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#103169 - 05/10/02 09:18 AM Bonding Rules 250.97, 2002 NEC
Joe Tedesco Offline
Member

Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA
QUESTION FROM: John J. Deery ,

Joe my question is about 250.97. If you run a branch circuit to a safety switch and the conduit enters the enclosure through concentrics or eccentrics, are you required to use bonding bushings when the voltage excedes 250 volts to ground and you pull an equipment grounding conductor and bond it to the enclosure?

My concern: "Is the conduit being properly bonded?"

I spoke to Kevin Huss from Square D at 800-634-2003 TEC support, and was told to date Square D does not have an enclosure on the market with pre-stamped ko's listed by U.L. for the purpose of bonding.

We have new branch circuits being run at our plant 480 volts where the conduits are being landed in pre-stamped ko's of Square D enclosures with equipment grounding conductors, but are relying on the eccentrics and concentrics to bond the conduits.

Thanks
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Joe Tedesco, NEC Consultant

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#103170 - 05/10/02 12:12 PM Re: Bonding Rules 250.97, 2002 NEC
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
The conduit needs to be effectively bonded to the installed EGC through a bonding bushing because if a fault developed in the raceway, the return path may not have a low enough impedance to assure opening of the OCPD.
Don,
are you wondering if the conduit is effectively bonded at the supply end, and therefore not required to be bonded through a bushing at the switch end?

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#103171 - 05/11/02 05:17 PM Re: Bonding Rules 250.97, 2002 NEC
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Some suggestions...Square-D makes NEMA-12 [NOT '12K' or ‘AWK’ suffix] XOP fusible disconnect switches without knockouts. Westinghouse/C-H makes NEMA-12 breaker enclosures of similar construction. Many 5½" depth panelboard cans are available with 'blank endwalls.' The 12’s are equal or somewhat less in price compared to 3R. ‘NOKO’ NEMA-1, -3 and -3R screw-cover gutters and pull cans are out there too.

KO reducing rings are {or should be} suicide.

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#103172 - 05/11/02 08:13 PM Re: Bonding Rules 250.97, 2002 NEC
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
Redsy,
That is exactly what I was thiniking. Most code experts say that only one end of a service raceway requires bonding, so I would think that if the supply end was properly bonded, there would be no need to bond the load end, assuming that the EGC is used to bond the enclosure.
Don(resqcapt19)
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Don(resqcapt19)

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