3-pole breaker in single phase panel

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Gategator37

Senior Member
A 120/240v single phase 3 wire panel is showing a 3-pole breaker feeding a 3-phase exhaust fan, this is not possible is it without a buck/boost transformer correct? Thanks
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
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Sorta retired........
A 120/240v single phase 3 wire panel is showing a 3-pole breaker feeding a 3-phase exhaust fan, this is not possible is it without a buck/boost transformer correct? Thanks sorry, I meant phase converter, not buck/boost

You are correct.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
A 120/240v single phase 3 wire panel is showing a 3-pole breaker feeding a 3-phase exhaust fan, this is not possible is it without a buck/boost transformer correct? Thanks
Well, there is another possibility: The panel is being supplied by a high-leg Delta, and a Delta breaker was used.
 

jetlag

Senior Member
Well, there is another possibility: The panel is being supplied by a high-leg Delta, and a Delta breaker was used.

Are you saying one can get 3 phases from a panel with only two phases, one of which is a delta high leg just by using a special breaker ? If the system had a high leg it must be 3 phase, so why didnt they run all 3 phases to the panel ?
 

winnie

Senior Member
Location
Springfield, MA, USA
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Electric motor research
Delta breakers were used when you had a majority of single phase loads along with perhaps 1 three phase load. They are called 'delta' because they usually went along with a high leg delta system, though I guess they would work with a wye supply. They are explicitly prohibited in current code.

Essentially you had a three phase feeder to the panel, but one of the feeder legs went directly to a pole on the 'delta' breaker, without hitting the panel main, and without using a bus on the panel. Useful, for example, if you had a single phase residential panel and wanted to add a single 3 phase hvac circuit.

If you used a three phase panel, then you would end up with one bus essentially unused.

-Jon
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Are you saying one can get 3 phases from a panel with only two phases, one of which is a delta high leg just by using a special breaker ?
No, I'm saying that one can get 3ph from an existing 1ph panel by adding one additional wire to the service and routing it to the line side of a specially-made 3p breaker.

The Delta breaker picks up two lines from the panel bus just like any 2p breaker. The third pole gets its power from a terminal on a fourth "dummy" breaker body, not the bus.

This method actually began as a modification to existing services, and only requires the power company to install one additional primary line and transformer to their equipment.


If the system had a high leg it must be 3 phase, so why didnt they run all 3 phases to the panel ?
Becuase, either the service was an existing 1ph, and they modified it for this one piece of equipment, or because it was more economical to build it this way new.

My guess is the first option. But, technically speaking, they did bring the third phase to the panel, if I'm right.

It's simple enough to look at the incoming power drop, if overhead, or at the meter to see if this is a 3ph service to a 1ph panel. Can you see the utility transformer connections?

Have you opened the panel and looked at the wiring to this breaker? Does it have four bodies and handles tied together, or just three? Can you look and describe, or take pics?
 

jetlag

Senior Member
Delta breakers were used when you had a majority of single phase loads along with perhaps 1 three phase load. They are called 'delta' because they usually went along with a high leg delta system, though I guess they would work with a wye supply. They are explicitly prohibited in current code.

Essentially you had a three phase feeder to the panel, but one of the feeder legs went directly to a pole on the 'delta' breaker, without hitting the panel main, and without using a bus on the panel. Useful, for example, if you had a single phase residential panel and wanted to add a single 3 phase hvac circuit.

If you used a three phase panel, then you would end up with one bus essentially unused.

-Jon

Ok I see now , never seen that before , as far as the buss not being used you can connect single phase 240 to high leg bus and another and still only have 240 . You just cant use the high leg for 120 to neutral . So I try to use the high leg on enough 240 circuits to use them up.:grin:
 
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