EMT as Equipment Grounding Conductor

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cschmid said:
I I I I I I I just could not help myself.....:D
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Thanks for having my back. You will be horrified to know I'm pulling less and less in branch circuit EMT.

Why? Trying to keep our company profitable.

Please forgive me.;)
 
iwire said:
It is becoming less of an issue as many boxes now have eccentric KOs that are listed for grounding.

Notable exceptions are some panel and disconnect enclosures that still use concentric KOs.
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Currently ALL outlet boxes with eccentric or concemtric (if there are any) are listed for grounding under and over 250 volts to ground.

I have searched, but I have not found any (none) cabinets, wireways, or pull boxes where the concentric or eccentric KO's are listed for grounding over 250 volts to ground.

I would be especially interested if anyone has seen any.
 
sandsnow said:
I have searched, but I have not found any (none) cabinets, wireways, or pull boxes where the concentric or eccentric KO's are listed for grounding over 250 volts to ground.

I would be especially interested if anyone has seen any.
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I was under the impression Square D disconnect enclosures with the eccentric KOs where listed for grounding. The fittings locknut digs into the enclosure itself. I could be mistaken.
 
The heavy duty disconnects come with what is called a tangental knock out except out the back where it stills has a concentric. All tangental KO's are listed for bonding over 250 volts to ground. They have multiple points of contact with the enclosure, and you can tell the difference because they are not circular, rather are made up of multiple straight pieces, or tangents, around the circle.
 
derf48 said:
The heavy duty disconnects come with what is called a tangental knock out except out the back where it stills has a concentric. All tangental KO's are listed for bonding over 250 volts to ground. They have multiple points of contact with the enclosure, and you can tell the difference because they are not circular, rather are made up of multiple straight pieces, or tangents, around the circle.
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I'd be really interested on some more info here. Doing a search for tangental on the UL site turns up seemingly unrelated hits.

http://database.ul.com/cgi-bin/XYV/cgifind.new/LISEXT/1FRAME/srchres.html

Under outlet boxes you find this:

CONCENTRIC OR ECCENTRIC KNOCKOUTS
All boxes with concentric or eccentric knockouts have been investigated for bonding and are suitable for bonding without any additional bonding means around concentric (or eccentric) knockouts where used in circuits above or below 250 V, and may be marked as such.

I could find nothing under enclosed switches about the KO's.
 
I tend to agree with Larry. Last time I looked into this, I didn't realize at the time that the NEC made a distinction between "eccentric" and "concentric", but the rules were the same regardless, IIRC.
 
A few years ago I was called to a plastics recycling plant where a shredder motor overheated its winding insulation, went to ground and the EMT did not enable the fault current to blow the fuses.

I believe the motor was around 100HP and the EMT ran across the roof trusses which had built up a 1 inch layer of fine dust particles.
The fault current through the EMT fittings blew sparks which ignited the dust and caused a fire.

At EVERY EMT joint along the 60 foot run there was a carbon flash trace, this was at all the coupling and connector double screws and where the connectors contacted the disconnect.

We ran a bare ground along the outside of the existing EMT and installed thermistors for the motor windings.

I always run a ground wire through EMT because of that experience. The code is only the minimum acceptable and I can sleep at night!
 
Isn't it the same as..

Isn't it the same as..

POCO's ground coming in lower ohm's.Then we add another ground which has more ohm's just in case we lose POCO's ground?
 
Ok i gotta add at least something to this thread. Do the smooth locknuts on diecast connectors really dig deep enough into the paint of each enclosure to make an effective path? (never backed one off to check)
Rick
 
RUWired said:
Ok i gotta add at least something to this thread. Do the smooth locknuts on diecast connectors really dig deep enough into the paint of each enclosure to make an effective path? (never backed one off to check)
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Let us know what you find. ;)
 
LarryFine said:
Let us know what you find. ;)
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I think you will find that there is sufficient continuity.

Roger
 
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This is getting to be one of those topics like grounds up or down, union or non-union....

FWIW both methods are acceptable by the NEC, if you choose to do more.. then good for you! [I usually do :grin: ]

~Matt
 
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