WSB9L-100 Mini Circuit Breaker

The WSB9L-100 is a low-voltage miniature circuit breaker designed to protect wiring and equipment against overload and short-circuit faults. It automatically trips (opens) the circuit when current exceeds the safe rating, preventing overheating, fire, and equipment damage. It is manually resettable, making it a reusable alternative to fuses.

It uses two sensing elements in series. The bimetal strip heats up under sustained overload and slowly bends to trip the mechanism (thermal inverse-time protection), while a solenoid/electromagnet trips instantly on a very high short-circuit current (magnetic instantaneous protection). The thermal element handles overcurrents slightly above rated, and the magnetic element clears bolted faults within milliseconds.

It is the rated current In = 100 A, the maximum continuous current the breaker can carry without tripping under normal ambient temperature (typically 30 °C / 40 °C). A circuit protected by this MCB should be loaded so its normal operating current stays below 100 A, and the supply cable must be sized to carry at least 100 A (e.g., ≥ 25–35 mm² copper depending on installation method).

Curves define the magnetic instantaneous threshold: B trips at 3–5 In, C at 5–10 In, and D at 10–20 In. Curve B is used for resistive loads and lighting, Curve C for general socket and motor circuits with moderate inrush, and Curve D for high-inrush loads such as transformers, large motors, or welding equipment. Selecting the wrong curve causes either nuisance trips (curve too sensitive) or failure to clear faults fast enough (curve too loose).

Breaking capacity is the maximum prospective short-circuit current the breaker can safely interrupt without failing. If the available fault current at the installation exceeds the MCB's breaking capacity, the breaker may weld its contacts, explode, or fail to clear the fault. Always calculate the available short-circuit current at the panel and select an MCB rated above it (commonly 6 kA or 10 kA for distribution boards).

It snaps onto a standard 35 mm DIN rail (EN 60715) inside a distribution board or consumer unit. The rear clip locks onto the rail, and line/load conductors are connected to the screw or clamp terminals on the top and bottom. No special mounting brackets are required, and breakers can be added or removed without disturbing adjacent devices.

Yes. A 100 A MCB is commonly used as the main incomer or main switch in residential, small commercial, or sub-main distribution boards where the total load is below 100 A. It provides both isolation and overcurrent protection in one device. For higher service entrances (e.g., 125 A+), an MCCB or isolator is normally selected instead.

Common causes include a genuine circuit overload (too many devices running at once), a developing short circuit or ground fault in wiring or appliances, a weak/aged breaker that has drifted below its rating, or ambient overheating inside a crowded enclosure. Unplug loads one by one to isolate the faulty circuit; if tripping persists with no load, the breaker itself or the wiring should be inspected by a qualified electrician.

It is designed and tested to IEC 60898-1 (the international standard for miniature circuit breakers for household and similar overcurrent protection) and carries CE marking for sale in the European Economic Area. Conformance ensures the declared tripping characteristics, breaking capacity, and endurance have been independently verified.

Typical uses include main switches in residential consumer units, sub-mains to outbuildings or garages, protection of high-current circuits such as electric showers, air-conditioning units, ovens, EV charger feeders, and three-phase distribution to smaller sub-panels. It is not intended for direct motor short-circuit protection where a D-curve or MCCB with adjustable settings is usually preferred.