Solved Building Electrical Breaker Tripping.

[ultrarunner]

Got a call the operating room corridor hallway lights went dark... this is one of the circuits on the life safety panel.

This wing was built in 1995 and circuit is lighting only... no outlets ruling out something like a heater being plugged in and overtaxing the 20amp circuit.

Reset the breaker and went to investigate and found nothing amiss.

Circuit tripped again an hour later and I opened the panel.

I found a 12ga copper conductor with insulation charred and loose where the wire connects to the circuit breaker. It’s the black wire in the picture.

So for 29 years it was ok until it wasn't

Checked the other breakers and found another with a loose conductor...

The panel has been untouched and I would have been the only one touching.

Sometimes it takes decades for a latent defect to materialize is my takeaway.

 

[grsthegreat]

Seen it alot of times. Wire was never torqued, so it kept heating and cooling causing arcing. Heating and cooling effects wire expansion and contraction.

 

[MossRoad]

At my old job, they hired a company to come in annually with thermal equipment and go through all the breaker panels, machine control boxes, power rooms, etc. and look for hot spots. They'd find them every time. 1/2 the building was over 100 years old, the other half only a few years old.

You can only imaging the number of electrical connections in a printing plant.

When we had a power outage, we had 1.8MW of generators come in, and could only run the press about half speed for half time before tripping them out.

 

[etpm]

That panel looked very well organized, pretty much like my work. Not quite as sharp of bends as mine (I'm kinda **** about wiring though) but still a very nice looking panel. Looking at that panel there would be no reason to suspect loose screws. sometimes folks just plain forget, especially when they are used to doing a very nice job.
Eric

 

[ultrarunner]

Easily 2 dozen panels not counting the big stuff like the 480v panels ..

Job was signed off 1995.

Conduit everywhere overhead with some underground.

The lighting circuit has no off switch as it is intended to be on 24/7

The T8 bulbs were a new energy saving feature back then and the wing was the first large scale application in the city.

The only time a hospital 120v breaker has ever tripped is when a receptionist brought in a cube heater from home.

I have had a few issues when an HVAC compressor siezed up but typically it's a disconnect cartridge fuse that goes.

A lot of institutional building specific knowledge will go out the door when I do... especially being the byword is outsourcing.

This week a question came up for the architect... He did the original designs in 1993... I said let me call him and the Doctors and CEO said you know how to reach him?

Next week he retires after 40 years... firm went from 2 to 240 in his 40 years...

 

[BigGG]

We bought an 8 year old house. I noticed the bathroom vent fan would slow down then speed back up. Took the switch plate off, the wires had been looped around the screws but the screws were all the way out. I went through the whole house and about half the switches were like that.

 

[jaxs]

For lack of knowing the technical term I just call it snowball effect. The same thing is responsible for many electric problems on cars and tractors. Trailer lights being one of the most common.
If for some reason there is voltage drop across a connection ,resistance grows with each heat cool cycle or passing of time until problem becomes apparent. Had lights been switched off and on every day the same thing would have happened much sooner.
You deserve for your ability to find it. 95% with your job title and soon to be 100% would have to call in a contractor leaving area in the dark much longer.

 

[gsganzer]

Your panel probably had solid wire, so it would most likely have been due to lack of tightening during termination.

However, this still applies to panels:
I do process instrumentation, electrical and controls. Our equipment has a number of control panels, both for controls and power distribution. We always recommend an annual "torque test" of power circuits, especially those that have stranded wire like DLO cable, which is fine stranded like welding leads.

Also, as Moss said, we also do a thermal inspection with a thermal camera when the panels are in operation. This will show you "hot spots", likely due to loose terminations.

On a side note: I had a mentor years ago that taught me the proper way to wire control panels with stranded wire and screw type terminal blocks. You never twist the wire before you land it, instead you pull the wires straight and flat using your thumb nail, before inserting and tightening. Heavily twisted wire eventually relaxes and becomes loose.

These days, I require ferrules on any stranded connections for panels I oversee. This prevents the "relaxing" of the wire, reduces the errant wire strand that touches something and makes it easier to disassemble/reassemble.

 

[3Ts]

Sometimes it takes decades for a latent defect to materialize is my takeaway.

Similar situation: I had a house with a leak, it soaked the carpet in a room which backed up to the laundry room. could not find it. Ended up cutting out the drywall in the laundry room. Turned out a drywall screw had penetrated the steel nail plate protecting the copper water pipe and had just touched the pipe (did not damage the pipe). After many years the corrosion between the copper and steel pitted the pipe enough to create a leak.

 

[EddieWalker]

... the proper way to wire control panels with stranded wire and screw type terminal blocks. You never twist the wire before you land it, instead you pull the wires straight and flat using your thumb nail, before inserting and tightening. Heavily twisted wire eventually relaxes and becomes loose.

I didn't know this and I've been doing it wrong forever. Mostly for 12 volt auto wiring, but in the back of my brain, I think I've done some stranded wire in the house somewhere. I'll have to think about it to see if I can remember where.