inspector141
Senior Member
- Location
- Westminster, MD
Can an existing 120/240, 4 wire delta service be fed from a 120/240 3 phase Y connected generator via a transfer switch? I'm assuming the existing service is not slash rated breaker(s)
4 wire delta service fed from 120/240 3 ph Y generator
- Thread starter inspector141
- Start date
- Status
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
You cannot have a "120/240 Y" connected 3-phase generator, however you can have a 208Y/120 one.
inspector141
Senior Member
- Location
- Westminster, MD
Yes, I thought the same thing. I'm going to look at it later this afternoon.
Assuming the generator is 120/208, 4 wire Y, would that be legal and safe for that generator to serve a 4 wire delta 120/240 volt service temporarily when a power outage occurs?
Assuming the generator is 120/208, 4 wire Y, would that be legal and safe for that generator to serve a 4 wire delta 120/240 volt service temporarily when a power outage occurs?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Other than the fact that your 240V loads may not be happy with only being supplied with 208V?
Will this be fed through a manual transfer switch?
nollij
Member
- Location
- Washington
A lot of equipment rated to operate at 240V will be fine with 208V but it should be verified with the equipment. A lot of equipment can tolerate +/- 20% voltage regulation however more sensitive eqiupment might be +/- 10%.
Also, this 4 wire delta system is not grounded at any point is it?
I would suggest using a transfer switch that transfers the neutral and does not bond them.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I'm guessing yes, as in high leg.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
I know of one like that at a pump station. It has apparently been working ok for years, don't know if it has a four pole switch or not. My cousin that works for the city water department told me about it, he was also concerned about any problems that might cause. I think they left it that way. Lightning had taken out the service, and they were replacing it when he discovered it was that way. I have used 208 single phase with small 240 single phase generators with automatic t-switchs, and have not had any problems.
- Location
- Connecticut
- Occupation
- Engineer
Cummins model DGDK, 125kVA Standby rated (for example) is available in 120/240 3 phase voltage.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Then it is a 240/120 delta 3-phase unit.
It is physically impossible to have 120/240 Y. The ratio between L-L and L-N voltages in a Wye connection is always 1.73 (actually it is the square root of 3).
- Location
- Connecticut
- Occupation
- Engineer
kwired
Electron manager
- Location
- NE Nebraska
A 4 wire delta system is grounded at the mid point of one phase.
Do you have a good reason to switch the neutral in the transfer switch - in most general purpose applications?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I have one lift station fed from the utility with a 240 volt grounded "B" and a Kohler 45kw 240/139 3-phase Y, but there is no neutral loads as it is only for fault current, 120 volt loads are from a derived 3kva 240/120 single phase transformer. utility monitor lines are 240 line to line, so no problem there.
nice thing about Kohler is their generators can be re tapped to about any voltage configuration, but this one came 240/139Y so I left it that way with no neutral loads it didn't really matter. oh and the main disconnect was rated 240 volts to ground also.
nice thing about Kohler is their generators can be re tapped to about any voltage configuration, but this one came 240/139Y so I left it that way with no neutral loads it didn't really matter. oh and the main disconnect was rated 240 volts to ground also.
- Status