RCD / RCCB Symbol
Definition: The RCD / RCCB symbol represents a Residual Current Device (also called a Residual Current Circuit Breaker) — defined in IEC 61008 / IEC 61009 and specified in ANSI/UL 943 — a protective switching device that interrupts an AC circuit within milliseconds when it detects a residual (imbalance) current between the Line and Load conductors, indicating a fault current path to earth that can cause electric shock or fire.
Also known as: RCCB, ELCB, earth leakage circuit breaker, ground fault circuit interrupter (GFCI, US equivalent), residual current breaker, safety breaker.
What the RCD / RCCB symbol means
The RCD / RCCB symbol denotes a safety device that continuously monitors the differential current between the live (Line) and neutral conductors. Under normal conditions these currents are equal; if a person touches a live conductor or insulation breaks down and current leaks to earth, the imbalance triggers the RCD to open the circuit, typically within 30 ms for 30 mA rated devices (IEC 61008).
In wiring diagrams the RCD symbol appears between the supply (Line pin) and the protected circuit (Load pin). The internal representation — a rectangle with a circle and dashed arc indicating the sensing toroid — distinguishes it from a plain circuit breaker, signalling that the device responds to earth fault current, not just overcurrent.
How to identify the RCD / RCCB symbol
The RCD / RCCB symbol is drawn as a rectangular enclosure (representing the device body) with a line entering at the top (Line) and exiting at the bottom (Load). Inside the rectangle a small filled circle (representing the tripping mechanism) connects to an angled line (the switching arm), and a dashed circle or arc represents the differential current sensing toroid. This distinguishes it from a simple MCB, which shows only a contact and trip coil.
Function in a circuit
An RCD detects the vector difference (residual current) between current flowing through the Line conductor and returning through the Neutral conductor. When this difference exceeds the rated tripping threshold (typically 10 mA, 30 mA, 100 mA, or 300 mA per IEC 61008), the device mechanically opens both poles within the trip time specified (≤300 ms at rated threshold; ≤40 ms at 5× threshold for 30 mA Type AC devices), disconnecting the load from the supply and protecting against electric shock and fire.
Standards: IEC vs ANSI
| IEC 60617 | IEC 61008-1 (RCCBs without integral overcurrent protection) and IEC 61009-1 (RCBOs with overcurrent protection). The symbol is derived from IEC 60617 general switching device notation with added current-sensing annotation. |
|---|---|
| ANSI/IEEE 315 | ANSI/UL 943 covers Ground Fault Circuit Interrupters (GFCI) — the US functional equivalent of an RCD. IEEE 315 does not define a unique schematic symbol; North American schematics typically label the device 'GFCI' or 'RCD' inside a box switch symbol. |
| Key difference | IEC schematics use the rectangle-with-sensing-circle symbol (IEC 60617-derived). ANSI/North American schematics use a labelled box or the GFCI symbol found in NEC-compliant wiring diagrams; the operating principle is identical but trip current and test requirements differ (GFCI ≤6 mA per UL 943; RCD 10–30 mA per IEC 61008). |
Terminals / pins
| Pin | Name |
|---|---|
| line | Line |
| load | Load |
Typical values
Rated residual operating current (IΔn): 10 mA (high sensitivity), 30 mA (personal protection standard), 100 mA, 300 mA (fire protection). Trip time at IΔn: ≤300 ms; at 5×IΔn: ≤40 ms (IEC 61008 Type AC). Voltage ratings: 230 V / 400 V AC. Current ratings: 16 A, 25 A, 40 A, 63 A, 100 A.
