1 x 120V and 3 x 12V AC power outlet.
Do landscape lighting transformers go bad. The picture included in this post includes a transformer that was not properly installed. If the wires are not tightly secured with all strands fully connected the power cannot be conducted efficiently. What is a landscape lighting transformer.
If you dont have a voltmeter use a phone charger or something similar. 20 lights X 7 VA 140 voltage Amps so its best to use a 300 Watt since 150W. One Light Bulb Is Out.
The first thing to check is whether you actually have power coming into your transformer. If the input power does not climb to the expected value then the problem lies. Now whenever the lights come on they will stay on for a little while than the transformer will trip its circuit breaker.
Why do transformers fail. Paradise by Sterno Home Low Voltage Smart AC Transformer WiFi 12V. Your transformer plugs into a standard outlet GFCI if outside or in an area that may get wet.
If the fixture is bad sometimes we can replace the socket assembly and that often fixes the problem. A bad fixture can be the cause of the problem. Do LED transformers fail.
When this happens the fixture is old and the insulation has worn off the wire. They fail shorted or open turns a lot more. This transformer worked well for about 4 years.

