Light poles connected in series?

[tortuga]

Here is one to chomp on after you finish your Turkey,
an interesting service call yesterday;
After replacement of 400W MH with LED a few Parking lot lights were dim and in different patterns each time the contactor was engaged.

After many hours of swapping lights, getting new lights and who knows how much troubleshooting we get called in to help.

The lighting contractor did not change any wiring at the pole bases.

There are two wires that go up each pole to the light heads so there is no chance the lighting contractor messed up anything.




I found two groups of two poles to be wired in series!

That is light pole 1 and 2 connected in parallel and pole 3 and 4 connected in parallel, however the two groups were connected in series to a two wire 208V supply (off a 208Y120 panel).




The connections were old and obviously unchanged from many decades ago.

How could this have worked fine for decades?

 

[LarryFine]

Theoretically makes sense.

Solution: rewire all in parallel for 120v, making one of the supply wires a neutral.

 

[tortuga]

After we figured it out it was a simple fix in pole 3 and they all run fine on 208 now. It just boggled me that these lights have worked since I presume the late 70's on magnetic HID ballasts until the LED's were installed. I did not get to see the how the old ballasts were connected I imagine they must have used the 120V leads to get them to work.

 

[kwired]

I did not check out your math, but you apparently figured out there is ~104 volts across each fixture that would be near enough to low tolerance for it to work if connected to the 120 volt supply tap.

Would likely present significant difference to affect the others if one lamp fails.