Transformer wiring questions

[allkindsa]

I am troubleshooting a sign that utilizes a transformer / auto transformer. The main label is destroyed, but the wiring information is still inside the cover.View attachment 9045View attachment 9046

I spoke with a tech at the company that I think made the unit, but he got frustrated with my ignorance. I rarely work with these devices.

I have (2) 277 legs input, so 480V. Sign needs 120VAC output. Prior to me, the device was wired with H2 & H3 joined, H1 joined with (1) 277 leg, and H4 joined with other 277 leg. X1 and X3 were joined and wired to the black wires of the (6) ballasts, and X2 and X4 were joined and wired to the (6) neutrals. (4) ballasts have a max. line curr. of 2.7A, and (2) have a max. of 3.5A, so 17.8A max. current. In this config., I was not getting any voltage from X1-X3 to ground or from X2-X4 to ground.

Device technician says that the output that is wired to ballast neutrals should also have been wired to the ground lug and that could have been why I wasn't getting 120V output. I am not sure if I metered X1-X3 and X2-X4 to each other, but I think I did. I have removed the device from service and don't have 480 to test, but I can take the device to appropriate power to test.

Please advise.

 

[iwire]

I am troubleshooting a sign that utilizes a transformer / auto transformer. The main label is destroyed, but the wiring information is still inside the cover.View attachment 9045View attachment 9046

I spoke with a tech at the company that I think made the unit, but he got frustrated with my ignorance. I rarely work with these devices.

I have (2) 277 legs input, so 480V. Sign needs 120VAC output. Prior to me, the device was wired with H2 & H3 joined, H1 joined with (1) 277 leg, and H4 joined with other 277 leg. X1 and X3 were joined and wired to the black wires of the (6) ballasts, and X2 and X4 were joined and wired to the (6) neutrals. (4) ballasts have a max. line curr. of 2.7A, and (2) have a max. of 3.5A, so 17.8A max. current. In this config., I was not getting any voltage from X1-X3 to ground or from X2-X4 to ground.

Device technician says that the output that is wired to ballast neutrals should also have been wired to the ground lug and that could have been why I wasn't getting 120V output. I am not sure if I metered X1-X3 and X2-X4 to each other, but I think I did. I have removed the device from service and don't have 480 to test, but I can take the device to appropriate power to test.

Please advise.

Was the sign working? I assume so due to the current readings.

Tie X2&X4 to ground.

Without the a bond to ground the output has a no refrance to ground and you would not read anything.

Also while that could be wired as an auto transformer it is not. It is simply a step down transformer.

 

[allkindsa]

Thanks, iwire!

It was not working when I arrived, and a different contractor had been in the cabinet attempting to service. They "disappeared", so they called me in.

The supply had a bad 277 leg. Owner had me go ahead and replace all lamps, ballasts, and a few bad HOT12 lamp sockets. A week later their electrical contractor fixed the bad 277 leg, but the sign wouldn't light. I went onsite yesterday and found the scenario I described. I will hook to a 480 source, tie the X2&X4, along with the ballast neutrals, to ground and see if it works.

 

[GoldDigger]

... tie the X2&X4, along with the ballast neutrals, to ground and see if it works.

Some fluorescent and other gas discharge tubes need to see a potential between the electrodes at one end of tube and the metal backing behind the tube for the starting arc to strike correctly, so that may be it. Make sure that the fixture itself is also properly grounded.