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

[Darryl Thayer]

Hi
As an electrican I always bond the conduit when
working over 250 volts, even if I run a ground wire in
the conduit.  I actually do not know the rule it is
just a habit. 
Darryl

--- "Bob-O Schultze, Electron Connection"
<econnect at snowcrest.net> wrote:

> 
> 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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