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About Greg Hughes
Expertise
Residential Electrical including Appliances and HVAC with 28 years experience.

Experience
Started training as an electrician in 1979, worked for major companies and the government.

Education/Credentials
Graduated from Electrician's School, Carrier Training, and various specialty schools.

You are here: Experts > Home/Garden > Home Improvement/Repair > Electrical Wiring in the Home > transformer plug- in hot

Electrical Wiring in the Home - transformer plug- in hot

Expert: Greg Hughes - 6/30/2009

Question
I recently had a digital cable tv receiver box hooked up; the receiver itself isn't hot but the small black plug-in transformer box that plugs into an electrical outlet (it's plugged into a surge protector outlet) is quite hot to the touch but not so hot that you can't touch it but it's definitely more than just warm and that's when it is turned off (the receiver being on doesn't make it hotter). I know plug-in transformers get warm but don't know if hot is normal. May main concern is, can something like that cause a fire? Thanks

Answer
Almost all newer electronic equipment is energized to some degree when it is plugged in. There are clocks, timers, memory circuits, etc that are being powered.

If you were to unplug the transformer you would notice that it cools down to room temp.

A transformer is simply two wires that are coiled up next to each other. As the electrons flow through the coiled wire it causes heat (much like if you rub your hands together) due to the resistance of the wire.

So a xfmr will create heat, but how much is too much heat? This is a good question and probably better answered by the engineers that designed it.
You would need to know the normal range of expected temp and then you would need to know the melting point of the plastic housing.

Then you would need to watch the temp with a thermometer.

Hope this helps.

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