Worried about wiring? We’re here to help
As a key contributor to the Wiring Regulations Advisory Group, SELECT helps provide answers to a wide range of technical questions. Here are some of the most recent queries
Along with our fellow industry organisations, SELECT is an enthusiastic participant in the Wiring Regulations Advisory Group (WRAG) hosted by Electrical Safety First (ESF).
A range of technical questions is raised at our monthly meetings, many of which are typical of the queries we receive from Members via our own Technical Helpline.
Where agreement is reached by WRAG, output is published in one of two relevant categories – New rewired and similar installations and Inspection, certification, testing and reporting.
With this in mind, we thought it would be useful to share some of the questions discussed during the group’s most recent meetings, along with guidance about where you can find further information.
New rewired and similar installations questions
Is it permissible to install electric vehicle charging equipment or other items of electrical equipment/switchgear within a meter cabinet – i.e. the cabinet specifically designed and intended to house distributor supply and metering equipment – at the service position of domestic and similar premises?
A. While a meter cabinet is owned by, and is the responsibility of, the homeowner, the space within the cupboard is designed for the use of electricity industry apparatus only, and no allowance is made for additional equipment to allow safe access for maintenance or replacement. For this reason, it is strongly recommended that such items of electrical equipment are not installed within a meter cabinet. A link to government guidance on this topic can be found at the end of this article.
Does BS 7671 require protective bonding of the metallic pipework within a building?
A. Protective bonding is only required where the pipework is an extraneous-conductive-part. Such protective bonding should be applied as near as practical to the point of entry of that pipework to the building.
Where plastic incoming service pipework – e.g. gas, water, oil, etc – enters a building, is protective bonding required?
A. One word: No.
Further information: Regulation 411.3.1.2
When would it be necessary for main protective bonding to be connected to metallic pipework within a dwelling?
A. When it is proved to be an extraneous-conductive-part.
Further information: Regulation 411.3.1.2
How can it be determined if a conductive part is an extraneous-conductive-part?
A. One method would be to carry out resistance testing using an insulation resistance tester at 500 V DC, between the main earthing terminal (MET) and the conductive part. Depending on the safe level of current deemed acceptable, the minimum resistance value where bonding would not be required could be within a range of 6.67 and 22 kΩ. The table above gives indicative values depending on example levels of current. Note: Other verification methods may be suitable.
Further information: Part 2 Definitions, (extraneous-conductive-part), Regulations 411.3.1.2 and 643.1
“Protective bonding is only required where the pipework is an extraneous-conductive-part. Such protective bonding should be applied as near as practical to the point of entry of that pipework to the building”
Where additional protection is required for a circuit connecting a generating set, e.g. PV generator to the installation, is the RCD required to switch all live conductors, including the neutral conductor?
A. Yes, for reasons as described in Best Practice Guide 3, Figure 2. This requirement was originally introduced in BS 7671:2008 17th Edition.
Further information: Regulations 522.6.202, 522.6.203 and 551.7.1
Does metallic pipework connected to a heat pump, which is located outdoors, require connection to the main earthing terminal (MET) by a main protective bonding conductor at the point of entry to the building?
A. Only if the metallic pipework is an extraneous-conductive-part.
Further information: Part 2 Definitions (extraneous-conductive-part), Regulations 411.3.1.2 and 544.1.2
Are there any particular requirements for heat pump installations in BS 7671 which preclude the use of a PME earthing facility as the means of earthing for the supply of such equipment?
A. One word – no.
Inspection, certification, testing and reporting questions
During a periodic inspection what classification code, if any, should be allocated where a Type AC RCD is fitted?
A. Type AC RCDs shall only be used to serve fixed equipment where it is known that the load current contains no DC components. It should be noted that some appliance and equipment manufacturers now specify that a Type A, F, or B RCD is installed where fault or additional protection by RCD is required. Where such an appliance or equipment is encountered or could foreseeably be connected and supplied via a Type AC RCD, a classification code C3, i.e. improvement recommended, would be appropriate. However, if it is identified and confirmed that an RCD in the circuit does not operate correctly when tested, a classification code C2 – potentially dangerous – would be appropriate. Where it is known that no connected loads can produce DC components that may impair the operation of the device no recommendation code is necessary. The recently updated BEAMA RCD Handbook provides further information on the different types of RCD and their suitability for connected loads. A download link can be found at the end of this article.
