The only down side is someone who is unaware of the other(s), meaning they lock out one, someone else locks out the other, then the first person removed his lock and can't figure out why it doesn't work. Been there, done that...
At my previous job (sawmill), there was a long waste conveyor (1100 feet) with many access points. In an effort to comply with lockout requirements "production" insisted on installing lockout disconnects at various access points. This was done in a piecemeal manner, rarely was a disconnect farther than 50 feet than the last installed disconnect. The original install was a 10 horsepower U frame motor with a 20 foot conduit run and 8 ga wire. Somehow a T frame 20 horsepower motor was substituted (only the shaft size changed, the mounting bolt pattern was the same). No one knows when the motor was changed or when the overloads and breaker were changed. The original blueprints (no revisions) showed the motor details. Shortly after I was hired on, I was asked to add another disconnect at yet another location. I did so in the same manner as those before me, and I thought no more about it. At some time later I became a "shift electrician" and was responsible for troubleshooting problems. This conveyor system had many problems (mechanical and electrical), one of the problems was that motor tripped the overloads. Many electricians including myself had suggested this was a mechanical overload, because we had tested the voltage at the disconnect next to the motor and observed the amperage was even on every phase. One night when things were slow (no breakdowns) I was investigating the problem motor and I realized that the disconnect physically next to the motor was not the disconnect "electrically" closest to the motor. Apparently at one point an electrician had "added" another disconnect electrically between the motor and the disconnect next to the motor.
We had been measuring the voltage drop 20 feet from the MCC bucket, not after an an approximate 2500 feet of wire! Doh! After checking the voltage at a different disconnect we found that the voltage was only 390 volts. I should add that I'm not sure this was the last disconnect before the motor!
The electrical chief made a decision to rewire the system with 1awg. The voltage drop went away and the mysterious overload trips went away.
Then the conveyor chain hung up mechanically and a 4 7/16" shaft twisted in two pieces. A post mortem autopsy showed that the original 10 horsepower motor was correct for the application!
how could this ever happen if they were following their written lockout procedures?
I'm presuming that Jraef was referring to the confusion about which disconnect was causing the non operation of the system.
We had the same issues after all we had more than 20 disconnects in the system. Axillary contacts and indicator lights were added to every disconnect so that it was easier to find the disconnect that was in the off position.
