How can you tell the exact load of a single phase transformer which is supplying a 3 wire circuit?
When checking the loading of a transformer with an ammeter, all that needs to be known is the amount of amperes flowing in each of the outside legs or hot wires. You do not have to measure the amount of amperes flowing in the neutral or grounded wire, but you have to know the voltage from each of the hot wires or outside wires to neutral. An example of this is a 3 wire lighting panel 120/240 volts. The ammeter readings for each of the outside wires are 50 amps and 30 amps. Let us assume that the transformer supplying this 3 wire power is a 10 KVA 120/240, 3 wire secondary. To check the load, multiply the ampere reading by the voltage from the line to neutral and divide by 1000. The first reading of 120 x 50 amps divided by 1000 equals 6 KVA. The second reading of 120 x 30 amps divided by 1000 equals 3.6 KVA. The total of these two equals 9.6 KVA. The transformer is 20% over-loaded even though the total load is within the transformer’s rating. The maximum current that can be drawn from