April 2008 Tech Talk Online Q & A
Q: Some of the techs have been arguing back in forth if end-of-line (EOL) resistors on alarm loops are really necessary? If it is a closed loop, any opening of the cable will cause an alarm eventually as the customer will have to try to arm their system.
A: You should always use the resources that are provided by the manufacturer. If you do not wish to take the extra time to install the EOL devices properly (at the end of the loop and not in the panel) then make sure the customer understands and has signed of on that option. In commercial accounts especially, you still have the chance that someone is smart enough to try to compromise a circuit. Every little bit helps and, as mentioned above, reduces you liability. Over the years, I have had a few commercial customers that were glad that they did not have to stay late to have a technician fix a faulty or tampered with alarm circuit. Don’t take unnecessary risk.
Q: How can I reduce some of the troubles I have with recessed magnetic contacts. Sometime I install them in new construction and come back later to find they are not working. It seems lately we are having a rash of problems. I have even tried different manufacturers and still have more failures than I would like.
A: First, can you link your problems to a specific tech? Recessed alarm contacts should be pushed in with a thumb and not rapped in with the end of a screwdriver butt. If there is undo shock putting on a contact when installing and the internal glass capsule is cracked, you have lost the integrity of the encapsulated reed switch. It will work for a while, but will gradually start acting up.
As you know not all drilled holes for recesses door and window alarm contacts are made correctly. An alarm switch by GE will give you some extra flexibility in uneven holes and holes in green wood. It will also help grab in holes that might be drilled a little too large. The device is the GE 1275 that comes with foldable wings to help keep it in place. This way you can drill a hole slightly oversized and reduce damage from any shrinking of the hole or forced insertion at time of installation.
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