Adding Sub Panel From Existing 3 Phase Service

[Buzzie8]

How would you wire a 230V 100 Amp Sub-Panel using the three phase wiring that previously went to a cat pump from a bay that you shut down? Keep in mind that one appliance will use three phase but everything else wired to the new sub-panel will be 120V.

 

[MEP001]

Straight off the old breaker, just make sure it's rated 100 amp for the new panel. Of course you'll have to leave every third breaker slot blocked off in the new panel if you have a high-leg.

 

[Buzzie8]

Can you please explain what you mean by "Of course you'll have to leave every third breaker slot blocked off in the new panel if you have a high-leg"
Thanks,
Buzzie

 

[MEP001]

If you have a high-leg that measures 277v to ground, you can't use it as a 120V source. The breaker slots are usually blocked off and unused. As far as I know, there isn't a breaker panel that has one 3-phase spot and the rest single or double-pole.

 

[2Biz]

I don't understand what Mep means about leaving the 3rd slot blocked in the new sub panel either? If the new panel will be single phase, wouldn't you pull (2) of the 120v leads off the three phase panel to make single phase 220v in your sub panel???

My ER is set up the same way. I have a 3 phase panel that supplies my pump stand. I also have a single phase 220v panel that supplies either 220v or 120v to everything else. Just make sure you don't use the "High" leg to power your sub-panel...

At my wash, Only 3 phase comes to the building from the transformer. It splits to 2 seperate meters then into the ER to the two seperate panels. If you power a single phase sub panel from the three phase panel, you might check to make sure you're not violating any codes.

 

[MEP001]

I don't understand what Mep means about leaving the 3rd slot blocked in the new sub panel either? If the new panel will be single phase, wouldn't you pull (2) of the 120v leads off the three phase panel to make single phase 220v in your sub panel???

He said one appliance off the new panel will be 3-phase, so it will be a 3-phase panel with every third breaker slot unusable for single phase (assuming he has a high leg).

 

[mjwalsh]

He said one appliance off the new panel will be 3-phase, so it will be a 3-phase panel with every third breaker slot unusable for single phase (assuming he has a high leg).

One thing that Buzzie8 needs to do is to make sure is ... that he adds up the amps for each specific leg so the end results are as balanced as possible & there is not an overload created for the main breaker. The potential high leg does make this balancing a bit more difficult when more non 3 phase circuits are now going to be used.

I quick call to the specific supervising electrical engineer at your utility company could help Buzzie8 understand if there is a wild leg & even possibly the specific type of wild leg involved at his car wash. In our case, the engineer happens to be one of our better customers ... so that helped me.

mike

 

[wash4me]

You also need to run a neutral and a ground wire. Check neutral to phase a,b,c voltage and if you have one much higher voltage you have a wild leg that cannot be used for 120 volt loads. By the time you figure all this out and get it right you may be better off hiring an electrician. Adding a panel like this is likely a small job and you will likely get a better install.