Westhomes WSB1L Series 125A 2P RCCB

A 2P RCCB is a single-phase residual current device that switches both the line (L) and neutral (N) conductors together while monitoring their vector sum through a toroidal current transformer. Under normal conditions the outgoing line current equals the returning neutral current, so no residual flux is detected. Any current leaking to earth — through a person or damaged insulation — creates an imbalance that triggers the trip solenoid and opens both poles simultaneously.

"2P" means the device has two poles that switch both line and neutral, so it fully isolates the load from the supply rather than switching only the hot conductor. Incoming L and N land on the supply-side terminals, and the same L and N exit on the load side. The PE conductor must never pass through the toroid and must never be switched; it runs continuously from the main earthing terminal to all exposed conductive parts.

The 125 A is the rated current (In) — the maximum continuous current each pole can carry at rated ambient temperature without overheating. Household RCCBs are commonly 40–63 A, so the 125 A rating positions this WSB1L unit as a high-current single-phase device suitable for a main incomer or large single-phase feeder. As with all RCCBs, it does not protect against overload or short circuit; an upstream MCB or MCCB must provide that backup.

A 30 mA IΔn is still the standard value for human protection, regardless of the rated current: sensitivity depends on the leakage level needed to protect a person, not on how much current the load draws. At 125 A the unit may feed large single-phase loads such as industrial heaters, shops, or small workshops, so the designer should also check the steady-state leakage of the installation; if it is high, a 100 mA or S-type device may be preferred for the main incomer, with 30 mA RCCBs used downstream for socket-outlet circuits.

Type AC detects only sinusoidal AC residual current, while Type A also detects pulsating DC residual current produced by rectifier and electronic loads. A 125 A single-phase feeder typically supplies shops, offices, or workshops that contain computers, LED drivers, variable-speed compressors, and battery chargers, so a Type A WSB1L is generally the safer specification. Pure Type AC is acceptable only when the load is purely resistive, such as a simple heating installation.

It clips onto a standard 35 mm DIN rail in a distribution enclosure, typically occupying two pole-widths (though a 125 A body is physically larger than a 63 A unit, so confirm the required pole-space in the datasheet). Connect L and N to the marked supply-side terminals, route the load-side L and N to the outgoing bars, tighten conductors to the nameplate torque (typically 2.5–4 N·m for 125 A), and keep the PE wire outside the device. Verify rail load rating — a 125 A RCCB is heavy, so the DIN rail and enclosure must be rated accordingly.

The test button injects a simulated residual current so you can confirm the trip mechanism operates; press it monthly with the circuit energized and the unit should trip instantly. If it fails to trip, replace the device immediately. Beyond testing, inspect terminals annually for tightness, check for discoloration or overheating, and keep the enclosure dry and dust-free. RCCBs have no user-serviceable parts; never attempt to open or repair the internal toroid or solenoid.

Large single-phase feeders often run long cable lengths, which have significant distributed capacitance between conductors and earth; this steady capacitive leakage can drift above 30 mA when many loads are switched on, especially at start-up. Switching power supplies and LED drivers also generate high-frequency leakage that can exceed the trip threshold of a Type AC device. Mitigate by using Type A or F units, selecting a higher IΔn for the main feeder, or using a time-delayed S-type to coordinate with downstream 30 mA RCCBs.

The WSB1L 125 A 2P RCCB is designed to IEC 61008-1, the product standard for residual current circuit breakers without integral overcurrent protection, covering tripping characteristics, conventional operating and non-operating residual currents, and endurance. The CE mark indicates conformity with the EU LVD and EMC directives. Local wiring rules still dictate installation practice, including maximum disconnection times, discrimination between upstream and downstream RCCBs, and the required sensitivity for particular circuits.

An MCB provides only overload/short-circuit protection, an RCCB provides only earth-leakage protection, and an RCBO combines both. The WSB1L 125 A 2P is therefore used as a high-current single-phase earth-leakage head, with upstream or downstream overcurrent devices providing fault protection. Common applications include main incomers for small shops and offices, large single-phase industrial heaters, welding outlets, car wash bays, telecom shelters, and retrofit upgrades where an existing single-phase installation needs 30 mA protection without redesigning the whole board.