An RCCB (Residual Current Circuit Breaker) senses current: it compares the current going out on the live conductor with the current coming back on the neutral, and trips when the difference, the residual current, passes its rated threshold. A voltage-operated ELCB (Earth Leakage Circuit Breaker) senses voltage: it watches the voltage that appears on the earth wire of the protected equipment relative to a separate earth electrode, and trips when that voltage rises too high. The RCCB is the modern, more sensitive and more reliable device; the voltage-operated ELCB is an older design that most current wiring rules no longer accept for new work.
Key takeaways
- RCCB works on current balance between live and neutral; voltage-operated ELCB works on fault voltage on the earth conductor.
- An RCCB does not need an earth connection to detect a fault, while a voltage-operated ELCB depends on both the equipment earth wire and a separate reference earth electrode.
- RCCBs are available with 10 mA and 30 mA sensitivity for protection of people, and 100 mA to 300 mA for fire protection; a voltage-operated ELCB cannot sense leakage that does not flow through its own earth wire.
- Neither device protects against overload or short circuit on its own. For that you need an MCB, or a combined RCBO.
- The name "ELCB" is now often used loosely for any earth leakage breaker, including current-operated ones, so check which type a datasheet or electrician means.
What is an RCCB
RCCB stands for Residual Current Circuit Breaker. It is a device that detects the imbalance of current between the live and neutral wires of a circuit, and trips the circuit when the residual current exceeds a certain threshold. RCCBs belong to the wider family of RCDs (Residual Current Devices), and in everyday use the two names are often treated as the same thing.
How it works
Both the live and the neutral conductors pass through a small toroidal (ring) core inside the RCCB. In a healthy circuit every ampere that leaves on the live comes back on the neutral, so the two magnetic fields cancel and the core sees no net flux. If some current escapes to earth, for example through damaged insulation or through a person touching a live part, the return current is smaller than the outgoing current. The core now carries a net flux, a sense winding picks up a voltage, and a trip relay opens the contacts. Typical devices are designed to open within a few tens of milliseconds at five times their rated residual current.
Ratings you will see
- Rated residual operating current (IΔn): commonly 10 mA, 30 mA, 100 mA or 300 mA.
- Rated current (In): the load current the contacts carry continuously, for example 25 A, 40 A or 63 A.
- Type: AC (sinusoidal residual current only), A (also pulsating DC), F (also mixed frequencies, for inverter-driven loads) and B (also smooth DC, used for EV chargers and some solar and three-phase drive installations).
RCCBs are covered by IEC 61008-1, and RCBOs (an RCCB and an MCB in one unit) by IEC 61009-1. Many national standards follow these, for example the Indian IS 12640 series.
What is an ELCB
ELCB stands for Earth Leakage Circuit Breaker. The classic device is voltage operated, which is why it is also called a VOELCB (Voltage Operated Earth Leakage Circuit Breaker). It detects leakage from the live wire to the earth wire of a circuit, and disconnects the circuit when the resulting fault voltage passes a set limit.
How it works
The voltage-operated ELCB has a trip coil connected between the earth wire of the installation, which is bonded to the metal frames of the appliances, and a separate reference earth electrode driven into the ground some distance away. When a live conductor touches an appliance frame, fault current flows down the earth wire and the frame rises in voltage. That voltage drives current through the trip coil, and when it is high enough (often in the region of 50 V, depending on the design) the breaker opens.
Why it fell out of favour
- It only sees fault current that flows through its own earth wire. If the fault current finds another path to earth, such as a metal water pipe, the device may not trip at all.
- A parallel earth path can also short out the trip coil, and a break in the earth wire or the reference electrode leaves the installation unprotected with no warning.
- It needs a second, independent earth electrode, which adds cost and is hard to keep separate in practice.
For these reasons voltage-operated ELCBs are not accepted for new installations under the IEC 60364 based wiring rules used in many countries, including BS 7671 in the UK. Existing units are still found in older buildings.
