The CST-05 liquid level controller relay is an electrode-type automatic level controller that switches pumps on and off for filling or emptying tanks, sumps and wells containing conductive liquids. Compact, DIN-rail or panel mounted, 220 VAC supply and a 5 A contact that switches small pumps or contactor coils directly – a simple, durable and virtually maintenance-free solution for pump dry-run protection and tank overflow prevention.
Equipment Industrial Solution Co., Ltd (ISE) supplies the CST-05 / CSR-05 level relay with wiring advice and electrode selection for each application.
How does a 3-electrode level relay work?
The relay is connected to three electrodes installed at different heights in the tank or well: upper electrode (U), lower electrode (L) and bottom/common electrode (B).
- When the level is between the lower and bottom electrodes, the relay is not energised.
- When the liquid rises to touch the upper electrode, the relay energises.
- When the liquid falls below the lower electrode, the relay de-energises.
The hysteresis between upper and lower electrodes prevents the pump from short-cycling, extending pump and contactor life.
| Relay state | 16 (NC) – 15 (COM) | 15 (COM) – 18 (NO) |
|---|---|---|
| Energised (liquid touches upper electrode) | Open | Closed |
| De-energised (liquid below lower electrode) | Closed | Open |
Contact selection: use 15–18 (NO) for emptying / drain pumping (pump runs when the tank is full, stops when empty); use 15–16 (NC) for filling (pump runs when the tank is low, stops when full). For two-electrode operation, connect U and L only and leave B unused.
Sensitivity adjustment
Sensitivity is set with the front knob, up to 100 kΩ. With the electrodes immersed, turn the knob towards 100 kΩ until the relay energises (LED on). For reliable detection, the liquid resistance must be lower than the set sensitivity.
Advantages of the CST-05 liquid level controller
- Fully automatic filling or emptying – no operator required.
- Pump dry-run protection, tank overflow prevention and borehole pump protection.
- Adjustable sensitivity up to 100 kΩ for clean water, well water and wastewater.
- Simple wiring with two LEDs for power and relay status.
- DIN-rail or screw mounting, compact size.
- No moving parts in the tank (unlike mechanical floats) – long life, few failures.
Applications of the level controller relay
- Automatic filling of rooftop tanks and storage tanks in factories and buildings.
- Borehole pump control with dry-well protection.
- Sump, wastewater pit and basement drainage pumps.
- Level control for water treatment tanks, cooling towers and boiler feedwater tanks.
- Conductive liquid level detection in machines and production lines.
CST-05 level relay specifications
| Parameter | Value |
|---|---|
| Operating voltage | 150 – 260 VAC |
| Frequency | 50/60 Hz |
| Power consumption | < 6 VA |
| Sensitivity | < 100 kΩ (adjustable) |
| Contact | 5 A / 250 VAC (resistive), 1 × NO/NC |
| Operating temperature | −20 °C to +55 °C |
| Altitude | < 2000 m |
| Ingress protection | IP20 (panel mounting) |
| Terminals | Screw terminals, up to 2.5 mm² |
| Indication | 2 LEDs |
| Mounting | DIN rail or panel screw |
| Weight | < 250 g |
| Dimensions CST-05 | 84.5 × 80 × 44 mm |
| Dimensions CSR-05 | 90 × 94.6 mm (mounting face) |
Installation and maintenance notes
- Install the relay in a dry electrical panel, not in damp locations.
- Always fit a switch and circuit breaker near the unit, clearly labelled as the relay disconnect.
- For larger pumps, use the relay contact to drive a contactor coil rather than switching the pump directly.
- For conductive, non-flammable, non-explosive liquids only.
- For cleaning: isolate power and disconnect wiring, wipe the housing with a dry cloth only, then test operation before returning to service.
FAQ
Which liquids can the level relay be used with?
Conductive liquids such as clean water, well water, wastewater and boiler feedwater. Not for distilled water, oil, petrol or flammable liquids.
Can the relay drive a pump directly?
The contact is rated 5 A / 250 VAC resistive. Small pumps can be connected directly; pumps from about 0.75 kW should be switched via a contactor.
Filling or emptying mode?
For pumping into a tank use filling mode (NC contact 15–16). For sumps and wastewater pits use emptying mode (NO contact 15–18).
Related products
Where to buy the CST-05 liquid level controller relay?
EQUIPMENT INDUSTRIAL SOLUTION CO., LTD (ISE) – Ho Chi Minh City, Vietnam – supplies genuine the CST-05 liquid level controller relay with technical consulting, fast quotation and on-site commissioning support across Vietnam and Southeast Asia.
Contact us: Sales +84 909 617 185 – Technical +84 979 117 185 – Email: [email protected]
