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Discussion Starter · #1 ·
We have been using a 277vac to 120vac transformer from one leg of a 3 Phase system to supply power at a light pole to our equipment. Basically, the neutral comes from a nearby Christy Box -- where the neutral for the lighting system is...one leg (277vac....actually 293vac) to the pole lights supplies the hot,

What this does is supplies the power to our 12 and 24vdc equipment via a 277 to 120 step down that is wired to an outlet. From there it's a power strip where 120vac to 12vdc and 24vdc transformers plug in. During the day, the entire system (low volt) runs off our UPS batteries, at night, the lighting electrical comes on, which then powers the system and recharges the batteries.

I was informed, today, that six weeks ago the system went down. The batteries were replaced, but only lasted 3 days because they weren't being re-charged.

I go out there today, and, find the system dead, power from the batteries (now down to 9volts from 12volts). At first I thought it was the transformer. Tested wiring coming in: 293volts. Connect to the transformer---goes down to 143volts-----with 68 volts coming out ----should be 120vac---down from 277.

Replaced the transformer----same problem. Disconnect incoming from the trans---goes back up from 143vac supply side to 293vac. Now, I am suspecting the supply side neutral has a problem ---it is connected to the supply side 277vac and Neutral wiring.

I have tested resistance on both the new and old transformers...and they test fine--7.5ohms supply---3.1ohms load.

My wiring from the supply neutral to the transformer is fine, no issues.

The fact is, this set up work perfectly for 2.5 years, now suddenly, it doesn't. To me, something changed 6 weeks ago in the lighting system wiring ---277vac 3 phase---and now we have a problematic neutral.

Does anyone with more experience have any thoughts on this?? What am I missing ?

PS: this is a commercial 3 phase 277vac parking lot lighting system with poles wired in series/parallel, the neutral is at one end of the system.
 

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bad connection on the neutral side?
measure the 277 supply voltage without load and with load.
 

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Discussion Starter · #4 ·
bad connection on the neutral side?
measure the 277 supply voltage without load and with load.
There may be a bad connection somewhere on the neutral in their wiring system.

293 volts with no load, 168 volts with load ----load being the transformer with neutral attached....all supply lines are 293 with no load ----measured back at the in-line fuses.

Like I said before....the system worked fine for over two years...now there are problems.

I tested the resistance on the old transformer and there are no problems.
 

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There may be a bad connection somewhere on the neutral in their wiring system.

293 volts with no load, 168 volts with load ----load being the transformer with neutral attached....all supply lines are 293 with no load ----measured back at the in-line fuses.

Like I said before....the system worked fine for over two years...now there are problems.

I tested the resistance on the old transformer and there are no problems.
Loose connection, perhaps the neutral feeds thru another device?
 
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