18th Edition Mythbuster

Guide to the New 18th Edition Wiring Regulations

Guide to the New 18th Edition Wiring Regulations


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18 TH EDITION<br />


Designed in the UK

www.cudis.co.uk<br />

Introduction<br />

<strong>18th</strong> <strong>Edition</strong> of the IET Wiring Regulations (BS7671:2018 Requirements for Electrical Installations) is now fully<br />

effective and installations designed after January 1st 2019 must comply with these requirements. The Regulations<br />

apply to the design, erection and verification of electrical installations, also additions and alterations to existing<br />

installations.<br />

In this guide we provide an overview of some of the changes including those regarding surge protection and RCD<br />

types. This information provided is no substitute for the BS7671:2018 regulations and designers & installers should<br />

follow the requirements & recommendations within the regulations.<br />

Low Voltage Assemblies (421.1.201)<br />

There has been no change in this regulation or any other regulation<br />

which results in the way consumer units and distribution boards are<br />

constructed. Within domestic/household premises, consumer units<br />

and similar switchgear assemblies shall comply with BS EN 61439-3<br />

(effective January 2016) and shall have their enclosure manufactured<br />

from non-combustible material or be enclosed in a cabinet or<br />

enclosure constructed of a non-combustible material.<br />

Integration of Devices and Components (536.4.203)<br />

In low voltage assemblies e.g. consumer units/distribution boards and incorporated devices/components shall<br />

only be declared suitable according to the manufacturer of the assembly. Essentially this means that you must<br />

use the board manufacturer’s approved control devices (MCBs, RCDs, etc). So, typically, the board and it’s<br />

component devices will come from the same manufacturer. Cudis only declare Cudis devices to be suitable for<br />

it’s boards. If a deviation from assembly manufacturer’s instructions is introduced then the person introducing the<br />

deviation becomes the manufacturer and takes on the corresponding obligations.<br />

Additional Requirements for Socket Outlets (411.3.3)<br />

Additional protection by use of a 30mA RCD is now required for all socket outlets with ratings up to and including<br />

32A and all domestic lighting circuits. Without exception, every socket outlet in a dwelling must have RCD<br />

protection. If the installation is not a dwelling and if RCD protection may not be desirable for certain applications<br />

(such as supply to a computer server), a documented risk assessment will be required to determine that RCD<br />

protection is not necessary.<br />


www.cudis.co.uk<br />

Caravan Parks (708.415.1)<br />

Every socket outlet and also a final circuit intended for the fixed connection (from the<br />

connection/metering point to the consumer) of a supply to a mobile or residential park<br />

home shall be both individually protected by an RCD having a rated residual operating<br />

current not exceeding 30mA. Devices selected shall disconnect all live conductors.<br />

Arc Fault Detection Devices (421.1.7)<br />

The use of Arc Fault Detection Devices (AFDDs) conforming to BS EN62606 is a recommended method for<br />

providing additional protection against fire caused by arc faults in AC final circuits.<br />

This device is specifically to detect and disconnect dangerous electrical arcs in both the fixed wiring and the<br />

connected equipment which could be the source of a fire. If used, AFDDs should be installed in consumer units/<br />

distribution boards at the origin of the circuit to be protected.<br />

Following are examples of when additional AFDD protection may be want to be considered:<br />

- Premises with sleeping accommodation<br />

- Locations with a risk of fire due to the nature of processed or stored materials (i.e. BE2 locations such as barns,<br />

wood-working shops, stores of combustible materials)<br />

- Locations with combustible construction materials (i.e. CA2 locations such as wooden buildings)<br />

- Fire propagating structures (i.e. CB2 locations)<br />

- Locations with endangering of irreplaceable goods<br />

In the schedule of inspections, under the section dealing with consumer units and distribution boards there is a<br />

reference to check for the AFDD six monthly test notice, similar to what is already common practice for RCDs and<br />

RCBOs.<br />

Although the use of AFDDs is not mandatory, at this time, Cudis are currently developing compact AFDD devices<br />

which should become available during 2019.<br />

Overvoltage Control (443.4)<br />

Protection against transient overvoltages is now required in a number of specified situations where overvoltage<br />

could result in:<br />

- Serious injury or loss of life<br />

- Interrupted public services<br />

- Damage to cultural heritage<br />

- Interrupted industrial and commercial activity<br />

- Affect a large number of co-located individuals<br />

or<br />

- In any building which has lightning protection system installed or is supplied via overhead lines.<br />

