RCCB in the home, why it matters and what rating to fit

Every circuit in a healthy installation is balanced: the current that flows out on the live conductor returns, exactly, on the neutral. A Residual Current Circuit Breaker (RCCB) sits across that pair and continuously compares the two. The moment some current goes missing, because it has found another route to earth, through damp or ageing insulation, through the metal body of an appliance, or through a person who has touched something live, the RCCB sees the imbalance and switches the circuit off. It does this in tens of milliseconds, and at a current far smaller than any fuse or MCB would ever respond to.

What it adds to the board

A home's distribution board already has MCBs (Miniature Circuit Breakers), and they do an essential job: they protect the wiring from overload and short-circuit, currents of tens or hundreds of amps. The RCCB works on a completely different quantity. It measures leakage to earth, in milliamps, and acts on a current far too small for an MCB to notice.

The two are partners, not alternatives: the MCB looks after the cable, and the RCCB looks after the people on the circuit and catches a slow insulation leak while it is still small. A board carrying both is covered on both fronts, which is why an RCCB belongs in every modern home.

The two ratings that decide an RCCB

Every RCCB carries two numbers, and they answer two different questions. Reading them correctly is most of the specification.

Sensitivity, how small a leak it acts on

The sensitivity, written I_Δn and given in milliamps (mA), is the leakage current at which the device trips. It comes in a few standard tiers, and for a home only one of them is the personal-protection figure:

• 30 mA, personal protection. This is the rating for the home. 30 mA is the threshold chosen for human safety: low enough, and fast enough, that if leakage ever passes through a person the supply is already switching off well inside the margin that keeps them safe. Wiring practice calls for 30 mA on the circuits people are in routine contact with, socket outlets, kitchens, bathrooms, and anything outdoors.
• 100 mA and 300 mA, equipment and earth-leakage protection. These higher tiers protect the installation rather than the person, catching a developing earth leakage early, and giving discrimination at a main or sub-main so a fault on one zone need not drop the whole supply. They are a complement to a 30 mA device on the circuits people touch, not a replacement for it.

The short version for a home: 30 mA is the number that protects people. A 100 mA or 300 mA device, on its own, does not.

Current rating, how much load it carries

The current rating, written I_n and given in amperes (A), is simply the working current the RCCB is built to carry continuously, the load of everything downstream of it, not the leakage. Common household values are 40 A and 63 A, sized to sit comfortably above the connected load and matched to the incoming supply.

One point that often surprises people: the RCCB does not provide overload or short-circuit protection. Its current rating is a carrying capacity, not a trip threshold for overcurrent. That job stays with the MCBs. So the RCCB's I_n is coordinated with the MCBs around it, chosen to sit above the largest load it will ever carry.

AC or A, the type of leakage it detects

Alongside the two ratings, an RCCB is specified for the kind of leakage it responds to.

• Type AC responds to ordinary sinusoidal AC leakage, the signature of conventional motors, heaters, lighting and plain socket loads. It has long been the default.
• Type A responds to AC leakage and to the pulsating-DC leakage that electronic loads produce, LED drivers, inverter air-conditioners, washing machines, induction cooktops, IT equipment and EV chargers. Because a modern home is full of exactly these loads, Type A is now the sensible default wherever the full mix of appliances isn't known in advance.

One RCCB, or one per circuit (RCBO)

There are two ways to put residual-current protection into a board.

A single RCCB on the incoming side covers every circuit behind it, the simplest and least-expensive arrangement, with each circuit keeping its own MCB for overload. The trade-off is that a leak on any one circuit switches the whole board off at once.

An RCBO combines an RCCB and an MCB in a single module, fitted per circuit. It costs more modules and more money, but it confines a trip to the one circuit that caused it, so a fault on the kitchen line leaves the bedroom lights on. For the circuits a household most wants to keep independent, per-circuit RCBOs are the more refined choice; many homes settle on a sensible mix of the two.

What a typical home needs

Putting the pieces together, the specification for an ordinary single-phase home comes out as:

• Sensitivity, 30 mA on every circuit people are in contact with: sockets, kitchen, bathrooms, outdoor points.
• Type, Type A, to cover the electronic and inverter-driven appliances now standard in a home.
• Current rating, sized to the incoming supply and connected load; commonly 40 A or 63 A for the main RCCB.
• Poles, 2-pole (phase + neutral) for a single-phase supply; 4-pole for a three-phase connection.
• Arrangement, a whole-board 30 mA RCCB at minimum; per-circuit 30 mA RCBOs where keeping circuits independent is worth the extra modules.

In India these devices are made to IS 12640-2 (and internationally to IEC 61008 for RCCBs, IEC 61009 for RCBOs), the marking to look for on the unit.

Sensitivity tiers, at a glance

What we stock

Shreetuvis is an Authorised Channel Partner for Hager RCCBs and RCBOs in Nagpur, the full matrix of 30 / 100 / 300 mA sensitivities, Type AC and Type A, 2-pole and 4-pole, in current ratings from 25 A to 125 A, supplied genuine from Hager India's authorised channel. See the Hager RCCB & RCBO page for the range, or send your supply rating and the circuits to cover through the contact form for a matched specification and quote.