Different phase different voltage?

[StaggeringGoat]

I was just playing with my new voltmeter at the shop and popped open my breaker panel. I have 125A 3 phase 208Y service. I'm reading 122 volts on 2 of the legs but only 118v on the third. Is this normal? Why would the other be lower? I did this with everything in the shop turned off.

 

[Provincial]

While it could be more resistance in the low voltage circuit, it is more likely that the transformer is tapped differently on that circuit.

Is the transformer supplied by the power company or do you own it? If the POWCO owns the transformer, call them and describe the situation. If you own the transformer, an electrician should examine the internal wiring to see if someone chose to hook up the taps differently. Many transformers have multiple choices for where to hook up to the windings. This is usually to compensate for voltage drop in the supply circuit.

 

[Steve from Socal]

Are these reading a conductor to ground? To check 3 phase you want to check leg to leg voltage.

Steve

 

[StaggeringGoat]

Are these reading a conductor to ground? To check 3 phase you want to check leg to leg voltage.

Steve

Yeah...leg to leg is 210 volts but I don't have any 3 phase equipment. (yet)

If the POWCO owns the transformer, call them and describe the situation.

The power company owns the transformer...is this really an issue I need to call them about though? 118 volts is fine with me, as long as something isn't wrong.

 

[OccupantRJ]

What voltage are you getting at your receptacles?

 

[rabidsquirrel]

You simply have a higher load on that leg than the others. Nothing to worry about.

 

[buzz4041]

Nothing at all to worry about with a 4 volt difference.

 

[Tscott]

Yeah...leg to leg is 210 volts but I don't have any 3 phase equipment. (yet)



The power company owns the transformer...is this really an issue I need to call them about though? 118 volts is fine with me, as long as something isn't wrong.

This is not an issue, you are well within acceptable range and you are not experiencing any problems. So to answer your question, no do not call the power company. This is not uncommon by the way, it just means the system is more heavily loaded on that one phase for some reason.

Tom

 

[Roots]

That is perfectly normal. Linemen and planners try and balance the load on a circuit across the phases, but at varying times the loads will be different. A high load will lower the voltage reading slightly, as can position on the circuit. That's all you're seeing and there's nothing to worry about.