We're doing a factory dismantle and rewire, and ran into a weird one today. Both electrical rooms have capacitor banks, and all MDP breakers have been de- energized except to the house lighting panel and a few others. Breaker feeding MCC-3 is off and locked out. We have detected voltage intermittently in the feeds to that MCC. Weird voltages too (A-B 200V, A-C 212V, B-C 12V, A-G 278V, B-G 76V, C-G 66V). All downstream switches and breakers are open on MCC-3, voltage persists, so it seems to be coming from the line side in the MDP. Cap bank breaker is open, as well as feed breaker to MCC-3. Levels seem too high for induction. Any other ideas? Also, voltage readings go to zeros for no discernible reason. Literally witnessed it tested at zero, left the site, and my guy called me back to show me the voltage reasons in- person. Where is this backfeed coming from?!?
Ghost voltage in an MCC
- Thread starter dweekly07
- Start date
ptonsparky
Tom
- Occupation
- EC - retired
Use low impedance meters.
A wiggy or solenoid type tester.
Have you inadvertently removed a system bonding jumper at a panel or transformer?
A wiggy or solenoid type tester.
Have you inadvertently removed a system bonding jumper at a panel or transformer?
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Probably a mistapped neutral somewhere. Turn off the panels you still have energized one by one to see if the voltage goes away, then if one panel seems to be the culprit, go through turning off six breakers at a time until a group is found, then narrow it down again. Divide and conquer!
DooWop
Member
- Location
- Corrales NM
- Occupation
- Hvac contractor
I have carried an analog meter for this problem. My ol' Radio Shack about 40 years old.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Does that old meter have a Category rating? I know my old Wiggy did not, so my safety department made me stop using it.
DooWop
Member
- Location
- Corrales NM
- Occupation
- Hvac contractor
I doubt that.
What's the problem with "wiggies"? I never had one. I did have an Amprobe though.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The problem is not genetically wiggies. The issue is being the correct safety category, which often requires fusing.
Last edited:
DooWop
Member
- Location
- Corrales NM
- Occupation
- Hvac contractor
Fussy ain't they....
ptonsparky
Tom
- Occupation
- EC - retired
...until you have had something do a rapid dissassembly within a couple feet of your face, it seems like a minor detail.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I was instructed to dispose of my old Simpson 260 because it didn't have a CAT rating... I took it out of my tool bin at the office, but it's still with me when I have to do some troubleshooting. A couple of years ago we had to downsize our office space and I found a "hidey-hole" where apparently our field service techs stashed their Simpson and Triplett analog meters, along with a number of older Techtronic scopes and an early Fluke scope meter that wasn't CAT III rated. I was instructed to toss them all, I did not.
An old d'Arsonval analog meter is especially useful for confirming voltage measurements on the output of VFDs, because it inherently reads the RMS voltage recreated by the PWM in the same way as the motor does. Digital recreations of this are, I find, less accurate due to harmonics.
A few years ago I left my 1978 vintage Wiggy at a jobsite that was 4+ hours away, asked the guy there to send it to me, he never did. I eventually replaced it but it's now yet another thing I have to keep hidden, because in the case of Inductive Testers (generically), we had to sign a form stating that we would no longer use them. It's an insurance thing. They gave me a Fluke 117 that has a "LoZ" (low impedance) voltage test mode, it seems to be adequate in not picking up stray voltage readings, but I have never compared it to a Wiggy yet. I have to remember to do that some day.
An old d'Arsonval analog meter is especially useful for confirming voltage measurements on the output of VFDs, because it inherently reads the RMS voltage recreated by the PWM in the same way as the motor does. Digital recreations of this are, I find, less accurate due to harmonics.
A few years ago I left my 1978 vintage Wiggy at a jobsite that was 4+ hours away, asked the guy there to send it to me, he never did. I eventually replaced it but it's now yet another thing I have to keep hidden, because in the case of Inductive Testers (generically), we had to sign a form stating that we would no longer use them. It's an insurance thing. They gave me a Fluke 117 that has a "LoZ" (low impedance) voltage test mode, it seems to be adequate in not picking up stray voltage readings, but I have never compared it to a Wiggy yet. I have to remember to do that some day.
Joethemechanic
Senior Member
- Location
- Hazleton Pa
- Occupation
- Electro-Mechanical Technician. Industrial machinery
The one that looked like a Simpson 260? I had one of them, it was a good meter. Damn thing fit about perfect in the Simpson leather case my buddy gave me
DooWop
Member
- Location
- Corrales NM
- Occupation
- Hvac contractor
The SMW local wanted to train service techs. They bought a bunch of tools the techs were going to be trained to use.
One was a Simpson 260. I always wondered who was the guy that bought the Simpson. There were no digital meters
in the tool box.
One was a Simpson 260. I always wondered who was the guy that bought the Simpson. There were no digital meters
in the tool box.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Another thread where the op disappeared!