Unique Troubleshooting Outcomes

[meby]

Does anyone have any unusual or unique electrical troubleshooting stories they'd like to share with the group. If I get enough material from this post, I'll turn it into an article and share it with my readers.

[wolfdog]

I had a process chiller for a CNC turret punch press that would act up on second shift. An un-airconditioned factory and Texas summer so the usual things were assumed and checked. Dirty coil, charge etc. Same problem. The location is About an hour drive North of Dallas so not quick or convenient to go look at.
Made 2 more trips and checked EVERYTHING........ GPM,SH,SC....everything I could think of. No problems. Started looking for dumb stuff. Started bumping the controls and control panel with a screwdriver handle. Got a trip when I hit the temp controller. It has a relay for high water temperature lock out. High water temperature is protected another way so this is a redundant protection. Jumpered it and wait a couple of days . No more trips. Order a new controller and replace it. Ask some questions and found they had a 150 ton press that the only ran second shift because it was too disturbing to the office staff. That explains the big vibration that tripped the weak control ...ONLY ...on second shift.

[timebuilder]

Great job.

"...when you have eliminated the impossible, whatever remains, however improbable, must be the truth."

[22nomo]

I have had several near arguements with electricians and one VFD factory start-up guy twice. They all kept telling me the motors (pumps and fans) were the cause of breakers and starter overloads tripping. After ohming then megging the motors and finding no problems I put the problem back on them. In all these years of using a megger I have yet to lose a battle (knocks on wood) about the problem being the motor or on the supply power side and some of them have gotten fairly heated, once to the point I pulled the new starter off one 60 hp pump and switched it with the older but same starter for second pump. The next day the second pump started tripping the overload and this was only using a 500v model before buying a 1000v.

Meggers are worth their wait in gold, I have found motors that ohmed out good but megged out bad. Buy a good one then learn how, when and where to use it.

[cjpwalker]

I had a no heat call at a 7-11. I showed up 5:30 or so in the evening, two trane package heat pumps on the roof purring away, store is at temp. New DDC controls were recently installed, everything is remote controlled off-site, but working.

They called back the next day, same thing. Again, I show up and no problems. Must be an issue with the new controls - setpoints, programming, something... They're closed, so I'll come back during business hrs.

Come back the next day and everything is dead. Power to both units, but no call for heat, fan, anything. Get off the roof, and find the new control panel - dark. No power. I start chasing conduit and eventually find that the genius contractor ran power for the new control board from the outdoor lighting circuit. This is the first time I had been there during daylight. A piece of electrical tape on the photocell and everything comes back to life until Sparky can get back on site to find a more consistent power source.

[meby]

I had a no heat call at a 7-11. I showed up 5:30 or so in the evening, two trane package heat pumps on the roof purring away, store is at temp. New DDC controls were recently installed, everything is remote controlled off-site, but working.

They called back the next day, same thing. Again, I show up and no problems. Must be an issue with the new controls - setpoints, programming, something... They're closed, so I'll come back during business hrs.

Come back the next day and everything is dead. Power to both units, but no call for heat, fan, anything. Get off the roof, and find the new control panel - dark. No power. I start chasing conduit and eventually find that the genius contractor ran power for the new control board from the outdoor lighting circuit. This is the first time I had been there during daylight. A piece of electrical tape on the photocell and everything comes back to life until Sparky can get back on site to find a more consistent power source.

Now that's an interesting story worth sharing. Thanks!

[D1DR]

When i was a young apprentice i got dispatched to a church that had volunteers making food 3 days a week for a fund raiser. Their commercial kitchen exhaust fan had stopped working. I opened the fan found a open winding in the motor. The fan had a list of replacement motors on the name plate so I called the wholesaler and started from the top, first one he had in stock i picked up (GE). Installed the motor and it was drawing high amps. it was a 120/208/230V motor rated about 10 amps for 230V. I was drawing 11-12 and after a while it tripped on thermal over load. I though well this fan Has been miss wound from the factory, so I took it back and replace the motor again, same thing 11-12 amps. Now I test my voltage and find its 248 High but not crazy high. I remove the belt and the fan still draws over rated amps. I take it back to the wholesaler and we put it on the bench there and it draws below rated amps. Now I'm really confused and get a another motor, and same problem. At this point i am pulling my hair out and have checked that i have wired for correct voltage had my journeyman come out and we can't get this thing working. Finally I go down the list of motors to the next available one, put it in amps are great and never had a call back after that.

At the wholesaler when we talked later I found out they are 208 3Ph supply so the single phase I was testing there was 208 and so lower voltage supply means lower amps (if resistance is fixed). turns out even though the GE factory said that my 248V supply on site shouldn't be a problem for their motors this one model wasn't really rated for what the name plate said it was rated for. I even took this motor around with me in the truck and when I was at a building with measured 230V I connected it and it was still over amps just barely.

I don't think I have ever learned as much from any other single service call as this one. This whole process played out over a few weeks.