Zombie neutral still energized?

[gene6]

A 480:280/120 transformer was shut off for removal a few days ago. Some coworkers verified it was off with a fluke, and proceeded to remove the conductors, when they lifted the secondary neutral there was a large spark and the lights flickered (the lights are powered from a different part of the building). They put the neutral back for now, the primary breaker is still off.
What would cause current to flow thru a dead transformer like that?

 

[ptonsparky]

Perhaps the neutral is tied into the other system somewhere. Wouldn't be the first time someone tied all the whites together just because it's easier.

 

[stretch12]

Possibly bad xo bonding at another xformer

 

[LarryFine]

Possibly bad xo bonding at another xformer

That's my first thought. The lighting transformer has been using this transformer's neutral, probably through the building's electrode system, to get back to the utility neutral.

This sounds similar to a house with a bad neutral maintaining voltage balance through the water supply.

 

[hillbilly1]

Perhaps the neutral is tied into the other system somewhere. Wouldn't be the first time someone tied all the whites together just because it's easier.

Exactly what happened. Or they tied to the wrong neutral. Had that happen a lot when changing transformers in big Orange and big Blues.

 

[hillbilly1]

A 480:280/120 transformer was shut off for removal a few days ago. Some coworkers verified it was off with a fluke, and proceeded to remove the conductors, when they lifted the secondary neutral there was a large spark and the lights flickered (the lights are powered from a different part of the building). They put the neutral back for now, the primary breaker is still off.
What would cause current to flow thru a dead transformer like that?

Go through with your amp meter on each neutral with the transformer off, when you find one(s) with current, you have found the mistapped neutral. That is the easy part. If you have a circuit tracer, you can put it in series with that neutral and trace it back to the breaker. No guarantee though that you may fry something. Another way is to turn panel by panel off until the current disappears, then go through breaker by breaker. Then the even harder part, is to find out what doesn’t work, and start checking taps. It is much easier though with a quality circuit tracer.

 

[gene6]

Go through with your amp meter on each neutral with the transformer off, when you find one(s) with current, you have found the mistapped neutral. That is the easy part. If you have a circuit tracer, you can put it in series with that neutral and trace it back to the breaker. No guarantee though that you may fry something. Another way is to turn panel by panel off until the current disappears, then go through breaker by breaker. Then the even harder part, is to find out what doesn’t work, and start checking taps. It is much easier though with a quality circuit tracer.

Great advice thanks everyone, it was a real head scratcher.
I was able to cut the main on the upper floor and the current went away, problem seems to be in a very old gutter where all the neutrals were tied together for both systems.

 

[kwired]

Was working in small town hospital one time, replacing an old (1950 was when building was put up) Frank Adams panelboard with new QO load center. Corridor lights were supposedly on emergency panel in a newer portion of the facility (1970ishconstruction) and they remained on when we killed this panel we were changing. As I was removing items from that panel the corridor lights went off when I lifted one the neutral conductors.

Those lights were that way for 35-40 years - ungrounded conductor from an emergency panel and grounded conductor from a normal power panel. had to straighten that out in the process.