Troubleshooting

[masterinbama]

Had a raw water pump that would shut down on it's own in the middle of the night. It was at a remote site on the river. Controls were via an Allen Bradley PLC coupled to the main plant via RTU's. Tried to duplicate anything I could think of that would cause this problem but I never could duplicate it. Come to find out that the RTU frequency was very close to the lock master's at the Dam 17 miles up river. Had one tug captain that would call as soon as he passed the channel marker in front of the pump station. As soon as he keyed his radio it would make the PLC think it had received a stop command from the main plant. Changed frequencies and the problem was solved.

 

[jimmyglen]

any PLC call would be my nightmare

 

[btharmy]

This very subject came up prior to taking my Journeyman's exam. My 5th yr instructor reminded us there is always a solution no matter how strange. He was on a call to a grocery store chain where patrons had complained of being shocked by one particular freezer display. He proceeded to tear the thing apart from top to bottom. Checked all grounds, no frayed or damaged wires. All connections were good. He was stumped. As he was packing up his tools he turned around in time to see a woman jump back from the freezer case. After a short Q&A session with her he pulls his wiggys from his pouch and reads more than 50v to ground from the middle of the glass in the door. The woman was shocked on the nose as she peered through the glass while opening the door. There was apparently some sort of conductive film laminated to the glass to prevent frost, which had malfunctioned. Who would have checked for voltage on the glass? Not me...... Well now I will, of course.

 

[hardworkingstiff]

an anger call

an anger call

Me and another electrician that worked under my supervision were wiring a service station that our competitor would wind up starting up the equipment. This was back in the 80's when those yellow shaded glasses were the craze. He was wearing them and I specifically told him to not wear them while he was terminating wiring.

The "other" company was starting up the equipment and called in to our shop that one of the submerged pumps was not working. I got the call to go check it out. I found the ground terminated to a motor lead and one of the hots terminated to the ground screw. It turns out he didn't take off those glasses and the colors looked goofy.

The tanks were fiberglass, the conduit was PVC except the ends as allowed by 514.8 exception 2. So everytime the pump was called to work, 110-volts went to the 240-volt pump and 110-volts went to the pump housing.

 

[MisterCMK]

Adressable fire alarm that had a detector somewhere on the loop that would randomly go into alarm and it would also occasionally short the data loop. When the detector went into alarm it would come in as a different detector and there was no indication of which one was in alarm.

 

[Houston]

I had a guy call me out because he kept gettin shocked in the shower. I go out thinkin bad neutral on the service end. Everything was fine there. I checked for power at the showers handle to ground nothing. Checked power from handle to drain 10 volts. Shut off all power to the house. Still voltage. Whenever the water was on voltage wasnt there. The bathroom was a renovation contractor couldnt be found. I deemed the problem a difference in potential issue. I couldnt really confirm but when I ran a wire to the main ground bar in panel,shower handle, and the drain voltage went away. I told him we will have to run a wire to the drain under the house to connect it to the main grounding system. He never called back. Really expensive. Must not have hurt that bad. What do you guys think? About that issue.

 

[cowboyjwc]

This very subject came up prior to taking my Journeyman's exam. My 5th yr instructor reminded us there is always a solution no matter how strange. He was on a call to a grocery store chain where patrons had complained of being shocked by one particular freezer display. He proceeded to tear the thing apart from top to bottom. Checked all grounds, no frayed or damaged wires. All connections were good. He was stumped. As he was packing up his tools he turned around in time to see a woman jump back from the freezer case. After a short Q&A session with her he pulls his wiggys from his pouch and reads more than 50v to ground from the middle of the glass in the door. The woman was shocked on the nose as she peered through the glass while opening the door. There was apparently some sort of conductive film laminated to the glass to prevent frost, which had malfunctioned. Who would have checked for voltage on the glass? Not me...... Well now I will, of course.

I thought this was the same issue we had on a new store here. Got a call from a lady saying that she keeps getting shocked off of the produce cases and nobody is doing anything. I went over to the store and talked to the manager and was told that the electricians had been out there several times and could find nothing wrong. Turns out that between the fancy flooring they used and the shopping carts, it was building up a static charge. They put some straps on the carts that drug on the ground and it cleared up the problem.

 

[RICK NAPIER]

This is going back over thirty years. An apartment kept getting a dead short in the middle of the night. We would show up durring the day and everything tested fine and opened everything up and it looked fine. The problem persisted. We asked the gentleman to walk us through everything he does prior to going to bed. Nothing. He then said he didnt know what his friend does. It turned out he had a friend staying with him. We had him show us his night time routine and we discover a hidden murphy bed behind bookselves. When the murhy bed was put in they built it around an existing BX cable that was now getting pinched in the frame when the bed was opened and with the resistance in the armored cable taking hours to overheat the breaker witch was why it was happening when everyone was asleep.

