corner grounded delta
- Thread starter andy7spc
- Start date
- Status
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: corner grounded delta
They are not common anymore. One corner of the deltat is tied to ground. Its 480 phase to phase and 480 to ground on two phases. The voltage stress is higher (480 not 277) and a ground fault can be 480 not 277. My POCO doesn't use anymore, we have one left and they would like it gone.
The fused disconnect has a bus bar in the grounded phase...
They are not common anymore. One corner of the deltat is tied to ground. Its 480 phase to phase and 480 to ground on two phases. The voltage stress is higher (480 not 277) and a ground fault can be 480 not 277. My POCO doesn't use anymore, we have one left and they would like it gone.
The fused disconnect has a bus bar in the grounded phase...
charlie
Senior Member
- Location
- Indianapolis
Re: corner grounded delta
There are also other voltages. A 240 volt delta is the most common outside of 480 volt.
The most common use is a pair of 240 volt transformers set up as an open wye primary, open delta secondary. The common point of the open delta is grounded. A triplex service drop is used to a full voltage rated single phase panelboard. The grounded conductor is taken to the neutral bar (in this case the grounded conductor bar) and the GEC is connected to the same bar. Full voltage circuit breakers are used with the grounded conductor to feed the three phase motors. These are used for small lift stations.
There are also other voltages. A 240 volt delta is the most common outside of 480 volt.
The most common use is a pair of 240 volt transformers set up as an open wye primary, open delta secondary. The common point of the open delta is grounded. A triplex service drop is used to a full voltage rated single phase panelboard. The grounded conductor is taken to the neutral bar (in this case the grounded conductor bar) and the GEC is connected to the same bar. Full voltage circuit breakers are used with the grounded conductor to feed the three phase motors. These are used for small lift stations.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: corner grounded delta
Charlie, thanks. Does your POCO still use the 240 or 480 CG delta?
Don't the CG deltas have voltage unbalance problems for the load?
Charlie, thanks. Does your POCO still use the 240 or 480 CG delta?
Don't the CG deltas have voltage unbalance problems for the load?
charlie
Senior Member
- Location
- Indianapolis
Re: corner grounded delta
We do not use nor have we ever used many corner grounded delta systems. Other electric utilities in Indiana do use the one I described. We use 120/240 volt, 3 phase, 4 wire delta service in both the open delta and closed delta configurations. Most of our small commercial services are open delta because we can serve them with two transformers.
We do not use nor have we ever used many corner grounded delta systems. Other electric utilities in Indiana do use the one I described. We use 120/240 volt, 3 phase, 4 wire delta service in both the open delta and closed delta configurations. Most of our small commercial services are open delta because we can serve them with two transformers.
lady sparks lover
Senior Member
Re: corner grounded delta
I would never use this system either, because one phase, usually "b" is grounded, so you can't but anything on that phase as a single phase. It's just having delta with a high leg.
I would never use this system either, because one phase, usually "b" is grounded, so you can't but anything on that phase as a single phase. It's just having delta with a high leg.
roger willis
Member
- Location
- Texas
Re: corner grounded delta
Lady Sparks,
There is no high leg on a corner grounded delta system.
Roger
Lady Sparks,
There is no high leg on a corner grounded delta system.
Roger
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: corner grounded delta
Two legs will be 240 or 480 to ground the other leg will be "0" volts to ground.
The service your thinking about is a 4-wire delta it has a center tap between "A" and "C" phases this will put the "B" phase at 208 to ground/neutral
Two legs will be 240 or 480 to ground the other leg will be "0" volts to ground.
The service your thinking about is a 4-wire delta it has a center tap between "A" and "C" phases this will put the "B" phase at 208 to ground/neutral
Re: corner grounded delta
Of the 240V 3? 3W corner grounded systems, I typically see two or three new installations a year for the last 18 years.
And I would not be surprised if not more if the building owner and the Poco are 'in agreement'.
Poco prefers 208/120Y systems, but I understand, the URC requires the Poco to provide what the customer wants, if available.
One of my concerns is that 1? 3W panelboards are sometimes used and many times using 240/120V CB's rather than 240V CB's and many of the two pole 240V CB's are only rated for 5Kair and the ASCC is much greater. See 240.85 slash / rating.
Of the 240V 3? 3W corner grounded systems, I typically see two or three new installations a year for the last 18 years.
And I would not be surprised if not more if the building owner and the Poco are 'in agreement'.
Poco prefers 208/120Y systems, but I understand, the URC requires the Poco to provide what the customer wants, if available.
One of my concerns is that 1? 3W panelboards are sometimes used and many times using 240/120V CB's rather than 240V CB's and many of the two pole 240V CB's are only rated for 5Kair and the ASCC is much greater. See 240.85 slash / rating.
charlie
Senior Member
- Location
- Indianapolis
Re: corner grounded delta
Glenn, unfortunately, I believe you are correct.
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