Concentric knockouts on circuits over 250 volts [RE-wrenches]

[William Miller]

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At 08:13 PM 8/27/2006, you wrote:

Bob-O:

I do not see where the citation excludes conduits that carry a separate 
equipment grounding conductor.  We always pull a ground, but it connects to 
the module frames and does not bond the conduit at either end.  The logic 
behind this?  My guess:  A nick in the insulation of a conductor carrying 
voltage could energize the conduit, I guess.

If you could point out where the citation excludes conduit in the situation 
you describe, I could win a pissing match with a local inspector.

William





>William
>If I read this right, this only applies to situations where one is
>using the EMT or the like as the grounding conductor. Where one
>carries a grounding conductor from the PVs down to the DC disco and
>it is bonded to all the metal boxes using a lay-in lug or the like, I
>don't see the need for the bonding bushings. Just my thoughts, I
>could be wrong.
>Bob-O
>On Aug 27, 2006, at 12:18 PM, William Miller wrote:
>
>>
>>Friends:
>>
>>It has come to my attention that bonding bushings are required in
>>our DC feeder conduit where it enters the DC disconnect via
>>concentric knockouts per NEC:
>>
>>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
>>(1).
>>Exception:  Where oversized, concentric, or eccentric knockouts are
>>not encountered, or where a box or enclosure with concentric or
>>eccentric knockouts is listed for the purpose, the following
>>methods shall be permitted:
>>(a) Threadless couplings and connectors for cables with metal sheaths
>>(b) Two locknuts, on rigid metal conduit or intermediate metal
>>conduit, one inside and one outside of boxes and cabinets
>>(c) 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
>>(d) Listed fittings that are identified for the purpose
>>
>>
>>250.92 Services.
>>(B) Method of Bonding at the Service. 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 bosses on
>>enclosures where made up wrenchtight
>>(3) Threadless couplings and connectors where made up tight for
>>metal raceways and metal-clad cables
>>(4) Other approved devices, such as bonding-type locknuts and bushings
>>Bonding jumpers meeting the other requirements of this article
>>shall be used around concentric or eccentric knockouts that are
>>punched or otherwise formed so as to impair the electrical
>>connection to ground. Standard locknuts or bushings shall not be
>>the sole means for the bonding required by this section.
>>
>>
>>
>>William Miller
>>
>>
>>__________________________________________________________________
>>William Miller
>>Miller Power and Communications
>>Voice :805-438-5600     Fax: 805-438-4607
>>email: wrmiller at mpandc.com
>>http://mpandc.com
>>License No. C-10-773985
>>_____________________________________________________________
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>
>
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