Bonding Around Concentric KO's over 250V

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infinity

infinity

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I'm confused about the requirement to bond around concentric KO's on enclosures where the voltage to ground exceeds 250 volts. Is the bonding bushing required to bond the enclosure or the raceway?

Here's one example:
I have an EMT branch circuit conduit run from a punched KO in a panelboard to a junction box with a concentric KO in the JB. Within the conduit is a EGC that terminates at the panel and is connected to the JB. Is a bonding bushing required at the JB?

I would say no, since the conduit is bonded at one end by the connector installed in the punched KO at the panel and the JB is bonded by the EGC connected at both ends. Am I reading the requirement correctly?


Here's example #2: Same as Example #1 but the conduit has concentric KO's at both ends and an EGC within the EMT. Are bonding bushing(s) required?


Trevor
 
Re: Bonding Around Concentric KO's over 250V

Trevor
Most Jboxes are listed as suitable for grounding these days. With that said, you will not be required to bond at that box even though you are installing a circuit rated greater than 250V to ground. ....250.97 the exception.
 
Re: Bonding Around Concentric KO's over 250V

The box won't be marked to indicate that bonding is not required about KO's it will be marked on the carton. But you can tell from the physical construction of the box, the KO's are very tight.
 
Re: Bonding Around Concentric KO's over 250V

Originally posted by pierre:
Trevor
Most Jboxes are listed as suitable for grounding these days. With that said, you will not be required to bond at that box even though you are installing a circuit rated greater than 250V to ground. ....250.97 the exception.
Click to expand...
I agree, but say the box isn't listed for bonding over 250 volts to ground. Would I be correct in my assumption that the use of an EGC would eliminate any requirement for a bonding bushing?
 
Re: Bonding Around Concentric KO's over 250V

opinion...
agree with you 1st scenerio, conduit is bonded due to termination at panel.
in the second scenerio, I would say one end would need to be bonded if neither end was suitable as a ground.
 
Re: Bonding Around Concentric KO's over 250V

Originally posted by augie47:
opinion...
agree with you 1st scenerio, conduit is bonded due to termination at panel.
in the second scenerio, I would say one end would need to be bonded if neither end was suitable as a ground.
Click to expand...
This brings me back to my original question. Is the bonding bushing bonding the JB or the raceway? I know that there is a requirement to bond one end of a service conduit but would this apply to a conduit with concentric KO's on both ends?
 
Re: Bonding Around Concentric KO's over 250V

The bonding bushing is for grounding the raceway not the enclosure.
 
Re: Bonding Around Concentric KO's over 250V

both are required to be bonded...in your case you had bonded the box from the EGC, and the conduit was bonia via teh panel.. I would say that if you didn't have the EGC then you would need the bond bushing and jumper, at the box, in the 1st scenerio to bond the box.
In the second case you would need bushings/jumpers as required to assure the raceways and boxes were all bonded.
 
Re: Bonding Around Concentric KO's over 250V

Originally posted by rhombus65:
The bonding bushing is for grounding the raceway not the enclosure.
Click to expand...
IMO it depends on the order of the run from the source.

If you run a raceway from a panel using a non-concentric KO than the raceway is bonded by the lock nuts.

At the other end of this raceway you install a J-box using a concentric KO you will need to install a bonding bushing to provide bonding of the J-Box.

If there are concentric at both ends of the raceway than you will need bonding bushings at both ends.

One at the start to bond the raceway one at the other end to bond the enclosure.

You have to consider the path you want the fault current to travel back to the source.

[ February 08, 2006, 05:43 PM: Message edited by: iwire ]
 
Re: Bonding Around Concentric KO's over 250V

I agree with Iwire.

There is nothing in article 250.97 that says you only have to bond one end. If you are going through concentric or eccentric ko's that are not listed for bonding, you must use a bonding jumper.
 
Re: Bonding Around Concentric KO's over 250V

Even running a EGC, as far as I know about 80% of the fault current will still use the conduit as the return path.

I have no backup for that statement.
 
Re: Bonding Around Concentric KO's over 250V

The bonding is not to bond either the box or the conduit...it is to bond them together to prevent arcing if a fault occurs.
Don
 
Re: Bonding Around Concentric KO's over 250V

Pierre,
Most Jboxes are listed as suitable for grounding these days.
Click to expand...
I don't use junction boxes with KOs, but I thought only the smaller 4" square and similar types of boxes had the multiple sized KOs listed for grounding.
Don
 
Re: Bonding Around Concentric KO's over 250V

Don,

I know for sure that some brands of nema3R disconnects with concentric's are listed for grounding.

frank
 
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