Control Transformer for Corner grounded delta source

[knorthouse]

We have a 3 phase corner grounded delta power source (230 Vac 3 PH 60Hz) that we'll be using to control a couple of 3 phase 230 Vac pumps. We're planning on installing a 230/115 vac single phase control transformer for control power. If we ground the secondary of the control transformer, would it be best to connect the primary to the 2 ungrounded phase conductors from the source? Would appreciate any comments on this.

 

[LarryFine]

Welcome to the forum.

It doesn't matter, but it would be a way to "monitor" the two ungrounded lines, especially with fuses.

 

[Joethemechanic]

are you sure you have a corner ground and not this?



OR

 

[Joethemechanic]

Welcome to the forum.

It doesn't matter, but it would be a way to "monitor" the two ungrounded lines, especially with fuses.

I agree for a small control transformer it probably won't matter if it's a full delta

If it's an open delta I wouldn't connect across B and C

 

[don_resqcapt19]

The transformer only sees the line to line voltage connected to the transformer primary...is does not matter if one of the lines has zero volts to ground.

 

[jim dungar]

I agree for a small control transformer it probably won't matter if it's a full delta

If it's an open delta I wouldn't connect across B and C

It would not matter. The OP said the system was corner grounded and the NEC requires the B phase to be the grounded conductor.

 

[Joethemechanic]

It would not matter. The OP said the system was corner grounded and the NEC requires the B phase to be the grounded conductor.

I'm just saying, if it's open delta, I wouldn't connect across the open legs. There is a little more voltage fluctuation there. If his transformer is just for a magnetic motor starter, it won't matter. If it's something electronic it could be sensitive to voltage or waveform

I questioned the trans connections because here on the east coast I've never seen a corner grounded 230 volt delta. Seen quite a few 480 corner grounds , but never 230-240

 

[knorthouse]

Appreciate the informative replies and the Welcome to the Forum.