Since most single phase transformers have a secondary voltage of
120/240, they are operated as a three wire system. Balance Loading
must be taken by properly distributing the load as the transformer
secondary consists of 2 separate 120 volt windings. Each 120
volt winding is rated at one-half the nameplate KVA rating. For
example: A 10 KVA transformer, 120/240 volt secondary is to
service an 8 KVA load at 240 volts and two 1 KVA loads at
120 volts each. If the incorrect method is used, one winding will be loaded at
6 KVA, and the other winding will be loaded at 4 KVA. These do total
10 KVA but, is not properly balanced. This will cause an overload of the transformer and failure.