Over Voltage Isolatation Transformer ?

[Randall]

Hey Folks

Is this a Nubie or a repair question ?

I'm a bit spooked by this issue.  I have Hospital Grade Iso Transformer which gives over 130 volts without a load.

My Home voltage here in Michigan is near 123 volts or so, and this Iso Transformer when connected delivers over 130 volts a bit.
I place this in repairs because It just doesn't seem right and I'm fearful to plug something into it.

What don't I understand ?

See Photo.

[bdunham7]

Hey Folks

Is this a Nubie or a repair question ?

I'm a bit spooked by this issue.  I have Hospital Grade Iso Transformer which gives over 130 volts without a load.

My Home voltage here in Michigan is near 123 volts or so, and this Iso Transformer when connected delivers over 130 volts a bit.
I place this in repairs because It just doesn't[t seem right and I'm fearful to plug something into it.

What don't I understand ?

See Photo.

There's absolutely nothing wrong.  What you haven't factored in is that the transformer has impedance(s) that would always result in lower voltages under any load if it were wound 1:1.  So what they do is wind it as a small step-up (perhaps 1:1.05) with impedances low enough to limit the voltage drop to something like 10% under load.  So at no load it will be +5%, at half-load it will be nominal and at full load it will be -5%.  And that's all within tolerances and a very common feature of isolation transformers.

[jdragoset]

Test to make sure the output neutral is not connected to earth ground.
An ohmmeter with no power applied will tell.

[Randall]

THx !

My paranoia is put to rest !

Yes, the neutral is disconnected from Mother Earth .... !