Scariest Electrical Work?

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JFletcher

Senior Member
Location
Williamsburg, VA
Today my boss and I were discussing the scariest work we'd come across. I'd forgotten about this one:

About 8 years ago, I was working maintenance at a large hotel. There was a call for a bad smell coming from the 7,000' sq ballroom. After about half an hour of looking for a dead animal in ductwork, I went outside and noticed a much different burnt electrical smell, coming from a non fused disconnect for one of the 3 3ph 10 ton AC units. So, I throw the disconnect and open the deadfront/cover to the disconnect. What I didnt realize is that when I threw that disconnect from on to off, the center phase of the knife/fork assembly was corroded solid, and it yanked the feed lug from the center phase to within 1/16" of that deadfront. That feed lug was fed (wrongly) by a 250A breaker, where all three units were fed from. Yeah, I probably shouldnt have been opening disconnects/deadfronts then, but I didnt know any better at the time. A licensed electrician was called to fix both problems.

To this day I always stand to the side of anything when I throw a switch, breaker or disconnect. I cant imagine how much fault current would have flowed given another fraction of an inch.

If anyone would share their stories of odd or scary electrical work, I'd like to hear them.. for interest sake, and for safety.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
This was over 30 years ago, and I am sure to get some of the details wrong. I was the Electrical Division Officer on a nuclear-powered aircraft carrier. The shore power connections were done with single conductors that were bolted onto bus bars inside an outdoor-rated enclosure. The LOTO for the feeder breaker on the ship’s distribution to this buswork was incorrectly performed, and the bus bars were live (at 4160 volts!). One of my senior electricians led the evolution of transferring to shore power. He first tested his voltmeter on a nearby 120V receptacle, confirmed (or so he thought) that the voltmeter was operating properly. He then tested the 4160V bus bars, and the VM told him that no voltage was present. He once again checked the VM on the 120V receptacle, confirming once again that the VM was working.

Then he clipped a grounding strap to a point on the hull, and tried to clip the other end of the grounding strap to the bus bars. Even before the clip touched the bus bars, it drew an arc. The force of the arc blast pushed him backwards. He survived, with no permanent physical damage. He left the Navy not long after that, and my guess is that he sought a different line of work than electrical installation and maintenance.

I don’t recall much more than that. I do not know what went wrong with the LOTO process, but at the very least it had to have involved tagging out the wrong breaker. Further investigation revealed that his VM had some type of defect in the sensor that reads the higher voltage ranges. We changed the process of checking the VM by testing on a 480V source, as that used the same sensor that would detect the presence of live 4160V.
 

Tony S

Senior Member
To this day I always stand to the side of anything when I throw a switch, breaker or disconnect. I cant imagine how much fault current would have flowed given another fraction of an inch.

If anyone would share their stories of odd or scary electrical work, I'd like to hear them.. for interest sake, and for safety.

It’s an American concept I was taught as a UK apprentice.

The “left hand rule”. If the operating handle is to the right, use your left hand and stand to the right.

Saved me a couple of times when switches have exploded due to flash over.
 

growler

Senior Member
Location
Atlanta,GA
One of my senior electricians led the evolution of transferring to shore power. He first tested his voltmeter on a nearby 120V receptacle, confirmed (or so he thought) that the voltmeter was operating properly. He then tested the 4160V bus bars, and the VM told him that no voltage was present. He once again checked the VM on the 120V receptacle, confirming once again that the VM was working.

Then he clipped a grounding strap to a point on the hull, and tried to clip the other end of the grounding strap to the bus bars. Even before the clip touched the bus bars, it drew an arc. The force of the arc blast pushed him backwards.

Testing the VM on a receptacle would be a pretty good indication that the VM was working.

I would think that he would need a high voltage probe to use a VM to measure high voltage (medium voltage). This is an accessory that will allow the meter to measure a reduced voltage. Testing the meter really wouldn't tell if this probe were functioning properly.
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician Semi-retired
Testing the VM on a receptacle would be a pretty good indication that the VM was working.

I would think that he would need a high voltage probe to use a VM to measure high voltage (medium voltage). This is an accessory that will allow the meter to measure a reduced voltage. Testing the meter really wouldn't tell if this probe were functioning properly.

But if (isn't hindsight wonderful!) he had tested the 120 V w/ the probe, it would be enough to register, and he would have known it didn't work.
 

big john

Senior Member
Location
Portland, ME
...I would think that he would need a high voltage probe to use a VM to measure high voltage (medium voltage). This is an accessory that will allow the meter to measure a reduced voltage....
Just an FYI: For reasons I cannot explain, it would be very dangerous to use any sort of high-voltage adapter probe on a multimeter to attempt to measure distribution voltage. The only probes I'm familiar with are designed for very limited-energy electronics circuits, and I have heard of a couple of accidents where guys have gotten blown up believing that a probe that says 30kVAC would be perfectly safe on a 5kV distribution circuit.

I think I even asked for an explanation on this forum many years ago about why that would not work, unfortunately, I don't remember the answer. My best guess is that there is a rapid heat-stress breakdown of the probe-insulation that low-energy electronic circuits are not able to cause.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Please don't read too much into the technical aspects of my story. As I said, it was over three decades ago, and the details are more than a bit fuzzy. The point of the story is that we had a very scary near miss, indeed a near fatality, that resulted from poor practices, both in the LOTO process and the testing process. Lessons were learned, and practices were improved.
 
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