Bonding conduit to cable tray

[Journeyman106]

Here is a little background on my situation before I ask the actual question. In a typical installation on my site we have conduit that extends from our panels or MCCs or MVC's up to a ladder type cable tray system. In a typical installation the feeder or branch circuits are pulled through the conduits up to the tray where they are then ran out to their respective loads or sources.

The question is this. I realize that the code requires for an electrical raceway or system to be electrically continous. I am also aware that both a conduit and a cable tray can be used as an equipment bonding conductor. With that said though, in this installation the equipment grounding conductor is actually pulled in with the circuits or feeders and in most cases is bonded to the conduit through a bond bushing inside the gear or MCC. When this is done I realize that the conduit is in effect bonded and is at the same potential as the equipment bonding conductor itself. The problem I am having however is that in alot of cases there is a gap between the conduit and the cable tray. The cable tray is bonded to the building steel itself and the conduit is usually bonded through the use of a bonding bushing or a locknut to the gear itself.

Since the code states that the ground shall be electrically continous it is my understanding that there should be a bond jumper between the conduit and the cable tray since there is an air gap. It is also my understanding when selecting the size of this bond jumper you should use table 250-122 so that way the bond jumper will be able to handle any fault current.

Am I correct in my interpretation?

 

[augie47]

I would not argue with your interpret ion, however, I don't see it entirely that way.
392.7 references 250.96 which, to me, requires "electrical continuity". With the raceway properly bonded at the enclosure by way of the equipment grounding conductor and proper fittings, and the tray properly bonded, you have achieved "electrical continuity". I see no requirement for it to have mechanical continuity,

 

[don_resqcapt19]

The cable tray has to be bonded to the EGC that serve the cables that are installed in the tray. You can't just bond the tray to the building steel. In your application the easiest way would be a bonding jumper between the conduits that the tray. Even easier would be to physically connect the conduits to the tray with clamp approved for the purpose.

 

[Journeyman106]

Thank you for your responses. I to agree that the tray should be connected to the equipment grounding conductor and the way the tray is bonded technically it is not. So yes I agree the easiest thing to do would be to just attach the conduit to the tray with the appropriate type clamps but unfortunetly alot of contractors did not do this.

Thank you again for your responses.

 

[kilowattEE]

I've been working on this very thing. I always try to think about what would happen if there was a fault... what is the path back to the source? We want the current to flow back on the EGC, not building steel. I think part of the intent of Article 250.96(A) is to tell use to bond everything (conduit, cable tray, enclosures, etc.) from source to load. Done correctly with the proper sized EGC will help you safely clear a fault, should one occur.

 

[DAWGS]

We usually use a corn clamp and bond with a bond bushing. The listed tray clamps are very expensive.