RCD Regulations 2022

RCD regulations 2022 - RCD Type Selection Explained

RCD Regulations 2022

The introduction of the 2nd amendment to the 18th edition of the wiring regulations in 2022 has brought some serious changes to the RCD Regulations.

RCD regulations 2022 - RCD Type Selection Explained

Quite frankly, the choice of RCDs and their application has become nothing short of confusing. We have more choice of types, all for different installations, yet little guidance other than the big brown book

And let’s be fair, BS7671 doesn’t give much in the way of guidance, it just lays out what the RCD Regulations 2022 are and expects you to know where to go.

In this FULL and frank guide, we’re going to look at what the different types of RCDs are, what they are for and how you should make sure you are selecting the right RCD for the right situation.

Before we get started, it’s worth mentioning that the different types of RCD protection discussed in this guide can apply to either standalone RCDs (ie: BS EN 61008) or else combined into overcurrent devices as is the case with RCBOs (ie: BS EN 61009). We will be doing a post on ‘RCD or RCBO’ very shortly and will link back to that as soon as it is ready!

RCD Types – What Are They?

You might have heard the different types of RCD mentioned and wondered what they mean.

The most general types can be summarised as below:

  • Type AC
  • Type A
  • Type F
  • Type B
  • **Type S**

**It’s worth noting that the “Type S RCD” means something totally different to the rest of the “types”, however no run down of the RCD Regulations 2022 would be complete without looking at these.

Ok, let’s have a look at each type below and what separates them. We’ll also include the typical scenarios where each RCD type should be used.

rcd regulations 2022 18th edition amendment 2 RCD types
RCD Regulations 2022 – Different RCD Type Symbols

Type AC RCDs & Their Uses

Type AC RCDs are the “standard” RCD which has now been in use for quite some time!

A type AC RCD will respond to any earth fault current which is of an AC current (which the name might suggest!), however they can easily be “blinded” by DC fault currents.

This means that any appliance which may produce a DC current under fault, could mean that a Type AC RCD could fail to respond in the required time, if at all.

Whilst this wasn’t such a problem in years gone by, over recent times with the introduction of so many electronical items this has meant that the RCD regulations 2022 have had to address this.

The 18th edition AMD2 have introduced some requirements surrounding the use of type AC RCDs. These are to be used ONLY:

  • For fixed equipment and NOT socket outlets of any kind
  • Where any type of DC fault currents are not to be anticipated

This is a serious departure from the previous RCD Regulations and is the first time that any particular type of RCD has been specified based on what type of fault currents are to be expected.

Type A RCDs & Their Uses

A much newer addition to the different types of RCDs is a Type A RCD.

Whilst also reacting to AC fault currents as per the original type AC units, Type A RCDs are also able to react to pulsating DC fault currents superimposed onto the AC fault current upto 6mA.

This protects against the “blinding” of a typical AC RCD from any possible pulsating DC fault currents caused by electronical equipment or semiconductors.

BS7671:2018(AMD2:2022) has introduced a set of RCD Regulations which basically mean that type A RCDs are now the minimum standard.

Although Type AC RCDs can still be used for fixed equipment with no possibility of DC fault current, Type A RCDs are now the absolute minimum for socket circuits and any fixed equipment which may produce DC fault currents.

Some of the fixed equipment which can cause DC fault currents includes modern dishwashers & washing machines, LED lighting & EV car chargers. We’ll have a look at this further down in another chapter, as the list goes much further than than would imagine.

Type A RCDs were quite expensive until the last couple of years where the cost has come down to pretty much comparable with type AC units as they gradually replace the older RCDs as the standard fitment.

Type F RCDs & Their Uses

Type B RCDs & Their Uses

Type S RCDs & Their Uses

Different Types Of Fault Current – How To Be Sure?

Sinusoidal AC Fault Current

DC Fault Currents

Variable Frequency Drives

Summary To RCD Type Choice

RCD Regulations 2022 – Other Resources

If you are looking for some further reading or other resources relating to the latest RCD regulations then please take a look at the following posts or videos:

A really important factor to consider when considering which RCD to use, is whether or not the existing consumer unit supports these devices. This can mean that an upgrade of the entire unit may be required. As such, please also read our full 18th Edition Consumer Unit Regulations Guide which can help you navigate the best way forward (ie: whether to use RCDs or RCBOs)


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