How Do I Hide End Of Line Resistor On Surface Window Contacts?

I got a design that is using a bunch of addressable modules for various windows throughout a building. Each sensor loop for the addressable module will have one or two surface mount window mag contacts in the loop. Need to use an end of line (EOL) resistor on the sensor loop, and having a hard time figuring out the best way to insert the EOL resistor without having it sticking out like a sore thumb and still be by the last window contact. The current plan is to use a normally closed loop, so the resistor needs to be in series with the contact(s). Anyone willing to share a "This is how we did it" idea?

Thanks for the ideas, Ari. I did think about under the windowsill, but hiding it with spackle is a good idea. Also, drilling a drop hole for it under the contact is something I hadn't thought about either.

I knew asking this group would be a good idea.

Under the windowsill, or in a hole directly under the contact. Dab a little spackle on, shape it with your fingers, and let it dry. Done.

You are welcome Scott. Good Luck!

The contacts with built-in resistors are the most elegant option, but another method that I haven't seen mentioned is to put the EOL on a short (4") pigtail. Generally soldered and shrink wrapped up. Then you can stuff it down the same hole as the wire feeding the contact (might have to drill the hole a a bit larger), or drill an additional hole to hide the EOL pigtail in. Generally looks clean and neat.

Thanks Mark, I think these might do it. I gave them a call and they support the resistor value I need. Waiting to get pricing, so thanks for the tip.

...and if you are really worried you would wire them as Open/Short using the 4 wire method. This requires Form C door contacts. Old school.


Echoing what Brian said, congratulations for being professional enough to place your EOL resistors where they belong. In about 95% of the installs I inspect, the resistors are back at the panel rather than at the device.

Some of the surface mount contacts have screw terminals on the back, and others are available with little covers that enclose the screw terminals. If you are careful, you can usually get a resistor behind the switch or under the cover.

I usually like to see stranded wire "pigtails" soldered to the resistors and the whole assembly covered with heat-shrink tubing. The solid leads on resistors are not really designed to take much stress.

As Mark indicated, contacts with built-in resistors would be the best choice if you can get them.

As a suggestion, you can get contacts with built in resistors. If fixes all of your problems and looks good too. I prefer GRI, there may be others. LINK.

There is one way I know of to put the EOLR in the can and not defeat it's purpose, though whether it's better depends on the distances and how important aesthetics are to the client.

Run four conductor wire, instead of two, from the panel to the sensor, then using the two additional wires to loop back to the panel, (in series), for the EOLR.

Thanks, Brian. I understand the importance of why it needs to be at the end of the line, for detecting shorts. Hadn't thought about color matching tape, so appreciate the idea.

I guess I'm still holding out hope I can find a mag contact with a big enough terminal cover to hide it under. So, far no luck though.

I applaud you for asking this question and seeking to install EOL resistors at the actual EOL instead of burying them in the head-end panel.

My tombstone epitaph may read:

If it says 'end of line', it does not mean 'start of line' if it is easier.

I have seen the EOL resistor exposed outside the sensor or module, but then covered by a small piece of tape (usually color matching the sensor housing) and pressed flush against it.