 

[LarryFine]

. . . we discover a hidden murphy bed . . .

Murphy's Law strikes again!

 

[gar]

091222-2257 EST

About 8 January 1951 I went on board the USS Wisconsin BB-64 in dry-dock at the Portsmouth, VA, Naval Shipyard. The cocoons had just been removed.

In the fall of 51 we became the flagship of the 7th Fleet in Korea under the command of Vice Admiral Harold. M. Martin. One day while operating north of the battle-line, are usual location, the main search radar failed. It was my job to fix it. This radar was used for navigation as well as monitoring what was around us.

The high power transmitter, a magnetron, and the thyratron that controlled power to the magnetron was very near the top of the superstructure, about 150 ft above the waterline. Also the power supply for the transmitter was at this level. The control circuitry for an unknown reason, and obviously the displays, were in the CIC room within the armor plate shell that housed critical parts of the ship. The CIC room was probably about the waterline.

Various measurements were made. The thyratron was burned out. Replaced it, powered up, and that one also failed. Studied the manual to try to figure out why. We were under pressure to get it working. Checked more parts and everything seemed OK. Had a scope setup to monitor the pulse width, but this was very much a single shot event for the occurrence of the failure. No memory scopes at that time. Tried another thyratron and it failed. This exhausted our supply of spare thyratrons. Now checked the ships with us for spare thyratrons. Found one, and had it transferred to us.

Now we were down to one last try. Note we had a 150 ft or more of vertical travel up and down to work on the equipment. In the CIC room there was a single-shot multivibrator that controlled the pulse width. There was nothing in the manual on pulse width except what it should be set to. It could not be adjusted and observed without the entire system running. There was no indication in the manual that the adjustment range was such that the pulse width adjustment range could allow operation that would cause component failure.

I made the guess that if the pulse width was too long this might be the cause of the problem. Set the pot for minimum pulse width. Tried one more time and no burnout. Now it was possible to adjust to the correct pulse width.

Why wasn't this tried earlier. Had no real idea of what the problem was, and one does not make changes in a complex system without a good reason. You can really mess things up that way.

So the problem was that the pulse was probably set too long and vibration and other variables moved it to a longer value and then failure. This may have never been reset since 1944 when the ship was first commissioned.

An interesting condition is that if a ship such as this goes into the Brooklyn Naval Shipyard it is necessary to remove the top part of the structure to clear under the Brooklyn Bridge, 135 feet.

.

 

[LarryFine]

Had no real idea of what the problem was, and one does not make changes in a complex system without a good reason. You can really mess things up that way.

You also should only make a single change between tests when troubleshooting, or you'll never be sure what the problem was.

 

[masterinbama]

You also should only make a single change between tests when troubleshooting, or you'll never be sure what the problem was.

I love it when the in house electricians take something completely apart, and then when they realize they are stumped the call me.

 

[mtfallsmikey]

Doing a (almost) complete rewire of a Traulsen commercial over/under freezer/fridge. It set idle for 2 yrs., all the stranded wire was corroded, had low voltage everywhere, and all switch functions/ thermostats were done on the neutral side.

 

[RichB]

Foam on the Flight Deck

Foam on the Flight Deck

While assigned to the USS Kitty Hawk back in the late70's we had a problem with our foam system just deciding to start up and soak the flight deck in foam. We had motor operated butterfly valves that when they opened the firefighting system automatically lit off and put foam to the flight deck. We fought this for about a year and a half that I know of, till one day we were replacing an operator motor. As I was stripping wire(22gauge control wiring) with that wire stripper between the front teeth--I got a pretty good tingle to the tongue. Looked in my tool bag and yup, the fuses and fuse blocks were still there. Hmm me thinks, must have just poked myself with the wire, tried again and zap!!.

Told my partner and he said I was crazy, after he looked and saw the fuses. Made him try it and zap> Told ya so. Went and check trhe breaker--still off, but we had 120VAC according to our wiggie nd a Simpson 260.

About 6 months later in the shipyard in Bremerton, while replacing the butterfly valves and controls with solenoid valves one of the civilian yardbirds gets shocked. All work stops and we go check fuses/breakers. All off and/or removed--then one of the opd timers says "watch this." Takes a 3 watt lamp out of his flashlight and hooks it across the leads and the power disappears.

The problem--since we ran an ungrounded system amd no conduit and the wiring ran hundreds of feet all over the ship and along side some 400 Hz even--Yep--you guessed it--Induced Voltage

 

[LarryFine]

It ain't dead until it's grounded.

 

[hockeyoligist2]

A stairwell light, the switch for it was two levels above, coming off of the circuit for the lights on that level.....

 

[peter d]

digging up pvc boxes buried at random in a yard. opening them up to find all the wires coated in black goo.

