JohnCalderwood
Member
Reading these recent ones reminds me of similar ones...
Working at my first commissioning job in a new factory, I was learning off the electrical contractor's technician. Dealing with Starkstrom VFDs, and yes he was measuring 4-20mA initially then went to measure the output voltage, and BANG went the Fluke meter. Thankfully I was standing a bit away from him, but he was not injured. Lesson learned - check the leads....
Same factory, few years later, once I had my feet under the table. I had been on call only a few times, and asked to come out to have a look see, as some analog values were not reading correctly from a PLC5 1771 remote rack. Out I came at 1 in the morning, discussed the issue with the shift tech, then got my meter etc and a torch. Up to the panel, looked at 16 slots of 1771-IFE analog cards - they all appeared to be indicating correctly, but readings were not right on any the channels. Looked around the panel, saw an open-case 24V DC power supply, went to measure it, and it seemed OK at 24V DC, but was not steady. So, isolate and disconnect to check on no-load. Isolated, then went to remove wires. Got a flash and a belt off the output wiring as I was trying to remove it. Better check the isolation again. Yes it was off, so no 24V DC. changed my meter to AC, measured a not steady 400V AC on the DC output.
Cannae remember all the detail, as I was still a bit dazed from the 400V belt I had got. The shift tech was concerned for me too...he still thinks he tried to kill me that night.
Upshot was that a Danfoss Oil Filled VFD had been replaced that dayshift, and it had a faulty 4-20mA card, such that the rectified voltage had somehow found its way back through the analogue lines and not blown the 24V Dc power supply, but had fried all the Analog Input cards on the rack.
We did not have enough spares, neither did Allen Bradley, so took a couple of days to get the parts shipped to us and get the line back up and running.
Thankfully we started phasing out the Danfoss Oil-Filled VFDs after that...
Working at my first commissioning job in a new factory, I was learning off the electrical contractor's technician. Dealing with Starkstrom VFDs, and yes he was measuring 4-20mA initially then went to measure the output voltage, and BANG went the Fluke meter. Thankfully I was standing a bit away from him, but he was not injured. Lesson learned - check the leads....
Same factory, few years later, once I had my feet under the table. I had been on call only a few times, and asked to come out to have a look see, as some analog values were not reading correctly from a PLC5 1771 remote rack. Out I came at 1 in the morning, discussed the issue with the shift tech, then got my meter etc and a torch. Up to the panel, looked at 16 slots of 1771-IFE analog cards - they all appeared to be indicating correctly, but readings were not right on any the channels. Looked around the panel, saw an open-case 24V DC power supply, went to measure it, and it seemed OK at 24V DC, but was not steady. So, isolate and disconnect to check on no-load. Isolated, then went to remove wires. Got a flash and a belt off the output wiring as I was trying to remove it. Better check the isolation again. Yes it was off, so no 24V DC. changed my meter to AC, measured a not steady 400V AC on the DC output.
Cannae remember all the detail, as I was still a bit dazed from the 400V belt I had got. The shift tech was concerned for me too...he still thinks he tried to kill me that night.
Upshot was that a Danfoss Oil Filled VFD had been replaced that dayshift, and it had a faulty 4-20mA card, such that the rectified voltage had somehow found its way back through the analogue lines and not blown the 24V Dc power supply, but had fried all the Analog Input cards on the rack.
We did not have enough spares, neither did Allen Bradley, so took a couple of days to get the parts shipped to us and get the line back up and running.
Thankfully we started phasing out the Danfoss Oil-Filled VFDs after that...
lol
