Near Miss Relating to Isolation

T

TVH

Senior Member
toolbox.energyinst.org

Testing if isolation has been effective

During a glycol aerial cleaning campaign, the fans started when they should not have, potentially causing severe injury or death to a worker. Upon investigation, it was found that the fan breaker knife switches were fused in the closed position.
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See link above.
Good example of the need to test circuits via voltmeter to verify zero energy state.
 
The very reason we added HOA switches for all controlled motors in one plant i worked at. That purpose being the verification of the lockout for non-electrical work. The hand position bypasses all interlocks other than the motor overload relay in the motor starter.
The procedure is try-lock-try. You go to the equipment and try to operate it there. Once you see the equipment operate, you lock out the equipment power source. Then you return to the HOA and put it in hand again, and if the equipment does not operate, you can do mechanical work on the locked out equipment.

Electrical work always requires verification of the de-energized state and cannot rely on not seeing the equipment operate with the HOA in hand.
 
Watch out for hidden power sources too. I had a switchgear that the utility turned off the transformer, I verified the gear was dead, proceeded to connect an EPO switch, got a little jolt! Found a very small sticker on the switch that a capacitor was used in that circuit for backup power for the shunt trip. Must have been custom ordered, as I have never run across the same thing before, or since.
 
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