Phase to ground v Phase to Phase voltage on 208/230V 3ø at disconnect

[David Goodman]

What voltages should you expect on a 208/230V 3ø?

I am working on a walk in freezer at a KFC. While I was on the roof, I kept hearing a compressor for one of the coolers try to start. It would start, run about 2 seconds and then stop.

The KFC manager told me that they have had several breakers trip in the last week.

So, I checked the voltage into the disconnect for the cooler condenser that was short cycling.

I was only using a Fluke T5 voltage tester at the time.

Phase to ground: 121/122/121
Phase to phase: 213/211/213

I would have expected to have phase to phase readings more like 244V.

Any thoughts for me?

[buford]

Amp draw over what it is rated at, voltage drop off when starting, loose wiring to breakers. Could be many issues

[VTP99]

On a Delta Wye service you'll most likely see closer to 208 voltage.
Around here 230 voltage comes from a Delta service.

[David Goodman]

On a Delta Wye service you'll most likely see closer to 208 voltage.
Around here 230 voltage comes from a Delta service.

I'll need to check with Valley Electric to find out if it is Delta wye service.

[VTP99]

Just look at the service coming in to the building. 3 wire w/ ground or 4 wire w/ground. If the latter the forth wire will be the neutral.

[northeastbeast]

did you amp compressor and gauge up to system ?

[David Goodman]

Amp draw over what it is rated at, voltage drop off when starting, loose wiring to breakers. Could be many issues

I had the disconnect off to the unit while testing. I did find several wire nuts on the unit I was working with corroded conductors underneath. Many nuts were facing down allowing condensation to accumulate in the nuts.

Here is a picture of the disconnect interior of the one I was working on. Notice the red nut that was touching the panel front.

[Juan Madera]

If all three lines to ground/neutral are in the 120V range, then you have a "Y" service coming in and the phase to phase voltage should be 208VAV or within 10%... Your seems kinda high, so I doubt that it would be an issue starting a 3phase compressor as higher V is less A

[Juan Madera]

If it were a Delta service, the phase to phase would be in the neighborhood o 240VAC and two of the line to neutrals would be 120VAV and one "wild leg" would be about 208VAC. Delta generally found in more industrial applications with a lot of 3 phase loads and not much in the 120V...

[David Goodman]

did you amp compressor and gauge up to system ?

No, I didn't have authorization to work on that unit.

[David Goodman]

Just look at the service coming in to the building. 3 wire w/ ground or 4 wire w/ground. If the latter the forth wire will be the neutral.

Three phase Wye makes a lot of sense now. Looking at the picture of the disconnect that I posted, the white wires under the broken wire nut appear to be the neutral.

[David Goodman]

If all three lines to ground/neutral are in the 120V range, then you have a "Y" service coming in and the phase to phase voltage should be 208VAV or within 10%... Your seems kinda high, so I doubt that it would be an issue starting a 3phase compressor as higher V is less A

Almost all of our voltages here are on the high side. We regularly measure 248V on 240V single phase residential circuits. In a couple of sections of town we get 254V readings.