Need Neutral from 3 Phase Grounded Delta

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iwire

iwire

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A friend of mine is working in a building with the following voltages at the service.

Phase to phase all 240 Volts

Phase A & B to ground 240 Volts

Phase C to ground 0 Volts

No neutral.

Is this corner grounded Delta?

Can he get a 240 delta to 208/120 Y transformer?

Is there anyway to get a neutral for 120 volt loads.

We do not run into this, we work on 480/277 and 208/120 3PH 4W or 240/120 1PH 3W, so we are a little lost. :roll:

Bob
 
Re: Need Neutral from 3 Phase Grounded Delta

Bob,
If this was an ungrounded delta then you could use a "zig-zag" transformer to derive a neutral. With a coner grounded delta the only way is to install a transformer like you suggested. 240 volt primary and a 120/208 Y secondary if 3 phase power is needed. If only single phase power is needed then you could use a 240 primary to 120/240 secondary transformer.
Don
 
Re: Need Neutral from 3 Phase Grounded Delta

Bob, sounds like a corner grounded delta to me. I agree with Don on the solutions.
 
Re: Need Neutral from 3 Phase Grounded Delta

Bob,

Definitely sounds like a Corner Grounded Delta, with ?C being the Grounded Conductor.

Use an Isolation Transformer (Typical Transformer with Primary and Secondary windings) for deriving a "Neutral" Grounded Conductor.

Could be a 240 VAC Delta ? 208Y/120 VAC Wye Transformer, or as Don mentioned, a 1? Transformer.

Scott
 
Re: Need Neutral from 3 Phase Grounded Delta

Thank you gentlemen. :cool:

I do not know if he truly needs 3 phase 208 or if just needs a neutral to feed 120 volt loads.

Is there a good reason to go single phase?

Wouldn't using a single phase transformer cause balancing problems on the original 3 phase service?

I do not know the size of the delta service or the load being added.

Anyway thanks for the replies I will pass the info onto my friend and I am sure he will be happy to know this is easily accomplished.
 
Re: Need Neutral from 3 Phase Grounded Delta

Bennie glad to have your input but I do not know and I don't know if my friend looked, I will ask him tomorrow. It's 10PM here and I do not want to Nextel him now. :)

We are both 24/7 on a Nextel leash. :roll:
 
Re: Need Neutral from 3 Phase Grounded Delta

Originally posted by iwire:


Is there a good reason to go single phase?

Wouldn't using a single phase transformer cause balancing problems on the original 3 phase service?
Click to expand...
Bob, you answered your own question. First choice would be 208/120 to evenly balance the load. You know the drill, delta input, wye output.

Second choice single phase. Pitfall unbalanced on the delta service.
 
Re: Need Neutral from 3 Phase Grounded Delta

Originally posted by dereckbc:
Bob, you answered your own question.
Click to expand...
Two sharp guys mentioned going single phase so I wanted to cover all the bases. :)

We will be spending money based on these answers. :D

Thanks all, Bob
 
Re: Need Neutral from 3 Phase Grounded Delta

If the service equipment and other panels are three phase(single phase equipment is permitted to be used with corner grounded delta systems) you might ask the utility about changing the service to 120/240 three phase with a high leg.
Don
 
Re: Need Neutral from 3 Phase Grounded Delta

Don, around here a, lot of small sewage lift stations are built with an open delta bank that is a corner grounded delta. They (not on the IPL system) install a triplex service drop to a full voltage rated service that looks like a single phase panelboard. Full voltage rated, 2 pole, circuit breakers are used for the three phase circuits. If you are not used to the installation type, you would think it is a single phase service.

Bob, if you have service is like this, you will not be able to just ask the power company to change the transformer configuration. All of the service equipment and service drop would be required to be replaced if they did change the configuration. :D
 
Re: Need Neutral from 3 Phase Grounded Delta

A 120/208 Y is a safer system, as the voltage to ground is 120, not 240 (on two legs), and phase to phase is bit less.
 
Re: Need Neutral from 3 Phase Grounded Delta

The service is similar to wah twe have in SE Wis. We have 240 volt, 3ph, 3w, grounded B phase. If you didn't know any better it would look just like a 1 phase service--2 pole breakers, etc. The main is a fusible disconnect because there is not a 2 pole main rated 240 to ground.
You can either install a delta-wye 3 phase transformer-240-208/120Y, or single phase 240-240/120, or 240-120. We've done many of these.
As for the POCO, ask about bringing a 1 phase service, if possible. We usually have a 3 phase and a 1 phase service on the buildings.
Normally the POCO will charge an arm & 2 legs to bring in something special--adding a neutral on a 240 delta 3p 3w. I also think you'd be in for a huge expense if that were the case--premise wiring would need to be changed.
 
Re: Need Neutral from 3 Phase Grounded Delta

Thanks for all the help, a 240 VAC Delta ? 208Y/120 VAC Wye Transformer has been ordered. :)
 
Re: Need Neutral from 3 Phase Grounded Delta

Originally posted by tshea:
The main is a fusible disconnect because there is not a 2 pole main rated 240 to ground.
Click to expand...
wouldn't a straight rated 2 pole breaker suffice?
 
Re: Need Neutral from 3 Phase Grounded Delta

240.85 Applications. A circuit breaker with a straight voltage rating, such as 240V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the circuit breaker?s voltage rating. A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1?3 to indicate such suitability.

A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the circuit breaker?s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the circuit breaker?s voltage rating.

FPN:proper application of molded case circuit breakers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the circuit breakers? individual pole-interrupting capability.

From the NFPA Handbook
A circuit breaker marked 480Y/277V is not intended for use on a 480-volt system with up to 480 volts to ground, such as a 480-volt circuit derived from a corner-grounded, delta-connected system. A circuit breaker marked either 480V or 600V should be used on such a system. In like manner, a circuit breaker marked 120/240V is not intended for use on a delta-connected 240-volt circuit. A 240-volt, 480-volt, or 600-volt circuit breaker should be used on such a circuit. The slash (/) between the lower and higher voltage ratings in the marking indicates that the circuit breaker has been tested for use on a circuit with the higher voltage between phases and with the lower voltage to ground.
 
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