Where Do End Of Line Resistors Go?

It is very common for alarm installers to put the EOL resistors at the alarm panel terminals, like so:

One installer commented he was taught to do it this way:

"They also installed the EOL's at the panel. When I was introduced to the industry, I was also taught the practice of EOL's at the panel."

This is so commonly done, I am not sure if this is incorrect. Some installers cite the security of installing the EOLR in a locking enclosure is a big benefit.

However, I have been taught the opposite, that installing EOLR at the panel is wrong and defeats the purpose. EOLR are used to provide a known load at the end of the alarm loop that is checked for by the panel. Installing the resistor at the panel only supervises the wiring between the resistor and the panel (nothing at all).

Which way is correct? Vote:

Note: We asked this over 4 years ago but with the increased experience and intrusion awareness of the site, it is worth asking again.

I see the technicians were taught the BOLR method.

The EOL resistor can be installed in the panel without defeating the supervision but two wires must be run to the device instead of one.

For the hassle of the extra wire you are spared the hassle of trying to conceal the resistor. Also having them all in one place is nice, esp. if one goes bad.

...but two wires must be run to the device instead of one.

Correction: four wires instead of two, as described below in Ari's Facebook post.

Two pairs instead of one.


Admittedly I have only my own panel to go by, but this method seems give the best of both worlds.

Why do you think it's not very popular (apparently)?

Because it's more work, that's why. It requires you to run two pairs of cables (or a multiconductor cable) instead of a two conductor cable, it takes longer to wire up, and it requires you to know what you're doing. Not conducive to finishing multiple panels in a single day, in other words.

This method is mandatory for commercial fire panels, however. I've seen AHJs instafail jobs over this, on the theory that if the installer skimped on proper supervision, they probably did a shoddy job everywhere.

Diagram example plz using 2 pairs of cables?

First off, if the device is a detection or notification device it should be at the end. The purpose is to alert on an open in the wiring. A short creates an alarm.

If it's an intrusion circuit there are switch manufacturers that would build the EOL into the actual switch. Some circuits provided a "dual EOL" circuit that supervised the wiring separately than the devices. High security and Europe.

You could run a 4 wire intrusion circuit that installs the EOL in the panel correctly or terminates on return terminals.

The way this panel is wired, you could twist the wires together anywhere in the field and disable the device. Maybe that's important, maybe not.

There is more concern when using normally open contacts.

the wires to NC contact can get cut and go into alarm if the resistor is at the panel, but if the contact is NO and the wires get cut there is no reaction.

But the wires to a NC contact could be shorted together with the resistor in the panel and also create no alarm.

The DSC Neo system we are testing specifically states EOL go at the far end:

So, I asked this on Facebook. It turned into quite the flamewar.

The majority of respondents were adamant that the resistor goes at the contact (hence EOLR= End Of Line Resistor).

  • "It goes at the end, at the device. End of story. If you can't get it there, go find a new job."
  • "End of the line, or EOL. In the panel is just lazy."
  • "If you understand the theory as to why a resister is used, you'd get why it's placed at the contact."
  • "For true supervision the resistor goes in the field."

Some respondents replied that the resistor goes in the panel.

  • "Theoretically the end of the line is at the panel since electricity makes a loop right? At the device would be middle of the line"
  • "Ok? Where is the end of line. The return voltage comes back on the negative. The negative ends at the panel. OR The cable goes out to the device and ends there. So which is End Of Line?"
  • "If it's a N/O circuit it definitely goes at the EOL, if it's a N/C and it's not a critical circumstance that requires it be at the device it gets put I'm the panel. Perhaps that's not ideal to an engineer that sits in a desk and doesn't work on them day in and day out but that's the way the cookie crumbles.
  • "On commercial jobs in field. Residential at panel except for fire devices and motion detectors or GB."

A few respondents mentioned that running a cable with four conductors instead of two allows the installer to leave the resistor in the panel while still ensuring proper supervision.

  • "Most installers home run all their wires and they will use a 2 conductor wire. If you have a window bay with 4 windows, you have 4 wires at the panel. Most panel will give you 8 zones, so with large installs you have to bundle your wires. The EOL resistor is to detect shorts on a N/C circuit. You cannot monitor all 4 wires for shorts, so putting the EOLR out there won't do much. What's important is to put the EOLR on the negative side of the wire to detect ground faults, this is important because a ground fault can bypass the devices and no one will know until it's tested."
  • "In NYC traditionally you run a 4-wire and put the resistor back in the box... but electrically still at the end of the line. Everywhere else, it should be at the end of the line... usually that means it's out at the device."

Now for my two cents: If the purpose of the resistor is supervision, the the argument for putting the resistor at the contact makes good sense to me. Many devices and most panels specify use of a resistor at the contact.In addition, the ESA says "Wiring should be done so that removing the device causes a trouble signal." That certainly implies a resistor at the contact to me.

That said, keeping the resistor in the can makes it more secure, and servicing is certainly easier.

