Odd issue

[Fred B]

Have a panel replacent that has supply to a low voltage flood alarm system. Have had to run several AFCI as wiring was extended beyond 6 ft, so was double checking existing circuits for potential shared neutrals. While checking found one very puzzling backfeed. A circuit we'll call #7 and the other we'll call #12. Now #12 has a plug in 120/12V transformer to the flood detector panel. When xfer is plugged in I have continuity to #7 neutral but whe unplugged no continuity. Can plug in other loads into #12 and have no continuity to #7, only one that causes issue is the xfer. Not familiar with this alarm system, or its internal wireing, but it does seem to be tied into the house fire/security alarm system as well, but that is powered from an entirely different panel. Now what could be causing this issue? For now told them not to be plugging in the xfer.

 

[ptonsparky]

Some of those liquid level controls use a transformer with secondary bonded to earth, or tank shell. That is then used as one of the conductors for control. Kind of different but works well. It has been awhile since I've worked on one. What control is it? Or is it a home brew?

 

[hillbilly1]

Some of those liquid level controls use a transformer with secondary bonded to earth, or tank shell. That is then used as one of the conductors for control. Kind of different but works well. It has been awhile since I've worked on one. What control is it? Or is it a home brew?

Unless the transformer has gone bad, the grounded secondary is isolated from the primary, so there should be no continuity. The only exception would be if it’s an auto transformer, but that would play havoc with gfi’s.

 

[Fred B]

Some of those liquid level controls use a transformer with secondary bonded to earth, or tank shell. That is then used as one of the conductors for control. Kind of different but works well. It has been awhile since I've worked on one. What control is it? Or is it a home brew?

Don't recall a brand on equipment. Have seen many sensors on basement floor in various locations, not sure if any sensors on specific equipment that maybe associates with #7, it is a 1Pole, point to explore? Did check for continuity between N-G of #7 and no problem. #12 is only panel receptacle and light and goes nowhere else. The odd thing to me that it cause issue on opposite leg of 1Ph panel and no other loads added to #12 replicates problem. Concerned if it is a safety issue, that is deeper than the xfer and the flood panel.
Maybe totally unrelated but is reason panel was replaced, Construction work was being done on home and a masonry saw load caused old panel to literally burn up (sparks and flames), main breaker L1 terminal screw was fused/welded and terminal melted the bakelite on old panel, Dryer breaker was fused to bus on same L1 side of bus, dryer wasn't on or even plugged in at time, no breakers tripped, worker witnessed event and had to run to the main panel to shut off power, that is reason for replacement. Entire dryer branch circuit replaced, panel feeder wire replaced.

 

[Fred B]

Unless the transformer has gone bad, the grounded secondary is isolated from the primary, so there should be no continuity. The only exception would be if it’s an auto transformer, but that would play havoc with gfi’s.

y
Agree the weird thing is that it is not causing a N-G issue on the #12 that its plugged into but a N-L issue on #7. Without it plugged in there is no continuity between L-N or L-G on #7 which is good, but plug it in and get about .130 ohm on #7 L-N. No breakers on just wire testing. With breakers in place and on but main off, no continuity even with xfer plunged in. Really puzzling. Afraid to actually power up xfer.

 

[ptonsparky]

y
Agree the weird thing is that it is not causing a N-G issue on the #12 that its plugged into but a N-L issue on #7. Without it plugged in there is no continuity between L-N or L-G on #7 which is good, but plug it in and get about .130 ohm on #7 L-N. No breakers on just wire testing. With breakers in place and on but main off, no continuity even with xfer plunged in. Really puzzling. Afraid to actually power up xfer.

Turn it on. The worst it can do is not work, burn up, or trip a breaker.