WSB1LE-125 1P+N Earth Leakage Circuit Breaker

A 1P+N RCBO is a single-phase residual-current circuit breaker with overcurrent protection that switches only the phase (L) pole while passing the neutral (N) straight through, without switching it. It occupies the narrowest DIN-rail width available (typically 18 mm), making it ideal for space-constrained consumer units and retrofit boards.

Both L and N pass through the internal toroidal differential transformer so the device still detects the full residual current, but only the L pole has the switching contacts and the overload/short-circuit trip mechanism. The N terminal is a straight-through bar. When the device trips, only the phase is disconnected; neutral remains connected, which is acceptable for most final circuits but means the circuit is not fully isolated on both conductors.

The main advantage is space: a 1P+N RCBO is about half the width of a 2P unit, allowing more circuits to fit in a single distribution board. It is also cheaper and simpler to wire. The trade-off is that neutral is not switched, so for work on downstream circuits the upstream main switch must also be opened to fully isolate the neutral.

The "125" is the frame rating — the maximum current the unit's terminals, housing, and internal conductors are designed to withstand. The actual rated current (e.g., 16 A, 20 A, 32 A, 40 A) is set by the internal thermal and magnetic trip unit. A 125 A frame means the housing can accommodate trip units up to 125 A, giving headroom for future load increases.

L and N both pass through the toroidal core. In a healthy circuit their currents cancel perfectly, so no magnetic flux is produced. When current leaks to earth through a person or faulty equipment, the balance is broken; the toroid detects the difference, and when it exceeds the rated sensitivity (typically 30 mA), the internal release opens the phase contacts within milliseconds.

The WSB1LE-125 1P+N is commonly supplied with a 30 mA residual-current sensitivity, which meets the direct-contact (personnel protection) requirements of IEC 61009 and most national wiring regulations. It is suitable for socket-outlet circuits, lighting circuits in damp locations, and portable equipment. Higher sensitivities such as 100 mA or 300 mA may be available for upstream fire-protection or equipment-protection roles.

The unit snaps onto a 35 mm DIN rail. Supply L is connected to the marked line terminal and N to the neutral terminal; load L and N are connected to the output terminals. Because N is not switched, the neutral bar in the board should be clearly identified, and downstream work must be carried out with the upstream main switch open to ensure full isolation.

The test button simulates a residual-current fault through an internal resistor to prove the trip mechanism still works. Press it once a month; the unit must trip immediately. If it fails to trip, it must be replaced because it can no longer provide electric-shock or fire protection. The test button is not a normal operating switch.

Common causes are leakage from LED drivers, switch-mode power supplies, UPS and inverter loads, long cable runs with high distributed capacitance, damp or aged insulation, and transient surges. Remedies include selecting Type A or Type F RCBOs for electronic loads, splitting heavy loads across multiple RCBOs, using 100 mA/S-type devices where personnel risk is low, adding an upstream SPD, and inspecting insulation resistance.

The WSB1LE-125 is designed to IEC 61009-1 and is CE-marked. Typical uses include residential and apartment consumer units, hotel rooms, office final circuits, lighting and socket circuits, retrofit upgrade projects where board space is limited, and small commercial sub-boards where compact combined earth-leakage and overcurrent protection is needed without sacrificing DIN-rail capacity.