Fault Current Mishaps

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bwat

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It wouldn’t surprise me if almost everyone here was able to provide some first hand (or possibly 2nd hand) knowledge of some electrical fire or other incident due to code violations such as incorrect wire ampacities… terminations issues… etc

However, I’m curious how many people here have been around an actual incident that occurred because equipment was installed that had too low of an AIC or SCCR rating?

Based on my experience, there are a good number of installations out there that aren’t properly rated for the available fault current (never the ones I’m involved in of course 😉). Yet, I don’t know that I’ve ever actually heard of of an incident related to it.
 
romex jockey said:
Burnt up terminations are common bwat

~RJ~
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Are you saying it is common to find burnt up terminations that were caused by the equipment being installed that has AIC or SCCR ratings lower than the available fault current? The cause here is key.
 
I only have second hand recollection of this:

Early on in my work on high phase order motors, an investor decided to push the research on their own. They contracted with a university research group near them to build an inverter and test a motor.

The group had even less clue then I, and built an inverter with a large capacitor bank and no precharge circuit.

They were also in a brand spanking new building with large transformers supplying power for each of the bays.

Apparently they simply threw the breaker to supply power to the rectifiers and capacitor bank, and had a mostly contained failure of the disconnect. No injuries but they were a bit embarrassed.

Jon
 
bwat said:
Are you saying it is common to find burnt up terminations that were caused by the equipment being installed that has AIC or SCCR ratings lower than the available fault current? The cause here is key.
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burnt terminations can have multiple causes bwat, aic may be one of them

~RJ~
 
bwat said:
It wouldn’t surprise me if almost everyone here was able to provide some first hand (or possibly 2nd hand) knowledge of some electrical fire or other incident due to code violations such as incorrect wire ampacities… terminations issues… etc

However, I’m curious how many people here have been around an actual incident that occurred because equipment was installed that had too low of an AIC or SCCR rating?

Based on my experience, there are a good number of installations out there that aren’t properly rated for the available fault current (never the ones I’m involved in of course 😉). Yet, I don’t know that I’ve ever actually heard of of an incident related to it.
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Probably because faults that draw the full available fault current are not very common.
 
My brother sent me a picture, he took, of a combination starter that failed violently causing the enclosure door to to fly off and land across the room. Luckily the person operating it was standing to the side.
 
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jim dungar said:
My brother sent me a picture, he took, of a combination starter that failed violently causing the enclosure door to to fly off and land across the room. Luckily the person operating it was standing to the side.
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Sounds like a “good” one there.

don_resqcapt19 said:
Probably because faults that draw the full available fault current are not very common.
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I’d agree. Seems logical.


It’s interesting with all the years of experience in this forum that it seems to be as I suspect - very rare.


I think there could be a few reasons for this. As Don pointed out, not only would a fault have to occur, but a very low (near zero) resistance/bolted fault would be needed to draw the full available current.

I also think our calcs for determining available fault current at certain points are fairly conservative and the values would be hard to achieve in real life.

Lastly, I have to imagine there’s some wiggle room with device ratings. If a breaker is rated 42 kAIC, it’s not going to fail at 42.1 kAIC. Where is the limit? Not sure, somewhere between 42 and 65 probably, and it could only fail sometimes at those higher values and sometimes work ok, but not good enough to carry the rating.


I’m not advocating for any type of change. We want our protective devices to be fully capable of doing just that - protecting people and property. This was just an observation I had through my own experiences and real life conversations and I wanted to see what would come from asking this group.
 
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