Further information: Regulation 531.3.3, Annex A53, Figure A53.1
When undertaking a periodic inspection, what classification code should be applied, if any, where the sheath has been removed such that basic insulation of a conductor that forms part of the consumer’s installation is exposed within an external meter cupboard which can only be opened with a key or a tool?
A. A meter cupboard which can only be opened with a key or a tool would be classified as an enclosure based on the definition given within BS 7671. Where all of the following conditions apply, no code would be applicable:
The cupboard door locking mechanism operates as it should
All hinges are intact and functional
There are no signs of damage to the exposed insulation.
If any of the conditions above are not met, then a classification code C2 would be appropriate. Note: Where inadequacies in the intake equipment are encountered, the inspector should advise the person ordering the work to inform the appropriate authority.
What code if any, should be attributed to isolating switches or switches for mechanical maintenance provided for showers, extractor fans, cookers, etc that aren’t lockable in the off position?
A. No code is required provided the requirements of BS 7671 are met, i.e. appropriate precautions to prevent unintentional or inadvertent closure are applied, e.g. located within a lockable space or lockable enclosure, padlocking, located adjacent to the associated equipment.
Further information: Regulations 462.3, 464.2 and 537.2.4
What classification code is required when cable green goo is found at electrical accessories/equipment?
A. An insulation resistance test to detect tracking, preferably at 500 V, should be applied to all circuits using the cable where green goo is thought to be present.If an unsatisfactory insulation resistance test result is recorded, a C2 classification code should be applied. It is also recommended that, where possible, you visually inspect and functionally test any equipment, including protective devices, the operation of which may have been adversely affected by the green goo. If any equipment which provides protection or has a safety-related function fails to operate, the inspector should record an appropriate classification code based on the item’s function and purpose. The inspector should also consider reducing the frequency to the next periodic inspection and test to monitor further deterioration more closely.
Further information: Regulation number 643.3.2: Electrical Installation Condition Report to evaluate safe continued use.
Are all cables installed at low level on the outside of a building subject to premature collapse in the event of a fire?
A. No. Wiring systems attached to the outside of a building at low level are not likely to experience premature collapse in the event of a fire. Although wiring systems attached to the outside of a building can eventually collapse, this will not necessarily be prematurely. In a situation where wiring systems are installed at low level and would not hinder evacuation and firefighting activities, no classification code would apply. In a situation where the premature collapse of a wiring system would likely hinder evacuation and firefighting activities, a classification code C2 should apply.
Further information: Regulation 521.10.202
“The recently updated BEAMA RCD Handbook provides further information on the different types of RCD and their suitability for connected loads”
When undertaking a periodic inspection in a single dwelling, what classification code should be applied, if any, where it is identified that wiring systems are not adequately supported to prevent premature collapse in the event of a fire?
A. Where premature collapse of the wiring system can hinder evacuation or firefighting activities in the event of a fire due to possible entanglement, a classification code C2 would be appropriate. Where it is identified that a wiring system is not adequately supported, however premature collapse of the system would not hinder evacuation or firefighting activities, then no classification code needs to be awarded.
Further information: Regulation number 521.10.202
During a periodic inspection it is identified that an RCD providing additional protection for a circuit connecting a generating set, e.g. a PV generator, does not switch all live conductors, including the neutral. Would a classification code be applicable for this observation?
A. Yes, a classification code C3 is advised.
What is WRAG?
Electrical Safety First (ESF) is the campaigning charity that aims to reduce deaths and injury caused by electricity in UK homes.
ESF provides important guidance on electrical safety issues, an important part of which is to provide specific professional resources, including the development of industry best practice guides and hosting the Wiring Regulations Advisory Group (WRAG).
WRAG is a now well-established group comprising experienced industry professionals, including representatives from SELECT, BEAMA, ECA, IET, NAPIT and NICEIC.
The group meets regularly at the end of each month to review questions which have been submitted on the application of BS 7671 by the industry and, wherever possible, to seek consensus and produce answers designed to help contractors, electricians and their clients.
Where agreement is reached, output from the group is published in one of the two specific categories relevant to the question and answer.
Find out more at www.electricalsafetyfirst.org.uk
FURTHER READING
WRAG guidance Guidance on new rewired and similar installations, and inspection, certification, testing and reporting, as discussed by WRAG.
Meter advice Government guidance on smart meters, relevant to all those involved in the specification of metering locations in domestic new builds.
RCD Handbook The recently updated BEAMA RCD Handbook provides information on the different types of RCD and their suitability for connected loads.
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