I have a customer with a high leg system and no more space for more breakers(doesn't want to add a sub panel). The only space open is a high leg single pole breaker which I fed his new 6hp compressor. Works fine, although I've never wired a single phase 208-230v motor this way. I can't recall this being a problem with running all the voltage on 1 leg with a grounded conductor on the other. Anybody have experience with this?
High leg used for 1 phase motor
- Thread starter yetiman
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From earlier posts on this subject, if I recall correctly, some of the members who have a great understanding of transformers/distribution, advise against doing so.
From an inspector's standpoint, for a normal 240 volt panel, I don't thing you can find a single pole breaker that is rated higher then 120 volt, therefore; from a codespeak standpoint you would be in violation of 240.85.
From an inspector's standpoint, for a normal 240 volt panel, I don't thing you can find a single pole breaker that is rated higher then 120 volt, therefore; from a codespeak standpoint you would be in violation of 240.85.
bluesmoke...oops
Senior Member
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- Tri-Cities, Washington
if it is a high leg panel, doesn't that mean that the breaker on the high leg would be rated for that voltage?
Augie47 is right on both counts.
The high leg (or wild leg) is a voltage that is inherently unstable..just because you read it at 208 at one point in time doesn't mean it stays that way. It is possible for that voltage to swing from a low of around 170 to a high of 240+ volts, depending on the loads on the other phases.
And you MUST have a single-pole breaker rated for 240 volts anyways.
Go back and do it right, add a subpanel and proper breakers before you end up smoking that compressor motor or exploding the breaker.
The high leg (or wild leg) is a voltage that is inherently unstable..just because you read it at 208 at one point in time doesn't mean it stays that way. It is possible for that voltage to swing from a low of around 170 to a high of 240+ volts, depending on the loads on the other phases.
And you MUST have a single-pole breaker rated for 240 volts anyways.
Go back and do it right, add a subpanel and proper breakers before you end up smoking that compressor motor or exploding the breaker.
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ericsherman37
Senior Member
- Location
- Oregon Coast
Here's a reference from a previous thread at this forum http://forums.mikeholt.com/showthread.php?t=122637
I wouldn't do it even if it works.
Well, maybe I would, but I would feel weird about it.
I wouldn't do it even if it works.
Well, maybe I would, but I would feel weird about it.
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It is extremely unlikely that you have a 1-pole breaker rated for 208V L-G. What brand panel and which style breaker are you using?
What are the sizes of the transformers feeding this system.
What is the 3-phase loading, and the 1-phase loading?
What is the nameplate current of your motor?
broadgage
Senior Member
- Location
- London, England
Provided that you can obtain a suitable breaker, this should work fine provided that the load on the high leg is small in proportion to the service.
Current drawn from the high leg passes through 2 transformer windings with losses/voltage drop in each.
The voltage will drop on load by more than might be expected, and the transformer bank could be overloaded despite a load that appears to be within its rating.
For a small load I would not worry.
Current drawn from the high leg passes through 2 transformer windings with losses/voltage drop in each.
The voltage will drop on load by more than might be expected, and the transformer bank could be overloaded despite a load that appears to be within its rating.
For a small load I would not worry.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
I would connect it between the high leg and another line, but not high leg to neutral.
stantonlw
Member
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- Alexandria Va and Crawfordville Fl
Anecdotal
Anecdotal
Previous owner had powered a 220v freezer from the wild leg, didn't last the day!
Larry
Anecdotal
Previous owner had powered a 220v freezer from the wild leg, didn't last the day!
Larry
dmagyar
Senior Member
- Location
- Rocklin, Ca.
High leg in delta system over 240 volts
High leg in delta system over 240 volts
First came across a 3 phase 120/240 volt delta system with a "stinger" leg. I don't recall what the voltage was but know that it was over 240, maybe 277?
One of the other electricians on the job hooked up a single pole c/b without measuring the voltage. They blew all of the 120 volt ballasts one a whole room of fixtures. Glad that it wasn't me. But after that whenever I see a panel with spaces that are in every third spot I'm on guard.
High leg in delta system over 240 volts
First came across a 3 phase 120/240 volt delta system with a "stinger" leg. I don't recall what the voltage was but know that it was over 240, maybe 277?
One of the other electricians on the job hooked up a single pole c/b without measuring the voltage. They blew all of the 120 volt ballasts one a whole room of fixtures. Glad that it wasn't me. But after that whenever I see a panel with spaces that are in every third spot I'm on guard.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The stinger/high leg will be a nominal 208V to the neutral on a nominal 240/120V 3PH 4W system. The laws of physics will not allow it to be any else.
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