Unique Troubleshooting Outcomes
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.
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.
"...when you have eliminated the impossible, whatever remains, however improbable, must be the truth."
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
RSES CMS, HVAC Electrical Specialist
AOP Forum Rules:
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.
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!
Originally Posted by cjpwalker
Editor-in-Chief, EC&M Magazine
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.
A small-time repair here compared to the large kilowatt equipment I've been into over the years.
While repairing food equipment, I got a call from a nursing home stating that their five well, electric steam table was shocking the dietary staff. This thing was on casters and plugged into a 208vac, 50a, single phase outlet. I'd rewired it years prior, so was antipating moisture intrusion again such as a leak from one of the water wells into its completely enclosed, stainless steel cabinet. Its overall design made it a mess to get into for ANY repair.
Got there, did a sweep with my Fluke VoltAlert on its cabinet - which lit up - so it was crawling with electricity. Popped off all the smallish, round control panels to check the inside wiring & insulation. Dry as a bone and what wiring I could see looked good. To be sure, I ohmed a control wire to ground and it showed much less than infinity - somewhere in the kiloohm range (I tend to always "verify").
So initially, THAT - which is usually instinctive to me, but had eluded me from thoughts in looking for moisture as the cause - CAME to me. "Start from the source." Okay, so once I knew moisture wasn't causing the electrical bridge to ground, I went for that power plug. Disassembled and inspected it. All seemed good...NO...wait...it wasn't. THERE...one, b-a-r-e-l-y visible, itsy-bitsy wire strand sticking out from the ground connection. AND...it ALONE was black as charcoal...AND... it was touching one of the line terminals.
SO...that wire strand wasn't large enough to carry ample current to trip a breaker. Yet, it wasn't a blowout either. It stayed its course once it had overheated and continued carrying electrical potential after that strand had attained its newly converted form - CARBON.
For my curiosity, I brought out the voltmeter and read about 80vac from a properly grounded unit to THIS one. Obviously if you include a person's body into that unintentional circuit, it's just enough to give that person a tingle...
Then I fixed it.
had a call for no cooling. went into attic to check and unit had started running. Since I had seen this before, wnet back downstairs and shut light off.
few minutes later the float switch in pump shut off a/c unit. Turned attic light back on at switch and ppump ran, a/c started. pump outlet was wired off attic light and system would always be running when a tech went upstrs to check on system.
Moving a furnace at a job, helper was in front yard w/threader cutting gas pipe. I was in the back area of house. He called out that threader was not running full speed.
As he demonstrated it running, I looked out the front door to see the proch light would turn on whenever he hit the threader footswitch, and would run half speed.
House had old, ungrounded box, and the neutral from pole had broke loose. When he hit threader switch, line one fed through porch light, back to neutral bar, out to threader and back to line two. 240v on two loads in series.
temporary ground to water line got 110v to threader, then we cut it loose, shut of main breaker and tagged the box.
questions asked, answers received, ignorance abated
This isn't all that complicated but it was confusing and led to multiple call backs.
Call is for no heat on a 90% furnace in a crawl space, the unit is newer and it's a nice install, you drop into the crawl through a trap door in a closet, outlet and switch for lights in the crawl right there when you drop in. Two techs had been there before me all said it checked fine, this was my first heating season as a tech, I drop in turned on the light and all checks great, spend two hours going over it. Next night the on call guy calls me, he's on that furnace, says he can't find anything but wants to know what I noticed when I was there, I think it over and say it seemed like the condensate pump ran for awhile when I dropped in but I didn't find any drain issues, he says the condensate pump was running when he dropped in too, the pump is plugged into the outlet next to the switch, he says he has an idea, he fills the condensate pump until it kicks in, he flips the lights off and the pump goes out, he flips the lights on and the pump comes on. The outlet was turned off and on by the switch as well as the lights.
Unique Troubleshooting Outcomes
207 is 90% of 230. What is actual voltage?
Majority of time its likely nominal.
We had converted a small state ran retirement community to geothermal one winter. I had multiple calls in the morning after they were started up. I would go check them over, all running perfectly. As more units were changed out, we had new calls with the same symptoms, and call backs. Perplexed, we stumbled across the answer. They were on the grid shared with a hospital next door. The 240v service climbed to 260ish voltages in the evenings. The climatemaster units check for under/overvoltage conditions based on the 24v power to the board. We replaced all the 240v transformers with 277v/24v ones and the voltage stayed in a useable range at night.