How to Choose the Right Lanx MCB Rating

You're back in the switchboard on a kitchen reno, running a new circuit for the dishwasher, and there's a spare 32A breaker already sitting in the board from the old range hood run. It'd save a trip to the van — but that rating was never picked for this load, and swapping it in without checking is exactly how nuisance trips and undersized protection happen. Getting the rating right takes a bit more than grabbing whatever's spare, and it's worth doing properly every time, the same way it's covered across the Lanx Australis electrical range.

The Rating Number Is Only Half the Answer

An MCB is specified by two things, not one: the amp rating and the trip curve. The amp rating is the obvious part — how much continuous current the breaker will carry before it trips on overload. The curve (almost always C-curve for general power and lighting circuits in a residential or light commercial board) determines how fast it trips on a short-term overcurrent, like a motor starting or an inrush spike. Grab a breaker with the right amps but the wrong curve and you'll either get nuisance tripping on startup loads, or protection that's slower to react than it should be. Every Lanx MCB in this range is C-curve, which covers the vast majority of general circuits — it's the amp rating that changes job to job.

Sizing a Single-Pole (1P) Circuit

Most general power and lighting circuits in a house run off a single-pole breaker on 230/240V. A lighting circuit typically sits at the lower end — 6A is common where the cable run and fitting load support it. General power circuits, including the dishwasher run from the hook above, commonly land on 20A, which covers a standard GPO circuit wired in 2.5mm² cable under typical run lengths. Heavier single-phase loads — a larger single-element appliance circuit or a higher-draw EV charger — push into 40A or 63A territory, but at that point cable sizing and voltage drop need checking against the actual run, not just the appliance nameplate. Lanx's 1P range covers that whole spread, 6A through to 63A.

This is a starting reference, not a substitute for checking cable size and run length against AS/NZS 3000 for the specific job.

Double-Pole (2P) and Higher-Load Circuits

Two-pole breakers switch both active conductors on a circuit, which is what a lot of fixed single-phase appliances need rather than a standard 1P/N arrangement — a hot water system or ducted electric heater is a common example. 10A and 32A cover a good spread of these loads, from a smaller instantaneous unit through to a full-size ducted system, but as with single-pole circuits, the rating has to match what the cable run can actually carry, not just the appliance's rated draw.

Three-Phase (3P) Circuits

Three-phase circuits show up most often on workshop equipment, larger compressors, and some EV chargers. Motor loads bring a wrinkle single-phase circuits mostly don't: starting current can spike well above the running current for a short period, and a breaker sized only to the running load will typically nuisance-trip on startup. 16A suits smaller three-phase equipment; 63A covers heavier machinery and main sub-circuits feeding a workshop board. As a general rule, three-phase sizing is worth cross-checking against the equipment's actual starting characteristics rather than the nameplate running current alone.

Common Mistakes

Reusing whatever spare breaker is in the board. It's the fastest option on site, but a breaker rated for the old circuit it came from isn't necessarily right for the new one — that's exactly the trap from the dishwasher circuit above.

Matching the breaker to the appliance instead of the cable. A breaker rated higher than what the cable can safely carry defeats the point of the protection — the cable's current-carrying capacity sets the ceiling, not the appliance draw.

Using a single-pole breaker where a double-pole is needed. Some fixed appliances need both actives switched together; a 1P breaker on a circuit that calls for 2P switching leaves one active still live when the circuit's meant to be isolated.

Under-sizing for motor starting current on three-phase loads. Sizing purely to running current on compressor or motor circuits is a common source of nuisance tripping the moment the equipment starts up.

Assuming the MCB has earth leakage covered. As above — an MCB by itself doesn't provide RCD protection, and treating it as if it does is a compliance gap, not just an inconvenience.

Frequently Asked Questions

Choosing the Right Rating

What size MCB do I need for a standard GPO circuit?

A 1P 20A C-curve MCB is the common size for a standard general power circuit, though the final rating always depends on the cable size and run length for that specific job.

Can I use a 32A MCB on a circuit wired for 20A?

No — the breaker rating has to match what the cable can safely carry, not be bumped up to whatever's on hand. A 32A breaker on 20A-rated cable removes the protection the cable actually needs.

What's the difference between a C-curve and B-curve MCB?

C-curve breakers, like the 2P 10A C-curve MCB, tolerate a higher short-term inrush before tripping, which suits general power, lighting, and light motor loads. B-curve trips faster on lower overcurrent and is typically reserved for circuits with minimal inrush, which is less common on general trade work.

Standards & Installation

Do I need a licence to install or replace an MCB in NSW?

Yes — switchboard work is licensed electrical work in NSW, and it's worth confirming current licensing requirements for the specific job against NSW Fair Trading before starting, since scope and exemptions can vary by circuit type.

Does an MCB protect against earth leakage?

No — an MCB covers overload and short circuit only. Earth leakage protection needs a separate RCD, or an RCBO that combines both functions in one device.

What rating three-phase MCB do I need for a workshop machine?

It depends on the machine's running and starting current, but a 3P 16A C-curve MCB is a common starting point for smaller three-phase equipment — always cross-check against the equipment's actual current draw rather than sizing on rating alone.

For more on the full electrical range this sits within, see the Shop section below.

The right rating still comes down to checking cable size and job conditions before ordering — the range below covers the common ratings across single, double, and three-phase.

Shop Lanx MCB Circuit Breakers at Schnap

These MCBs are trade priced with same-day dispatch on in-stock items from the Kingsgrove NSW warehouse.

• Single-Pole (1P)
• MCB 1P 6A
• MCB 1P 20A
• MCB 1P 40A
• MCB 1P 63A

• Double-Pole (2P)
• MCB 2P 10A
• MCB 2P 32A

• Three-Phase (3P)
• MCB 3P 16A
• MCB 3P 63A

Find the full circuit breaker rating range at Schnap — trade pricing and same-day dispatch from Kingsgrove NSW.