A Comprehensive Guide to Choosing the Right RCD for Your Campervan

In the latest amendment to the BS7671 wiring regulations there were a few updates made to circuit protection, in particular, an update to the section 531.3.3, types of RCD. This update is in relation to the ongoing decline of the type AC RCD. By fitting one, your installation may no longer be compliant. We’ll discuss this in more detail below.

British Standard 7671 wiring regulations state: ’RCD Type AC shall only be used to service fixed equipment where it is known that the loads current contains no DC components’

Both the self and professional builder need to ensure that they are adhering to this regulation otherwise they could be leaving themselves open to using or supplying the incorrect components which can potentially result in an RCD that is unable to trip under fault conditions.

In this article we will delve into the type of RCD you should be using in your camper vans electrical installation. The type of RCD you choose has a detrimental effect to the safety of your system so this is a really important guide to help you through this process.

Types of RCD

There are two main types of RCDs:

1. Type AC: This type of RCD is designed to protect against AC fault currents only. It detects and disconnects the circuit when there is a difference in the current flowing through the line (live) and neutral conductors, which may be caused by a fault to earth. Type AC RCDs are commonly used in domestic and similar installations where the risk of DC faults is low.

2. Type A: This type of RCD is designed to protect against both AC and DC fault currents. It can detect and disconnect the circuit when there is a difference in the current flowing through the line and neutral conductors, as well as when there is a fault current to earth caused by a DC component. Type A RCDs are commonly used in industrial and commercial installations where the risk of DC faults is higher.

In addition to these two main types, there are also other types of RCDs available, including:

3. Type B: This type of RCD is designed to protect against AC, pulsating DC and smooth DC fault currents. It is commonly used in medical locations and locations where the electrical supply is generated from a renewable energy source.

4. Type F: This type of RCD is designed to protect against AC and DC fault currents, including high-frequency DC residual currents. It is commonly used in locations with electronic equipment and installations with frequency converters.

5. Type B+: This type of RCD is designed to provide additional protection against DC fault currents, including those caused by high-frequency ripple currents. It is commonly used in installations with electronic equipment and renewable energy sources.

IMPORTANT NOTE:

If you intend on buying a consumer unit from a wholesaler then it could be possible that the unit will be supplied with a type AC RCD. Why? Well it is the cheapest model of RCD available, but, this does not provide the correct level of protection for an electrical system containing DC electronics.

Be assured, if you purchase a consumer unit for your campervan via our Tiny Build Electrics store, the unit will come supplied with the correct type A RCD.

How an RCD operates

A residual current device constantly measures the current balance between the line and neutral conductors. The device will open its contacts (trip) if it detects an imbalance between the two conductors.

In a safe, operational system the supply and return current are balanced and therefore no current is leaking to earth. RCD’s are designed to prevent electrocution by detecting the earth leakage and disconnecting the supply before it causes any harm.

RCDs are designed to prevent electrocution by detecting this leakage current, which can be far smaller than the currents that are needed to trip conventional circuit breakers or fuses (several Amperes). RCDs are intended to operate within 25 – 40 milliseconds. This time is faster than the time needed for the electric shock to drive the heart into ventricular fibrillation, the most common cause of death through electric shock. A safe system is a system that protects against short-circuit, overload and earth leakage currents.

Why Type AC RCD’s are becoming obsolete

Type AC RCD’s have worked perfectly well in the past because the loads put through the RCD were simple resistive loads with very little in the way of electronics. However, as time has gone on systems are becoming ever more sophisticated with a larger amount of electronics present. Loads with DC electronics within them have a nasty habit of leaking DC electricity down the line into our AC network and then on into the RCD.

This DC current has the potential to leak into the type AC RCD and ‘stun’ it, stopping it from tripping when an earth fault occurs. As that’s what an RCD is designed to do, this causes a massive issue. This therefore means the fault will not clear and cause damage to the installation and worse, the user.

This therefore means that a type AC RCD is no longer suitable for many installations, especially camper vans with inverters, battery chargers and other DC operated electronics.

Which RCD do I need for my campervan?

We recommend that you fit a Type A double pole RCD in your camper vans electrical distribution board. Type A RCDs are specifically designed to detect alternating current (AC) residual currents with a sinusoidal waveform, such as those produced by electronic devices with switching power supplies or equipment with variable speed drives. These types of electrical loads can produce harmonic currents that can be difficult for Type AC RCD’s to detect, making Type A RCDs an important safety measure in many any electrical system containing DC electronics.

Do you need help specifying which RCD you should use? Get in contact with us here!

We at Tiny Build Electrics will not only design and specify your consumer unit, RCD and circuit breakers, but will also build the equipment before its sent out to you. Get in touch and we will be happy to help!