 2/0 to a 4/0 for the 1200 amperes feeders and main OCPD using T250.66 maybe they don't need to be bonded with a wire at all based on the exceptions being met in 250.97 exceptions. The second response from the engineers stated that surfaces the hubs are attached must be prepared properly and ground down to bare metal. I have mentioned the hubs not being listed for connectors and I thank you for your research. Definitely educational!
 
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