Expect The Unexpected

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
I posted this on another forum site (ET) in answer to Brian Johns post regarding the hazards of working around Bolted Pressure Switches (BPS) made by Pringle, Boltswitch, Square D, etc. I am posting here to maybe reduced the risk of injury to someone and also stress the need of wearing proper PPE especially around high energy (large fault current) circuits.
"Hey BJ
That's a great story. Now I've got one for you.
When I was a young buck many moons ago and working as a FSE for an Independent testing co sent to do an acceptance test on a GF relay system on a 2000 A Pringle BPS, after the EC finished the cable terminations on the line side. The line side was hot. No cables on the load side. This was a main to the bldg fed from a poco transformer (12kv-480v) in a vault in the adjoining room. I asked the EC if the switch was ever closed, he said No. I announced to the electricians in the power room that I was going to close the switch. This was before the time of wearing any PPE when working around live equipment. And besides, just closing the blades of a switch even with the line side hot with no load cables, what is the risk?
Well, after I struggled to move the handle down on the switch, and after it closed there was a loudBOOM! Luckily I was near the floor but above me the panel cover of the termination section above the switch blew off, flew cross the room and cut an electrician on the leg across the room! I was ready to quit the business at this point!
Turned out one of the line side 500MCM B phase cables contacted the A phase lug connection resulting in a phase to phase short. The cable lug was never torqued and the tight cable routing caused it to spring loose due to the shock of the switch closing causing the short. The vault transformer line side fuses blew clearing the fault.
This is another reason these BPS should be eliminated. "
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
If you ever operated a Pringle switch you know it takes 2 hands and all your strength to pull the handle downward
and plus my reaction to closing any switch is to move away from the device when closing it.
 
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