 

[LarryFine]

It ain't that funny. :roll: ()

 

[czars]

Newest Mystery

Newest Mystery

A lady called me yesterday and said that all the lights in her bedroom were out, the ceiling fan didn't work and the TV didn't work. I went over there and sure enough, she was right ? all the lights in her bedroom were out, at least on one circuit. I asked her what happened just before the lights went out and she said all the power in the house flickered and then the lights went out. The Lakes of Melbourne area has been having a lot of short-term power outages lately, so her description wasn't unusual. This lady has a real problem too because she is wheelchair bound while recovering from two broken ankles and her husband has severe Alzheimer's disease and does a lot of unpredictable things.

I opened the circuit breaker panel door and saw that the panel had the circuits marked. However, as it turned out, they were all marked wrong. Never mind. I saw a tripped 15 amp breaker and reset it. Wallah ? all the lights came one and the TV worked. I looked at all the receptacles in the bedroom and saw one with an extension cord plugged in and the cord was running under the desk leg. Thinking that the cord might have been crushed, I extracted the cord from the desk leg and it looked OK, probably because it was embedded in the carpet rather than being crushed. I couldn't find anything else obviously wrong, so I left her with a reset breaker, charged her nothing, and left.

She called me today and told me that the lights were out again, but that there was no flicker before they went out this time.

I went over there and the same breaker was tripped. When I reset it, it immediately tripped again. Great! I might stand a chance of finding the problem if it still exists. Again I asked her what happened just before the lights went out or what was different from when I left yesterday. She couldn't remember anything, so I started looking.

I removed the wire from the breaker and sure enough, I measured about 2 ohms to neutral, a nice solid short. Well, I started looking by going to each receptacle on the circuit in the master bedroom to see what was plugged in. I found nothing that looked unusual in the master bedroom, so I unplugged some things from the first receptacle and the short remained. Then I unplugged some things from the second receptacle and the short remained. Then I unplugged two cords (clock, power bed power) from the third receptacle. When I went back to the circuit breaker panel to look at my ohm meter, the short was gone. Ah-hah. I took my meter back to the cords that I had unplugged and checked each one. NO SHORTs. Must be in the receptacle. However, the receptacle is behind a very heavy power operated bed and I couldn't move the bed. I plugged my test light into the receptacle and reconnected the wire to the breaker and turned it on. Everything was OK. NO SHORT. I wiggled my test light in the receptacle and nothing bad happened. Now what?? I removed the test light and plugged in the bed and clock and all was OK. NO SHORT! What is going on?? All I did was remove two plugs, the short went away and the plugs weren?t shorted. I replaced the plugs and now the short is still GONE!

Well, I gave up in the master bedroom and moved to the adjacent bedroom. That bedroom also had several receptacles and a closet light on the same circuit. I checked two receptacles with the power ON and all seemed OK. Then I set the switch by the door to ON and the BREAKER BLEW. Hurrah!! I set the switch to OFF and reset the breaker and all was OK. I set the switch back to ON and the breaker blew. GREAT!! I turned the switch OFF and reset the breaker. Now I was getting somewhere.

I asked what the switch controlled and the lady said it controlled the light on the bed table. There was an extension cord plugged into the receptacle and it went to the light. I unplugged the extension cord from the receptacle and turned on the switch. The breaker didn't blow ? all was OK. I ohmed the end of the cord and sure enough the resistance was about 2 ohms. I unplugged the extension cord from the light cord and the extension cord was OK. I ohmed the light cord plug and that was OK too. I turned the light switch ON and still no short. WHAT'S GOING ON???

I removed the light bulb and noticed that the socket was a 3-way socket, however the light bulb was a standard (non 3-way) bulb. Looking closely, I noticed a ?" long scratch on the bottom of the outside of metal part of the bulb socket. On a non 3-way bulb the socket base wraps around the base of the bulb a little. On a 3-way bulb, the base ends near the bottom and there is a small toroidal space and then there is the ring for the second filament contact. Apparently, what was happening was that when they screwed the bulb in it barely missed coming in contact with the second filament contact in the socket. When the bulb heated up, apparently the base expanded a little and the outside portion of socket touched the second filament contact and caused a short. When the power went off the bulb cooled down and short went away.

My problem, in the master bedroom, with the short appearing and disappearing and when the lights went off (breaker tripped) two times before was due to the husband going in and out the second bedroom and turning the light switch ON and OFF. Since the bulb had to heat up before the short occurred, we didn't connect his comings and goings with the problem.

I replaced the lamp socket with a standard socket and all problems went away. Things are almost never what they seem to be or are reported to be.

 

[LarryFine]

I went over there and the same breaker was tripped. When I reset it, it immediately tripped again. Great! I might stand a chance of finding the problem if it still exists.

At that moment, I would have wired my rubber socket and 100w bulb between the breaker and the load wire, and had someone watch the bulb while I explored.

Great story.