High leg delta

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petersonra

petersonra

Senior Member
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Northern illinois
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Semi-retired engineer
So, today I got to the clients location to continue a startup, one of the field electricians told me that he had to shut off power to the control room for a while. I asked him why. He said they had found that the panel that they had wired power out of that was labeled 208 120 was actually fed by a 240 volt high leg delta transformer. One of the phases was like 200 volts to neutral instead of 120. God knows how long it's been that way.
 
That is not an unusual service, especially in older facilities. If there are single pole breakers, the first clue is that every 3rd space in the panel does not have a breaker in it.
 
don_resqcapt19 said:
That is not an unusual service, especially in older facilities. If there are single pole breakers, the first clue is that every 3rd space in the panel does not have a breaker in it.
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Had one I saw was all 3pole breakers but when I opened panel only 2 of 3 breaker terminals were connected. So can't assume absence of high leg just from not having an open space.
 
Fred B said:
Had one I saw was all 3pole breakers but when I opened panel only 2 of 3 breaker terminals were connected. So can't assume absence of high leg just from not having an open space.
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and that is why my post said single pole breakers.
 
Right breaker for the voltage.
Like the single pole breaker reference.
Should have noticed the high leg marking unless it was hidden by a line protection cover. Maybe a word change should be considered when these devices are used. So it will be visible when cover is removed.
Marked and visible when line cover protection is used. Of course it should be labeled out side on cover already. Usually not done untill final and wire marking done at time of installation.
It is a good thing some caught it.
 
Tulsa Electrician said:
Right breaker for the voltage.
Like the single pole breaker reference.
Should have noticed the high leg marking unless it was hidden by a line protection cover. Maybe a word change should be considered when these devices are used. So it will be visible when cover is removed.
Marked and visible when line cover protection is used. Of course it should be labeled out side on cover already. Usually not done untill final and wire marking done at time of installation.
It is a good thing some caught it.
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Older installation may not have that marking as the requirement to provide that marking first appeared in the 2008 code.
 
ptonsparky said:
At least you had someone that checked. In the past it was usually found after the smoke escaped.
Not that I would have made that discovery in my formative years.:rolleyes:
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Years ago when I was a rookie engineer designing control panels, we had one for a 208V system, so I just tapped off of a phase and neutral for control power. The senior guy that reviewed my plans made me put in a CPT and when I told him it was not necessary, he explained to me it was, “because you never know what’s really out there.”

Turned out he was right. When the panel was installed, it was a 240V high leg system. Apparently someone had measured only B phase to ground, saw 208V and reported to everyone that it was a 208V system. SO many people don’t understand this issue.
 
So yesterday I was in the control panel we supplied. I could hear this click about every 20 seconds. I'm thinking what the heck is that eventually I found that it was coming from a GFCI in the panel every 20 seconds it would click and a red light would come on for an instant. I'm guessing the application of 200 volts to the GFCI caused it to fail. Nothing else failed because everything else is dual rated 120 240.

I'm going to have to talk to my boss about getting a replacement and I'm sure there's going to be a lot of argument about who has to pay for it. It will cost more to argue about it than just replacing it.
 
petersonra said:
So yesterday I was in the control panel we supplied. I could hear this click about every 20 seconds. I'm thinking what the heck is that eventually I found that it was coming from a GFCI in the panel every 20 seconds it would click and a red light would come on for an instant. I'm guessing the application of 200 volts to the GFCI caused it to fail. Nothing else failed because everything else is dual rated 120 240.

I'm going to have to talk to my boss about getting a replacement and I'm sure there's going to be a lot of argument about who has to pay for it. It will cost more to argue about it than just replacing it.
Click to expand...
I would change it and move on. A 20 dollar gfi isn't worth listening to the customer ask me why my men didn't check the voltage beforehand.
 
Tulsa Electrician said:
Right breaker for the voltage.
Like the single pole breaker reference.
Should have noticed the high leg marking unless it was hidden by a line protection cover. Maybe a word change should be considered when these devices are used. So it will be visible when cover is removed.
Marked and visible when line cover protection is used. Of course it should be labeled out side on cover already. Usually not done untill final and wire marking done at time of installation.
It is a good thing some caught it.
Click to expand...
I’ve seen them marked wrong too, black red blue.
 
Tulsa Electrician said:
That's very true and note Worthy.
One should check voltage and not assume.
Thank you
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I was once assigned to design a PV system for a building where the MDP was "labeled" with a Sharpie on duct tape as 240 delta high leg but the service conductors were color coded 208/120V three phase. Turns out that the service had been converted from 208/120V at the transformer but the service conductors were never retaped with the correct color coding. Always check the voltage.
 
Hv&Lv said:
For a red leg delta, that’s correct..
that’s the way they were marked way back (60’s-80’s)
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I don't believe that there is a "correct" color code per the NEC except for neutral and ground.
 
ggunn said:
I don't believe that there is a "correct" color code per the NEC except for neutral and ground.
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I understand that. So “correct” is the wrong word..
But that’s the way it was done for years.
How about “the norm”
Like that better?
 
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