Housing Providers & the New Wiring Regulations
There are several new regulations that are relevant to the electrical installations within domestic household premises that housing providers need to know about. For example it’s now a requirement for all lighting circuits within domestic household premises to be protected by 30milliamp residual current devices. There are no exceptions in 411.3.4. It’s also a requirement to avoid any dangers that can occur from unwanted tripping of these devices. For lighting circuits the best solution is to use individual 30mA RCBOs on each lighting circuit so that the power to the healthy circuits remains on and residents are not plunged into darkness when the lighting circuits are not faulty.
The consumer unit in image 1 (below) uses two 30mA RCBOs next to the main switch (for lighting circuits) while other circuits are protected in groups by 30mA RCDs. Putting lighting circuits on individual RCBOs should be standard practice in all domestic household premises.
Types of RCD
The regulations now give extra information on some of the types of RCD that are available, and require the designer and installer to select and install the appropriate type for each application. Although correct selection of devices is not a new consideration this additional guidance will no doubt be very useful as an aid to selection in the design process.
Four types of RCD are mentioned in regulation 531.3.3 Type AC, Type A, Type F, or Type B. Each RCD type has different operating characteristics to suit particular applications - including those where DC components and varying frequencies are present.
The requirements here are clearly stated. Designers and installers must select and specify the correct device for each circuit or item of equipment being protected, and that choice must be made through a proper technical assessment.
However Regulation 531.3.3 is only part of the story when selecting RCDs other regulations also apply for example;-
• 30mA RCDs are used for additional protection (415.1)
• For general purposes Type AC RCDs may be used (531.3.3)
• For EV chargers Type A or B are required (722.531.2)
• For PV installations Type B or AC could be appropriate
Avoiding unwanted tripping from PE Currents
Unwanted tripping must be avoided to protect people within the building from hazards and dangers that can arise from unnecessary tripping and unwanted power outages. Regulation 531.3.2 is another ‘new’ regulation that is intended to help designers make better design decisions.
This supports the principles of Regulation 314.1 (which is not new) this requires every installation to be divided into the number of circuits required to avoid danger and hazards caused by unwanted tripping of RCDs – it is intended to make sure that a single fault on one circuit should not cause the loss of power to other circuits and introduce hazards dangers or risks to occupants.
Regulation 531.3.2 gives designers two options to use to avoid unwanted tripping of RCDs from earth leakage (PE current is current - in the earth path - from equipment that is used in the installation) and flowing during its normal operation.
Divide the installation into individual circuits, each using its own 30mA RCBO protection. This guarantees full compliance and ensures that all healthy circuits remain in service and unaffected by faults on other circuits. This prevents hazards, dangers or risks to occupants from unwanted tripping.
Design the installation so that the PE current cannot be more than 30% of the rated trip current i.e. no more that 9mA for a 30mA RCD. But how easy is that to achieve? The designer will need to know the PE current values for each item of equipment in order to be sure of providing a compliant installation. This information may not be easy to acquire.
Additional protection against electrical fires
Protection against electrical fires is provided to a great degree by the design and installation process. The regulations require good workmanship by skilled or instructed persons, proper materials, and due account to be taken of manufacturer instructions. But still electrical fires occur. In England alone there were more than 13,000 fires last year from electrical distribution or electrical appliances (source Government statistics, fire statistics data tables)
However, the 18th edition has introduced a new protective device that is recommended for the purpose of providing additional protection against fire caused by arc faults in AC final circuits. This device is an Arc Fault detection Device or AFDD. AFDDs can detect faults that MCBs, RCDs and RCBOs cannot detect.
Protective devices such as MCBs are required to provide protection against overcurrent (overload) conditions overloads can lead to fires. The use of RCDs is an accepted method for protection against potential faults to earth that could lead to ignition of combustible materials if unchecked. Every electrical connection must be of proper construction for mechanical strength conductance, insulation and protection.
However, poorly made or failing connections can become a source of heat and ignition. Impact damage, crushed & compressed cables, damaged or aged / failing insulation can also bring about arc fault conditions. Regulations 421.1.7 is a new regulation that has been added to section 421 which deals with protection against fire caused by electrical equipment
421.1.7 states the following; Arc Fault Detection Devices conforming to BS EN62606 are recommended as a means of providing additional protection against fire caused by arc faults in AC final circuits. When used AFDD must be placed at the origin of the circuit i.e. in the consumer unit.
Regulations 421.1.7 also give examples of where AFDDS can be used this includes premises with sleeping accommodation, and several other types of location where particular risk of fires exist or serious losses can occur.
Protection against overvoltage
There are now requirements for protection against transient overvoltage if the consequences of such overvoltage could result in serious injury or loss of human life, or affects a large number of co-located individuals. If any of the consequences listed in 443.4 can result from transient overvoltage then protection against that overvoltage must be provided.
For all other cases a risk assessment must be carried out. But if a risk assessment is not carried out then protection against overvoltage must be provided. The risk assessment method is a fairly simple mathematical calculation, but the information required to carry out that calculation might not be easy to obtain e.g. length of the underground / overhead service cables to the property. The calculation is designed to determine whether overvoltage protection is required. However, in single unit dwellings an additional consideration is included i.e. whether the total value of the installation and the equipment therein justifies the protection.
The consumer unit in image 2 (above) uses 30mA Type A RCBOs throughout for each individual circuit and includes integral overvoltage protection to provide the best 18th Edition Consumer Unit
To find out more important information on the Requirements for Electrical Installations BS7671:2018 go to www.electrium.co.uk and download the free Bitesize Guide.