EOL Resistor Calculator: Precision Intrusion Loop Supervision & State Solver

EOL Resistor Calculator sizes, configures, and troubleshoots Single (SEOL), Double (DEOL), and Triple (TEOL) end-of-line resistor loops on hardwired intrusion alarm zones, across panel architectures like DSC PowerSeries/Neo, Honeywell Ademco Vista, Paradox EVO/Spectra, Bosch B/G Series, and Texecom Premier Elite.

It is built around a small set of non-negotiable rules. Resistors must sit inside the sensor housing at the far end of the cable run, never stacked at the panel's screw terminals - panel-terminal placement only protects the metal cabinet and leaves the whole run to the sensor unsupervised. A Double-EOL loop is a 4-state truth table: 0 ohms reads as Tamper (short), the nominal EOL value reads as Normal, EOL-plus-alarm-resistor reads as Alarm, and an open circuit reads as Tamper (cut wire) - giving supervised discrimination between an intruder tripping the sensor and someone sabotaging the wiring.

RESISTANCE_PER_M = {18: 0.0209, 20: 0.0333, 22: 0.0530, 24: 0.0842}

For long cable runs it compensates for copper wire resistance using R_loop = 2 x D x resistance-per-meter (a 150m run of 22 AWG adds roughly 15.9 ohms) and checks the result against the panel's ADC acceptance window, computed from the pull-up resistor and reference voltage that the panel uses to measure zone voltage. It carries a reference matrix of nominal EOL values per panel brand (DSC 5.6k, Honeywell 2.0k, Paradox 1.0k, Bosch 1.0k/2.0k, Texecom 2.2k/4.7k), and a pre-emit checklist that verifies resistor placement, manufacturer-correct values, wire-gauge compensation on long runs, all four DEOL states documented, that fire-loop logic is never conflated with burglary DEOL logic, and that soldered or crimped connections are specified over twisted tape splices.

Use it when sizing, retrofitting, or diagnosing hardwired security loops - wiring double EOL on a DSC panel, calculating zone loop resistance for a long cable run, troubleshooting a constant zone tamper fault, or looking up which resistor values a given panel brand expects. It differentiates Normal, Alarm, Tamper (short), and Cut (open) states across each panel's threshold window and accounts for copper wire drop on long perimeter runs so wire resistance alone doesn't trigger a phantom fault.

Do not use it for wireless sensors or addressable polling-loop multiplexers, which use digital transponders instead of passive EOL resistors. It never advises bypassing or defeating safety or life-safety supervision circuits, and it is not a substitute for consulting panel-specific polarity and current-limiting specs on 2-wire smoke detector loops.

Inputs are the panel model and its nominal EOL/tolerance values, the wire gauge and one-way cable run distance, and whether the loop is single, double, or triple EOL. Output is the wiring topology (resistor placement and series/parallel arrangement), the expected resistance and voltage readings for each of the four loop states after wire-drop compensation, a check against the panel's acceptance window, and a multimeter-based field diagnostic sequence for verifying a loop's actual state against those expected readings.

Alarm and security system installers and technicians sizing, wiring, or diagnosing hardwired EOL resistor loops - matching resistor values to a specific panel brand, compensating for wire resistance on long runs, and reading multimeter diagnostics correctly instead of guessing at or bypassing a trouble condition.