Where the RCD / RCCB symbol is used
- Bathroom and kitchen circuits where water and electricity proximity create shock hazard (30 mA personal protection)
- Outdoor socket circuits, garden lighting, and EV charger supply points
- Main distribution boards as whole-house earth leakage protection (100–300 mA fire protection grade)
- Industrial control panels protecting personnel from ground fault on motor circuits
- Medical premises where 10 mA or 6 mA high-sensitivity RCDs protect patients
- Swimming pool and hot tub electrical installations per IEC 60364-7-702
Example
In a residential wiring diagram, an RCD / RCCB symbol (30 mA, 40 A) is shown at the top of the consumer unit with its Line pin connected to the incoming supply bus and its Load pin feeding the ring-main circuit; any earth fault on a downstream appliance causes the RCD to open both poles, removing voltage from the entire protected circuit within 40 ms.
Key facts
- An RCD / RCCB has two terminals in the schematic: Line (supply side) and Load (protected circuit side); both live and neutral conductors pass through the sensing toroid.
- Standard personal-protection RCDs trip at 30 mA residual current per IEC 61008; the 30 mA threshold is below the ~80 mA level that causes ventricular fibrillation in adults.
- IEC 61008 Type AC RCDs respond only to sinusoidal AC residual current; Type A adds detection of pulsating DC residual current from rectifier loads; Type B detects smooth DC residual current from VFDs and EV chargers.
- The RCD does not protect against overcurrent or short-circuit — a separate MCB or fuse must be used in series, or an RCBO (RCD+MCB combined, IEC 61009) substituted.
- RCDs must be tested monthly by pressing the TEST button; the test circuit injects a residual current to verify the mechanical trip mechanism operates correctly.
- The US equivalent is the GFCI (Ground Fault Circuit Interrupter) per ANSI/UL 943, with a lower trip threshold of ≤6 mA for personnel protection as required by NEC Article 210.8.
- An RCD installed at the main board provides earth leakage protection for all downstream circuits but will lose all circuits on a single trip; splitting into zones with multiple RCDs or RCBOs improves selectivity.
Frequently asked questions
What does the RCD / RCCB symbol mean in a wiring diagram?
The RCD / RCCB symbol represents a residual current protective device that disconnects a circuit when it detects a current imbalance between the live and neutral conductors (earth fault current). It protects against electric shock and fire caused by insulation failure or direct contact with a live conductor.
What does the RCD symbol look like on a schematic?
The RCD symbol is a rectangle (device body) with a line in at the top (Line pin) and a line out at the bottom (Load pin). Inside, a small circle connected to a switching arm and a dashed arc or circle represents the differential current sensing toroid, distinguishing it from a plain circuit breaker symbol.
What is the difference between an RCD and a GFCI?
An RCD (Residual Current Device, IEC 61008) and a GFCI (Ground Fault Circuit Interrupter, UL 943) perform the same earth fault protection function. The main difference is the trip threshold: IEC personal-protection RCDs trip at 30 mA; US GFCIs trip at ≤6 mA. Both open the circuit within milliseconds.
What standard defines the RCD / RCCB?
IEC 61008-1 defines RCCBs without integral overcurrent protection, and IEC 61009-1 defines RCBOs (with overcurrent protection). The US equivalent is covered by ANSI/UL 943. In wiring diagrams, the symbol follows IEC 60617 conventions for switching devices.
What is the difference between an RCD Type AC and Type A?
IEC 61008 Type AC RCDs only detect sinusoidal AC residual currents; Type A additionally detects pulsating unidirectional (half-wave rectified) residual currents produced by switch-mode power supplies and motor drives. Type B detects smooth DC residual current and is required for EV charger circuits.
How many terminals does an RCD have in a schematic?
A single-pole RCD schematic symbol shows two terminals: Line (supply/input, top) and Load (protected output, bottom). In practice, both the live and neutral conductors pass through the device body so that the sensing toroid can measure the differential current between them.
Does an RCD protect against short circuits?
No. An RCD protects against earth fault (residual) currents caused by insulation failure or direct contact — it does not respond to overload or short-circuit currents between live and neutral. For complete protection, an RCD must be used in conjunction with a fuse or MCB, or replaced with an RCBO (IEC 61009) which combines both functions.
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