Re: EOL's

["Russell Brill" <russwbrill@xxxxxxxxxxxxx>]

"Robert L Bass" <sales@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:asqjv1d8jnf12olkr8a5hhao0bf4961psn@xxxxxxxxxx
> 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.

That's funny, I've given magnetic contacts a few taps with the end of a
screwdriver and had them start working again (They got replaced anyway)....
>
>> 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.

That hasn't been my experience, I've had to replace EOLR's that were toast
and the panel was just fine...
>
>> 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. ???????????????

Hmmm..... I've always been told, "There is no way to predict how Lightning
will or won't behave"... There have been cases were the Grounding electrodes
provided the path for the Lightning to enter into the building's electrical
system...

>
>> 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.