Open Delta, High Leg

[ctrane]

I have a service that is Open Delta, High Leg, served by 2-wire primary. I am comfortable with the fact that Phase A and C, with respect to ground, may be used for Lighting/Receptacle, and with the fact that 240V-3Phase can be utilized for loads. But, the question is, can 240V-Single Phase be used without restriction? Meaning, Phase B to C, and A to B? Any help will be most appreciated. All this assumes that the B-Phase is the high leg.

 

[jim dungar]

The only "prohibited" connection is from the high leg to the neutral.

Depending on the size of the individual transformers your utility may have some specific requirements for load balancing.

 

[augie47]

high leg

high leg

as far as the voltage goes it can be used without restriction..ie: CA, BA, BC...the only "glich" I can think of is you can not use a slash/rated breaker (240/120) when incorporating "B" phase. You must use a fully rated 240 volt breaker.

 

[LarryFine]

But, the question is, can 240V-Single Phase be used without restriction? Meaning, Phase B to C, and A to B?

In theory, absolutely. In practice, note that there is more impedance, and thus less "stability" across the open side of the Delta. The high leg should have the lightest loading.

I have used an open Delta to supply two 3-pole breakers and three 2pole breakers in a 12-space panel, but I did make sure the smaller 2-pole loads used the high leg.

I could be wrong, but something I can't explain tells me that a larger proportion of 3-phase loading somehow helps stabilize the voltage across the open side of the Delta, but I have no evidence.

 

[ctrane]

Thanks to all that have replied thus far, and look forward to all that will...One more question, how do you calculate loads for such a system? Do you just take the total kVA, and divide it by 240(root 3)? Should I calculate what is on each phase?