For other circumstances a risk assessment must be carried out to determine if protection against transient<br />

overvoltage is required. Designers should note that if they do not do a risk assessment, protection against<br />

transient overvoltage must be provided. The only exception is for individual dwellings if the total value of the<br />

electrical installation and electrical equipment therein fails does not justify such protection.<br />


www.cudis.co.uk<br />

There are different types of surge protection devices (SPDs) for different<br />

applications.<br />

• Type 1:<br />

For structures equipped with an external lightning protection system or<br />

requiring protection against effects of direct lightning (i.e. fire and electric<br />

shock) such as structures supplied via overhead TT cables and metal<br />

structures. The devices should be installed at the origin of the electrical<br />

installation. Type 1 devices do not provide protection for sensitive<br />

electrical and electronic systems.<br />

• Type 2:<br />

For structures not requiring protection against effects of direct lightning<br />

but require protection against the effects of man-made transients including<br />

switching of inductive or capacitive loads (i.e. motors, transformers, LV<br />

generator supplies, etc). They should be installed at the origin of the<br />

electrical installation and Cudis recommend additional type 2 devices be<br />

installed in sub-distributions boards or close to the sensitive and critical<br />

equipment to be protected.<br />

• Type 3:<br />

For additional protection of particularly sensitive equipment Class 3<br />

devices should be installed in the fixed electrical installation close to<br />

the equipment to be protected.<br />

Cudis are an established supplier of Class 1, 2 and 3 surge protection<br />

devices for both 3 phase and single phase applications. New products<br />

and devices are being introduced and recent introductions include:<br />

• single phase retrofit boards for existing installations<br />

• 22 way split load consumer unit board with a surge<br />

device pre-installed in the unit<br />

• RCBO loaded boards with a surge device preinstalled<br />

in the unit<br />

• Combined Class 1+2 devices<br />


www.cudis.co.uk<br />

Unwanted Tripping (531.3.2)<br />

RCDs shall be selected and the circuits subdivided in such a way to avoid unwanted tripping by protective<br />

conductor currents and/or earth leakage currents. The accumulation of such currents shall be not more than<br />

30% of the rated residual operating current e,g, 30% of the RCD rating of 30mA. Another option is to have more<br />

individual RCD/RCBO circuits or even use a RCD/RCBO for every circuit and Cudis have recently introduced a<br />

range of RCBO loaded boards to cater to meet this need.<br />

Current Ratings (536.4.202)<br />

The rated current of a switch or RCD shall be based upon one of the following:<br />

- Sum of final circuit current demand after any applicable load diversity factors or<br />

- As above together with allowances for diversity between final circuits or<br />

- The sum of the OCPD’s rated current multiplied by a diversity factor<br />

Cudis recommend a diversity factor of 60% for it’s OCPDs and also recommend that designers conduct proper<br />

electrical design assessments rather than standardising on 100A RCDs in consumer units, as currently suggested<br />

by one OCPD supplier, as this may result in inappropriate device selection.<br />

Type of RCD (531.3.3)<br />

Differing types of RCDs behave differently in the presence of DC components or different<br />

frequencies. The appropriate RCD should be selected for the specific application:<br />

Cudis have decided to retain their high integrity dual RCD boards with Type AC RCDs but<br />

have available Type A RCDs and Type A miniature RCBOs which the installer can buy, and<br />

separately change, for less common applications.<br />

RCDs are marked with a different symbol according to their type and the most common types<br />

are shown below.<br />

Type AC:<br />

RCD can detect & respond to sinusoidal residual AC currents. May be used for general<br />

purposes and suitable for the majority of applications. Other RCD types, described below, use<br />

more expensive electronic tripping technology and are used in special applications.<br />

Type A:<br />

RCD can detect & respond to sinusoidal residual AC currents and residual pulsating DC<br />

currents up to 6mA.<br />

Suitable for electric vehicle charging.<br />

(722.531.2.101: each charging point shall be protected by it’s own RCD if at least Type A having<br />

a rated residual current not exceeding 30mA).<br />

Type F:<br />

RCD similar to Type A but for composite residual currents and pulsating DC currents up to<br />

10mA.<br />

Suitable for equipment with frequency controlled speed drives.<br />

Type B:<br />

RCD can detect & respond to sinusoidal residual AC currents and pulsating DC currents and<br />

smooth DC currents up to 20kHz.<br />

Suitable for electric vehicle charging, photo voltaic and wind generators.<br />


Let Cudis shine some light on the <strong>18th</strong> <strong>Edition</strong>.<br />

Do I need to install an <strong>18th</strong> <strong>Edition</strong> Consumer Unit?<br />

No. There has been no change to the design of a metal consumer unit since the 17th <strong>Edition</strong>,<br />

