The value printed in the installation manual of the panel or module that supervises the circuit, and no other. There is no universal end-of-line (EOL) resistor: Fire-Lite MS-5UD panels use 4.7K, Fire-Lite MMF-300 modules 47K, the Simplex 4006 uses 3.3K on initiating circuits and 10K on notification circuits, and Potter's PFC-4064 uses 5.1K.
Those figures come from the manufacturers' own documents and are listed with part numbers below. If your panel is not in the table, open its manual at the wiring diagram for the circuit in question. The EOL value and the manufacturer's part number are printed next to the last device.
What is an end-of-line resistor and what does it do?
It is a resistor installed after the last device on a Class B circuit so the panel can monitor the wiring for continuity. The panel passes a small supervisory current through the pair and expects to see the resistor. A broken wire removes it and the panel reports a trouble. On an initiating device circuit, a detector or pull station closing across the pair looks very different from the resistor, and the panel reports an alarm. The panel's thresholds are designed around one resistance, which is why the value has to match.
Which resistance value does each panel or module family use?
| Product | Circuit | EOL value in the manufacturer's document | Manufacturer part number |
|---|---|---|---|
| Fire-Lite MS-5UD, MS-10UD | Class B IDCs and NACs | 4.7K, 1/2 W | 71252 |
| Fire-Lite MS-4424B (24 V) | IDCs and NACs | 4.7K, 1/2 W | 71252 |
| Fire-Lite MS-4412B (12 V) | IDCs and NACs | 2.2K, 1/2 W | R-2.2K |
| Fire-Lite ES-200X | Class B NACs | 4.7K, 1/2 W | 71252 |
| Fire-Lite MMF-300, MMF-301 monitor modules | Class B IDC | 47K | ELR-47K, supplied with the module |
| Fire-Lite MMF-302 module | Module circuit | 3.9K | R-3.9K, supplied with the module |
| Simplex 4006 | Class B IDCs | 3.3K | 4081-9002 |
| Simplex 4006 | Class B NACs | 10K, 1/2 W | 4081-9008 |
| Simplex 4098-9756 duct sensor housing | Remote relay circuit | 10K, 1/2 W | 4081-9008 |
| Potter PFC-4064 | Class B IDCs and NACs | 5.1K | Potter 3005013 |
| Kidde FX-5R, FX-10R | IDC set as combination waterflow and supervisory | One 3.6K and one 1.1K | EOL3.6-1.1 |
| System Sensor COSMOD4W module | Detector loop | 3.9K | Supplied with the module |
Two things stand out. The MS-4412B and MS-4424B are the same panel family in 12 V and 24 V versions and use different resistors. And the MS-5UD panel takes 4.7K on its zones, while a Fire-Lite monitor module wired to the same building's devices takes 47K. Reading one resistor off a neighbouring circuit is not a safe way to choose.
Can I substitute a different value?
No. A resistor of another value, or a pair of resistors combined to approximate it, is not what the panel was listed with. The exceptions are the ones the manual itself documents:
- Potter's PFC-4064 manual provides a reference EOL input on the NACs. Connect a resistor from 2.0K to 27K there and the panel supervises all NAC wiring against that value.
- Fire-Lite's ES-200X data sheet lists NAC end-of-line resistor matching, with a range of 1.9K to 22K.
Both are set up by the procedure in the manual, and the limits in the manual still apply. Circuits you are not using still need a resistor at the panel: the MS-5UD manual says to dummy-load every unused circuit with 4.7K.
Where does the EOL resistor go, and do Class A circuits need one?
On a Class B circuit it goes at the far end, across the pair after the last device. Simplex describes its harnesses as Class B end-of-line resistors for remote locations, and its duct housing sheet puts the resistor at the last relay.
A Class A circuit returns to the panel or module, and in the manuals we checked no field resistor is installed at a last device:
- On the Fire-Lite MMF-300, the Style D (Class A) diagram notes that the EOL resistor is internal to the module.
- The MS-5UD and MS-10UD need the CAC-5X converter module for Class A circuits.
- The PFC-4064 needs the CA-4064 expansion board for Class A NACs.
Follow the Class A diagram in your own manual. The circuit classes themselves are defined in NFPA 72.
How do I identify a resistor's value from its colour bands or part number?
