Re: EOL's

["Al Colombo" <securitymission@xxxxxxxxxx>]

> It's my understanding that in certain parts of the country Lightning can be
> a problem, the voltage and current that a nearby strike causes on the
> protection loop blows the resistors...... Its been known to weld contacts
> closed also......

This is one of the possibilities with regards to the original poster.
If there were a nearby lightning strike last summer, providing the
alarm site is in an area where lightning is common, the contacts could
have been lightly welded together so that when he began to work with
the switch, flexing it for example or merely inducing a vibration, it
could have released them.  If the switch is magnetic, and it probably
is, the relatively high current could cause them to magnetically stick
together as well I suspect, but I'm not an switch engineer so we'll
leave that explanation to Sentrol or GRI.

In fact, the 53% increase in ohmage with regards to the EOL would point
to this possibility as well as the induced high current from the strike
would have created undue heat inside that EOL.  The carbon would change
properties, gaining resistance in the process.  Lightning does not
always burn resistors open, especially if the strike took place some
distance from the alarm system site.

As to why the initiating circuit was not damaged, perhaps there's an
MOV or a zener diode in the circuit that clamped the high voltage
current off before it reached the circuitry in the panel.  Some boards
are designed with arc points as well at the terminals so such a high
voltage will simply circle and not enter the board.

Al


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