Amendment 3. However the installation itself and circuit protection included must comply with<br />

the current regulations.<br />

Do I need to install 100A RCD’s in split load boards?<br />

No. The use of diversity factors to determine maximum demand when designing an installation<br />

is still an accepted practice in the <strong>18th</strong> <strong>Edition</strong> (following the manufacturers guidelines). In<br />

most cases a 63A or 80A RCD would be appropriate, in cases where there is a possibility of<br />

overloading the RCD protecting the downstream circuits, then it may be more suitable to install<br />

100A RCD’s.<br />

(BS 7671 Chapter 314.1)<br />

Do I need to install Type A RCCB’s as standard?<br />

No. For general purposes, Type AC RCD’s may be used.<br />

Certain installations require the use of Type A, Type B or Type F RCD’s to protect against DC<br />

fault current which may become present on the installation. Such installations include Solar<br />

PV and Car Charging Equipment. These devices can be installed at the location of the DC<br />

installation (at the AC side) and will prevent any DC earth leakage current entering the rest of<br />

the installation.<br />

(BS 7671 Chapter 531.3.3)<br />

Do I need to install a board with RCBO’s to overcome unwanted tripping of<br />

RCD’s/RCCB’s?<br />

No. The total earth leakage of the circuits protected by an RCD should not be more than 30%<br />

of the rated residual operating current (eg. a 30mA RCD, regulation state no more than 9mA of<br />

earth leakage detected on the downstream circuits).<br />

Bearing in mind that some circuits will naturally have more protective conductor current / earth<br />

leakage eg, circuits powering power supply units (like in PC’s) or transformers like LED Drivers.<br />

Careful consideration of subdivision of circuits between the 2 protective RCD’s may be enough<br />

to combat the accumulation of fault leakage.<br />

Although installing all RCBO’s will give more flexibility in the design of installation and reduce<br />

the consequences from tripping as only individual circuits will be affected.<br />

(BS 7671 Chapter 531.3.2)<br />


www.cudis.co.uk<br />

Can I use another brands circuit protection in a Cudis consumer unit?<br />

Cudis, as the original manufacturer, do not recommend the use of another manufacturers circuit<br />

protection product be used in our enclosures, as they have not been designed or tested for use<br />

in our enclosures, therefore we cannot guarantee compatibility.<br />

As per the <strong>18th</strong> <strong>Edition</strong>, if incompatible products are installed inside a Cudis consumer<br />

unit, then the person introducing the product becomes the original manufacturer with the<br />

corresponding obligations.<br />

(BS 7671 Chapter 536.4.203)<br />

Do I need to install AFDD’s?<br />

No. Arc Fault Detection Device’s at the moment are only recommended as a means of providing<br />

additional protection against fire caused by arc faults in AC final circuits.<br />

Although they may be specified in an electrical installation design, if so they should be<br />

installed at the origin of the final circuit to be protected and in AC single phase circuits not<br />

exceeding 230V.<br />

(BS 7671 Chapter 421.1.7 & 532.6)<br />

Do the provided clip in plastic blanks, to cover unused ways in a consumer<br />

unit, comply with the <strong>18th</strong> <strong>Edition</strong> Regulations?<br />

Yes. All of our consumer units conform to BS61439-3 and we ensure that the blanks are firmly<br />

secured in place with sufficient stability and durability to maintain the required degrees of<br />

protection and appropriate separation from live parts under normal service conditions, taking<br />

account of relevant external influences.<br />

However, we also offer an MCB Blank which clips into the din rail offering greater levels of<br />

stability and durability which may be more suitable in some circumstances.<br />

(BS 7671 Chapter 416.2.3)<br />

Do I have to install an SPD in a domestic single dwelling?<br />

No. Not always. If a risk assessment is carried out and there are NO unacceptable<br />

consequences that exist and there is not an increased risk of lightning present. Then an SPD<br />

only has to be installed where the total value of the installation and equipment therein, justify<br />

having an SPD installed.<br />

This will involve a conversation with the customer to determine whether an SPD is required,<br />

however it should be considered that the cost of an SPD is usually far less than even one<br />

electronic device that may be attached to the installation.<br />

(BS 7671 Chapter 443.4)<br />


- Lumo® Consumer Units - Control Gear - Rotary Isolators - Circuit Protection -<br />

- 3 Phase Distribution - Surge Protection - Voltage Optimisation -<br />

Designed in the UK<br />

www.cudis.co.uk - 0161 765 3000<br />

sales@cudis.co.uk - Power House, Parker Street, Bury, Lancs BL9 0RJ

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