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10,000 5,000

2000 1000 500


200 100 50

20 10

0.1 0.2 0.3 0.5 1 2 3 5 10 20 30 50 100 200 300 500 1,000 2,0003,000 5,000

Body current in milliamperes (RMS) 100mA


As the equipment is fed from the mains electrical supply, in the event of an earth fault the presence of semi-conductors may result in the normal ac waveform being replaced by a non-sinusoidal fault current. In some cases the waveform may be rectified or chopped. These waveforms are said to contain a pulsating dc component which can either partially desensitise or totally disable a standard Type AC RCD. International standards IEC 61008 (RCCBs) and IEC 61009 (RCBOs) divide RCDs into two performance classes:

Type AC RCDs for which tripping is ensured for residual sinusoidal alternating currents, whether suddenly applied or slowly arising.

Type A RCDs for which tripping is ensured for residual sinusoidal alternating currents and residual pulsating direct currents, whether suddenly applied or slowly arising.


The RCD employs the current balance principle which involves the supply conductors to the load (phase and neutral) being wound onto a common transformer core to form the primary windings. Under healthy circuit conditions, the current in the phase conductor is equal to the current in the neutral, and the vector sum of the current is zero. In the event of an earth fault, an amount of current will flow to earth, creating an out of balance situation in the transformer assembly. This out of balance is detected by the secondary winding of the transformer and at a pre-determined level of out of balance will activate the trip mechanism.

Single phase and neutral or three phase and neutral units (suitable for 3 or 4 wire systems) are available, the latter being suitable for balanced or unbalanced 3 phase loads.

The RCD trip mechanism will operate at a residual current of between 50–100% of its rating tripping current (sensitivity).


All Wylex residual current devices incorporate a high level of immunity to tripping when subjected to transient earth leakage currents. Such transients can occur when there is a significant level of capacitance to earth as can result from cable capacitance (particularly MICC) or RF filter networks. Wylex RCDs are therefore less susceptible to nuisance tripping due to transient earth leakage currents.

Typical current

Limits due to body resistance at 230V

To ensure the correct level of protection, check for the following symbols:

TYPE AC normal ac sensitivity 2 3 4 ab c1 c2 c3 IEC 60479

Zone Physiological effects 1 Usually no reaction effects (no danger).

2 Usually no harmful physiological effects (usually no effects).

3 Usually no organic damage to be expected. Likelihood of muscular contraction and difficulty of breathing, reversible disturbances of formation and conduction of impulses in the heart, and transient cardiac arrest without ventricular fibrillation increases with current magnitude and time.

4 In addition to the effects of zone 3, probability of ventricular fibrillation increased up to 5% (Curve C2), up to 50% (Curve C3) and above 50% beyond Curve C3. Increasing with magnitude and time, pathyphysiological effects such as cardiac arrest, breathing arrest and heavy burns may occur.

10,000 mA


TYPE A pulsating dc sensitivity

Wylex RCDs are available as both Type AC and Type A devices.


Used in special applications where additional protection against contact is essential due to the nature of the installation.

30mA- Tripping current designated by the IEE Wiring Regulations to provide additional protection.

100mA- Suitable for use where protection is provided to guard against firehazard, etc, rather than to provide additional protection to personnel, and where the earthing requirements need supplementing by RCD protection.

100mA time delay- Suitable for use when total RCD protection is required to supplement the system earthing and where local 30mA RCDs are used to give additional protection. The time delay RCD will discriminate with the 30mA RCD.

300mA- For use in large installations where plant and equipment protection are the main considerations and high levels of earth leakage are experienced.

If using RCDs in series, discrimination can only be achieved by using Type S devices in series with Types A or AC. See chart below.

BSEN61008-1:1995 RCBOs BSEN61009-1:1995 l Rated Residual Current (In) Tripping

Type of RCD RCD to Trip between Standard

A & AC Time Delay

(S) times

50%-100% In 1x In 2x In 5x In 500Amps Scope Any Value, eg 10, 30, 100mA 300ms 150ms 40ms 40ms


Greater than 30mA, eg 100mA 500ms 200ms 150ms 150ms Maximum-Trip 130ms 60ms 50ms 40ms Minimum-Non Trip

Lifeline Range RCDs – Technical Data

Time in milliseconds

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