Shuntme
Member
- Location
- San Diego California
- Occupation
- Instrument Control Tech
Lost 120Vac (15A brK Electrical panel) for my IOC cabinet #1. 24Vdc UPS. 120Vac power in through a LAS(surge suppressor) 15A(internal fuse). Lost the IOC as the UPS drained out(2hrs), 15A breaker(panel) did not trip. Had 120V in for the LAS unit but no 120V out. Quick fix was pigtailed a 120V to my 24Vdc power supply to power the IOC get plc and scada back up and running for Operations.
Troubleshooting Vac power: LAS unit was mounted upside down in the cabinet and tight to the bottom. Did not see the pop out 15A internal fuse until unit was removed - Fuse was blown. Tested in/out terminals and no indications of any shorts. With the LAS unit out and 15A panel breaker off I tested hot to neutral and got 67V. Hot to ground 48V and neutral to ground 117V.
Used a LoZ meter the 67V and 48V went away but the 117V neutral to ground was still there. Turned breaker on, 117V hot /neutral, but 117V neutral/Gnd still present.
Reinstalled LAS unit with new fuse(15A) but isolated the plc 24Vdc controls section so it's still running off the pigtail(120V) to DC power supply only.
Smoked the LAS unit immediately.
Weird scenarios:
1. The LAS unit smoked but internal 15A fuse(LAS) for IOC cabinet #1 did not blow and the 15A panel breaker did not trip.
2. My other IOC cabinet #2(exact duplicate but 30ft away) lost its 120V power and went on UPS power for 1hr. I caught it before it shut the operation down. This IOC is on it's own separate 15A breaker but on the same leg in the electrical panel. Replaced the LAS unit(spare) and 120V power was restored right away. However checking this LAS unit the 15A internal fuse was blown and the 15A panel breaker did not trip.
- Do I have a broken neutral in IOC #1 ?
- Why did the 15A LAS internal fuse in IOC #1 did not blow and the panel breaker did not trip ?
- Why did the fault in IOC #1 cause the LAS fuse in IOC to blow ?
Troubleshooting Vac power: LAS unit was mounted upside down in the cabinet and tight to the bottom. Did not see the pop out 15A internal fuse until unit was removed - Fuse was blown. Tested in/out terminals and no indications of any shorts. With the LAS unit out and 15A panel breaker off I tested hot to neutral and got 67V. Hot to ground 48V and neutral to ground 117V.
Used a LoZ meter the 67V and 48V went away but the 117V neutral to ground was still there. Turned breaker on, 117V hot /neutral, but 117V neutral/Gnd still present.
Reinstalled LAS unit with new fuse(15A) but isolated the plc 24Vdc controls section so it's still running off the pigtail(120V) to DC power supply only.
Smoked the LAS unit immediately.
Weird scenarios:
1. The LAS unit smoked but internal 15A fuse(LAS) for IOC cabinet #1 did not blow and the 15A panel breaker did not trip.
2. My other IOC cabinet #2(exact duplicate but 30ft away) lost its 120V power and went on UPS power for 1hr. I caught it before it shut the operation down. This IOC is on it's own separate 15A breaker but on the same leg in the electrical panel. Replaced the LAS unit(spare) and 120V power was restored right away. However checking this LAS unit the 15A internal fuse was blown and the 15A panel breaker did not trip.
- Do I have a broken neutral in IOC #1 ?
- Why did the 15A LAS internal fuse in IOC #1 did not blow and the panel breaker did not trip ?
- Why did the fault in IOC #1 cause the LAS fuse in IOC to blow ?
