School lights, engineering Q

[sw_ross]

Working at a lighting upgrade at the school today. System voltage was 120/208. Gym had 5 rows of 3 fixtures, setup as 5 circuits (3 lights per circuit). The existing lights were 6-lamp, T8's. Not sure if they were original or not. School was built in mid-80's.

When upgraded fixtures to led lamps (kept fixtures, just upgraded lamps and bypassed ballast), the lamps wouldn't come on. Checked voltage at fixture and got 295v. I knew they were fed off a 120v circuit in panel so I figured something was up.

Eventually found this site constructed enclosure containing 15 xfmr's/ballast, 1 for each fixture. Each one was basically a ballast (choose lead for input voltage, output was labeled lamp, and there was a capacitor also).




Why would they engineer this setup? The panel and xfmr's is adjacent to gym so don't think vd is an issue.
The existing lights that were fed by these worked fine. They also would've worked fine on 120v (we tested some of them before converting them).

This setup seems like a waste of money for the existing lights that were there when I showed up. I'm assuming there was a different type of fixture there previously that needed these ballasts and when they upgraded they didn't bother to change the setup?

Other lights in gym, and throughout school were all 120.


We ended up bypassing these xfmr's and running the lights on 120.
Just curious.


Also, didn't realize that when label (on LED lamp) says 120-277v it means it! 295v was too high.

 

[sameguy]

How is a t8 going to work on 120v, what you have is a remote ballast setup, done it many times.
The t8 needs the higher voltage to start the lamp, it's remote to make the fixture easier to work on, lower the fixture weight, reduce sound, heat, reduced fixture size.

 

[kwired]

Look harder at information on those ballast's to see if you can tell what they actually are.

My guess is original lighting was metal halide and those were remote ballasts for them. Whoever upgraded to T8's never even thought about removing them, yet volt output must have been in the correct range and the T8's worked. Mentioned capacitor also tells me this is likely a MH ballast. Probably 16 mfd if they were 400 watt lamps.

 

[Montana1987]

The t8 needs the higher voltage to start the lamp, it's remote to make the fixture easier to work on, lower the fixture weight, reduce sound, heat, reduced fixture size.

 

[Little Bill]

Two year old thread