Originally Posted By: Bob Badger
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Could be a breaker lock out device as already mentioned.
OSHA and the NEC require these when you want to use a breaker as the disconnect.
They will accept a pad lock.
I carry in my truck a LOTO (Lock Out Tag Out) kit, this has the required tags and locks to lock off almost anything.
Or and these are perfectly acceptable a breaker lock.
A breaker lock is designed to keep a breaker from being manually shut off.
No matter what you do to a breaker handle it will still trip, that is a UL requirement.
Breaker locks are required for dedicated circuits feeding emergency lighting and the feeds to fire alarm panels many times.
An optional use of breaker locks comes in when the breakers are used daily to turn the lights on and off in commercial locations.
We will put breaker locks on all breakers except the lights, you do not want people shutting off necessary circuits.
Taking another look at the picture it looks to me like this could be used to lock on or lock off the breaker, nice unit. 
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Bob (AKA iwire)
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