The main differences between RCCB and ELCB
| Point | RCCB | Voltage-operated ELCB |
|---|---|---|
| Sensing principle | Current sensing: difference between live and neutral current | Voltage sensing: voltage between the earth wire and an external electrode |
| Earth connection needed to detect a fault | No | Yes, both the equipment earth and a reference electrode |
| Sensitivity | High: 10 mA or 30 mA for shock protection | Lower: responds to fault voltage, not small leakage currents |
| Direct contact (person touches a live conductor) | Gives additional protection at 30 mA or below | No protection, the current does not pass through its earth wire |
| Indirect contact (person touches a faulty metal frame) | Protects | Protects, if the fault current flows through its earth wire |
| Effect of parallel earth paths | No effect on detection | Can stop it tripping |
| Overload and short circuit protection | None (use an MCB or an RCBO) | None |
| Status in new installations | Standard practice | Generally no longer permitted |
In summary, RCCB is based on current sensing, while ELCB is based on voltage sensing. RCCB measures the difference between the current flowing in the live and neutral wires, while ELCB measures the voltage between the earth wire and an external electrode. RCCB does not require an earth connection, while ELCB does. RCCB is more sensitive and can detect lower levels of residual current, while ELCB is less sensitive and responds only to larger leakage.
Correction to the earlier version of this post: it said an ELCB can only protect against direct contact. It is the other way round. A voltage-operated ELCB can protect against indirect contact, when a metal frame becomes live, but it cannot protect against direct contact with a live conductor, because that current never flows through the earth wire it watches. A 30 mA RCCB covers both.
A worked example
Take a 230 V circuit protected by a 30 mA RCCB. A person standing on a damp floor touches a live terminal. Assume, for illustration, a body plus floor resistance of 2,000 ohms.
- Current through the person: 230 V / 2,000 ohms = 115 mA.
- Outgoing live current minus returning neutral current = 115 mA, which is almost four times the 30 mA rating, so the RCCB trips quickly.
- A voltage-operated ELCB on the same circuit would see nothing, because the 115 mA flows through the person to the floor, not through the earth wire.
The figures are illustrative. Real body resistance varies widely with contact area, moisture and voltage, which is why the 30 mA level was chosen as a conservative limit for additional protection.
The applications of RCCB and ELCB
- RCCB is used to prevent electric shock and to reduce the risk of fire caused by earth leakage current. A 30 mA RCCB is the normal choice for socket circuits, bathrooms, kitchens and outdoor circuits; 100 mA or 300 mA units are used upstream for fire protection. RCCBs are widely used on circuits that feed everyday appliances such as computers, TVs and refrigerators. Note that an RCCB does not protect the appliances themselves against overcurrent or surges, and some electronic loads with filter capacitors leak a few milliamperes each, so many of them on one 30 mA RCCB can cause nuisance trips.
- ELCB is used to prevent electric shock caused by a live fault on earthed metalwork. It was used on circuits with metal-bodied appliances that are bonded to earth, such as water heaters and washing machines. Today the same circuits are normally protected by an RCCB or RCBO instead.
Common mistakes
- Treating an RCCB as a replacement for an MCB. It does not trip on overload or short circuit unless the fault also produces a residual current.
- Choosing Type AC for circuits with inverters, EV chargers or variable-speed drives. DC components can blind a Type AC device; Type A, F or B may be needed, as the equipment maker specifies.
- Never pressing the test button. Most makers recommend testing regularly, often every three to six months, to make sure the mechanism still trips.
- Assuming "ELCB" on an old panel means a voltage-operated device. Look at the wiring: a current-operated unit has live and neutral through it, a voltage-operated unit has an extra earth electrode connection.
FAQ
Is an RCCB the same as an RCD?
An RCCB is one kind of RCD. RCD is the general term; RCCBs, RCBOs and socket-outlet RCDs are all residual current devices.
Can I replace an old ELCB with an RCCB?
Usually yes, and it is the normal upgrade. The installation earth still needs to be sound, and a qualified electrician should check the earthing arrangement and choose the right rating and type.
What rating should I use for home protection?
For protection of people, 30 mA is the usual figure, and wiring rules based on IEC 60364 call for it on most socket circuits. Follow your local regulations.
Why does my RCCB trip with no visible fault?
Common causes are moisture in outdoor fittings, a failing appliance heater element, a neutral-to-earth fault, or the combined standing leakage of many electronic loads on one device.
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