There are lots of things to consider while replacing a consumer unit or CU in a residential premise. These include potential pitfall, the necessity to fulfil the requirements of the Electricity at Work Regulations 1989, the requirements included in BS 7671 and above everything else the best industry practices. In this blog post let us explore the issues one needs to consider while CU replacement.
The initial survey
Before replacing an electrical consumer unit, it is important to conduct an EICR or Electrical Installation Condition Report. This step or effort proves equally benefitting for both the customer and the electrician or installer.
However a customer may not always be willing to get an EICR done. In that case the installer should perform a pre-work survey to identify any immediate or potential threat to the system, suggests a tradesman associated with consumer unit replacement in London. This pre-work survey is simply crucial to get done; it proves useful identifying the probable reasons that may cause tripping of an RCD. To make it easier, a pre-work survey is the safety measure to protect an installer’s interest.
The power connection needs to be shut down during a pre-work survey. Therefore the customer has to be taken into confidence beforehand
More on pre-work survey and inspection
An internal visual inspection of the consumer unit is required to know the type and the state of the wiring that exists. And so you need isolating the CU. If in the course of inspection you come across lighting circuits without any circuit-protective conductor or CPC, such circuits cannot be reconnected until and unless the necessary remedial work is done. This includes replacing all the associated metal accessories with plastic ones.
As per BS 7671 specifications there is no need to upgrade existing circuits to current standards before making reconnections to a replacement CU. But any faulty or defective circuit categorised as being immediately or potentially dangerous or that needs undergoing more investigation is not to be reconnected to the CU. It is the installer’s responsibility to make this thing clear to customers so that there is no dispute or misunderstanding over the issue.
A circuit that is classified as C3 or ‘improvement recommended’ can be reconnected to a new CU provided it is noted in the Comments on existing installation Section of the EIC or Electrical Installation Certificate.
The CU replacement programme is to be aborted then and there on coming across lead-sheathed or insulated cables
If rubber insulated or lead-sheathed cables are found during the survey, it is strongly recommended not to go ahead with the CU replacement until the cables are changed. An external visual inspection of other accessible accessories should also be made.
Pre-work survey tests
Pre-work survey tests should include as a minimum:
- (Pfc) prospective fault current.
- (Ze) external earth fault loop impedance.
- (Zs) earth fault loop impedance at readily accessible socket-outlets.
- (Cpc) circuit protective conductor continuity at the end of each final circuit.
- End-to-end continuity checks of all conductors of each ring final circuit.
- Insulation resistance measurement of the whole installation
If any condition is detected that may lead to CU tripping it is important to inform the customer that CU replacement can go ahead only if the remedial work is performed. The same holds for if the condition detected in the survey is classified under C1, C2 or F1 category.
A distress change
A distress change occurs when an existing CU undergoes damage. The damage may result from overheating or mechanical corrosion. The damage may have placed the system in a dangerous condition. In plain and simple words it means the CU is to be replaced immediately. However in such situation too meeting the BS 7671 requirements is mandatory. Therefore it is better to inform the customer of the overall situation in details so that they can take an informed decision easily.
If the customer wants the necessary remedial work may continue along with the CU installation. This way the installation can be done safely meeting all the compliances. The payment for those remedial jobs is to be made additionally and that brings up the overall cost. It is better for both parties to include such provisions of additional work and extra payment in the agreement itself although the customer’s consent for the extra remedial work may also come in an e-mail. .
While carrying out a distress change, you are supposed to come across circuits that are found to have massive faults that require enough time for correction. It is advisable to leave those circuits temporarily disconnected so that the other circuits that are in good condition can run smoothly. However those faulty and disconnected circuits must be repaired as soon as possible.
Considering all these facts it is obvious that consumer unit replacement cost depends varies from case to case depending on many factors. Please feel free to contact us for our services as well as more information on relevant matters.