Re: EOL's

[Robert L Bass <sales@xxxxxxxxxxxxxxxxxxxxx>]

On 20 Feb 2006 05:49:54 -0800, "Al Colombo"
<securitymission@xxxxxxxxxx> wrote:

> > 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...

Clearly you're not an engineer.  Lightning can weld magnetic
contacts open or shut.  When it does, the switch won't restore by
"flexing it" since the actual switch is enclosed in a
hermetically sealed, glass capsule.  It doesn't flex when you
move the leads or "work the switch".  If it was responding to the
movement of the magnet in the first place, it wasn't welded.  If
it was not responding, moving the magnet some more would not have
made it better.

> 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...

Nice theory but it's wrong.  If there had been a lightning hit
sufficient to alter the EOLR by 50% there would also have been
other damage to the system and/or the sensors.  Resistors are
much more sturdy than magnetic contacts.

> 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.

Wrong.  See above.

> 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...

Your understanding of lightning protection is exceeded by your
understanding of resistor tolerance.


--

Regards,
Robert L Bass

Bass Burglar Alarms
The Online DIY Store
http://www.BassBurglarAlarms.com

--

Never underestimate the power of very stupid people in large groups.