Westhomes Solar WSB9Z-80 Normal Type Circuit Breaker

The WSB9Z-80 is a normal-type DC miniature circuit breaker (MCB) rated around 80 A, designed specifically for direct-current (DC) photovoltaic (PV) circuits. It is installed between solar PV strings/combiners and the inverter to provide overcurrent and short-circuit protection while allowing manual isolation of the DC side.

Unlike AC, DC has no natural current zero-crossing, so the arc that forms when contacts open does not self-extinguish. The WSB9Z-80 uses a dedicated DC arc chute with magnetic blowout and optimized contact geometry to stretch, split, and cool the arc until it extinguishes. A standard AC MCB lacks this design and can weld its contacts or sustain a dangerous arc.

The "80" indicates the rated current (In) of approximately 80 A. Size the breaker so that In is at least 1.25 times the PV string short-circuit current (Isc) and within the conductor's ampacity, so it carries normal operating current without nuisance tripping but opens on genuine overload or fault.

As a solar DC breaker it is rated for DC photovoltaic system voltages (commonly up to 1000 V DC, and higher for extended pole versions). Its voltage rating must always exceed the maximum open-circuit voltage (Voc) of the string calculated at the lowest expected ambient temperature.

It mounts on a standard 35 mm DIN rail inside a DC combiner box or PV distribution panel. Connect the PV source positive (+) and negative (-) conductors to the line side and the inverter to the load side, observing the marked polarity; many DC breakers are polarity-sensitive and will not interrupt safely if reversed.

It uses a combined thermal-magnetic trip: a bimetal strip heats and bends slowly on sustained overload (inverse-time characteristic), while a magnetic solenoid trips instantaneously on a short-circuit fault. This dual mechanism is the key advantage over a single-use fuse, because the breaker can simply be reset after the fault is cleared.

Yes — it is selected as the upstream DC-side protective device that must safely interrupt a DC fault without damaging the inverter's input stage. Its breaking capacity and trip curve should be coordinated with the inverter's maximum DC input current and the available fault energy, so the DC breaker clears a fault before the inverter is stressed.

Common causes of nuisance tripping include undersized breaker relative to Isc, loose conductors causing overheating, partial shading or a failing panel feeding abnormal current, a fault on the cabling, or an inverter inrush. Measure the operating current against In, check terminal torque, and inspect the string for ground faults before assuming the breaker is defective.

DC miniature breakers for PV are tested to IEC 60947-2 (low-voltage switchgear and controlgear — circuit breakers), and PV-specific installation requirements follow IEC 60364-7-712 (solar PV power supply systems). Always verify the product certificate carries the correct DC rated operational voltage and breaking capacity.

Inspect it periodically for loose terminals, discoloration, or arc damage, and exercise the manual trip lever once per year to keep the mechanism free-moving. Because PV DC arcs can be destructive, any breaker that has interrupted a high fault should be replaced rather than reused, and torque all connections to the manufacturer's specification.