Some respondents said they actually hide the resistor.

  • "I run every door contact THROUGH the nearest glass break's box and leave a loop. This way, if I can't get it in the jam, I can put it in that box rather than at the panel."
  • "Neither. Try to put them in a finished ceiling half way between contact and panel. The goal is to make nearly impossible to find."

All I can say to that is, I hope I never have to troubleshoot their jobs.

ummm.... at the END OF THE LINE?

If your going to put the EOL resistors in the can why not just turn off the "Zones require EOL resistors" in the zone programming.

IIRC DSC Section 13, option 1

I priced out an ADT takeover today. There is an Ademco installed but we use DSC so there are 2k resistors installed behind a bunch of 3/8" contacts that will have to be dealt with and replaced with 5.6k.

Anyone have a go to method to deal with this? These contacts are not easy to get out and have paint around them. Trying to get them out will likely damage them.

Has anyone ever left them in place and modified the resistance in the panel by adding more resistors? If so, is there an easy way to calculate how to do so

Has anyone ever left them in place and modified the resistance in the panel by adding more resistors? If so, is there an easy way to calculate how to do so?

Resistors in series simply add up. So you need a 3.6k resistor in series.

Yes, I’ve added resistors in series to reach a specific value on a perimeter intrusion circuit and have never had an issue.

This is the only example of this meme I have actually found funny:

At-least the meme is not talking about the AWG of his 1 conductor and whether or not it is shielded or non shielded.

When we first got into intrusion a couple years ago, I had to keep asking about the resistor as almost every panel I saw had resistors in the panel. I kept sending pics to my DSC rep and he was like yup, that's wrong... lol

Then when I was interviewing techs, I had some tell me panel was the correct location.. some told me last device but admitted they were trained and instructed to put them in the panel...

When i first got into the industry, I was also taught to put them in the panel, not because it was the right way but because it was easier. I accepted this for a while until I started asking an electrical forum about resistors. Almost all answers were "it goes in the field" or "if it's in the panel, why use resistors at all". Armed with this information and a very bad case of OCD, when my boss stopped looking over my shoulders all the time, i did it the way i thought was more secure and placed them in the field at the device.

I worked for a company a long time ago that had a requirement for wiring all contacts with 22/4 in a specific manner to route the loop through the contact, back to the panel and through a resistor, and then another cycle out to the field and back to the terminal board. It was cumbersome but their logic was it added supervision but made the system much more serviceable than burying the EoL at the device.

I would be that almost every DSC system I've seen has either had resistors at the panel or supervision disabled in programming.

This was great except when you had several door or window contacts in series. Then you had one hot mess in your panel. I too worked for a company that tried to mandate this. We did it for about a month and then said forget it. Many called this the poor mans attempt at a Class A circuit.

The survey should have another option: "At the end of line", which would be the correct answer.

Key word "line" which could be at the last device, or if the line extends back to another location (including the panel), where the high and low side of the circuit end.

For those that say using four conductors and placing the EOL in the panel, when wired correctly, are correct.

For us older techs, close your eyes and imagine UL certificates, lace wire, window foil and Simpson analog meters.

Window foil. Now there's a lost art. Other than a door getting beat up virtually no false alarms when window foil was installed properly.

I might add with decent takeoff devices, good blocks and left alone. The art of painting advertisements on windows with constant washing, adding window tint inside a window and other issues certainly made servicing it challenging.

I guess the moral of the story is that time fades the memory of the pain.

I saw this on a museum I visited while traveling east. The tape might be about as old as I am.

Image may contain: indoor

Please don’t take this the wrong way but the first few times I read your comment I really thought maybe you were high. Read it to yourself and you might see what I mean. Like I said after tests few times I get what you are saying. Yes being a good way to monitor glass foil was also a royal pain in the a$$. Especially depending on which version of taps you got. Not sure what the difference was but one had a blue stripe on the peel off part and the other red. Not sure which but one was almost impossible to get apart.

I’ve seen this pop up a few times so I guess I’ll mention the obvious. Where you put the resistor or resistors (yes, there are double EOL systems) only matters if you also program the loop correctly.

Just sayin’

I would say it matters if one wants to supervise the integrity of both a circuit and and the integrator.

Besides door contacts does other device wiring get monitored by EOLs? Like Rex pir, motion sensors, window contacts, readers, etc?

Fire devices of all types in the US are supervised as Class B (old school) for alarm on short and trouble on open.

Hold-Up and Panic buttons are usually supervised the same.

Some Fire circuits are supervised and wired in Class A (again, there are newer terms) with a 4 wire circuit at the panel and in high rise a separation of conduits.

This allows for a broken wire and notification of the open, but still give an alarm if shorted on either side of the break.

24HR intrusion zones can be supervised for Day Trouble on Open if disarmed and Alarm on either if armed. This is also for window foil.

About the only inputs I don’t recall requiring an EOL is the cabinet tamper.

It should be an easy answer, it’s called an “end of line resistor” for a reason!!!