Isolation Transformer Steps Up VAC

[TomCarlos]

MEF Members....

A general question about Isolation Transformers. I have a Tripp Lite Isolator (converted from hospital grade, removing the ground strap from the neutral lug to the chassis) and a transformer that was pulled from a Viz WP-32 Isolation /Variac all in one. Both isolation transformers are stepping up the VAC from 117 vac that comes out of the wall to 123 vac. Is this common or any reason for the step up?

Thanks, Tom

[Chuck H]

Just a guess, but it's probable that the transformers are more accurate when at or near their current rating. If they provided a 1:1 unloaded then they would sag below that with a load.

[Helmholtz]

Transformers need nominal load for nominal output voltage. No load voltages will be higher than nominal taking care of sag (= voltage drop across internal resistance).

[TomCarlos]

Thanks to you both...

I thought about the no load vs loaded scenario. So just to play it safe, I use a Variac after the iso to dial in vac before testing.