LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
No, only a 208/120Y system can do that. Of course, you can use transformers to reduce the 240 to 208.sparksaflying said:
Delta tranformer
- Thread starter Riograndeelectric
- Start date
- Status
hardworkingstiff
Senior Member
- Location
- Wilmington, NC
I was informed by (older, now deceased) electricians I worked with as a helper that you could use the high leg with one of the other legs to serve a 240-volt single-phase load.
Can I get some confirmation as to the validity of that statement?
Can I get some confirmation as to the validity of that statement?
ptonsparky
Tom
- Occupation
- EC - retired
Yes, you can, but you need to look at the ratings of your circuit breakers. Most of the existing buildings in this area with Hi leg Delta have the typical plug in style three phase panels that were added as demand grew. Only in the last few years has anyone paid attention to the 120/240 rating on the circuit breakers. These breakers are not intended for use with the 208 or hi leg. Right or wrong these types of installations are scattered through out the area and do "work".
I would think that trying to do a fault calculation on an open wye, open delta with one transformer bigger than the other would be a challenge. Could this be why only SQ D has a two pole QO breaker rated for this use?
I would think that trying to do a fault calculation on an open wye, open delta with one transformer bigger than the other would be a challenge. Could this be why only SQ D has a two pole QO breaker rated for this use?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
hardworkingstiff said:
The high leg only voltage is only different from the others when it is referenced to the neutral. Between the other two phases and the high leg the voltage is equal. Think of a 3 phase, 3 wire Delta, the voltage between the phases for AB, BC, and AC is the same. This would also be true for a 4 wire Delta, the voltage between all three phases wouldn't change.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
I remember reading a thread (and linking to it since) about using the high leg-to-neutral to power 208V line-to-line loads. Charlie Eldridge and other members said that the high leg voltage was not stable for this application, even if the appropriate 277V single-pole breaker was used.
If pressed I could go looking for it.
Please disregard the above, I misunderstood the question.
)
So, realistically, Larry's answer is most correct.
If pressed I could go looking for it.
Please disregard the above, I misunderstood the question.
I would say yes: If, instead of a 240V line-to-line voltage, a 120V line-to-line voltage was acceptable to the installer/user. But I can't see any practical application for such a setup in the real world. (And, I wonder if a transformer exists to do that, but I'll bet it could be found.
)So, realistically, Larry's answer is most correct.
Last edited:
- Status