Above shows 3 common type of RCD’s and the symbol you will find on the RCD, most RCD’s use the symbol rather than the letter. In Domestic properties the AC type RCD has been getting installed for years now.

With the advance of modern technology in the home generating an element of direct current (DC) the use of type AC RCD’s can no longer be considered safe for continued use except under very limited circumstances.

What are the hazards and problems?

Type AC RCDs have been installed for many years and are effective for equipment which is resistive, capacitive, or inductive and fitted with minimal electronic components. This used to be the case for most installations when lighting was of the tungsten type, and the electrical appliances or equipment did not contain any electronic equipment.

Modern appliances are becoming increasingly more sophisticated, featuring microprocessor technology with an emphasis on energy reduction. This has led manufacturers to incorporate energy-saving measures, which by the nature of their operation have an element of DC residual fault current.

What types of equipment have DC residual leakage
current?

Some modern equipment can create DC residual fault current. Such items include, LED lighting, washing machines, dishwashers, computer equipment, and televisions.

Where electric vehicle charging equipment is likely to create a residual DC fault current, manufacturers may provide the correct type of RCD within the charging equipment, however, problems could still arise if the charging equipment is installed downstream of an existing Type AC RCD, which could be blinded by the residual DC fault current.

What are the effects of DC residual fault current
on RCDs?

Where equipment produces an element of residual DC, for example, the electronic circuits in your washing machine, the DC component can saturate the magnetic core and effectively blind or lock the RCD and could either prevent the RCD from operating or reduce the sensitivity resulting in a dangerous situation.

Electrical Regulations (BS7671)

Following the publication in March 2022 of the latest
IET Wiring Regulations, BS7671:2018 Amendment 2 :2022. Regulation 531.3.3
states: RCD Type AC shall only be used to serve fixed equipment, where it is
known that the load current contains no DC components.

What Does this mean for my electrical installation?

If you have had an EICR done this would result in an unsatisfactory report and require changing before a satisfactory.

If you looking at having work done it has for many years been a requirement to have an RCD, now the requirement is to have a type A RCD fitted if the load contains any DC components.