Cable tray grounding

[relkap]

What grounding/bonding is necessary for cable tray when it is not to be used as the equipment grounding conductor (EGC)? How is the tray bonded at the power source? Is it necessary to bond conduits that enter the tray system? Is it necessary to bond trays to end equipment such as switchgear or MCC's? What is the minimum grounding requirement for trays if an EGC is part of the multiconductor power cable? I know this is alot, but the code does not elaborate far enough in ART.250.96 "Bonding Other Enclosures"
Thanks,
Fred Pakler

[tom ogryski]

Fred,

If you have access to the 2002 NEC Handbook, see the commentary after 392.7(A) and take a look at Exhibit 392.1

Also, 392.7(B)(4) for additional bonding requirements for tray sections & conduits. Bonding jumpers are sized per 250.102

Tom

[relkap]

Thanks Tom,
I reviewed the articles and exhibit that you had referenced.Thanks for the quick response! Its clear now that these articles apply only if the tray is used as the EGC. If I assume correctly,in a cable tray system where the multiconductor power cables include an equipment grounding conductor, then only supplemental grounding is required for the metal trays.That has been our practice in the past. We ground the tray at either end of the run to a ground bus or building steel (connected to a grid) and bond the discontinuos sections,hinges,expansion splices,etc. as required.Do you see a problem with continuing this practice?
Thanks very much,
Fred Pakler