End-of-Line Resistor Values for Alarm Panels and Access Control: Field Guide

Every supervised zone or door input needs the right end-of-line (EOL) resistor. Put the wrong value in and the panel shows a trouble, a fault or a zone that never restores. This guide lists the values the manufacturers' manuals specify for the panels and controllers techs run into most, and shows how to work out an unknown one on a takeover.

How EOL supervision works

The panel puts a small voltage on the loop and reads the resistance back. With a resistor at the far end, it can tell three states apart: normal (it sees the resistor), open (cut wire or open NC contact) and short (shorted wire or closed NO contact).

• NC (normally closed), single EOL: contacts in series. The resistor goes in series after the last device. (S1)
• NO (normally open), single EOL: contacts in parallel. The resistor goes across the loop at the last device. (S1)
• DEOL (dual end-of-line): one resistor across the contact and one in series at the end of the line. The panel can now tell an alarm apart from a cut wire or a short, which it reports as tamper. (S3, S6)
• Zone doubling: two contacts on one loop, each with a different resistor value, so one pair of terminals reports as two zones. (S1, S11)

Quick reference by panel

"Not covered here" means the source we used didn't give a value. It doesn't mean the panel lacks the feature.

Honeywell / Resideo VISTA-15P and VISTA-20P

• Zone EOL: 2k. Zones can be programmed as NC, NO, NC-EOL or NO-EOL using the Hardwire Type prompt in zone programming. Zone 1 is EOL only. UL commercial burglary installs must use EOL zones. (S1)
• Zone doubling (20P only): Hardwire Type option 3. Use 3k and 6.2k, 5%, 1/4 W or larger (supplied with the panel). Zones pair 2/10, 3/11 and so on up to 8/16. Don't zone-double fire zones. A short across either zone of a doubled pair shows as a tamper (CHECK). (S1)
• 2-wire smoke: zone 1, terminals 8 (+) and 9 (–). Up to 16 detectors, or 10 with Clean Me. EOL resistor across the loop at the last detector. (S1, S2)
• 4-wire smoke: zones 2–8. Use a relay (4204/4229) or trigger 17 programmed as zone type 54 to reset power. (S2)
• Bell supervision resistor, VISTA-21iP, VISTA-128/250: Not confirmed. Check that model's manual.

DSC PowerSeries and PowerSeries Neo

• Zone EOL: 5.6k. Single EOL, DEOL (5.6k + 5.6k) or NC with no EOL are set in programming. (S3, S5)
• Fire and 24-hour supervisory zones: single EOL only, never DEOL. (S3)
• Bell: the output is supervised. If no siren is connected, put 1k across Bell+ and Bell- or the panel will show a trouble. (S3, S4)
• PC1864 2-wire smoke: program PGM2 for 2-wire smokes. Connect detector + to AUX+ and – to PGM2, and put 2.2k across the last detector. Don't use 5.6k here. (S5)
• PC1616/1832, PC1555/PC585: Not confirmed in this guide. They're commonly 5.6k, but check the manual.

Bosch B Series (B3512, B4512, B5512, B6512)

• Zone EOL: 1k, part ICP-1K22AWG-10 (brown-black-red). 1k resistors ship with the panel. Wire and contact resistance, not counting the EOL, has to stay at 100 Ω or less. (S6)
• DEOL: set Point Profile > Circuit Style to Dual. Put one 1k at the device and one 1k at the end of the line. (S6, S7)
• Unused points (Point Profile 0) don't need a resistor. (S6)
• NAC: no onboard NAC. Use a D192G with a 1k EOL (P/N F01U033966). (S7)
• GV4/D9412 and Solution 2000/3000: Not confirmed. Check the manual.

DMP XR150 / XR550

• Zones 1–8: 1k EOL (DMP Model 311) by default. You can change it to 2.2k in System Options when taking over an existing panel. (S8)
• Zones 9–10: 2-wire powered zones with reset, 3.3k EOL (DMP 309). (S8)
• Bell: add 1k, 1/2 W across terminals 5–6 for supervision when using a horn or siren. (S8)

Elk M1

• Zone EOL: 2.2k. (S9)
• 2-wire smoke on zone 16: move JP1, program Wire Type 6, and use the 680 Ω EOL from the hardware pack instead of the 2.2k. Maximum wire resistance is 60 Ω. (S9)

Interlogix / GE NetworX NX-8

• Zone EOL: 3.3k. (S11)
• DEOL: enable it in System Options and use two 3.3k resistors per zone. (S11)
• Zone doubling: the NX-200 kit has 3.74k and 6.98k resistors. (S11)
• Loop resistance: 300 Ω maximum on a standard loop, 30 Ω on 2-wire smokes. (S11)
• GE Concord: Not confirmed.

Napco Gemini

• Zone EOL: 2.2k per supervised hardwired zone. (S12)

2GIG GC3 / EDGE

• Hardwire zones: 2.2k at the far end of the loop, with the zone programmed as EOL. (S13)

Qolsys IQ Hardwire 16-F

• Standard: 4.7k. Newer modules have a legacy/learn mode that accepts 1k–10k, which helps on takeovers. Zone 16 stays 4.7k.

Access control inputs

Not confirmed: Genetec Synergis, Honeywell Pro-Watch/WIN-PAK, AMAG, Paxton, Avigilon Alta (Openpath) and Verkada. Many of these run on Mercury hardware, so 1k/1k is likely, but check the controller's manual. For a fire alarm interface, the fire panel usually supplies a dry relay contact to the controller input or the lock power. Supervise it the way that controller's inputs are supervised, and follow local code and the AHJ.

Resistor color band chart (4-band, 5%)

The fourth band is tolerance: gold is 5%. Read from the end opposite the gold band.

What to stock in the truck

This list is based on how many panels and controllers in this guide use each value. It isn't a market-share ranking.

1. 1k (and 1k 1/2 W for bell circuits)
2. 2.2k
3. 5.6k
4. 2k
5. 4.7k
6. 3.3k
7. Specialty: 680 Ω, 3k + 6.2k (VISTA doubling), 3.74k + 6.98k (NX-200)

Troubleshooting

• Measure the loop: disconnect the zone at the panel and meter across the pair with the device closed and the door shut. You should read the EOL value plus a little wire resistance. Open the device and check the reading changes the way it should: open for NC-EOL, near 0 for NO-EOL, or about double for DEOL in alarm.
• Reading about 0 Ω: a short, or the resistor is at the panel or across an NC contact by mistake.
• Reading infinite (OL): a broken wire, a missing resistor or an open contact.
• Reading about twice the expected value: you're probably on a DEOL loop (two resistors in series).
• Takeover with unknown resistors: meter every loop before you pull the old panel. Then either set the new panel to match (DMP allows 2.2k, Qolsys 16-F learn mode accepts 1k–10k, Mercury allows custom EOL in software (S8, S15)) or replace the resistor at the last device.
• Resistor found inside the panel can: move it to the last device, or the run isn't supervised. (S1)
• High loop resistance: stay under the panel's limit: 100 Ω on Bosch (not counting the EOL) and 300 Ω on NetworX. (S6, S11)

Related tools

• Resistor decoder: read color bands, check a meter reading against the loop, and look up the EOL value by panel