Getting ready for change
Following a number of recent Member queries, the newest recruit to our Technical team looks at what should be considered before work can start on replacing a consumer unit
When an electrician is to replace a consumer unit, there are a number of factors that need to be taken into account before any work can proceed.
However, the very first thing to be aware of is that there is NO specific requirement for a replacement or upgrade of a consumer unit which has been installed to an earlier version of BS 7671 where it is in a satisfactory condition.
In fact, the introduction to BS 7671:2018 specifically states: “Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect.
This does not necessarily mean that they are unsafe for use or require upgrading.”
This infers that an older installation – with, for example, BS 3036 rewireable fuses – may still be acceptable for continued use!
Reasons for replacement
So what might be valid reasons for organising a replacement consumer unit? Some examples are provided below:
Has the consumer unit been damaged, e.g. by fire, flood or impact etc, which has led to it becoming obviously unsafe? Perhaps this has resulted in the exposure of live parts or components or improper functioning of the equipment?
Has the client requested that the installation be upgraded for a specific maintenance reason, e.g. to provide an easier means of resetting the power after a fault by replacing rewireable fuses with circuit breakers?
Is a new circuit being installed or is there to be an addition to an existing circuit which requires appropriate protection, e.g. provision of a suitable residual current device (RCD)?
Can new components not be retrofitted into the existing consumer unit or can replacement components not be sourced as they are no longer manufactured?
Has the consumer unit been reported unsafe following recent periodic inspection and testing (PI&T)?
Has it been noted in the ‘Comments on the existing installation’ section of an Electrical Installation Certificate (EIC) or Minor Electrical Installation Works Certificate (MEIWC), or identified in Section K of an Electrical Installation Condition Report (EICR) that there are signs of thermal damage or that suitable ingress protection (IP) protection levels are not being achieved, perhaps resulting in potential exposure to live parts etc?
Has there been an incident where an existing protective device did not function correctly or has been damaged during a fault?
Does high earth fault loop impedances on final circuits mean existing protective devices aren’t able to operate satisfactorily to achieve the disconnection times required in BS 7671?
“the very first thing to be aware of is that there is NO specific requirement for a replacement or upgrade of a consumer unit which has been installed to an earlier version of BS 7671 where it is in a satisfactory condition”
Recommended investigations
Before replacing a consumer unit, there are also other factors within the existing installation that may need to be considered and agreed with the client or property owner.
Regulation 132.16: Additions and Alterations will need to be carefully considered in particular – after all, a consumer unit replacement IS an alteration!
This regulation states: “No addition or alteration, temporary or permanent, shall be made to an existing installation, unless it has been ascertained that the rating and condition of any existing equipment, including that of the distributor, will be adequate for the altered circumstance. Furthermore, the earthing and bonding arrangements, if necessary for the protective measure applied for the safety of the addition or alteration, shall be adequate.”
The recommended solution to satisfy the above requirement would be to carry out a periodic inspection and test of the existing installation and to provide an EICR on its condition to the client prior to the replacement work going ahead.
This should hopefully identify any safety issues such as low values of insulation resistance on final circuits, incorrect polarity, and the adequacy of the earthing and bonding.
“No addition or alteration shall be made to an existing installation, unless it has been ascertained that the rating and condition will be adequate for the altered circumstance”
Any necessary remedial work should then be organised with the client and any defect or omission that will affect the safety of the alteration rectified prior to the replacement of the consumer unit.
NOTE: With the increasing amount of electrical equipment which now produces earth leakage currents as part of normal operation, it may also be advisable to use a suitable clamp test instrument to measure the level of earth leakage in the installation. This may help decide how the installation may be divided up to ensure correct operation of any RCD protection.
If the rectification of safety issues is not possible, e.g. due to the client’s budgetary constraints, it would be recommended to have a written agreement with them to agree that you will leave any unsafe and non-compliant circuits disconnected from the new consumer unit. This should also be recorded in the ‘Comments on the existing installation’ of the EIC produced on completion of work.
If the client does not agree to a PI&T, it is recommended that a few basic checks including basic inspection and tests are carried out – these may also be useful to highlight areas of concern.
Tests that should be carried out include:
Ze – measured at the incoming supply
Zs at Db – measured at the consumer unit
Check of polarity – verified at the incoming supply
Continuity testing of protective conductors and ring final circuits – use Test Method 2 to test the continuity of the main equipotential bonding conductors and either Test Method 1 and/or Test Method 2 for continuity of circuit protective conductors (CPCs). Use the three-step method to verify all live conductors and the protective conductors of ring final circuits.
If minor deviations not affecting the safety of the installation are found, record these in the ‘Comments on the existing installation’ section of the appropriate certification.
If any major problems are found, it is recommended that the replacement of the consumer unit does not proceed until further investigation and agreement on the necessary remedial work has been reached with the client.
If the outcome of the inspections and tests or the PI&T are satisfactory and the replacement of the consumer unit work has been agreed with the client, discuss their budget, protection requirement options, division of installation and possibility of installing a consumer unit with more circuit capacity for future expansion.
NOTE: Further guidance on inspection and testing is available in Guidance Note 3 from the Institution of Engineering and Technology (IET).
Incoming supply
Where a PI&T has already been conducted, the incoming supply should already have been inspected for suitability. If not, an assessment should be made to ensure that a suitable isolator is installed so that the consumer unit can be isolated safely without tampering with the equipment owned by the distribution network operator (DNO). If not, the client will need to contact their electricity supplier to have one installed.
