Hypothetical Transformer Question

[TwoBlocked]

This was posed to me by and excellent apprentice a few years ago:

Let's say you go into a room and there is a transformer there. Conduits going to disconnects and continuing out of the room. You open the disconnects, look at the wiring, take voltage readings, and determine that the transformer is 480/277 3ph on one side and 208/120 3ph on the other, both with grounded neutrals, but not grounded in the transformer nor in the disconnects, but somewhere outside of the room.

With no more information, and without opening the circuit on either disconnect, and with just a normal meter, can it be determined if this is a step up or a step down transformer? In other words, is the power coming from the 480V or the 208V side?

I can think of a way with additional equipment, but not with just a regular meter, but that doesn't mean there isn't a way.

 

[electrofelon]

IT would be very rare to have a wye-wye transformer

 

[LarryFine]

IT would be very rare to have a wye-wye transformer

Agreed; the primary would likely have no neutral connection.

 

[TwoBlocked]

It's hypothetical.

 

[Deltaforce]

Check building service first step

 

[Deltaforce]

Two wattmeters one on each side
.higher reading primary
Chech voltage on that side know step up or stepdown

 

[Deltaforce]

Transformer no load case
Check side no load current
That primary
Measure voltage that side know step up or step down

 

[electrofelon]

I don't think there is a way without a more advanced meter. Would need watts, or power factor. My amprobe ACDC-54NAV could do it.