Belimo 22HL-520 : Liquid Leakage Switch, Conductivity Sensing (~10 uS), Rope/Cable Detection 65 ft (20 m), SPDT Relay (1A @ 24V) Output, LED Indicator (Green/Red), Automatic Reset, 24 VAC/VDC, 1/2" NPT Conduit, NEMA 4 / IP65, 5-Year Warranty

What does the 22HL-520 detect and how does it signal a leak?

It detects the presence of liquid (water or water-glycol mixtures) via conductivity sensing at the sensing contacts, with a threshold of approximately 10 µS. Detection happens anywhere along a 65 ft (20 m) sensing cable that runs along the floor or area being monitored. When liquid is detected, the SPDT relay activates, changing state from normal to alarm position. The on-housing red LED illuminates to show the alarm condition visually. After the sensing contacts dry, the unit automatically resets — no manual intervention needed.

How do I install a 65-ft leak detection cable?

The sensing cable runs along the floor, perimeter, or critical area where you want leak coverage. Common deployment: lay the cable in serpentine pattern under a raised floor in a server room, or along the perimeter of a mechanical equipment skid, or in trays beneath suspended cooling coils. Secure with installer-supplied cable ties (one is included for the sensor housing itself, but additional ties for the run length are not supplied). The cable's outer jacket is conductive on two parallel conductors — when water bridges them at any point along the length, the conductivity threshold is crossed and the sensor triggers. Avoid running the cable directly under HVAC drip pans where condensation could cause nuisance alarms; aim for the floor itself where only real leak water would pool.

Where should I install this sensor?

Run the 65 ft sensing cable along the floor or critical perimeter of the area you want to protect. Server room sub-floors, data center cold aisles, telecommunications equipment rooms, suspended ceilings above critical equipment, and large mechanical room floors are typical applications. The sensor itself (the housing) mounts on a wall or panel near the cable's start point, with the cable extending out from there. Avoid running the cable directly under HVAC drip pans where normal condensation could cause nuisance alarms.

What media can this sensor detect?

Water and water-glycol mixtures — anything with conductivity above the ~10 µS threshold. This includes essentially all hydronic system fluids (chilled water, hot water, condenser water, glycol loops). The sensor will NOT reliably detect: deionized water (too low conductivity), oils, refrigerants, fuels, or non-conductive solvents. For oil or fuel leak detection, a different sensing technology is required (typically optical or hydrocarbon-specific). Operating fluid temperature range is -4 to 158°F (-20 to 70°C).

How is the relay output wired?

SPDT (Single Pole Double Throw) changeover dry contact — three terminals: Common (C), Normally Open (NO), Normally Closed (NC). The relay is a passive dry contact, no internal voltage source. Wire the load circuit's voltage through C and NO (for normally-open behavior — circuit closes on alarm) or through C and NC (for normally-closed behavior — circuit opens on alarm, fail-safe). Max switching current is 1 A at 24 V; min is 3 mA at 10 V. Use NC wiring for fail-safe applications where loss of sensor power should also trigger the alarm condition.

Does the sensor reset automatically after a leak event?

Yes. After the sensing contacts dry (no longer detect conductive liquid), the relay automatically returns to normal state and the LED returns to green. No manual reset button to press, no field re-arming required. This is particularly valuable for installations in hard-to-access locations (suspended ceilings, sub-floors) where a manual-reset sensor would require an extra service call after every transient event. If the BAS needs to record the alarm event for audit purposes, the controller should latch the alarm signal internally — the sensor's own reset is automatic and doesn't preserve event history.

How does this differ from the other 22HL variants?

All 22HL variants share the same chassis, conductivity sensing principle, auto-reset behavior, NEMA 4 / IP65 housing, and 24 VAC/VDC power. The differences are: 22HL-50 = point detection on housing, 1× SPDT 1A relay; 22HL-502 = point detection, 2× SPDT 3A relays (dual, isolated); 22HL-505 = 16.4 ft (5 m) rope/cable detection, 1× SPDT; 22HL-520 = 65 ft (20 m) rope/cable detection, 1× SPDT. Choose point detection for known leak locations (drain pans, equipment bases); choose rope detection for extended areas (server rooms, data center sub-floors). Choose the dual-relay 22HL-502 when you need simultaneous valve-shutoff and BAS-alarm actions from a single sensor.

Does it need 24V power?

Yes. 24 VAC or 24 VDC supported (AC 21.6-26.4V / DC 13.5-26.4V). Power consumption is 1.5 VA AC / 0.6 W DC — very low draw, compatible with standard 24V control transformers shared with actuators and other sensors. Note that the relay output is a dry contact (passive) — the supply voltage to the load circuit must be provided externally.