208 volt high leg

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difowler1

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I am normally a romex jockey. I am working on a warehouse with a 3 phase service with a delta high leg. Using 2 pole breakers, the previous electrician ran circuits to air compressors using one of the 120 volt legs, and the 208 volt leg. Is this the conventional way to achieve a 208volt single phase circuit, and if so I guess you have to see the manufacturer's instructions on which side to connect the high leg?
 

Dennis Alwon

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Location
Chapel Hill, NC
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Electrical Contractor
I don't believe there is any issue with using a high leg with another phase. I have heard of some even use the high leg and a neutral for a 208 pump.
 

augie47

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Tennessee
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State Electrical Inspector
One word of caution. Two pole breakers, where one pole is connected to the "high leg", must be 240 v "straight rated", not 240/120 slash rated. They are higher priced as a rule.
 

ActionDave

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Location
Durango, CO, 10 h 20 min without traffic from wing
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wire pulling grunt
I am normally a romex jockey. I am working on a warehouse with a 3 phase service with a delta high leg. Using 2 pole breakers, the previous electrician ran circuits to air compressors using one of the 120 volt legs, and the 208 volt leg. Is this the conventional way to achieve a 208volt single phase circuit, and if so I guess you have to see the manufacturer's instructions on which side to connect the high leg?
The phase to phase voltage on a Delta system is 240V, just like a single phase service. Any two pole breaker is going to send 240V to the load. The only 208V you will find is high leg to ground. On the other two phases you will have 120V to ground.

Standard now is for B phase to be the high leg. That was not the rule in days of yore so get your meter out and test.

And, as usual Augie is correct, any two pole breaker that has one pole on the high leg need to be straight 240V rated.
 

don_resqcapt19

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Illinois
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retired electrician
The only time using the high leg and one of the other legs to power equipment would be a problem is if the equipment has line to neutral loads in addition to line to line loads.
 
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