Confirmation that the rating of the cut-out fuse and the size of the supplier’s meter tails are suitable should also be part of the inspection where the consumer unit is being upgraded to incorporate additional loading, e.g. to install electric vehicle charging equipment. If these are not suitable – e.g. 60A fuse 16mm2 meter tails – the client will need to contact their supplier to arrange for the DNO equipment to be upgraded.
“If any major problems are found, it is recommended that the replacement of the consumer unit does not proceed until further investigation”
A visual inspection shall be made to ensure there is no sign of damage, overheating and/or deterioration of the supplier’s equipment, and the length of the meter tails from the isolator to the consumer unit does not exceed 3m to comply with Regulation 433.2.2.
If all is suitable and satisfactory, then the correct safe isolation procedure can be undertaken so that the consumer unit can be replaced. The safe isolation procedure shall be carried out in accordance with the Electricity at Work Regulations, HSG85 and GS38, ensuring that:
Permission is gained
There has been a controlled shutdown of the installation
Alternative supplies have been identified and isolated, if applicable
Discharge of electricity from equipment has been conducted
The correct switch-off, lock-off, tag-off and proving dead procedure is followed, and
All risk assessments and methods statements are adhered to, if applicable.
NOTE: For guidance on safe isolation protocols and procedures, please refer to the video, infographic and downloadable brochure produced by SELECT which can be found at bit.ly/safe-isolate
Replacing the consumer unit
“most of the work should be carried out through investigation, inspection and testing and client consultation”
Where applicable, the following regulations must be adhered to when replacing a consumer unit to achieve compliance with BS 7671:2018 +A2:2022:
Non-combustible consumer unit or in a non-combustible enclosure (Regulation 421.1.201)
Line and neutral brought through the same entry of steel enclosure (Regulation 521.5.1)
For incoming supply meter tails, ensure a suitable cable gland is used for specific cables and/or to maintain IP ratings (Regulation 416.2.1 and Regulation 416.2.2)
Cables adequately protected at their point of entry into the consumer unit. Grommet strip (Regulation 522.8.1 and Regulation 522.8.11)
Cables of final circuits brought through openings that are not excessively large (Regulation 416.2.1, Regulation 416.2.2 and Regulation 421.1.201)
Manufacturer’s instructions followed during installation (Regulation 134.1.1)
Maintain earth continuity if the wiring system is used as the CPC (Regulation 543.2.1 (v) (vi) and Regulation 543.3.6)
Double insulation maintained or single core cables enclosed if required (Regulation 526.8)
Division of the installation (Regulation 314)
Protective devices suitably selected for design current, current carrying capacity of conductors etc (Regulation 433.1.1)
The correct type of RCD is installed. Type AC is now not recommended unless load currents do not contain components of DC current (Regulation 531.3.3)
No more than 9mA protective conductor current or earth leakage current per RCD where the consumer unit is split load type to prevent unwanted tripping – consider the use of RCBOs (Regulation 531.3.2)
Selectivity between protective devices (OCPD, RCD) is achieved if supplying another consumer unit, e.g. garage, shed etc (Regulation 536.4)
The correct type of surge protection device (SPD) is installed (Regulation 534.4.1)
Make sure protective devices are clamped onto the busbar and all connections are tight and secure using appropriate torque settings (Regulation 526.1)
Line, neutral and CPC conductors are correctly coordinated between protective devices and the neutral and earth bars (Regulation 514.8.1)
Beware of borrowed neutrals if applicable, e.g. lighting circuits (Regulation 314.4)
No undue strain on the conductors (Regulation 522.8.5)
Conductors identified with appropriate sleeving or numbering as per Table 51 (Regulation 514.4)
Connections in conductor properly made and suitably enclosed (Section 526)
Consider if there is adequate working space to leave spare ways in the distribution board for future expansion of the installation (Regulation 132.3 (vi))
Identification of switchgear, e.g. the main switch disconnector. Make sure it is suitable for the purpose and capable of being secured in the off position (Regulation 514.1.1, Section 462 and Regulation 537.2.7)
Correct identification of circuits (Regulation 514.9.1
NOTE: The requirements for provision of a circuit chart need not be applied for domestic, i.e. household, premises or similar installations where certification for initial verification, complete with Guidance for Recipients as detailed in Appendix 6, has been issued to the person ordering the work.
Appropriate labelling to be positioned at consumer unit, e.g. ‘Safety electrical connection’, ‘Danger 230V’ etc (Section 514).
NOTE: The requirements of Regulation 514.12.1 (Periodic Inspection and Testing Notice), 514.12.2 (Presence of an RCD) and Regulation 514.16.1 (SPD Notice) need not be applied for domestic premises or similar installations where certification for initial verification, complete with Guidance for Recipients as detailed in Appendix 6, has been issued to the person ordering the work.
Inspection, testing and certification
After work to replace the consumer unit has been completed, and following inspection and testing required for initial verification, an EIC with completed schedule of inspections, schedule of circuit details and schedule of test results should be completed and given to the client or person ordering the work.
NOTE: Inspections and testing will be carried out in accordance with Chapter 64 of BS 7671:2018 + A2:2022 with additional guidance given in the IET Guidance Note 3, Inspection & Testing.
In conclusion
The information above is not exhaustive as there are many other factors, regulations and criteria that may have to be considered and will come into play when replacing a consumer unit.
However, most of the work should be carried out through investigation, inspection and testing and client consultation before the old consumer unit has been removed.
This article isn’t a step-by-step or ‘how to’ guide – it is intended to raise awareness of the circumstances, requirements and procedures that should be considered when undertaking work that entails the replacement of a consumer unit.
If you have any comments or queries, do not hesitate to contact your Technical Adviser or call us on the Technical Helpline on 0131 445 9218 and we will do our best to help.
