HUM18-40 40A MCB

HUM18-40 40 Amp Miniature Circuit Breaker – Compact 18 mm Protection with Neutral Switching

HUM18-40 is the ideal circuit breaker for those installers who are tight on space in their distribution boards and require 40 amp circuit breakers with neutral disconnection (i.e., switching off both the phase and neutral line). The HUM18-40 from HUYU Electric has a frame width of 18 mm and can provide an Icn rating of 6 kA while providing overload and short circuit protection. It is designed for use in single-phase circuits of 50 Hz 230 V with voltage ratings up to 40 amps, in accordance with IEC 60898-1, and is available in type B, C, and D curves.

Unlike standard single pole MCBs, this 1P+N configuration protects both the phase and neutral lines; this is a requirement in many local electrical codes for circuits that feed socket outlets, water heaters, and fixed appliances. The narrow design of the HUM18-40 creates more opportunity to install additional devices in the same consumer unit. Additionally, HUYU Electric’s range of clip-on accessories for the HUM18-40 makes it a versatile building block for the automated distribution of power through options such as shunt release, undervoltage release, and auxiliary contact. HUYU Electric offers the HUM18-40 at OEM and ODM factory-direct pricing with private labeling and complete documentation, making it a competitive alternative to equivalent 40A MCBs manufactured by Hager, Legrand, Chint, BG, MK, Crabtree, Wylex, Havells, and Fusebox.

Why 1P+N? Dual Protection with Half the Space of a 2P MCB

The HUM18-40 offers dual protection in an 18mm width, identical to a standard single pole MCB, but with switched neutral. This feature is particularly important for circuits such as electric showers, cookers, and socket outlets, where local regulations mandate neutral disconnection. A standard 2P MCB would require 36mm of DIN rail space for a similar function. Optimizing a 12-way consumer unit by using 1P+N configuration instead of 2P could save up to 216mm of rail space, allowing for two extra circuits.

Accessory Support – Remote Indication, Tripping & Undervoltage Protection

The HUM18-40 can integrate three clip-on accessories: an auxiliary contact delivers a volt-free signal for remote status monitoring, useful in equipment rooms or building management systems needing centralized breaker status, a shunt release permits remote tripping through external logic controllers or switches, and the undervoltage release disconnects circuits automatically under low voltage conditions, shielding devices against damage. These accessories are tool-free and offer flexible installation during setup or retroactively.

Technical Specifications

OEM/ODM Supply – A Compact 40A MCB Alternative for Volume Buyers

Buyer’s Guide

How to Specify a 40A MCB – Current Rating, Cable Size & Curve Selection

A practical guide to choosing the right HUM18-40 configuration and wiring it correctly.

1. Adjusting the Current Rating

The HUM18-40 comes in seven current ratings from 6A to 40A. Lower ratings like 6A or 10A suit lighting circuits, while 16A or 20A are ideal for general-purpose circuits and sockets. Ratings between 25A and 32A are used for appliances like water heaters and air-conditioning, and the highest rating, 40A, fits larger loads like electric showers, cooker circuits, or feeding smaller consumer units. Always size the breaker according to the circuit cable, ensuring the MCB trips before the cable reaches its thermal limit.

2. Cable Size Considerations

A common query is whether a 6mm² cable can be used with a 40A MCB, given its current capacity ranges from 32 to 41A depending on installation conditions. According to IEC and UK wiring standards, 6mm² is not appropriate for 40A breakers; instead, a 10mm² cable is recommended as the minimum size. HUM18-40 terminals accommodate conductor sizes up to 25mm², enabling compatibility with larger cables. For a 6mm² cable, consider using a 32A MCB instead for compliance.

3. Selecting Tripping Curves

Type B curves suit resistive circuits like lighting and heating (3–5× In). Type C works for inductive loads like air-conditioners and pumps (5–10× In). Type D, with a tripping range of 10–20× In, is for high-inrush equipment like transformers and motors. The HUM18-40 supports all three curves, offering flexibility for various circuit types.

4. Loop Impedance and Max Zs

The maximum Zs (earth fault loop impedance) value ensures the MCB trips in the designated disconnection interval (0.4s for final circuits): Type B MCBs allow up to 1.15Ω, Type C permits 0.58Ω, and Type D accepts 0.29Ω. Installers must check the measured Zs against these thresholds. Exceeding the limit requires adjustments, such as decreasing cable length or increasing conductor size.

Frequently Asked Questions

What is a 40A MCB used for?

A 40A MCB is typically used for circuits that draw up to 40 amps — electric showers, cooker circuits, sub-main feeds from a main consumer unit to a garage or shed board, and larger fixed appliances. In a residential setting, the 40A rating is commonly seen protecting a dedicated shower circuit or a dual-appliance cooker connection point. In commercial settings, it may feed a small distribution board or a dedicated HVAC circuit.

Can you put a 6mm on a 40A MCB?

No. A 6mm² copper cable is generally not rated for a 40A circuit under standard installation conditions. The typical current-carrying capacity of 6mm² is around 32–41A depending on installation method, which is insufficient for a 40A protective device. The minimum recommended cable size for a 40A MCB is 10mm². Using an undersized cable with a 40A breaker creates a fire risk — the cable could overheat before the breaker trips.

Is there such a thing as a 40 amp breaker?

Yes. A 40 amp breaker is a standard MCB rating available from most manufacturers, including HUYU Electric. The HUM18-40 is exactly that — a 40A miniature circuit breaker in a 1P+N configuration. It is one of the most commonly stocked ratings in the 6A–63A range, widely used in residential and light commercial distribution boards for dedicated appliance circuits.

Will 12/2 wire carry 40 amps?

No. 12/2 AWG wire has a typical ampacity of 20A under standard conditions — well below the 40A required. Using 12/2 on a 40A breaker would violate wiring regulations and create a serious safety hazard. For a 40A circuit, the minimum conductor size is 8 AWG copper (for North American installations) or 10mm² (for IEC markets). Always match the conductor size to the breaker rating — not the other way around.