End-of-Line Resistors - FAQ

I have just posted an FAQ on this topic. Many of our threads get off topic when this gets mentioned, so maybe this is a way to get some questions answered without bogging down the thread. It is posted in the Wiring Diagrams section of the Download section of Cocoontech. Here is a link.

Please let me know if you find a glaring error in there.

The link doesn't seem to work.

Should work now. File had to be approved. Would love to see this moved to the wiki once I re-enable editing, so it's easier to update. Thanks Sandpiper!

Sandpiper, that write-up is awesome!

I always pictured faults differently though, for multiple contacts in series in a single zone.

Like this:



So that an EOLR would, in fact, be useful for a zone with multiple contacts. Am I misunderstanding the usual wiring?

Edit - the blue lines are faults, and of course the contacts are usually closed.

Wow, very nice writeup.

Neurorad said:

Sandpiper, that write-up is awesome!

I always pictured faults differently though, for multiple contacts in series in a single zone.

So that an EOLR would, in fact, be useful for a zone with multiple contacts. Am I misunderstanding the usual wiring?

Click to expand...

You are correct. They could be wired this way, but I doubt if many alarm companies wire that way anymore. I know my house was wired this way 20 years ago, and is still that way. They ran a wire around the foundation wall, and cut into one conductor to splice in a jumper wire to window and door contacts. I believe most everyone now just home runs everything, but some things could be jumpered in the field.

Good catch. I will add another diagram to show this case.

For each alarmed room, I have 1 cable that runs from the panel to the first window, and then on to the second window. One cable per zone. I don't think many installers use 1 cable per contact (though it seems some of the OCD-ers here at CT prefer that, I know I would ).

Home running every window seems a bit extreme to me. I have banks of windows with as many as 6 windows that open. Home running each of those would be confusing. Plus they are double hung windows with 2 contactors per window, that would mean 12 wires for a bank of 6 windows.

I did my EOL resistors just as neurorad depicted for each of those banks. The only advantage that I see with home running each window is that if one of the contactors fails open, it requires more legwork to hunt down.

Sandpiper said:

I have just posted an FAQ on this topic. Many of our threads get off topic when this gets mentioned, so maybe this is a way to get some questions answered without bogging down the thread. It is posted in the Wiring Diagrams section of the Download section of Cocoontech. Here is a link.

Please let me know if you find a glaring error in there.

Click to expand...

Very nice document well put together.

Highly recommended for those needing clarification when it comes down to EOL'rs

Lou Apo said:

Home running every window seems a bit extreme to me. I have banks of windows with as many as 6 windows that open. Home running each of those would be confusing. Plus they are double hung windows with 2 contactors per window, that would mean 12 wires for a bank of 6 windows.

I did my EOL resistors just as neurorad depicted for each of those banks. The only advantage that I see with home running each window is that if one of the contactors fails open, it requires more legwork to hunt down.

Click to expand...

That is exactly why we home run each contact, then series them in the panel. We have a technique to quickly troublshoot any contact that is not working right. If you have to troubleshoot at each window, it becomes quite tedious and time-consuming. I've seen up to 40 windows split onto 2 zones and will still fit nicely inside a standard 14" panel. With more than that, I believe it would be time for extra cans and zone expanders.

But in any case, the point has been made and accepted. I'll be placing a new diagram into the document at the next revision, and also mention the point that partial supervisory monitoring is achieved in this case.

FYI, I also posted THIS reply complete with drawing of the four most common EOL scenarios.

Neurorad said:

Sandpiper, that write-up is awesome!

I always pictured faults differently though, for multiple contacts in series in a single zone.

Like this:

View attachment 3749

So that an EOLR would, in fact, be useful for a zone with multiple contacts. Am I misunderstanding the usual wiring?

Edit - the blue lines are faults, and of course the contacts are usually closed.

Click to expand...

Neurorad,

I want to thank you again for pointing this out. It hit me like a ton of bricks last night that by daisy chaining from contact to contact, 100% of the wiring could be supervised. I had been doing it for so long in the home-run fashion, this fact just didn't occur to me. As a result, the FAQ has certain sections that will need to be re-written, and I will do so.

Glad I could help, Sandpiper!

I feel like less of a noob.

Sandpiper said:

That is exactly why we home run each contact, then series them in the panel. We have a technique to quickly troublshoot any contact that is not working right. If you have to troubleshoot at each window, it becomes quite tedious and time-consuming. I've seen up to 40 windows split onto 2 zones and will still fit nicely inside a standard 14" panel. With more than that, I believe it would be time for extra cans and zone expanders.

But in any case, the point has been made and accepted. I'll be placing a new diagram into the document at the next revision, and also mention the point that partial supervisory monitoring is achieved in this case.View attachment 3750

Click to expand...

That diagram is exactly how I have my window banks run. I suppose it is a trade-off between the for-sure added PITA of running 12 wires (in my example) vs 1 wire, as compared to the possible but unlikely PITA of figuring out where a failed "open" contactor is. Sort of a pay me now or (maybe) pay me later.

You also only lose one window if something happens to the wire instead of all of the windows. The value of this is debateable since it only makes things easier if you decide to let the one unprotected window stay that way with the thought process "oh well, what are the chances the burgler picks that window?"

The EOLR works well for situations as depicted in your diagram. It is very hard to get a short that the EOLR would miss becuase I didn't run the wires together. Once the wire gets to the bank of windows I split the two wires and made a big cirlce around the bank of windows. A short missed by the EOLR can only occur at the contactor and is easy to detect becuase all it takes is opening the window and seeing that the zone didn't violate.

Very nice write-up. I would love to hear more about how multiple resistors can be used.

Nice EOLR explaination. This should help a lot of people understand End Of Line Resistors. We need more write ups like this.

I will state one other fact concerning EOLR's and lightning transients. Most security controls reference one side of their zone loop to the negative side of the power supply. Without the end of line resistor in the circuit, any lightning transients are quickly bled off to negative. With an end of line resistor installed, there is more of the lightning transient having to be bled off through the transient protection network located on the control panel. You will have more chance of lightning damage with the EOLR installed rather than the zone loop connected directly to negative.

If you are not wiring the EOLR at the end of the zone loop and the control allows for programming the EOLR to a normally closed zone loop, remove the EOLR from the circuit for better lightning transient protection.