EOL Resisters Use and Placement


When I installed the alarm system in my previous home I didn't install resisters. The system could be configured to not use them. The system worked fine without the resistors.

I am currently installing an ELK M1 Gold in the home I recently bought and have been installing EOL resisters.

Could someone educate me on the purpose of the resisters? Also I've been putting them near the furthest sensor on the loop - which is what I thought the instructions said. It seems other people put them in near the panel? Where should they be placed?

My assumption was that they helped the system to know if the wires were shorted somewhere between the panel and the end of the wire. With a shorted wire and no resister the panel would always show the zone as closed. If that is the case, then putting a resistor in near the panel doesn't really accomplish anything?
I'm going through the install process myself, M1 Gold. Slowly because of time. Just got finished installing a 48 zone wireless reciever, 2 recessed wireless, 2 (2 wire smoke detectors).

Isn't the M1 awesome? I'm just waiting for the network and Zwave controller to come out.


Is there any reason you are installing these resistors in the panel (besides being able to access them)? As the glossary entry points out, it kind of defeats the purpose if you install them in the panel.
The glossary is correct, but there is a reason other than hitting the wire with a nail for the EOL to be at the end of the line and NOT in the panel.

If a burglar tries to bypass the alarm by shorting the zone loop, it can be detected and immediately sound the alarm. That's why they came up with the idea in the first place.
In jlehnert's excellent discussion on EOL, he mentions "there is a method using 4 conductors that puts the EOL electrically at the end of the loop, but physically inside the panel. While this techniques is better, it is still better to put the EOL resistor"

My system is an Omni Pro II.

What is this method using 4 conductors? I am restoring an old house and have wired it for security, etc using 4 conductor wire to each security zone (there are 46 zones.) Unfortunately I was not aware that I needed a 1000 ohm resister at the end of each loop near the sensor. I have covered up the sensors now and it is not practical to go back and add in 1000 ohm resistors at each sensor location. All my security zones will be normally closed. I understand I can configure the Omni Pro II to accept no 1000 ohm resistors for NC zones but wish I had installed the resistors before I "buttoned" up the sensors. Is jlehert's method applicable/advisable for me?

Thanks, Harold

No reason why I'm doing this. Just testing everything out as I have only 1 wired Zone so far not counting the smoke detectors. I was just going by BSR pic. that he was so kind to draw. I'm also doing this with 4 conductor fire wire so I'll prob. just keep it in the panel just arrange the wires different. This is definitely my first panel installation and I’m learning more everyday.

If a burglar tries to bypass the alarm by shorting the zone loop, it can be detected and immediately sound the alarm

100% true, and I am aware of the original reason. I probably should add it in. However, having a burglar attempt to do this in a residential situation is VERY rare. I went with the nail example because it is the problem you are most likely to see in a DIY residential installation. (Maybe I should remove the "DIY" and just say "residential". After seeing the way some contractors go at it with nail guns, I'm surprised I don't see more reports in the news of people with nails embedded in their bodies ;) )

What is this method using 4 conductors?
Hmmn. I thought I put it in the description. Another note to myself about changes.

In the meantime though, conductor #1 goes from the panel to the contact(s). Conductor #2 returns from the contact(s) to the panel, where it is connected to one end of the EOL resistor. Conductor #3 runs from the other end of the EOL resistor back out to the contact location, where it connects with conductor #4 and returns to the panel. Using this technique, the EOL is electrically in the middle of the run, while physically at the panel. There is still a weakness with this technique, ie if a nail shorts out conductors #1 and #2, but it provides more protection than no EOL or the EOL in the can.
Picture worth 30-40 words or so... (sorry for the quality - my scanner is acting up)


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I'm wondering if it would be better to put the resister EOL, or use 4-wire and put them back at the panel. Do resisters ever go bad, if I put them in the panel they would me much easier to access and replace. If I put them EOL I might have to tear out sheet rock.

Any opinions?


Best is to put them at the far end of the loop were they belong. Resistors don't go bad, short of physical wear and tear. As they will be inside the wall, there should be no wear and tear, so they should last the life of the house.
Thanks, that's what I'll do -- EOL 'em. It'll also make the wiring job neater. I assume solder and plastic heat shrink will make them permanent and protected.
One more thing to think about.

Since I frequently upgrade my HA components as better technology becomes available, a few years ago I changed out my panel from Ademco to Caddx. Unfortunately, there is no universal standard for alarm panel resistor sizing. I had to change out the resistors - a real pain in the butt if you have to dig them out of jambs and walls.

The only reason my resistors are in my panel is to make it easier to change to the next generation panel. My wires and contacts are pretty well concealed in the walls and jambs. If an intruder is willing to go through that much trouble to try to access those wires, in order to silently open a door/window, in order to break into my house, then he is seriously misinformed as to the worthiness of that endeavor!