At 05:03 PM 8/3/02 +1200, you wrote:
> > Thanks for all the replies.  It all makes sense now.
>
>Perhaps someone can do a similar explanation for
>relays and switches. Relays sometimes have a label
>that says something like "Do not break tab off before
>cleaning", and the tab covers a hole in the relay case.
>Why would you want or need air getting to relay and
>switch mechanisms ?

There are gases and metal vapors produced by the contacts when they
switch, particularly power and/or inductive loads at high voltage.

Taking the tab off or snipping the plastic vent will increase the
lifetime of the relay in those cases. OTOH, if the environment
has contaminants in it such as powder, then the life may be
reduced. For switching low currents, it probably doesn't matter
much.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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