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#2342 07/05/01 12:35 AM
Joined: Nov 2000
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I'm getting ready to go for the 1 and 2 family dwelling test for Electrical Inspectors given by Experior. I'm reasonably confident in my ability to pass the test given that the questions are straightforward... but in the study guides I've ran into a couple that may even be considered "wrong" because in my opinion, either not enough data is in the question to derive the answer from the 4 choices, or the answer should be "none of the above" when it's not available.

Case in point...

Quote

20. Which one of the following methods is NOT acceptable for bonding metal conduit to a service panelboard enclosure?

A. Threaded hub on top of enclosure
B. Bonding type locknut on inside of enclosure
C. Bonding bushing with bonding jumper
D. Standard locknuts and bushings with locknuts both inside and outside of enclosure


According to the answer sheet, the correct answer is "D"... but I feel that there is not enough information, or the answer is "none of the above", because there is no mention of whether or not eccentric or concentric knockouts are being used.

Refer to 250-94 '99 NEC

Am I just missing something here (again)?

[Linked Image]


[This message has been edited by sparky66wv (edited 07-05-2001).]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#2343 07/05/01 01:02 AM
Joined: Oct 2000
Posts: 4,067
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'66,

Glad to see some initiative going on there. [Linked Image] Good Luck!

Check the last sentence of 250-94
Quote
.. Standard locknuts or bushings shall not be the sole means for the bonding required by this section

Go get 'em

Bill


Bill
#2344 07/05/01 01:08 AM
A
Anonymous
Unregistered
Perhaps what the NEC meant to say is that while no one denies that std lock nuts and bushings provide some electrical connectivity, they are not to be considered electrically bonding.

#2345 07/05/01 05:47 AM
Joined: Oct 2000
Posts: 5,392
S
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Virgil;
how to take a test is the real Q, most multiple quess tests subscribe to a certain philosiphy, one Q is out in left field, one Q is headed there, the two remaining Q's compete for the A, usually determined via a key word in the original question, which may be slightly shy of pertinent data as you mention.

good luck!

[Linked Image]

#2346 07/05/01 09:23 AM
Joined: Nov 2000
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OK... Now I see, I was reading into it too much since it's all in the same paragraph, the part about concentric and eccentric KO's... But it's not in the same sentence... I got it now... I hope there aren't too many others like this that I'm goofing on...

Thanks for the help...

And I've come to the realization that you can't buy a 2" nipple without buying a bonding bushing to go with it...Regardless of the presence of KO's or not... I had thought in the past that the rule only applies to Boxes with KO's... Do I have this right?

[Linked Image]


[This message has been edited by sparky66wv (edited 07-05-2001).]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#2347 07/05/01 03:15 PM
Joined: Nov 2000
Posts: 2,236
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Uhhh..

Now I know where I got confused...

Why does the NEC bother mentioning the concentric and eccentric KO's in 250-94 if it doesn't matter? It seems to only confuse things with extrapolated "exceptions" that aren't really there...

I thought it had meant that if the hole has been drilled, cut, or the largest size eccentric or concentric KO used, then standard locknuts and bushings were OK... Where the heck did I get that?

If the bonding cannot rely on standard locknuts and bushings on a GRC nipple between the meter can and the disco, regardless of the type, then I can safely say that I have installed the only legal service using a GRC nipple in Greenbrier County WV!

Or am I analyzing to the point of blindness here?

[Linked Image] [Linked Image] [Linked Image] [Linked Image]


[This message has been edited by sparky66wv (edited 07-05-2001).]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#2348 07/05/01 03:57 PM
A
Anonymous
Unregistered
>If the bonding cannot rely on standard locknuts
I think they mean that you can use bonding-type locknuts... "standard locknuts" are not suitable for effective bonding in this case.

#2349 07/05/01 04:10 PM
Joined: Nov 2000
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Maybe I don't know what a bonding locknut is...

I thought it was similar to a bonding bushing in having a lug to terminate #4 bare Cu wire for bonding... Or is it a locknut that simply makes better contact with the boxes surface?

My supplier knows nothing of bonding locknuts, only bushings.

The standard Locknuts and Bushings readily pass inspection here... That is until I left a message on his machine to bear in mind 250-94...

The whole mess didn't even come to light until I had broken a KO in a meterbase and had to see what I needed to do, go here to "relive" that...


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#2350 07/05/01 05:04 PM
A
Anonymous
Unregistered
Bonding-type locknuts are designed to gouge the box when tightened whereas grounding-type bushings have a set screw and a lug for a copper jumper.

I would use a bonding locknut directly only when the hole was at its maximum size with nothing left to be knocked out. Otherwise the locknut may chew out the frangible attachment of the remaining KO.

The NEC need to include sample illustrations in case folks are using different terminology. It is obvious that many of us still say "grounding" rather than "bonding".

#2351 07/05/01 05:31 PM
Joined: Nov 2000
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So what I'm calling "standard" locknuts, they fit you're description of "bonding" locknuts in that they are designed to dig in as they are tightened... And I was out of line on the phone call to the AHJ...

Apparently, my supplier carries bonding locknuts but not the standard ones...

Boy I am mixed up....

Just discovered that some of my assumptions may have come from one of the questions on Mike Holt's Code Quiz... I don't think a URL link will work with the exact page the question is on, though, being a CGI script.

[This message has been edited by sparky66wv (edited 07-05-2001).]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
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