Westhomes WCM8L-125 MCCB | AC 400V/690V Moulded Case

The WCM8L-125 is a 125 A frame molded case circuit breaker for low-voltage AC systems. Its dual voltage rating means it can be used on standard 400 V three-phase distribution and also on 690 V systems (common in mining, heavy industry, and some renewable-energy installations), although the breaking capacity may be derated at the higher voltage.

At 125 A, an MCCB is generally preferred over a large MCB because it offers adjustable trip settings, a higher breaking capacity, and a longer mechanical/electrical life. MCBs above 63–100 A are often limited in breaking capacity and selectivity, while a 125 A MCCB can be coordinated with downstream MCBs to achieve selective tripping.

It combines a bimetal heater for inverse-time overload protection with an electromagnet for instantaneous short-circuit protection. On the "L" (thermal-magnetic) variant, the overload and/or short-circuit thresholds may be adjustable by screws or dials, allowing the breaker to be matched to the cable and load without changing the frame.

The 125 A frame typically accepts trip units from 15 A up to 125 A. This makes it a flexible choice for feeders that may grow over time — the same breaker housing can be re-rated by changing the trip unit as loads change, rather than replacing the whole device.

It is offered in 3P and 4P versions. Use 3P for three-phase loads where neutral is not switched; use 4P when the installation requires neutral isolation (e.g., switching between two sources, TT systems, or when the neutral must be broken for safe maintenance). Confirm local wiring regulations, as some jurisdictions mandate 4P for certain applications.

A 690 V rating allows the same breaker to be used on medium-voltage industrial distribution, mining, and 690 V wind/solar installations. However, breaking capacity (Icu) is usually lower at 690 V than at 400 V — always check the nameplate curve to ensure the rated breaking capacity at the actual system voltage exceeds the available fault current.

The long-time (overload) dial sets Ir between typically 0.8 and 1.0 In, and the short-circuit (instantaneous) dial sets Ii between, for example, 5 and 10 In. Set Ir to protect the cable, and set Ii above any normal inrush (motor starting, capacitor switching) but below the downstream device's withstand so selectivity is maintained.

It is bolt-mounted on a panel plate or DIN adapter in a distribution board or control panel. Conductors are typically 16–70 mm² copper depending on the set current, connected with suitable lugs to the line and load terminals at the specified torque. Maintain minimum phase-to-phase and phase-to-earth clearances per IEC 60947-2 and the enclosure design.

It is commonly used as a sub-main breaker in commercial buildings, protection of large HVAC and chiller units, motor control center feeders, industrial machinery supply, generator and UPS output protection, and as a main breaker in smaller distribution boards. Its 690 V rating also makes it suitable for mining, oil-and-gas, and renewable-energy installations.

The WCM8L-125 is manufactured to IEC 60947-2 and carries CE and other regional certifications. Routine maintenance includes annual visual inspection, terminal torque checks, and mechanical operation; trip settings should be verified by secondary injection test every 1–3 years, and insulation resistance measured during planned shutdowns to confirm the breaker remains in good condition.