Delta High Leg question: Any two phases = 240 v ?

[Stevenfyeager]

According to my diagram, voltage across any two phases is 240 volts in a delta 208 high leg panel.....is this correct ? ( From one who doesn't do much commercial work) I need some more spaces and am going to add a 120/240 v subpanel. In the past, I've added a subpanel using I believe phase A and C to get a 120/240 v subpanel. But may I use Phase B (high leg) with A or C for this ? Since every 3rd space (high leg) is empty in this panel, this would require me to only remove one circuit and move it to the subpanel as opposed to removing two circuits. Is this correct ? Thank you !

 

[gar]

230303-0619 EST

Stevenfyeager::

The simple answer is no. Note: you have one wire from the high leg panel that is 120 V relative to ground ( neutral ). and a second wire that is 208 V above ground.

If you had a 240 V single phase load that did not require a relationship to earth ( the single phase on this floating phase ) it would work if adequate insulation of that load existed. Can't tell you about code problems.

In you used an isolation transformer with adequate insulation from that 240 V source, then you could get that transformer's outputs directly referenced to ground.

.

 

[infinity]

According to my diagram, voltage across any two phases is 240 volts in a delta 208 high leg panel

The correct voltages of the 3 phase, 4-wire Delta system would be 240-208-120. If you're trying to connect a single phase 120/240 load you would use the phase that has the center tap.

 

[Hv&Lv]

You use B phase,(center) you will certainly fry some devices.
Use A&C as you have in the past.
Leave B empty.
Use A&C, voltages should be 120LG,120LG,240LL
Use B&(A or C), voltages will be 120LG, 208LG, 240 LL
120 appliances don’t like 208V

Use the voltmeter.
Make sure the sub panel voltages line up with a 120/240 residential house service you would install.

 

[Stevenfyeager]

Thank you. By using A and C, am I chancing unbalancing the load, the system ? ( Just a phrase I read but don't know anything about.)

 

[ptonsparky]

Thank you. By using A and C, am I chancing unbalancing the load, the system ? ( Just a phrase I read but don't know anything about.)

You still have a balanced load on the center tapped single phase transformer. The three phase loads will be balanced.

 

[jim dungar]

Thank you. By using A and C, am I chancing unbalancing the load, the system ? ( Just a phrase I read but don't know anything about.)

Yes you are, but it is immaterial unless the source/utility transformer is undersized.

 

[Stevenfyeager]

Thank you so much, men ! You are a really big help.

 

[hillbilly1]

Thank you. By using A and C, am I chancing unbalancing the load, the system ? ( Just a phrase I read but don't know anything about.)

Really depends if it is poco provided, or customer owned. Poco oversizes one of the two or three transformers if pole mount, so balance is not as critical, where a pad mount or regular dry type does not tolerate the imbalance well.

 

[LarryFine]

I disagree. There is a usable 240v across the open side.

I have done it, and the loads worked as expected.

 

[wwhitney]

I disagree. There is a usable 240v across the open side.

Yes, for 2-wire 240V loads. But despite the thread title, the OP said:

am going to add a 120/240 v subpanel.

That requires supplying the subpanel A-N-C.

Cheers, Wayne

 

[LarryFine]

Yes, for 2-wire 240V loads. But despite the thread title, the OP said:

That requires supplying the subpanel A-N-C.

Absolutely correct. My mistake.