Motor voltage

[mstrlucky74]

Basic question....

When a motor, pump or other load is fed from say a 277/480 volt panel how do you know whether the load is either 277 or 480? Do you have to look at the nameplate info or can you tell just by looking at the panel schedule? Thanks

 

[GoldDigger]

Basic question....

When a motor, pump or other load is fed from say a 277/480 volt panel how do you know whether the load is either 277 or 480? Do you have to look at the nameplate info or can you tell just by looking at the panel schedule? Thanks

If all you see is that the load is connected to three phase wires, you have no way of telling whether the load itself is wired as 277wye or 480delta.
(If no neutral wire is run to the load, you can be pretty sure it is delta, but that is about all you can say from there.) Even the panel schedule may not list whether the load is wye or delta.
The relationship of the load power to the current in the three phase wires will not change though.

 

[kwired]

If all you see is that the load is connected to three phase wires, you have no way of telling whether the load itself is wired as 277wye or 480delta.
(If no neutral wire is run to the load, you can be pretty sure it is delta, but that is about all you can say from there.) Even the panel schedule may not list whether the load is wye or delta.
The relationship of the load power to the current in the three phase wires will not change though.

Many motors are wye connected yet we do not run a neutral to them. The motor operates as a 480 volt load, but does have three 277 volt coils internally. Keeping the applied voltage equal on all three phases and keeping the load on the motor equally applied to all three windings will result in equal currents and voltages across and through those windings.

Mrlucky, do you understand how and why multiwire branch circuits work the way they do?

 

[mstrlucky74]

If all you see is that the load is connected to three phase wires, you have no way of telling whether the load itself is wired as 277wye or 480delta.
(If no neutral wire is run to the load, you can be pretty sure it is delta, but that is about all you can say from there.) Even the panel schedule may not list whether the load is wye or delta.
The relationship of the load power to the current in the three phase wires will not change though.

The reason i ask is because i was inputting values into a voltage calculator and, obviosly, one must input the voltage.

 

[GoldDigger]

The reason i ask is because i was inputting values into a voltage calculator and, obviosly, one must input the voltage.

Into a voltage drop calculator?
If so, then if the current you use is the line current, the voltage you should use is 277. And you should be looking at the voltage drop for the one way distance not the two-way/two-wire distance. That factor in the calculation will not change between wye and delta.

 

[kwired]

Into a voltage drop calculator?
If so, then if the current you use is the line current, the voltage you should use is 277. And you should be looking at the voltage drop for the one way distance not the two-way/two-wire distance. That factor in the calculation will not change between wye and delta.

kind of depends on how you look at it. Many use one way distance @ 480 volts then end up using a 1.73 factor in the formula which will ultimately in the end give same results as using 277 and no 1.73 factor to start with.

If three phase load is balanced then the drop from phase to phase should be 1.73 times what the drop from any phase to neutral point is.

 

[GoldDigger]

kind of depends on how you look at it. Many use one way distance @ 480 volts then end up using a 1.73 factor in the formula which will ultimately in the end give same results as using 277 and no 1.73 factor to start with.

If three phase load is balanced then the drop from phase to phase should be 1.73 times what the drop from any phase to neutral point is.

True, which makes the percentage drop across the load the same in either case, and the drop in the phase to neutral voltage at the load will be exactly the same.
You have your choice of taking the 1.73 in the current or in the voltage.

 

[mstrlucky74]

Into a voltage drop calculator?
If so, then if the current you use is the line current, the voltage you should use is 277. And you should be looking at the voltage drop for the one way distance not the two-way/two-wire distance. That factor in the calculation will not change between wye and delta.

Yes, sorry. There are some 20a motors being fed from a 277/480 panel amd the panel schedules are calling for #10's in 3/4" EMT. They are 280' away. The calculator came up with #8's...:?

 

[GoldDigger]

Yes, sorry. There are some 20a motors being fed from a 277/480 panel amd the panel schedules are calling for #10's in 3/4" EMT. They are 280' away. The calculator came up with #8's...:?

