Service 240V Hi-Leg 3-Wire

[Dratek]

I came across a service I've never seen before:

240V Hi-leg 3-wire
A to B, B to C, A to C is 250V
A to ground C to ground is 125V
B to ground is 216V

It seems like typical 240V hi-leg except it only has 3 wires - no grounded conductor.
How do you deal with service like this? We need to add new panel and connect some motors.

It is old manufacturing facility, they have secondary service for lighting 120/240V single phase.

 

[Little Bill]

I came across a service I've never seen before:

240V Hi-leg 3-wire
A to B, B to C, A to C is 250V
A to ground C to ground is 125V
B to ground is 216V

It seems like typical 240V hi-leg except it only has 3 wires - no grounded conductor.
How do you deal with service like this? We need to add new panel and connect some motors.

It is old manufacturing facility, they have secondary service for lighting 120/240V single phase.

You have a delta connected system, very common in older industrial areas. Make sure you mark the high leg and don't use it for any 120V circuits. Any 240V single or 3ph can go between any of the legs/phases.

 

[Dratek]

I understand breakers have to be straight 240V rating. How do I order my panel? Should it be just 3-wire without neutral bar? Is it even available?

This forum is great and I read it all the time. Thanks to all people willing to spread knowledge and help others!

 

[infinity]

I understand breakers have to be straight 240V rating. How do I order my panel? Should it be just 3-wire without neutral bar? Is it even available?

This forum is great and I read it all the time. Thanks to all people willing to spread knowledge and help others!

Yes, just order a 3 ?, 3 wire Delta panel with an equipment ground bar.

 

[jumper]

Okay, I am confused. This is not an ungrounded or corner grounded service, so how do we have a high leg delta with no neutral? I am missing something.:?

 

[infinity]

Okay, I am confused. This is not an ungrounded or corner grounded service, so how do we have a high leg delta with no neutral? I am missing something.:?

I might guess that one of the transformers is center tapped and the tap is grounded. Good question.

 

[Volta]

I came across a service I've never seen before:

240V Hi-leg 3-wire
A to B, B to C, A to C is 250V
A to ground C to ground is 125V
B to ground is 216V

It seems like typical 240V hi-leg except it only has 3 wires - no grounded conductor.
How do you deal with service like this? We need to add new panel and connect some motors.

It is old manufacturing facility, they have secondary service for lighting 120/240V single phase.

I'm with Jumper here. What does 'ground' mean in your OP? The metal of the enclosure? Are you reading the 'to ground' voltages ultimately through the single-phase's neutral?

Section 250.24(C) will require the grounded conductor to be brought to the service disconnect. Is it an overhead drop? If so, what is being done with the load-end of the supporting messenger?

 

[hillbilly1]

I came across a service I've never seen before:

240V Hi-leg 3-wire
A to B, B to C, A to C is 250V
A to ground C to ground is 125V
B to ground is 216V

It seems like typical 240V hi-leg except it only has 3 wires - no grounded conductor.
How do you deal with service like this? We need to add new panel and connect some motors.

It is old manufacturing facility, they have secondary service for lighting 120/240V single phase.

Is the other service feed from the same transformer bank? I have yet to see a Poco not bond the center tap on one of the transformers at the bank on a 240 volt delta service, 480 delta, yes, but 240 no. But of course we do things a little different in the south. The other service gives your reference to "ground".

 

[Hv&Lv]

With those voltage readings, it seems to be an open delta secondary.

 

[kwired]

My guess is it once was either corner grounded or ungrounded. When it was changed to mid point of a phase grounded, nobody bothered to make necessary changes to existing equipment, or simply did not know any better.

If you do not have a grounded service conductor with a grounded system, this is completely wrong. If an inspector here ran into this situation he has authority to order the POCO to disconnect that service until made acceptable, and probably will, even if it was existing. They don't order immediate disconnection of service very often, but I think they would on this one.

 

[jim dungar]

With those voltage readings, it seems to be an open delta secondary.

Voltage readings alone cannot tell you if it is Open-delta or Closed-delta, both of which are available with either one leg center tapped and grounded or one corner grounded.

 

[Hv&Lv]

Voltage readings alone cannot tell you if it is Open-delta or Closed-delta, both of which are available with either one leg center tapped and grounded or one corner grounded.

Yea, I kinda posted without thinking...
Hoped it would be ignored.
Still confused on where the OP referenced his ground readings though....
I woalso wonder where the neutral was dropped, at the point of delivery, or at some point beyond another panel. I don't think it would have been a POCO error because the OP stated 3 wire. Surely the POCO didn't try to supply 3 phase with triplex :slaphead:

 

[jim dungar]

Still confused on where the OP referenced his ground readings though....

So am I.

 

[Dratek]

I took the voltage readings against grounding conductor. It seems like they had all 3-phase loads so they just pulled three legs without neutral.
I've never seen this before. Its been stripped of cooper...

 

[jim dungar]

How many transformers?
How many wires from the utility to the meter?
How many from the meter to the service disconnect?
Where is the GEC connected?

 

[jimmac49]

Maybe the ground readings are a result of capacitive coupling. You could use a test lamp between each phase and ground to see if it is a phantom voltage.Try checking the voltages in the main switch with all downsteam circuit breakers open and see what you have to ground as well. If it is an ungrounded delta system you may want to consider adding a grounded phase indicating device or ground indicating lamps.
Jim

 

[kwired]

Maybe the ground readings are a result of capacitive coupling. You could use a test lamp between each phase and ground to see if it is a phantom voltage.Try checking the voltages in the main switch with all downsteam circuit breakers open and see what you have to ground as well. If it is an ungrounded delta system you may want to consider adding a grounded phase indicating device or ground indicating lamps.
Jim

You really think he would get the readings he had if if there was not a solid ground someplace on the mid point of one phase? Those readings were right on what should be expected for that type of system.

 

[kwired]

I took the voltage readings against grounding conductor. It seems like they had all 3-phase loads so they just pulled three legs without neutral.
I've never seen this before. Its been stripped of cooper...

Neutral does not need to be there if it is not needed.

Equipment grounding conductor whether it is a wire or a metal raceway is required.

If it is a grounded source the grounded conductor must be brought to service disconnect. Is there a grounded conductor at the service? From there on if no neutral is needed and you have qualifying metal raceways for the equipment ground no wire is required for the equipment ground.

 

[jimmac49]

You really think he would get the readings he had if if there was not a solid ground someplace on the mid point of one phase? Those readings were right on what should be expected for that type of system.

The 240 volt tapped delta services I have seen are 4 wire systems...

 

[Dratek]

There is absolutelly nothing connected and I took the readings right on the service disconnect swith. I will take some pictures...