EOL Resistors for zones w/multiple contacts

[autoidiot]

Hi all,
I've got a question regarding EOL Resistors. I've read the posts regarding them, and believe I understand their purpose, and the correct way to implement them in a zone with a single contact.

But what is the way to correctly install an EOL resistor in a zone with multiple (in my case NC) contacts? Is the method different depending on whether you're wiring each sensor on a home run (and connecting them serially at the panel)?

My plan (for an Elk M1G) is to do home runs on each of the contacts, which I think will give me a maximum of 3 runs in a single zone. The instructions specify a 2200 ohm EOL. Can I divide this by three (~730 ohms) and put one by each contact? I don't hink this will work, because if one leg gets shorted it will still see 1460 ohms which I think will be in the OK range. Am I better off wiring the sensors serially w/o home runs? If I do that, I assume I just put the single EOL at the farthest contact?

Thanks for any advice you can offer.

Dan

 

[FrankMc]

Hi

I think your correct in assuming that the change in resistance may not be enough to trigger the input.....Although you could proabably test it to prove your thinking....

I would do as you suggest and put the 2k2 resistor on the farethest contact......

HTH
Frank

 

[bfisher]

If you want to wire these sensors in serial (so if any of the windows is open - that zone is open), you can still do it if it's homerun... you will do your "serialization" in the panel (will look messy but will work).

Take the wire from contact 1, and the + goes to the zone board, the - to the + of the next sensor... and so on.

As for your question about the EOL - you are correct - you use just 1 resistor and put it at the end of the chain (after your last sensor).

Hope this helps

 

[upstatemike]

I think the term "home run" confuses a lot of people. A home run to a single device is just that. a dedicated run of wire with an end of line resistor at the device.

For multiple devices, the home runs consist of a feed and a return so the return from one run can connect to the feed of the next and so on. The end of line resistor would go on the return pair of the last device.

This means you have to run the right number of conductors out to each device. If you are running home runs for normally closed door or window contacts you can use 2 conductor wire but for normally open devices use 4 conductor wire so you have a pair of feed wires and a pair for the return. If you are running a powered device like a smoke detector or a motion detector, you need to run an 8 conductor wire so you have a zone and power feed plus a zone and power return.

It is then a simple matter to wire several home runs to one zone by connecting the return wires from each run to the feed wires of the next. The end of line resistor for the zone goes on the return wires from the last home run you are connecting to the zone.

 

[BraveSirRobbin]

Here is a diagram showing how the above posts were referencing for wiring your contacts in "series".

Interesting note is you do give up the "tamper" feature that an EOL resistor on the end of a contact provides for the first two zones (contacts #1 and #2).

In other words, someone could "short out" those contacts with a jumper wire and the system would not know it.

At least you would know if there was a short in the "overall" system so I guess there is some merrit to an EOL methodology.

 

[upstatemike]

In other words, someone could "short out" those contacts with a jumper wire and the system would not know it.

My understanding is that end of line resistors are not meant to detect a short across an individual switch (unless it is the only switch on that zone) but rather an attempt to disable a zone by shorting the wire at some point between the panel and the contact switches.

 

[autoidiot]

Thanks for all the responses. Now for some follow-up questions/responses:

This means you have to run the right number of conductors out to each device. If you are running home runs for door or window contacts, use 4 conductor wire so you have a pair of feed wires and a pair for the return. If you are running a powered device like a smoke detector or a motion detector, you need to run an 8 conductor wire so you have a zone and power feed plus a zone and power return.

Not sure I understand why you need twice the number of wires for this. For contacts, wouldn't you just have 1 feed wire to contact 1, 1 return wire from contact 1 to feed wire for contact 2 (connected near panel), then return from contact 2 to the panel?

It is then a simple matter to wire several home runs to one zone by connecting the return wires from each run to the feed wires of the next. The end of line resistor for the zone goes on the return wires from the last home run you are connecting to the zone.

That's pretty much what I assumed, but then only the last contact is protected by EOL. If I'm going to go that way, it seems like I should just put the EOL at the panel, since that will increase my future flexibility, and only minimally reduce the system effectiveness.

Here is a diagram showing how the above posts were referencing for wiring your contacts in "series".

Interesting note is you do give up the "tamper" feature that an EOL resistor on the end of a contact provides for the first two zones (contacts #1 and #2).

Thanks for the diagram. That did help clarify the situation. I'm thinking the degree to which the "tamper" feature is reduced depends on how the wire is physically run (and thus the likelihood that the wiring will end up accidentally shorted). In other words home-running multiple contacts that are wired in series near the panel seems more dangerous because you have the feed & return running in the same jacket (nail could easily short across). On the other hand, wiring in series seems safer, because the only place where a short wouldn't be detected is right near the contact itself (between the contact and where it's spliced into the main wire run).

Based on all of this, it seems like I should choose one of the following, depending on whether flexibility (i.e. home-run) or line supervision (i.e. EOL) is my priority:
1) Wire in series (not home-runned), with EOL at farthest contact
or
2) Do homeruns with EOL at panel

Am I missing something here?

Thanks,
Dan

 

[rfdesq]

Based on all of this, it seems like I should choose one of the following, depending on whether flexibility (i.e. home-run) or line supervision (i.e. EOL) is my priority:
1) Wire in series (not home-runned), with EOL at farthest contact
or
2) Do homeruns with EOL at panel

Am I missing something here?

