Bonding grounding electrodes conductors

[pgcusa]

Is it necessary to bond the grounding electrode conductor when it enters metallic enclosures at the sevice equipment and separately derived systems. My design did not call for a connector at the point of entrance to the metallic enclosure and the Electrical Inspector is requiring that I use the appropriate listed fitting.

 

[waross]

Are there two issues confused here. A conductor must enter an enclosure through a listed fitting or connector. Whether or not that fitting must bond the conductor or just support and protect it is a seperate issue. It would be well to clarify this with the inspector before proceeding.
Remember, if you start a war with the inspector, he has bigger "Guns". You may win some battles but you will definitely lose the war. Your best course of action is to ask the inspector politely what he requires, listen quietly, and proceed with his wishes.

 

[pgcusa]

The inspector quotes NFPA 780 and applicable NEC articles. Compliance with his request is not an issue, but bonding at the enclosure has never been a NEC code requirement. Although, I believe there's supporting Code for his argument. The inspector is also concerned with the choke effect under severe faults or loss of grounded conductor and lightning strikes.

 

[waross]

Hi pqcusa
My copy of the NEC is out of date, but it covers induction heating, which is a direct result of the "Choke" effect the inspector is concerned about. It gives a specific exemption for grounding conductors.
I respectfully disagree with the inspectors interpretation of the code. However, after discussion with him, I would comply with his wishes.
Now if this was 50 completed housing units, and I was looking at a large labour expense to correct it, I may consider a challenge to the ruling.
Further more, the main result of the choke effect is to heat the metal enclosure by the action of circulating currents. It will not limit the current to the extent that over current devices fail to operate.
I was aware of some tests conducted about 30 years ago by an Electrical Contractors association. They ran several hundred amps through a test conductor. They then passed the test conductor through a 10' length of 1/2" steel conduit. They found that the conduit choked the current of to about 100 amps. They then connected to conductor to the conduit at each end and found that about 100 amps flowed through the conductor and the rest flowed through the conduit.
I would suspect that the choke effect caused by a sheet metal enclosure would be related to the ratio of the thickness of the panel to the length (10') of the steel conduit.

How big is this installation? Sometimes size makes a difference. Is there something out of the ordinary here?
respectfully

 

[pgcusa]

Thanks for your response. The inspector claims NFPA recommends bonding grounding electrodes due to side flash due to a lightning strike and 250.8 NEC for applying a listed fitting for grounding. Also 110.3(B), 300.15 NEC listed for the purpose and when a conductor enters a box a listed fitting is required. 800 Ampere service is the size but he applies the rule to all service panel installations.

 

[waross]

Out of curiosity, is the exception listed in the older code editions still in effect?
NEC index under
Conductors; Parallel
Induced Currents in Metal Enclosures or Metal Raceway.
In an older edition, rule 300-20 (a), Exception number 1.
What type of connector is he requireing?
Is this grounding requirement applied anywhere else in the country?
respectfully.

 

[pgcusa]

300.20 is still in the code, I don't believe it applies to grounding electrode conductors. Although, the application or theory may be the same. The connector is called a kenny clamp, new to the market for approximately 1.5 years. Its listed for bonding and grounding under UL/Ansi 467 standard and UL/Ansi 486A standard for connectors. The alternative is to use a nonlisted connector which has been except for many years, until it was bought to my attention.
Thanks for the imput.

 

[waross]

Thanks for the information on the Kenny Clamp.
respectfully