Cable tray grounding

[skeshesh]

Hello everybody; hope you're all having a fine friday.

I have a question from a contractor regarding cable tray grounding. I was not the original designer of this detail and am by no means an expert on cable trays. The detail (see attached) calls for bonding to expansion joint or tray. I was wondering if doing both is necessary in your opinion. All other thoughts on grounding practices for cable trays are also welcome and would be much appreciated.

 

[dicklaxt]

You need a copy of NEMA Standards VE1 & VE2 which will cover everything on tray design,loading,allowable spans and installation etc.

The detail you have a picture of is correct to a point.The flange(weak point) of the tray when drilled should not be drilled but the web(much stronger) itself.You should use a tray connection bolt round head inserted from the inside of the tray thru the lug on the bonding jumper.Tray hold down clamps and expansion clamps should be looked at closely and coordinated with the anchor points of any and all elbows.

Trays are to be electrical continuous from start to finish bonded to the MCC, across any loosely assembled fitting ie: expansion joints,horizontal & vertical hinged fittings etc. as well as bonding to any adjacent trays and taken to the ground grid at these points,usually every 100'.The tray itsself need not be continuous but needs to be bonded together when changing direction.

Tray fill is critical by cable type and spacing tray to tray .IEEE has spacing standards if you general spec calls for that as a standard document.

Well designed tray systems take a lot of thought.

dick

 

[kingpb]

In the detail the arrow is pointing to the tray and it should pointing to the expansion plate. Minor issue.

The connection across the expansion plate is necessary to maintain continuity along the tray. If the expansion plate is bolted to one side and only slips along the opposite side as shown in detail, I would see no reason to bond to the expansion plate.

Refer to NEC 392.7 for additional information on grounding requirements.