A transformer is reading unusual voltages from the secondary winding to ground.

Issue:
Transformers with ungrounded secondaries can exhibit unusual and varying voltages to ground.

Product Line:
LV Transformers

Environment:
Applies to most Transformers made by SquareD/Schneider Electric, both single phase and three phase.

Cause:
High Impedance Digital Voltmeters will often read Stray Induced Voltages from ungrounded secondaries to ground.  Low Impedance devices, such as a "Wiggy" or solenoid type voltage indicators, will not show these voltages.

Resolution:
When a transformer secondary is ungrounded or "floating", certain types of High Impedance meters such as Digital Voltmeters can read unusual voltages to ground.  These voltages may also vary with transformer secondary loading.  The only way to obtain predictable voltage readings to ground in such situations would be to physically ground one of the secondary phases (such as in a grounded delta configuration), or the center tap/neutral ( X0, H0, X4, X2/X3, etc., if available).  Before doing this, the customer should check with the local Electrical Code Inspector or AHJ (Authority Having Jurisdiction) to be sure that grounding the secondary winding is permitted by local codes.  With any secondary element grounded, the secondary coil windings have a hard-wired ohmic reference to ground, and such Stray Induced Voltages will not be present.

Released for: Schneider Electric USA