The high leg

A case of PEBKAC (Problem Exists Between Keyboard and Chair)? Tell us about your war stories!
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Sam Buca
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The high leg

Post by Sam Buca » Sat Aug 27, 2011 10:33 pm

We have 4 wire delta. Electrician said the rotation was correct. IT protector went boom. UPS threw the breaker and does a nice arc flash/pop when you try to turn on its internal breaker.

Moral of the story: have your electrician pay attention to where the high leg is. Trust not the colored electrical tape on the wires, but rather trust in your $5 DMM.

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Shane
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Re: The high leg

Post by Shane » Sat Aug 27, 2011 11:39 pm

Well, I sorta like the way the soot blew out the little hole in the corner of the j-box and decorated the wall behind.
Mike Shane, CBRE
---Omaha---

n9lhm
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Re: The high leg

Post by n9lhm » Wed Sep 21, 2011 2:26 pm

I absolutely HATE high leg delta three-phase service. It is an accident looking for a place to happen. It should have never been allowed, IMHO. Brian

jeeisenz
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Re: The high leg

Post by jeeisenz » Thu Dec 07, 2017 10:36 am

We had this happen too - when we put in a new transmitter (and new power service to support it) - electrician wired the high leg to one side of the breaker box. Smoked our lighting controller.

Good news about the situation: The power is now a lot more stable than with the old transmitter and service. Plus I never really liked that lighting controller anyway - it was hacked around and nobody really documented anything. We got a new one and it's wired to the remote control - so all is happy...until it calls daily about a side marker out. :lol:

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davedybas
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Re: The high leg

Post by davedybas » Fri Dec 08, 2017 11:15 am

Three-Phase Delta, with a High Leg, is called Open Delta and it is always troublesome. It may cost you several thousand to convert it to Closed Delta *(with all three phases operating at the same voltage) but it is well worth it if you want to keep your transmitter happy. If you have an older rig...you'll save lots of lost air time and save your rectifiers by paying to convert to Closed Delta. Been thru that excercise many times and always had good results after it was done.

awsherrill
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Re: The high leg

Post by awsherrill » Fri Dec 08, 2017 12:04 pm

Correct me if I'm wrong, but I think the OP was referring to three-phase closed delta with a high single phase leg, sometimes called a "stinger". Pretty common around here.

Two of the single phase legs are the normal 120V, the high leg is around 208V. You have to be careful not to use that leg for single phase 120V loads.

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kkiddkkidd
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Re: The high leg

Post by kkiddkkidd » Fri Dec 08, 2017 8:19 pm

awsherrill wrote:
Fri Dec 08, 2017 12:04 pm
Correct me if I'm wrong, but I think the OP was referring to three-phase closed delta with a high single phase leg, sometimes called a "stinger". Pretty common around here.

Two of the single phase legs are the normal 120V, the high leg is around 208V. You have to be careful not to use that leg for single phase 120V loads.

But you can do some serious drilling in concrete with a hammer drill wired to a stinger leg... At least briefly.

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davedybas
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Re: The high leg

Post by davedybas » Sat Dec 09, 2017 5:47 pm

Thanks for reminding me about the tapped delta "stinger" configuration.... that certainly will get ya...if you aren't careful...

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Deep Thought
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Re: The high leg

Post by Deep Thought » Sat Dec 09, 2017 10:59 pm

I once had someone tell me that "there is plenty of room for more breakers in the panel...a third of the slots have blanks over them" when I asked where we could add a 120VAC circuit for an equipment rack.

Uh, no. :roll:
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com

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