Bonding Bushings (When required)

[LarryFine]

Re: Bonding Bushings (When required)

Originally posted by hurk27:
Have you notice there has been some changes in our state building department?

I have: here in Richmond, we have to go through a metal detector to apply for a permit. It takes me 15 minutes just to empty my pockets before I go in!
:roll:

 

[pierre]

Re: Bonding Bushings (When required)

UL 2004
"...and where installed in accordance with ANSI/NFPA 70, 'National Electrical Code'."

NEC '02
"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)."


250.92
"(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.


Not trying to stir the pot... but I like Don and a few others (even though the washers are listed) cannot see this as working properly. I have seen too many instances where these washers have impeded the ground fault path and created many problems.

The above reference to the NEC is just what the last sentence of UL refers to.

" Standard locknuts or bushings shall not be the sole means for the bonding required by this section."

I have to hang my "hat" here to say that the NFPA supercedes the UL document.

 

[ryan_618]

Re: Bonding Bushings (When required)

Pierre...what about the exception to 250.97, which overrides the general rule of 250.97? There are 4 items that can be employed to bond these circuits when concentrics are not encountered, including standard locknuts and listed fittings that are identified for the purpose.

 

[derf48]

Re: Bonding Bushings (When required)

Take a moment to look at what bonding really is, the permanant joining of metal parts.
Now apply that definition to the installation of a standard locknut connection and reducing washers in a circuit with more than 250 volts to ground. The reducing washers are by article 100 a fitting and are listed for bonding for over 250 volts. The exception to 250.97 applies to when oversized, concentric, or eccentric knockouts are not encountered...(I as skipping the second half of that sentence because it applies to a box or enclosure). If I must use reducing washers. then I have encountered oversized knockouts, and the exception does not apply. Because it does not apply, I must revert back to the text of that section which requires me to ensure bonding using 250.92(B), except (B)(1).
The NEC, as written, does not allow reducing washers for bonding over 250 volts unless there is no oversized knockout, and if that is the case, then why use them?

Fred Bender

 

[dillon3c]

Re: Bonding Bushings (When required)

Originally posted by gsrandy:
The conduit contains (3) 277 volt circuits with a ground and a neutral. Does this application require a bonding bushing? And where can I find this in the NEC?

Fred on a personal note,
I went back and pulled up the original posting, to this thread.

When I first seen iwire's responce to this thread,I must admit my first response- before any other replies- was paste and post..

But in the knowing,he would never make such a bizarre mistake in statement, without the data in backing this up..

So before returning in the posting,I had to go hunting in UL website.

In according to UL,it seems like it doesn't leave much interpretation of the imagination, in this matter.

I'm just as confused ...As in the first time I read this data, on there site.

I just don't understand,or agree in their way of thinking on this matter.

It just goes against the grain,of what I know and have been taught, and otherwise interpret..

I just do not understand their finding and statement, at all in this installation.. Man I am

[ June 16, 2005, 01:11 PM: Message edited by: dillon3c ]

 

[ryan_618]

Re: Bonding Bushings (When required)

Fred, that is a great point!!!

I didn't notice the "oversized" part of the exception, I was simply looking at the concentric/eccentric KO portion. that really does nullify their usage!

Thanks again, and great catch!

 

[dillon3c]

Re: Bonding Bushings (When required)

ryan sir, in all due respect..
help me out here, what am I missing..

Why else would you need the installation of reducing washers,unless KO's were oversized?

 

[ryan_618]

Re: Bonding Bushings (When required)

I guess the bottom line is that you would have to bond around them, since 250.97 requires "service" type bonding. The exception for this is wehn you use listed fittings (such as reducing washers), but the exception only applies if the KO's are not oversized or concentric or eccentric.

 

[iwire]

Re: Bonding Bushings (When required)

Originally posted by dillon3c:
When I first seen iwire's responce to this thread,I must admit my first response- before any other replies- was paste and post..

But in the knowing,he would never make such a bizarre mistake in statement, without the data in backing this up..

So before returning in the posting,I had to go hunting in UL website.

Dillon, looking it up yourself is what I feel everyone should do when reading posts on this or any other forum.

No one here should take my word for anything here without verifying it.