Secondary Voltage Varies

Transformer secondary voltage can be too high, too low or there may be no voltage. Please note that transformer voltage is a ratio of the primary voltage. If the primary voltage is too high or too low, the secondary voltage will also be too high or too low.

Check: Solution:
Incoming line voltage varies. A transformer is a voltage ratio device so the secondary voltage will generally vary as the primary voltage varies. This is a systems issue a transformer can not fix.
Verify all connection points (lugs and pads) are tight, smooth and cleaned of any insulation. Smooth or replace pads and lugs if damaged or rough. Tighten any loose mechanical connections. Clean off any insulation remaining on electrical connection points.
Verify the neutral connection is properly wired and grounded per the applicable codes. All three coils should be attached to a common neutral point. If the transformer neutral is damaged, it will have to repaired. Wire and ground the neutral per applicable codes. A coil may have been inverted during manufacturing and would have to be replaced.
Are there any large loads that occur where total standard or momentary inrush load exceeds the kVA rating of the transformer. During high current, such as when a large motor is started across the line or during a short circuit, the output voltage will be lowered. The total load will either have to be decreased, limited by devices such as reduced motor starting devices or a larger transformer will have to be installed.