By part number if the resistor came in a manufacturer's harness or bag, by colour code if it is bare. Simplex publishes the values of its 4081 Series harnesses:
| Simplex part | Value |
|---|---|
| 4081-9002 | 3.3K, 1 W |
| 4081-9003 | 4.7K, 1/2 W |
| 4081-9004 | 6.8K, 1/2 W |
| 4081-9008 | 10K, 1/2 W |
| 4081-9011 | 100 ohm, 1/2 W (a line matching resistor for annunciator communications) |
| 4081-9018 | 10K, 1 W |
For a loose four-band resistor, the standard colour code for the common fire alarm values is:
| Value | First three bands |
|---|---|
| 2.2K | Red, red, red |
| 3.3K | Orange, orange, red |
| 3.9K | Orange, white, red |
| 4.7K | Yellow, violet, red |
| 5.1K | Green, brown, red |
| 6.8K | Blue, gray, red |
| 10K | Brown, black, orange |
| 47K | Yellow, violet, orange |
A fourth band in gold means 5% tolerance. Note how close 4.7K and 47K look: only the third band differs. If the bands are faded, disconnect the resistor and measure it with a meter. Wattage matters too, so use the manufacturer's listed part.
What is an EOL power-supervision relay, and when is it needed?
It is needed when 4-wire smoke detectors are on the zone. Those detectors take power on a separate pair, and the panel has no way to know that pair has failed. The relay is installed at the end of the detector power run with its contacts in the zone wiring, ahead of the EOL resistor. If power is lost the relay drops out, the zone opens and the panel reports trouble.
System Sensor's 4-wire i3 instructions name the EOLR-1, and its i4 data sheet lists the EOLR-1 as required with 4-wire systems. The Fire-Lite MS-5UD manual shows a power supervision relay on the zone and refers to the Device Compatibility Document for the relays it accepts.
The store stocks EOL resistors from Fire-Lite, Simplex, Potter, Kidde and others, including the Potter 5.1K assembly; match the part number in your manual before ordering. In-stock orders placed by 3 PM ET ship the same business day. Confirm every value against the control panel's listing documents, and install to NFPA 72 and your local AHJ. If the part you need is not listed, request a quote with the panel model and the circuit type.
Sources
- Fire-Lite, MS-5UD and MS-10UD Series Manual (52626): prod-edam.honeywell.com/.../52626.pdf
- Fire-Lite, MS-4412B and MS-4424B data sheet (DF-51195): prod-edam.honeywell.com/.../df-51195.pdf
- Fire-Lite, ES-200X Series data sheet (DF-60957): prod-edam.honeywell.com/.../ES-200XP-Data-Sheet.pdf
- Fire-Lite, MMF-300 Monitor Module Installation and Maintenance Instructions (I56-3653): prod-edam.honeywell.com/.../i56-3653-003.pdf
- Fire-Lite, MMF-301 Monitor Module Installation Instructions (I56-1193): prod-edam.honeywell.com/.../I56-1193-003.pdf
- Simplex, 4081 Series End-of-Line Resistor Harnesses data sheet (S4081-0003): docs.johnsoncontrols.com/simplex/.../KftHfeeaXwIIBFlIXDOEQg/content
- Simplex, 4006 Series Fire Alarm Control Panels data sheet (S4006-0001): docs.johnsoncontrols.com/simplex/.../zJNaolBCM4CCRf5462j~Rg/content
- Simplex, Addressable Duct Sensor Housings data sheet (S4098-0030): docs.johnsoncontrols.com/simplex/.../9nV823vah63qrU2BRu~aQg/content
- Simplex, 4606-9101 LCD Annunciator data sheet (line matching resistor 4081-9011): docs.johnsoncontrols.com/simplex/.../HOsk72sIYewt0q5gB1TNWg/content
- Potter, PFC-4064 Installation, Operations and Programming Manual (5403638): pottersignal.com/product/manual/5403638_PFC-4064.pdf
- Kidde, FX Series Conventional Fire Alarm Systems data sheet (K85005-0126): myeddie.edwardsfiresafety.com/.../K85005-0126
- System Sensor, i3 Series Installation and Maintenance Instructions (I56-2170): prod-edam.honeywell.com/.../i3_Thermal_Manual_I56-2170.pdf
- System Sensor, i4 Series data sheet (CODS303) and i4 Series Interface Module manual (I56-3871): prod-edam.honeywell.com/.../i4Series_Datasheet_CODS303.pdf, prod-edam.honeywell.com/.../i4Series_Module_Manual_I56-3871.pdf