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Joined: Apr 2004
Posts: 156
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rad74ss Offline OP
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HVAC lab. Last year several safety devices were installed. E-Stop for main and control voltage at the distribution panels for each work station, along with remote toggle switches to turn main and control on/off at the unit. Strobe lights were placed at each station to indicate if any power was being used at the station.

After testing the unit the technician began to disconnect the power leads to the unit. The remote switch is a box with two toggle switches with push to test lights cord mounted back to the panel.

The cord was draped over the units enclosure door with the switches out of view of the tech. He reached over the door and hit the switches. Or so he thought. The audible click was the 120/240 switch. Without verifying the power was off he began to remove the 460 main wires. L2 and L3 came off without touching anything. L1 hit the units panel board.

The Arc caused first and second degree burns on his right hand. Luckily he just received flash burns and did not get shocked. The main terminal block blew completely off the panel. The main fuse blocks fuses blew off. One is embedded in the sheetrock and we can't find the other two. The contactor nearest the point of impact shattered on the inside. The coil was broken in three pieces.

Good news? Now the technician will only use the E-stops on the distribution panel itself. Not only is he sure the power is off, he has to face the strobe and ammeters when he does it. We have also started to place blinders on either side of each work station due to the fact that we noticed when more than one strobe was going you couldn't tell if it was the one in your station unless you looked directly at it. The metal enclosures and abundance of vaccum and charging piping caused so many reflections it was impossible to know if it was your strobe or the next guys over if you had your back to the light.

Lesson well learned.

Robert

Arc Flash PPE Clothing, LOTO & Insulated Tools
Joined: Feb 2002
Posts: 183
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Member
It sounds like they need to implement and requre lockout/tagout in that lab before someone gets killed. Looking for strobes isn't good enough - what happens if the strobe is dead or a contactor gets welded?

Joined: Apr 2001
Posts: 507
G
Member
"The Arc caused first and second degree burns on his right hand. Luckily he just received flash burns and did not get shocked. The main terminal block blew completely off the panel. The main fuse blocks fuses blew off. One is embedded in the sheetrock and we can't find the other two."

That 480v power is just not very forgiving. The good news is no one got killed.

GJ

Joined: Nov 2000
Posts: 2,148
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Member
The use of "e-stops" is not permitted for lockout purposes, the actual disconnect or breaker that feeds the power to the circuit must be locked open. Also you must always test the circuit with a tester that is known to be functional before working on the circuit even when it has been locked out.
Don


Don(resqcapt19)
Joined: Jul 2002
Posts: 8,407
Member
Darned good point Don!.
Using an E-stop as a means of isolation, is stupid to say the least!.
What ever happened to good ol' Voltage Indicators proving that the circuit was de-energised?.
Control Circuits are always live, at least up to the first NC contact, this could be an E-stop that you are working on!.
Be aware!. [Linked Image]


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