Troubleshooting

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chris1971 said:
What was the most puzzling electrical troubleshooting that you ever encountered?
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A home with buried boxes in the block walls and under the plaster ceilings the owner said his brother in law was a maint electrician and did all the wiring when he built the house. They had a dozen different EC's try to find problems, and they all walked off the job, when we got there, we used tone generators and receivers to follow the cable and circuit paths.
 
Guy did all of his own rough in and when they turned it on they had all kinds of shorts, I worked on it for two days and every time I thought I had it cleared, one last breaker would pop as soon as I turned it on.

Told the guy I would have to come back again, but still wasn't sure if I could find it, about 3:00 AM I sat bolt upright in bed and thought, got it.

I had listened to him when he explained what had happened when they turned on the power, but it didn't really click what he said, until I remembered that he had mentioned something about the dishwasher making a funny noise and going off. Disconnected the dishwasher and cleared the last problem. He had fried the motor on the brand new dishwasher.

Might not have been the most puzzling one, but it was the one that took me the longest to fix.:roll:
 
What brand of tone generator? That sounds like a challenging trouble call. I had one where the finished basement receptacles had an open ground. A few hours latter I traced the open ground to two buried boxes in a finished sheetrock wall. Not quite as bad as you call.
 
I was troubleshooting a high speed production machine. It had an old Modi-con PLC. The machine kept stopping at a certain point. I was looking at all the input and output lights on the PLC, (I did not have the sofware to look at the program with a laptop) I was comparing them to the program on paper trying to figure out what was going on. I saw an output that was not coming on. So I backed up one more rung in the program to see what the PLC was waiting for. All conditions were met,,,,scsratching my head?? What is it waiting for?? I double check again, the machine has recieved all inputs it needs to proceed, but will not. Scratching my head again??? What the heck??It turned out, I was right, the machine did have all inputs needed, in fact it WAS proceeding to the next output rung,,,,,but the problem was, with a Modi-con PLC, the output light uses the NEUTRAL of the load to light up the light. So I had an output with 120 volts on it, but because it was terminated to a solenoid valve, that had an OPEN COIL, the output light would not light up. That really fooled me, It took me a long time to realize that the output was there, but it would not light up do to an open coil, therefore, no neutral. It all made sense in the end, but for a while, it was whipping on me.
 
I dodged my hardest one. A customer called for an exterior GFCI
receptacle that wasn't working. Sounded easy. Before I went, he called back. His wife had reminded him that the exterior receptacle was controlled by a light switch in the house (something they thought they needed when they built the house, in case they wanted to turn christmas lights on and off).

I don't know how long it would have taken, but there sure would have been a lot of other boxes & etc. took apart before I would have started checking light switches.
 
I've been on a few calls where I go in and reset a GFCI. Those are real tough especially when they ask you how much for the service call.
 
277/480 HVAC only getting almost, but not quite ~120/240.... (like 100v each leg) Tracking down the circuit took forever, and turned out that someone repurposed a panel, and didn't change the unit or relocate the circuit - just refed it as 120/240 from a different transformer - because there were no other 120's left... Go figure there would be no 3 poles left in the 277/480 panel left either. Because it got loaded with all the others the guy who did it moved over - except this one... I spend days looking for a 277/480 circuit through conduits and gutters through a whole building, but didn't bother looking in a 120/240 panel for it... However the result was correcting the lack of circuits with a new transformer and panel...
 
Had a run i needed the last part off. Turned it off went and disconneted the splice and turned back on. Both parts were still hot. After a hour or two of looking around i found a hidden box that was the home run that was then run to two different boxes of the same ciruit creating a giant loop of power. I thought i was going crazy.
 
digging up pvc boxes buried at random in a yard. opening them up to find all the wires coated in black goo.
 
Old ansil system can be a pita when fire marshal tests and kitchen equipment stays on.
Once had a rooftop disconnect with line load reversed. Got a suprise when I tried to pull out the fuses. Should of used testers first.
Any problem with parking lot lights usually turns into an all day adventure.
 
T-Shooting Challenge

T-Shooting Challenge

chris1971 said:
What was the most puzzling electrical troubleshooting that you ever encountered?
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This was part of another thread. Do a search for VFD FRIED to read the complete thread. Also, see attached incident report & pix.

Tony


Originally Posted by Jraef
The chances of "programming related" component failures all happening at the same exact time in 4 different drives in 2 different sites is astronomically small. All evidence points to an event of some sort.

Something I just saw recently that I never saw before was a VFD failure like that where there was a packaged piece of equipment on rubber vibration isolators that was properly grounded when originally installed, but some time in the last year or so (when this was happening a lot), someone stole the EGC. So the packaged equipment had been "floating" for who knows how long and an overhead cable fell across it. VFD transistors are an easy place for energy to transfer and once it happens, everything blows.

Were your chillers on a packaged air handler? Did you check the integrity of the ground connection? Ground conductors on rooftop air handlers were easy targets for copper thieves because nobody could see them cutting wires up there. A passing storm could have discharged onto framework attached to them, and the lack of a ground path would make the transistors an easy target.

I tend to agree with Jraef. Any simultaneous failures I have seen are almost always related to an overvoltage condition. One thing to consider here is the phenomenon of the restriking ground on an ungrounded or HRG system.
Even though the VFDs may be fed from a Y transformer with a grounded neutral, if they are at a great distance from the supply transformer then it could act like a HRG system. A restricking (intermittent) ground can cause the phase voltages on this system to rise sharply and puncture winding insulation in transformers, circuit boards & motors. This is exactly what happened several years back on the shuttle train project I was on at SFO airport (see attached root cause analysis report.)
A loose traction motor brush was touching ground on a HRG system while the train ran on the track and caused the ground detection control transformers to fail and trip the smoke alarms in all 5 substations at the same time.

I would go thru the grounding system with a fine tooth comb and look for
cut wires or loose connections. Good luck.
Attached Thumbnail pix
Attached Files KMurthy_Multiple Failures Root Cause Analysis.doc (81.0 KB, 6 views)

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LarryFine said:
What's a VCR? :confused:
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VO-1600_005.jpg
 
One that took me a while to find was a "rouge ground" caused by a loose connection that caused a few HMI screens to burn out. It was seeking 24vdc through a serial connection instead of the actual power leads.

PS; VCR= Voltage Current and Resistance :roll:
 
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