What Are the Different Types of RCD?

Different types of RCD exist, depending on their behaviour in the presence of DC components and frequencies. The appropriate RCD (RCCB or RCBO) shall be selected from the following:

RCD Type AC

RCD Type AC: RCD tripping on alternating sinusoidal residual current, suddenly applied or smoothly increasing. Examples of suitable circuits are electric showers, oven, hob, immersion heater, and tungsten lighting.

For general purposes, type AC RCDs may be used.

RCD Type A

RCD Type A: RCD tripping on alternating sinusoidal residual current and on residual pulsating direct current, suddenly applied or smoothly increasing.

These are installed to protect circuits where equipment with electronic components are installed such as inverters, class 1 IT equipment, power supplies for class II equipment, lighting equipment including dimmers and LED drivers, induction hobs, and electric vehicle charging equipment with smooth residual DC current less than 6 mA.

For RCD Type A, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct current up to 6 mA.

RCD Type F

IEC 62423 establishes additional requirements to IEC 61008-1 and IEC 61009-1, according to which type F and type B RCDs are available. Type F RCDs are designed to protect electrical circuits to which frequency converters are connected.

RCD type F: Residual current device for which tripping is ensured as for Type A according to IEC 61008-1 or IEC 61009-1, as applicable, and in addition,

  • for composite residual currents, whether suddenly applied or slowly rising, intended for circuit supplied between line and neutral or line and earthed middle conductor;
  • for residual pulsating direct currents superimposed on smooth direct current.

For RCD type F, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct current up to 10 mA.

Examples of equipment include: air conditioning controllers with variable speed drives, some class I power tools, washing machines, dishwashers, and tumble driers which contain synchronous motors.

RCD Type B

RCD type B: Residual current device for which tripping is ensured as for Type F and in addition,

  • for residual sinusoidal alternating currents up to 1 kHz;
  • for residual alternating currents superimposed on a smooth direct current;
  • for residual pulsating direct currents superimposed on a smooth direct current;
  • for residual pulsating rectified direct current which results from two or more phases;
  • for residual smooth direct currents, whether suddenly applied or slowly increased, independent of polarity.

Examples of equipment include: inverters, uninterruptible power supplies (UPS), photovoltaic systems, lifts, escalators, welding equipment, industrial machines, and electric vehicle charging equipment with smooth residual DC current which is greater than 6 mA.

For RCD type B, tripping is achieved for residual pulsating direct currents superimposed on a smooth direct current up to 0.4 times the rated residual current (IΔn) or 10 mA, whichever is the highest value.

Type B devices are also suitable for Type AC, Type A and Type F applications.

RCD Type S

Depending on the presence of a time delay (in the presence of a tripping residual current), there are residual current devices without time delay, namely the type for general applications, and RCDs with time delay, namely the S type for selective operation. RCDs of the S type are specially designed for selective operation when connected in series with RCDs for general applications.

RCDs of type S are considered to be sufficiently proof against unwanted tripping even if the surge voltage causes a flashover and a follow-on current occurs.

Annex B of IEC 60755-2017 gives, for different electronic load architectures, the possible load and residual current waveforms, and proposes the suitable types of RCD for each case. (see Table 1).

Table 1 shows, for common line-side circuit configurations which are used in electronic equipment and switched mode power supplies, the waveforms of residual currents and the cases where an earth fault with DC component can occur.

Circuit diagram with fault locationShape of load current ILShape of earth fault current IFRCD tripping characteristic
1Phase control
Phase control
AC, A, F, B
2Burst control
Burst control
AC, A, F, B
3Single-phase
Single-phase
A, F, B
4Two-pulse bridge
Two-pulse bridge
A, F, B
5Two-pulse bridge, half
controlled
Two-pulse bridge half controlled
A, F, B
6Frequency inverter with
two-pulse bridge
Frequency inverter with two-pulse bridge

F, B
7Single-phase with
smoothing
Single-phase with smoothing
B
8Frequency inverter with
two-pulse bridge and PFC
Frequency inverter with two-pulse bridge and PFC

B
9Two-pulse bridge between
phases
Two-pulse bridge between phases
B
10Frequency inverter with
two-pulse bridge between
phases
Frequency inverter with two-pulse bridge between phases

B
11Three-phase star
Three-phase star
B
12Six-pulse bridge
Six-pulse bridge
B
13Frequency inverter with
six-pulse bridge
Frequency inverter with sixpulse bridge

B
Table 1 – Possible fault currents in electronic loads and suitable RCD types

A single-phase rectifier and a capacitor in circuit number 7 are able to generate a hazardous DC fault current. This circuit is unlikely to be used, but if it is used, an RCD of type B is able to detect smooth DC and should be used.

For circuit number 2, the time of each pulse train is in general much more than 0,5 s. For that reason, RCDs of types AC, A, F and B can be used.

Symbols for Marking Depending on the Type of RCD

Below shows the symbols used for the different types of RCDs which can be found on the front of the device.

  • RCDs of type AC with the symbol: RCBB AC symbol (IEC 60417-6148:2012-01)
  • RCDs of type A with the symbol: RCBB type A (IEC 60417-6149:2012-01)
  • RCD of type S with the symbol: RCBB AC symbolsymbol S
  • RCDs of type F with the symbol: RCD of type f (IEC 60417-6149:2012-01 + 6160:2012-04)
  • RCDs of type B with the symbol: RCD of type B (IEC 60417-6149:2012-01 + 6160:2012-04 + 6297:2014-11)

Note – This information may be on the inside of any cover which has to be removed in order to connect the supply wires.

References

  1. IEC 61008-1
  2. IEC 61009-1
  3. IEC 60755-2017
  4. BS 7671:2018+A2:2022

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