How to Wire a Liquid Level Relay
A liquid level relay is a device used to monitor liquid level and automatically control circuit on/off, commonly applied in automatic water supply or drainage control for water tanks and pools. Its wiring must be determined according to the specific model and function (such as automatic water supply or drainage). Below are general wiring methods and precautions: Liquid，Level Relay，ac contactor wiring diagram，contactor 1p 25a 24vcontactor air conditioner，contactor connection diagram，contactor for air conditioner，contactor not pulling in，contactor on ac unit，contactor wiring schematic，dc contactor，double pole contactor，electric contactor，how does a contactor work，how to check a contactor，how to wire a contactor，relay and contactor 15ampl，relay contactor，reversing contactor，square d mechanical lighting contactor 4 pole，telemecanique contactor，surge protector
*I. Core Components and Terminal Identifications of Liquid Level Relays*Chint NXR series thermal overload relays price*
*1. Main Components*CHINT circuit breaker price*
- **Power Terminals**: Connected to AC power (e.g., 220V AC).
- **Liquid Level Detection Terminals**: Connected to liquid level detection electrodes (usually divided into three levels: High H, Medium M, Low L).
- **Relay Output Terminals**: Include Common (COM), Normally Open (NO), and Normally Closed (NC) contacts, used to control loads such as water pumps.
*2. Common Terminal Identifications (Taking a Typical 3-Wire System as an Example)*CHINT contactor price*
| Terminal Identification | Meaning |
| L, N | Power input terminals (connect to 220V AC) |
| H, M, L | Liquid level detection electrodes (High, Medium, Low) |
| COM, NO, NC | Relay output contacts (Common, Normally Open, Normally Closed) |
II. Typical Wiring Scenarios and Methods**
*Scenario 1: Automatic Water Supply Control (Start the pump when the water level is below the low level, stop when above the high level)**
**Requirement**: Start the water pump when the water level is below the Low (L) level; stop the pump when the water level reaches the High (H) level.
**Wiring Steps**:
1. **Power Connection**:
- Connect the **L and N terminals** of the liquid level relay to the 220V AC power supply (L to live wire, N to neutral wire).
2. **Liquid Level Detection Electrode Connection**:
- **High Level H**: Connect to the high-level detection electrode in the water tank.
- **Medium Level M**: Connect to the medium-level detection electrode (optional; some models do not require a medium level).
- **Low Level L**: Connect to the low-level detection electrode in the water tank.
- **Common Terminal COM**: Connect to the metal shell at the bottom of the water tank (or a separate common electrode).
- *Principle*: When the water level rises, the electrodes conduct through water, and the relay detects the conduction signal.
3. **Relay Output Connection (Controlling the water pump contactor)**:
- **Use Normally Open (NO) contacts**:
- Connect one end of the water pump contactor coil to the live wire, the other end to the relay's **NO terminal**, and the relay's **COM terminal** to the neutral wire.
- *Logic*:
- When the water level is below L, H, M, and L are not conductive, and the relay's NO contact closes → the pump starts.
- When the water level reaches H, H and COM conduct, and the relay's NO contact opens → the pump stops.
*Scenario 2: Automatic Drainage Control (Start the pump when the water level is above the high level, stop when below the low level)**
**Requirement**: Start the water pump to drain when the water level is above the High (H) level; stop the pump when the water level is below the Low (L) level.
**Wiring Steps**:
1. **Power and Detection Electrode Connection**: Same as automatic water supply (L, N to power, H, M, L to electrodes, COM to common terminal).
2. **Relay Output Connection (Controlling the water pump contactor)**:
- **Use Normally Closed (NC) contacts**:
- Connect one end of the water pump contactor coil to the live wire, the other end to the relay's **NC terminal**, and the relay's **COM terminal** to the neutral wire.
- *Logic*:
- When the water level is below L, H, M, and L are not conductive, and the relay's NC contact remains closed → the pump does not start (normal state).
- When the water level reaches H, H and COM conduct, and the relay's NC contact opens → the pump starts draining.
- When the water level drops below L, H is disconnected, and the NC contact resets to closed → the pump stops.
*III. Key Precautions**
1. **Electrode Installation Requirements**:
- Detection electrodes must be vertically installed on the inner wall of the water tank, with heights corresponding to High, Medium, and Low levels (H > M > L).
- Electrode materials must be conductive (e.g., stainless steel) and avoid direct contact with the water tank's metal shell (unless the shell serves as the common terminal).
2. **Contact Capacity Matching**:
- Liquid level relay contacts have a low current capacity (usually within 5A). Use a contactor to control high-power water pumps to avoid direct connection to the load.
3. **Power and Voltage Matching**:
- Confirm the rated voltage of the liquid level relay (e.g., 220V or 380V) to prevent damage from incorrect wiring.
4. **Insulation and Anti-Interference**:
- Use shielded or insulated wires for detection electrode leads, keeping them away from high-power lines to prevent interference and false operations.
5. **Manual Testing**:
- After wiring, simulate water levels with the power off (e.g., short-circuit H and COM with a wire) to observe whether the relay indicator lights and contact actions are normal.
IV. Common Faults and Troubleshooting**
| Fault Phenomenon | Possible Causes | Solutions |
| Pump does not start | Power not connected, poor contact, electrodes not conducting | Check power supply, clean contacts, test by short-circuiting electrodes |
| Pump does not stop | Oxidized electrodes, stuck contacts, circuit short | Polish electrodes, replace relay, inspect wiring |
| Frequent false operations | Low water conductivity, high interference | Replace with water of higher conductivity, add shielded wires |
*V. Reference Wiring Diagrams**
Automatic Water Supply Control (NO Contacts)**
*Explanation*: When the water level is below L, NO closes → contactor coil energizes → pump starts; when the water level reaches H, NO opens → pump stops.
Automatic Drainage Control (NC Contacts)**
*Explanation*: When the water level is above H, NC opens → contactor coil de-energizes → pump starts; when the water level is below L, NC closes → pump stops.
Summary**
For liquid level relay wiring, first clarify the control objective (water supply or drainage), then select corresponding NO/NC contacts, and ensure correct connection of detection electrodes and power supply. Always power off before operation and refer to the product manual to avoid equipment damage or safety hazards due to incorrect wiring.
