Hi Pat,
Often, breakers in both residential and commercial applications remain
motionless for years. The result can be just as you describe: the breaker
contacts fail to open when a trip is called for. If the failed breaker feeds
a 20A circuit and the next upstream breaker is rated 200A, there can be a
bit of a problem. The fault current may never reach the level required to
trip the 200A breaker, so the best you can hope for, is for the fault to
clear without a fire, or with a self extinguishing fire.
What I've also seen happen is the breaker mechanism bind on tripping, due to
corrosion / contamination. This can result in the spring pressure being
taken off of the main contacts, but the contacts failing to open. The
resistance across the contacts then increases dramatically. Since the
breaker attempted to trip due to overcurrent, it's reasonable to say that
there is a lot of load on the circuit, and that a good deal of heat will be
developed by the breaker contacts. The breaker then burns and melts from
heat, possibly melting the main before it trip's from the fire's heat. This
scenario just gets worse.
In an industrial situation where voltages are higher and maximum fault
current is much higher, a breaker failure can result in a very prompt,
violent explosion and fire with white hot metal sprayed about the room. Any
by-standers are usually burned badly or killed.
So, yes, cycling all of the breakers annually is definitely good preventive
maintenance...it also helps keep you familiar with the procedure for setting
the digital clock on the VCR ;-)
73,
Jeff - K1LE - CT ><>
----- Original Message -----
From: "Pat Barthelow" <aa6eg@hotmail.com>
To: <K1LE@arrl.net>; <amps@contesting.com>
Sent: Friday, April 11, 2003 3:00 PM
Subject: Re: [Amps] Re: PS project part2
> Is it possible or likely that a circuit breaker's mechanical motion
> mechanism can lose reliability due to non-use? I think of my home
breakers,
> and until a couple of years ago, most of them might have not been tripped
> for decades. Could corrosion, dust, dirt, old lubrication, etc, combine
to
> cause the breaker to 'stick' at a time when it should trip? Would cycling
> them, say yearly, at least, enhance reliability?
> Pat, aa6eg@hotmail.com
>
> Jeffery Wrote:
>
> From: "Jeffrey Madore" <K1LE@arrl.net>
>
> Lynn,
>
> >You might want to take a look at the circuit breaker to determine that it
> >is functioning properly. (snip)
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