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Joined: Mar 2005
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I need some help from line men or eng. familiar with high voltage on this question.
An installation is going in that has 138 Kv primary service. There are uninsulated bus tubes (bars) from the disconnect switch arms to the top of the distribution panel. The bus tubes are four feet apart until the get to the top of the equipment and then they are reduced to being only 8 inches apart where they enter. The bus bars inside the equipment is insulated, the ones coming in are bare. Outside they are exposed to the elements, i. e. snow, rain, etc.
Is 8 inches of clearence enough at 138 Kv. ??
This is a customer owned installation and I can't find this in the NEC. Would the Life Safety Code have it ? Any good formulas on clearence or sites would be appreciated. Thanks. Alan--Inspector
Alan-- If it was easy, anyone could do it.
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Joined: Mar 2001
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How about the NESC? National Electrical Safety Code.
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Joined: Sep 2005
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Are you saying 138 KV or 13.8 Kv?
8 inches isn't nearly enough at 138 KV.
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Joined: Mar 2005
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WFO It is 138 Kv that is 138,000 Volts !
That is what has me asking. I don't think an eight inch clearence is enough. But, I don't know how much it should be, especially the clearence between bare conductors exposed to the elements. This stuff is on the border between electricity and lightning. If I'm going to challenge the spacing I need a reference. I'll check out Royal's reference it is a start. Alan--
Alan-- If it was easy, anyone could do it.
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Joined: Jan 2005
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Curiosity killed the cat, but...
What sort of facility uses so much power that 138kV is required to feed it? I mean, we're talking *transmission* level voltage here! Scary stuff.
-Z
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Joined: Oct 2005
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Alan, What have you found out so far? From a post from resqcapt19 on another topic we get this information: http://www.highvoltageconnection.com/articles/highvoltagespacing.pdf And form what it looks like it is saying to me is 138 kv*3)/10000= 41.4 inches minimum spacing for bare conductors. I hope that this helps and that I understand this properly. Tim
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Joined: Jan 2003
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Alan are you sure about the voltage?
Is it possible someone wrote or said 138 KV when they really meant 13.8 KV?
In my area 13.8 is a very common voltage for neighborhood and industrial distribution.
I agree with the others that 138 KV would be unusual for all but a few installations.
Bob Badger Construction & Maintenance Electrician Massachusetts
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