How to best put 5 window sensors into 1 zone

Mr Spock

Active Member
The question is regarding how to put the 5 windows in this one room shown below onto a single input zone of an HAI panel. The windows are casement type with magnetic sensor switches. I wanted to home run each window's 22/2 wire pair to the panel for optimum flexibility and troubleshooting capabilities. However when I schematically think of how to wire this up, including EOL resistors, I don't see how to do it without some potentially big downsides.

1) When a magnetic switch is "secure" (window closed) it is low impedance or effectively a short.
2) The panels must be presented with approximately 1k ohms if secure (from EOL resistor), a short if in a "trouble" condition, and an open if in alarm.

1) I could put each window on a separate zone, but that eats up input zones real fast.
2) I could put all 5 windows on one zone by wiring up the 5 windows in series at the server room with one EOL resistor at the panel. However if there is a short in any one of the wires then it will always look like that window and therefore the whole zone is OK (no trouble indication).
3) I could put the wires in series at the windows (no individual home runs) with one shunt EOL resistor for the group. However making all the connections at the windows will reduce my flexibility and make it much harder to identify where a bad connection is located.
4) I could put all 5 windows on one zone by wiring up the 5 windows in series at the server room with an EOL series resistor at each window. However the trouble condition that will not register with the HAI panel because there are 5 resistors and each must be 1/5 of the total required (nominally 1k ohm, or 200 ohms each). The voltage drop change provided by removing a 200 ohm resistor from the loop would be too low to register as a trouble condition.

So unless I've missed something this is how it works and what my options are. I would probably go with option 2.

Please weigh in with your comments and suggestions.


EDIT: assumptions.


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A series loop and EOLR's being effective are two mutually exclusive items.

First: DON'T attempt to split the EOLR value by dividing it X/RT among the openings, as when a single point is opened, you will generate a high resistance fault and not an open condition.

Homerun with a single EOLR, you can still have a short on any of the 4 other pairs and as long as it's not the pair with the EOLR, the panel and you won't know any different. Troubleshooting would be somewhat easier than a single series loop.

A single series loop and EOLR in the field, the panel would at least be able to discern a short on a wire pair, but troubleshooting would be more difficult.

I'd opt for homerunning, but the EOLR location really doesn't make much of a difference with multiple devices in a series loop, as supervision of the remaining pairs is not possible.

Better would be to run a 4/22, tie a pair together and a pair to the contact, then series in the panel (typically referred to as "form A" contact wiring) and put the EOLR in the panel. Downside is the loop resistance ends up being doubled.
When I look at your photo, I think 2 zones. One for abc, one for de. I think that would be nice compromise for not using a million zones and also making troulbe shooting just a bit easier.

In my home I ran my series loops with the pairs separated so shorts are impossible. I have double hung windows with sensors on each sash. The double stranded wire came from the panel to the first window. At that point, the one strand entered a contact, then exited it. That one wire then went (by itself) to the upper sash where it entered/exited that contactor. Then over the top of the window to the next one where it did the top sash, then to the next top sash (if 3 windows) then down to the bottom sash and across the bottom sashes until it came back to the main double wire. Basically, the wire made a circle around the bank of windows with little "jog-ins" for the contactors. The EOLR can be located anywhere on that single strand section.

Shorts not detected by EOLR are not possible with this setup since the 2 wires are never next to each after the EOLR.
I'd homerun as well and then worry about in the panel. I have mulled windows and ran 22/4 (1 pair per contact) to each of them and then put it in series in the panel.
In FL the prewire had homerunned all of the two sides of the sliding glass doors (6 of them) and I just put each one in their own zone (6 zones)and put a EOL resistor by the doors on one side or the other. The alarm company used 22/2 for the prewire.
You have many options for the wiring as suggested but I wanted to just say your assumption 2 is incorrect. You do not have to use EOLRs if you don't want to. You can do straight open/short.