Types of RCDs

RCD’s (Residual Current Device) are available in many types, the type is not to be confused with overcurrent protective device “curve” type.

RCD’s on their own do not offer any kind of overcurrent protection unless it is an RCBO (Residual Current Breaker with Over-Current) to BS EN 61009.

The correct selection of an RCD type all depends on what the RCD is required for, it is the designers responsibility to ensure the correct RCD or RCBO is selected for the job.

BS 7671:2018 regulation 531.3.3 states ‘different types of RCD’s exist, depending on their behaviour in presence of DC components and frequencies. The appropriate RCD shall be selected.

Type AC RCD

Type AC: Resistive, inductive and capacitive loads.

Note: If any DC current is present then a Type AC RCD may not function – It does not detect DC currents.

Type AC RCD is the most basic of all types of RCD’s and is becoming less and less suitable for todays modern world where most electrical appliances and equipment contain electronic components.

It has been mentioned that type AC RCD’s are now only really suitable for immersion heaters / electric panel heaters / tungsten lighting and the like, however this may not be the case if the equipment includes an electronic timer or electronic thermostatic controls or for tungsten lighting if electronic dimming controls are used.

Example Uses for a Type AC RCD

• Electric Shower
• Oven
• Hob
• Immersion Heater
• Tungsten / Halogen Lighting

Type AC RCD’s are now banned in some countries.

Type A RCD

Type A: Electronic components with pulsating DC residual currents up to 6mA.

Note: If a smooth residual DC current greater than 6mA is present then a Type A RCD may not function – It does not detect smooth DC currents.

Example Uses for a Type A RCD

• Induction Hobs
• Lighting with LED drivers
• Lighting with Dimmers
• EV Chargers with less than 6mA smooth residual DC current

Type A variant –  Type A-APR : As Type A + High immunity to unwanted tripping (Source: ABB)

Type F RCD

Type F: Frequency controlled equipment.

Note: If a smooth residual DC >10mA is present then the Type F RCD may not function – It does not detect smooth DC currents.

Example Uses for a Type F RCD

• Air con controllers with variable speed drives (VSD)
• Washing machines
• Tumble dryers
• Dishwashers

Some manufactures of white goods such as washing machines, tumble dryers and dishwashers specify the use of a Type F RCD.

Type EV RCD

Type EV: In some countries a Type A RCD which also incorporates a RDC-DD is referred to as a Type EV.

The Type EV RCCB has been developed specifically for EV charging systems and can detect AC and DC residual currents in accordance with the requirements of IEC62955. This provides a lower cost option to the Type B RCD, and has been designed specifically for use in Mode 3 and Mode 4 EV charging applications. (Source: westernautomation.com)

Type B RCD

Type B: Variable speed drives (VSD) with smooth DC residual currents.

A Type B RCD will detect smooth DC currents and will operate (trip) if the smooth DC current exceeds the trip threshold.

Type B variant – Type B+ : Type B+ devices are sensitive to all residual currents while also being equipped with a special tripping curve that limits the tripping current to maximum 420 mA for frequencies up to 20 kHz. (Source: EATON)

How to Identify RCD Type

The RCD symbols below demonstrates the type of RCD and its associated RCD symbol.

RCD Type Symbols

Below are the symbols for various types of RCD.