Must provide ground conductor in Tray Cable?

[richwaskowitz]

336.10 (7) says "equipment grounding for utilization equipment shall be provided by a conductor within the cable." I am looking to see if I misunderstand this or perhaps there is an exception which would permit one to use a 3 conductor cable for the 3 phase conductors and then run a single conductor EG along side the cable. That is what my customer is trying to get me to do and I need to understand this before I object. Perhaps the words "utilization equipment" are the key. In this application, the cable in question is the 480 volt supply to a control panel in an auto assembly plant. This is a metallic tray system where the tray may or may not be bonded to the control panel, but that is not my issue (I don't think).

 

[Buck Parrish]

It reads pretty clear to me.

 

[don_resqcapt19]

Rich,
Take a look at 300.3(B)(3).

 

[tryinghard]

I?m sure you know this but here?s some ammo anyway that may help you with your customer. An effective ground fault path is extremely important to enable - hopefully instantaneous - opening of protection when fault occurs. If too much resistance exists on the fault path to source it may not open leaving touch voltage, this is all the more important in higher voltages.

If your case is a grounded system an example can be 277V/18A = 15 ohms revealing what could be assumed as ?good enough equipment grounding?, while potentially allowing high amperes and not open the circuit.

In my opinion tray cable environments are often abused, usually naively but we certainly don?t want to encourage this. I don?t know of any exception.

 

[richwaskowitz]

Don, Thanks but I am aware of the requirement of 300.3 (B) but could this not be used by them to actually defend their position? They could argue that it not only says "the same cable" but also says the same tray. Because, although not contained in the same cable, the EGC would be contained within the same tray..... If i did not think that this could be interpreted in more ways than one, I would not be seeking advice. On the other hand (devil's advocate here) if they were to try that reasoning, then one could also try to argue that 300.3 (B) would permit one to run a conduit with the phase conductors and a separate EGC in a different conduit just as long as they were in the same trench for example. I am pretty sure that this is not the intent of 300.3 (B). Uh, I think I just came up with my own answer.........

Tryinghrad, I agree wholeheartedly and would never advocate using a large and circuitous tray system as THE only means of bonding an installation like this.

 

[tryinghard]

Tryinghrad, I agree wholeheartedly and would never advocate using a large and circuitous tray system as THE only means of bonding an installation like this.

I'm sure your giving every effort for your customer and this is good. But size & length really don't matter it simply needs to comply with 392.7, 392.3(B)(1)(c) any less is an electrical hazard.

Great word by the way "circuitous" This should get the word of the week award.