What size wire do I use for a transformer?

Question

I have 16 lights at 18 watts for my deck lighting. This is 282 watts total and they are running on 12v. This is roughly 23.5 amps. I am using 10 gauge landscape wire for the outdoor lights and a 500 watt transformer. Do I need to run 10 gauge wire to the transformer and put it on a 30 amp breaker? Someone told me this is overkill. If there is 23.5 amps of load on the lights, don't I need 30 amp breaker which calls for 10 gauge wire?

Answer 1

the total load (FLA) that a 500 watt or 500VA trans on 120Vac primary can handle is 4.165 amps      500/120 = 4.165 primary side amps

or 41.65 (FLA)secondary amps at 12 Vac

Answer 2

On the output side of the transformer, you should have the 12 ga or 10 ga wire, for the input /line side/ house side you only need  1/10 of the output side of the transformer. The current which is how the wire is sized, is inversely proportional to the voltage. so 24 amps at 12 volts  would be 2.4 amps at 120 volts.

Answer 3

Down-stream from the transformer you've got it right.

Up-stream, 282W. @ 120V. is only about 2.4A.

You can tap this much off a local circuit.

If you'd rather wire a new circuit a 15A. breaker

and #14 wire, (Cap. 1440W.),   is more than adequate.

If the transformer is outside, make that breaker a GFI type.

Answer 4

Converting the 18 volts to the 120 volts coming from the house, you will have 2.35 amps (280W/120V=2.35A)  Therefore, you do not need a 30A circuit to run your lights.  There is very little draw.