lighting transformer questions?

Thread Starter


Joined Jun 30, 2006
First of all I'd like to introduce myself...I'm brrRabbit.....please dont throw me in that briar patch! lol

i have a general 240 v to 120 volt step down lighting transformer and do not have any voltage out put from the output side. I have 288 volts on the primary side, but nothing on the secondary side....I even unhooked my leads from the secondary side and measured it to ground, together and everything. What am i doing wrong?
oh and by the way the first one was bad so I ordered and installed a second one, and it basically has the same problems??


Joined Jul 31, 2004
How many lead wires (or terminals) does this transformer have? A normal transformer will have a minimum of four. (See link below) An autotransformer may only have three.

Assuming a transformer with four leads, we need to wire up the correct pair of primary leads, hopefully identified on the transformer as 240 Vac to your 288 Vac. If you connect a pair of leads to the 288 Vac there should be an audible hum from the transformer.

If you get no hum you are not connected. Maybe one primary lead and one secondary lead by mistake.

If the 120 Vac secondary winding is connected to the 288 Vac source, a louder than normal hum, with rapid overheating of the transformer is the result.

It is unusual to get more than one bad transformer, especially large ones.

If you do get this working, with the 240 Vac winding connected to 288 Vac, observe the transformer for overheating over a period of an hour or two, as the 288Vac is about 20% higher voltage than the transfromer rating.

Note that we have said nothing about connecting the secondary so far. That should not be a problem if you get the primary connected.

A second approach it to disconnect all the transformer leads, and use an Ohmmeter to identify the 1) primary pair of leads and the 2) secondary pair of leads. The Primary (240 V) pair will have a higher resistance than the secondary pair of leads. An open (infinite) reading indicates the wrong pair of wires. or in rare cases an open winding.

Thread Starter


Joined Jun 30, 2006
I hooked up a new transformer. (it did have 4 leads on primary H1 thru H4 ) The H2 to the H3 and the leads came in on H1 and H4..........turns out it was a 480 volt x 120 volt transformer...and I didnt have 480 volts on it between my leads coming in only 288 volts. After I figured out I didnt have the 480 across the primary leads...(I had been checking everything from one leg to ground...rookie mistake). like I was suppose too.I traced it back to a bad fuse. Plus (and I already knew this but didnt do like I needed to) i used my transcat pocket tic tracer to check the top side of the showed power, The fuse was obviously not completely blown...but was not letting the full 480 volts thru...strange! Afterwards I checked the same fuse with my ohm meter again, and instead of showing open line or OL on my fluke it showed some connection but was blinking instead of showing a good solid number.I've never seen a fuse show anything other than open line and still be bad....... Learning more everyday....

here is how it was wired.
two fuses
primary side of transformer (480volt to 120 volt)

I had the secondary disconnected after installing the new transformer in....still nothing..of course now I know why! lol

one of the two fuses was bad but showed good when measureing across it (with it out) on ohms....
live a learn. I am fairly new to electrical...but do enjoy it very much.
thanks for the reply