how to size wire for a transformer to a power panel?

Answer 1

Wire size is based on current flow.

Find out how much current will be drawn by the transformer, then look up the wire size requred for this current flow at someplace like http://www.powerstream.com/Wire_Size.htm

The just make sure the wire is rated for the voltage that will be present, this is basically the rating of the insulation on the wire.

Answer 2

First, you need to know the VA or kVA of the transformer.

Next, you need to calculate the current flow for BOTH the incoming (line) and outgoing (load) sides of the transformer. Current for a single phase AC transformer is Voltage divided by VA (1kVA = 1000VA). For example, a 480/120, 1kVA transformer will have 2.1 amps on the line side and 8.3 amps on the load side.

Finally, you can choose wire. The wire must be rated for the AMPERAGE, VOLTAGE and TEMPERATURE. However, wire is cheap; I would just err on the higher side. In my example, I would use 14 AWG (gauge) machine wire. It is rated for 20A, but is normally rated for high voltages and is safe to use for any temperature.

Also, do not forget fuses on both the line AND load wire. A time-delay fuse or breaker rated 1.0 to 1.25 times the current would be sufficient. BUSS makes fuses for this type of application. Most hardware stores have load centers and breakers for this application.

Hope this helps

Answer 3

It depends on the maximum full load current to be drawn. Also, you must conform to the National Electrical Code. I suggest you enlist the aid of someone local who is NEC qualified.