Well, using the Southwire calculator, I get a voltage drop of 4.25% for that configuration with #10 copper, and 2.4% voltage drop with #8. Since the code does not mandate a maximum voltage drop, the right answer to your question hinges on what would be an acceptable drop.
Consider motor starting when pulling LRA.
Consider power lost to a voltage drop of 5%.
Consider cost of wire and allowed fill and derate in 3/4" EMT.
Make a choice on that basis.
Or just go with what the EE drew up.

 

[heavyaslead]

Check the Breaker

Check the Breaker

The breaker poles will tell you if the motor is 480 3phase or 277 single phase. Theres a remote chance it could be 480 single phase but that would be extremely rare.

Of coures most motors in this voltage range will be 480V 3P.

And the motor nameplate can be checked as well.

BTW My calculator indicates #8 for 480V 3P at 3% VD if the load is 20A continuous. (This does not figure derating for ambient or conduit fill)

 

[mstrlucky74]

The breaker poles will tell you if the motor is 480 3phase or 277 single phase. Theres a remote chance it could be 480 single phase but that would be extremely rare.

Of coures most motors in this voltage range will be 480V 3P.

And the motor nameplate can be checked as well.

BTW My calculator indicates #8 for 480V 3P at 3% VD if the load is 20A continuous. (This does not figure derating for ambient or conduit fill)

Thanks. So if its 1p it usually is 277.... 2&3pole it is 480?

 

[GoldDigger]

Thanks. So if its 1p it usually is 277.... 2&3pole it is 480?

That would be a good first approximation. If 3P with all three poles connected, it could be wye or delta. But most likely delta and so 480.
If 2P, or 3P with only two connected, it would have to be single phase and connected from one phase line to the other, hence 480.
If 1P, or 2-3P with only one connected, it would have to be single phase and wired for the wye (line to neutral) voltage, hence 277.

 

[kwired]

Not that they don't exist, but a 277 volt single phase motor is pretty rare to find. 480 volt single phase motors are probably more common than a 277 volt motor I would guess.

 

[Jraef]

Not that they don't exist, but a 277 volt single phase motor is pretty rare to find. 480 volt single phase motors are probably more common than a 277 volt motor I would guess.

I have seen quite a few small 277V labeled single phase motors in packaged HVAC equipment, things like damper actuators mostly that are intermittent duty (so maybe they just SAY they are 277V to satisfy inspection, but are really 240V wound). Prior to that I was under the impression that they did not exist at all. I suppose it's because for that industry it's all about the cheapness, so the difference between a 1 pole breaker and a 2 pole breaker is a big deal to them.

I don't think I have ever seen a 480V single phase motor, but I know they exist because I've talked to farmers in far flung rural areas who are only given 480V single phase power by the PoCo to run an irrigation pump or something. They buy VFDs that will give them 3 phase from the single phase, mainly because they have a hard time replacing a bad 480V single phase motor, but can get a three phase version off the shelf.

 

[kwired]

I have seen quite a few small 277V labeled single phase motors in packaged HVAC equipment, things like damper actuators mostly that are intermittent duty (so maybe they just SAY they are 277V to satisfy inspection, but are really 240V wound). Prior to that I was under the impression that they did not exist at all. I suppose it's because for that industry it's all about the cheapness, so the difference between a 1 pole breaker and a 2 pole breaker is a big deal to them.

I don't think I have ever seen a 480V single phase motor, but I know they exist because I've talked to farmers in far flung rural areas who are only given 480V single phase power by the PoCo to run an irrigation pump or something. They buy VFDs that will give them 3 phase from the single phase, mainly because they have a hard time replacing a bad 480V single phase motor, but can get a three phase version off the shelf.

A commonly seen 480 volt single phase motor in the farming area is a 10 hp motor - usually wound for 480/240 dual voltage. It is commonly used to drive a hydraulic pump motor for a particular irrigation machine that is driven by hydraulics rather than electric motors at each driving location. They are not necessarily easy to find at the motor shops, but the dealers for these systems do have them. I have no idea how much they may cost, as I have never replaced one. I have connected many of them up though.

I have also seen several fractional HP single phase 480 volt motors used as condenser fan motors on cooling towers or even as a blower motor in an electric unit heater.

Anything I have ever seen in agriculture applications that is more than 10 hp where only single phase supply is all that is available is usually driven by a phase converter or VFD.

I do remember connecting a submersible well pump one time that was single phase 277 volts.