Darren Staniforth, Head of Technical Engagement with Scolmore Group, looks at some of the key potential changes affecting circuit protection in the forthcoming Amendment 2 of the 18th Edition and how the company has future-proofed its Elucian consumer unit range to satisfy these.
Β Due for publication in March 2022, Amendment 2 of the 18th Edition Wiring Regulations features a number of potential changes as far as circuit protection requirements are concerned. These include:
Mandating of AFDDs on circuits with a rated current not exceeding 32 A
The current version of the wiring regulations suggests that AFDDs are recommended for a small number of installations. We believe the 2nd Amendment will see them become mandated on a number of final circuits.
Other countries mandated the use of AFDDs, in line with Harmonised Documents, many years before JPEL/64 (the committee responsible for the development of BS 7671) decided to take another look at the requirement for them to be installed.
This was mainly down to different methods of construction on building sites, along with the belief that our electrical systems are more robust in the UK.
AFDDs offer protection against a single series fault within one single conductor. Many of the other devices mentioned in this article require a fault to interact with another conductor, or to Earth via a known or unknown path. These are commonly known as parallel faults.
AFDDs monitor a number of characteristics within the final circuit at the same time, using a microprocessor. Itβs true to say that most of the electrical items we use on a day-to-day basis have arcs within them when switching occurs.
The signatures of many electrical devices and appliances have been added to the electronic chip. This allows the device to differentiate between a normally occurring arc and one that could lead to a potential fire hazard. The device is constantly monitoring the final circuit in question, and therefore needs an ultra-low amount of energy to do its job.
We continue to invest in the Elucian consumer unit range to make sure installers can meet the requirements of the proposed regulation updates, and a range of AFDDs is in development.
- Types of RCD
Currently the Regulations recognises four main types of RCD:
AC β for use with alternating sinusoidal currents.
A β for use with alternating sinusoidal currents and where pulsating direct current is present up to a maximum of 6mA.
F β for use as Type A above and where other DC characteristics are present.
B β for use as Type F above and where the frequency has been altered.
The proposed changes suggests a move away from AC devices on general installations. The proposal sees type A devices referred to as suitable protective devices going forward.
As many installations now have a number of electronic devices that naturally produce DC, we believe this change to be good. Therefore, we’ve taken the decision to only provide type A RCBOs and RCCBs in the Elucian range so as to eliminate the need for the contractor to have to decide which device is suitable for a customer.
The merits of a type A device make it a natural selection for todayβs installations. Any DC present in the install can have a detrimental impact on the effectiveness of the standard AC type RCD. Where the DC has the ability to affect the RCD this is known as DC blinding. This method was previously used by some test instrument manufacturers to allow the measurement of Zs when an RCD was in circuit.
Selectivity of RCDs is also a vital consideration if the contractor is going to install a number of RCDs in series with each other. The different types of RCDs available must be deliberated by the installer before the installation is carried out.
By selecting an RCD type which is unable to handle DC upstream, the installer could compromise the safety of the users. A type A RCD must only be installed downstream of a device equal to, or higher than, its own classification type.
Clarification on the use of RCCBs and RCBOs
Residual Current Device (RCD) is a term widely used in the electrical industry. In fact, the general definition can be broken down to a specific device type. All of them use the ability to monitor the residual current that occurs when a leakage to Earth takes place.
However, they also have other characteristics that the installer needs to consider – for instance, Residual Current Circuit-Breaker with Overcurrent protection (RCBO). These one or two module devices also have overcurrent protection built into the unit. This device not only offers overcurrent protection to the final circuit but to the device itself.
The other widely used RCD is the Residual Current Circuit-Breaker without Overcurrent protection (RCCB). These are mounted within consumer units such as the split load boards commonly installed across the UK.
BS 7671 18th Edition requires installers to consider the current rating of the RCCB when carrying out a new installation or, when adding to or altering an existing installation.
If the current rating of the RCCB risks being exceeded due to the total current rating downstream of the device, the installer is required to take action to restrict the overload risk. The installer has a few options at this point:
- Limit the total amount of current downstream to a suitable value so the overload condition is not possible.
- Ensure that the protective device at the origin of the installation (upstream) is of a sufficient rating to offer protection to the RCCB. To do this it would need to be of an equivalent rating or lower than that stated on the RCCB. This requirement is necessary because the standard BS EN 61008 does not allow for any overcurrent tolerance of the device.
If the installer decides that the first option is their best and easiest, the use of diversity is limited in this application. The Regulations confirm βdiversity must not be the sole means of confirmationβ. They also go on to state that the installer can consult the manufacturer for their specific requirements when installing these types of devices.
We’ve taken the step to supply 80A RCCB devices in all Elucian consumer units, in an effort to take away some of the worry contractors have when selecting consumer units and the devices within.
SPD requirements
Surge Protection Devices (SPDs) were introduced into BS 7671 around 10 years ago and they were originally thought to be required only when an installation had a lightening protection system.
Overvoltage protection is currently a major part of the Wiring Regulations. Contractors are required to offer protection from overvoltage if it’s believed that a consequence of the overvoltage could cause danger to human life, loss of data from banking institutions, damage to cultural and heritage installations or where there is a large number of individuals. Any installation outside of those definitions is required to have a risk assessment completed to determine if SPDs are required. If the risk assessment calculation is not completed, then the default position is to install SPDs.
However, for single dwelling units the financial implications of these additional devices can be discussed with the client. If it’s believed that the additional cost of the SPD outweighs the cost of the installation and the equipment within, then the contractor can make the choice not to install an SPD.
The reduction in the cost of SPDs has now made it a viable option for installers to offer to all their clients.
The introduction of the 18th Edition of BS 7671 saw a lot of attention on the overcurrent rating of these devices. This led to many manufactures offering the SPD device in conjunction with a dedicated MCB.
We’ve chosen to ensure that the rating of the SPD offered by Elucian is sufficient to rely on the overcurrent protection offered by the main fuse to the installation. This allows for more outgoing ways for the contractor to use in the installation of their final circuit.
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