Airport lighting grounding

[Ebuzz]

Our company uses a constant current high voltage airport lighting system for our street lights. the lights ar in a series loop. the source transformer feeds one terminal of the first lights step down transformer using direct burial high voltage cable. The other terminal feeds one terminal of the next light. it continues that way until it returns to the source trans former. The original installer drove and connected a ground rod next to each metal pole. There is no equipment ground following along with the feeder cable to bond each pole. It is my opinion, that if somehow, the feeder touched the the pole, the pole , the ground rod and the soil surrounding it would be energized. (about 2400 volts). am I missing something??

 

[Dennis Alwon]

I am having trouble understanding the layout. If there is high voltage going to the lights then there should be an equipment grounding conductor. If there isn't an equipment grounding conductor then using a ground rod will do what you stated... It will not trip the circuit in a ground fault condition.

 

[hbiss]

It's the old series string street light setup. Back then they didn't use transformers at the fixtures, bulbs were actually low voltage wired like a Christmas light string. So you can imagine how many lamps you could have in series across 2500 volts.

Back to the OP's question. No part of the string is grounded so a fault to ground isn't going to cause a problem. And if there were two faults at different poles all you would see is the difference between the two locations.

-Hal

 

[hbiss]

I'm understanding here that there is a transformer at each light pole to supply a conventional 120V fixture? Doesn't change anything, just the math.

-Hal

 

[Fred B]

Does 250.4(A)(5) apply to this installation, if not how is fault cleared?

 

[Fred B]

Also if you are looking at an ungrounded system 250.4(B)(2)(3)(4) seem to be in play.