Now I'm confused. Why aren't you homerunning everything and putting EOL resistors at the farthest end away from the panel of each run? Why run multiple contacts in series when the M1 has 208 zones? Why aren't you using input zone expanders so from distant locations all you have is a single Cat X wire running to the data bus hub? Just a few of my questions.

 

[upstatemike]

Not sure I understand why you need twice the number of wires for this.  For contacts, wouldn't you just have 1 feed wire to contact 1, 1 return wire from contact 1 to feed wire for contact 2 (connected near panel), then return from contact 2 to the panel?

I think I did a bad job of making my point because I was trying to be general enough to include all types of zone devices and not just magnetic contacts. I think you are correct in your description with respect to magnetic contacts.

That's pretty much what I assumed, but then only the last contact is protected by EOL. If I'm going to go that way, it seems like I should just put the EOL at the panel, since that will increase my future flexibility, and only minimally reduce the system effectiveness.

If you put the resistor at the panel then the zone is not tampr protected. With a resistor at the end of the line the entire loop is protected against somebody shorting the zone wire in an attempt to bypass it.

End of line resistors do not protect against shunts at individual contacts.

Why aren't you homerunning everything and putting EOL resistors at the farthest end away from the panel of each run? Why run multiple contacts in series when the M1 has 208 zones?

This is a good question. It would certainly simplify things.

 

[autoidiot]

Why run multiple contacts in series when the M1 has 208 zones? Why aren't you using input zone expanders so from distant locations all you have is a single Cat X wire running to the data bus hub? Just a few of my questions.

I'm embarassed to admit it, but I didn't realize that the zone expanders existed. I thought I was limited to 16 zones, and so I was trying to work with that. I'm not thrilled about having to buy 2 zone expanders, but I think your suggestion is the overall best way to go. Well I'm off to go wire now...thanks for all the advice!

Dan

 

[rfdesq]

Don't be embarrased, I've only installed a couple of ELK M1's and I'm still learning. Thank heaven for ELK tech support when I get stumped. You are wise to use expanders and not series your windows. With individual zones you will know which zone tripped in case of a true or false alarm, you could bypass a window for ventilation or in case you have a bad switch. Good luck, I've only been doing this for 30+ years. My first panel was a one of a kind home brew, nothing like the M1.

 

[BraveSirRobbin]

In other words, someone could "short out" those contacts with a jumper wire and the system would not know it.

I think this diagram was meant to show the switches in a normally closed position. (Normally open switches wired in series would not make any sense).

End of line resistors are not meant to detect a short across a switch but rather an attempt to disable a zone by shorting the wire at some point between the panel and the contact switches.

It's just a drawing showing switches, you can use normally open or closed, but normally closed (on magnetic contact) is the norm.

And I'm correct in the fact that if you wire the switches in series someone can short out (i.e. place a wire across the magnetic contact) and bypass those first two zones and the system would never know it.

EOL's ARE meant to prevent someone from doing this BUT you have to have them on the END of the magnetic contact to achieve this. That is, if you have the EOL in the alarm panel, someone could still short out the sensor.

If I'm not explaining this in enough detail, please let me know!

 

[FrankMc]

Isnt that why they call them EOL ....END OF LINE ;-)

Frank

 

[elcano]

End of line resistors are not meant to detect a short across a switch but rather an attempt to disable a zone by shorting the wire at some point between the panel and the contact switches.

EOL usage and location depends on your perceived need for security and sensor location.

Each person knows better than anybody how much security do they need in their respective situation. And even this is relative. Perception of security can be different for two people living in the same area. I have been in Latin America countries several times. There medium to high income people go to the extremes for security - and they really need it.

A single EOL will provide you the safety that you will know about accidental shorts in the overall wiring. For most people in the US this is all what they need. Also, if your wiring is exposed to tamper in any way (before reaching the sensors), they will add security to your installation against tamper attempts.

However, if the most exposed point of your wiring is very close to the sensor (or is the sensor itself*), then you might want to install an EOL in series with the sensor inside the sensor. Its a little cramped, but I did it once. Some sensors are closed and do not let you do it. Other are too small. Again, this depend on your requirements for security and situation. This is more appropriate for outdoor sensors like garage doors and fences.

So if your application requires it, you will need a single zone by sensor using an EOL at the sensor.

*The sensor can always be bypassed using a strong magnet. If your situation merits it, you might want to get the MagnaSphere contact sensors. They would trigger the alarm at any attempt of tampering using a magnet, but they are expensive, and I dont know anybody using them (even on this forum). See them here:
http://www.grisk.com/high_security/magnasp...itch%20sets.htm

 

[FrankMc]

Personally i would always recommend putting the EOL at the detector/door contact etc....and not just for security reasons.....For instance if you have some plumbing or carpentry work done and they accidently drive a nail through the wire and short the alarm pair this will not show up if the EOL is located at the alarm panel.......

As mentioned above , i prefer to use "Tamper Detection" you actually install 2 resistors in a sensor / door contact and this allows the alarm panel to determine if the sensor is in alarm or in tamper condition using one pair of wires for both.......

Frank