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Discussion Starter · #1 ·
I have a 2" sealtite coming out of a xfmr to a Square D tub. I'm coming into the tub in a concentric KO. I will have a bonding locknut at the xfmr and an equipment ground in the sealtite. The bond to building steel will be in the xfmr. Do I need a ground/bond busing on the sealtite connector at the panel? The secondary will be 240 grounded B.

If this depends on if the concentric KO's are rated for carrying the ground, where can I find that information out? Would that be in the tub's literature or in the listing?
 

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I have a 2" sealtite coming out of a xfmr to a Square D tub. I'm coming into the tub in a concentric KO. I will have a bonding locknut at the xfmr and an equipment ground in the sealtite. The bond to building steel will be in the xfmr. Do I need a ground/bond busing on the sealtite connector at the panel? The secondary will be 240 grounded B.

If this depends on if the concentric KO's are rated for carrying the ground, where can I find that information out? Would that be in the tub's literature or in the listing?

250.92 (B) Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bushings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s).
Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:
(1) 
Bonding equipment to the grounded service conductor in a manner provided in 250.8
(2)


Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
(3) 
Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables
(4) 
Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers



250.97 Bonding for Over 250 Volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).
Exception:  Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection, the following methods shall be permitted:
(1) 
Threadless couplings and connectors for cables with metal sheaths
(2) 
Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
(3) 
Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
(4) 
Listed fittings.



*********

There are other articles to read too.

Look here as well...

http://www.ul.com/global/documents/...nical/ul_BondingAroundConcentricKnockouts.pdf









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Discussion Starter · #3 ·
I like to compare questionable situations to other known situations. For a typical service, we run EMT out of the meter socket (always concentric KO's) to the concentric KO's in a panel. We are only required one ground/bond bushing at either connection, not both. Since I already plan on having a bonding locknut at the xfmr, do I need the one on the tub side?

I think I do need to bond the connector at the tub, but I can't see the difference in the residential example I posted.
 

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I have a 2" sealtite coming out of a xfmr to a Square D tub. I'm coming into the tub in a concentric KO. I will have a bonding locknut at the xfmr and an equipment ground in the sealtite. The bond to building steel will be in the xfmr. Do I need a ground/bond busing on the sealtite connector at the panel? The secondary will be 240 grounded B.

If this depends on if the concentric KO's are rated for carrying the ground, where can I find that information out? Would that be in the tub's literature or in the listing?
Tub, you putting the sealtite in water? A bath tub????
 

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Why the bond bushing at the transformer? Couldn't you just put it on the panel side and punch your own hole in the transformer
 

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Discussion Starter · #7 ·
My boss wants all bonding done at the same location. SOP is to install bonding lock nut at the xfmr and bring building steel to xfmr. We usually don't get tubs with premade KO's, but this one had them on one of the ends.
 

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Like the emt service you've mentioned, solid groundING is required, without the possibility of a dual noodle Deepone....

~CS~
 
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