Hager’s Ask The Expert – RCDs Type A

RCD selection is an important aspect of any installation, ensuring adequate protection against potentially fatal electric shocks.

Paul Collins, Technical and Training Manager from Hager, covers some of the most frequently asked questions from contractors on RCDs and its recommendation that Type A selection is the best answer for the majority of electric circuits.

What type of RCD should I use?

RCD use has been in existence for a long time, and the revised 18th Edition regulations clarified their selection and specification to further enhance safety standards. Electrical contractors need to carefully consider the type of RCD required depending on the type of equipment which may be connected in the installation.

There are four types of RCD, with each reacting differently depending on the presence of DC components or different frequencies. In order for contractors to specify the correct product, the different types of RCD can be classified as:

  1. Type AC RCD – general purpose use

Type AC RCD can detect and respond to AC sinusoidal residual current only.

2. Type A RCD – equipment incorporating electric components

Type A RCD can detect alternating sinusoidal residual current and residual pulsating direct current suddenly applied or smoothly increasing. It is important to remember that Type A is also suitable for Type AC applications.

3. Type F RCD – equipment with frequency controlled speed drives

Type F RCD can detect and respond to high-frequency residual current as well as pulsating DC residual current.

4. Type B RCD – electric vehicle chargers, PV supplies

Type B RCD can detect and respond to all types of residual current including smooth DC residual current.

What does Hager recommend?

Due to the style of circuits, the nature of loads connected to these circuits and the frequent use of RCDs to protect a group of circuits, Hager believes that the majority of electrical circuits in residential and commercial applications will require a Type A RCD solution.

What type of equipment/load is best protected by a Type A RCD solution?

Single-phase with electronic components, which would typically comprise items such as:

  • Single-phase invertors
  • Class 1 IT and multimedia equipment
  • Power supplies for Class 2 equipment
  • Appliances such as a washing machine that is not frequency controlled
  • Lighting controls such as a dimmer switch and home and building electronic systems
  • Induction hobs
  • Electric vehicle charging where any smooth DC fault current is less than 6 Ma
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