sizing conductor for NGR

[JLuc]

Hi,

what conductor size should I use to connect NGR to neutral bushing of txfo.

NGR is 5A continuous.

the code (canadian) says to size the conductor to 5A (max let through current of the resistor)

But, in our installation, the resistor is in a switchgear about 250 feet away from the txfo. Is it safe to still use a small conductor in this situation?

Thank you.

JL

 

[CoryA]

I found the following excerpt in my copy of the “Canadian Electrical Code Part I: Safety Standard for Electrical Installations.”

10-1108 Conductors used with neutral-grounding devices

1. The conductor connecting the neutral-grounding device to the neutral point of the transformer shall be

(c) sized to conduct the rated current of the neutral-grounding device, and in no case less than No. 8 AWG

I can’t seem to find anything that relates to conductor distances, but I doubt that 250 feet of 8 AWG conductor would dissipate much wattage during a bolted ground fault. I did some back-of-the-napkin calculations, and found that 5 A of current in an 8 AWG conductor would dissipate less than 5 watts over the full 250 feet. My thoughts are that it is safe JLuc – but there may be a concern with the continuing integrity of that conductor over time. If the cable was cut anywhere along its length, you would be left with an ungrounded system. You may already be aware of this, but I thought I’d mention it.

I’m curious to know if anyone else has found any codes relating to conductor distances.

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Cory Anderson

http://startco.ca/