Consumer Units (Fuseboxes) and Electrical Safety

An RCBO (Residual Current Breaker with Overcurrent protection) combines the functions of both an RCD (Residual Current Device) and an MCB (Miniature Circuit Breaker), while an RCD protects only against earth leakage (residual current). An RCBO provides both earth leakage and overcurrent protection, while an RCD only protects against earth leakage.

RCD (Residual Current Device):

• Primary Function: Protects against electrical shocks caused by earth leakage (where current flows to earth instead of through the intended path).

• Mechanism: Detects an imbalance in current between the live and neutral wires, indicating a leakage to earth. If the imbalance exceeds a certain threshold (e.g., 30mA in some regions), the RCD trips, disconnecting the circuit to prevent shock.

• Overcurrent Protection: RCDs do not provide protection against overloads or short circuits.

• Cost: Generally less expensive than RCBOs.

RCBO (Residual Current Breaker with Overcurrent protection):

• Primary Function:

  Protects against both earth leakage (like an RCD) and overcurrent (overload and short circuits).

• Mechanism:

  Combines the earth leakage detection mechanism of an RCD with the overcurrent detection mechanism of an MCB.

• Overcurrent Protection:

  The MCB part of the RCBO trips when the current exceeds the breaker's rating, providing protection against overload and short circuits.

• Cost:

  Generally more expensive than RCDs ( used in split type main boards) but have many advantages

• If you only need protection against earth leakage (and potentially save money), an RCD is sufficient.

• If you need protection against both earth leakage and overcurrent (and are willing to pay a bit more), an RCBO is a better choice.

Questions and Answers

Do landlords in Scotland require RCD/RCBO protection of all circuits in order to let out a house?

Yes.

The requirement for RCD protection is explicitly detailed in Sections D.54 and D.55 of the Scottish Government's Statutory Guidance for Private Landlords on the Repairing Standard

Do the Wiring Regulations require all circuits in a dwelling to be RCD protected?

No but........

BS 7671 does not explicitly mandate RCDs on every single circuit, but the exemptions are so rare that RCD protection applies to virtually all domestic circuits.

In practice, this means:

• All socket outlets up to 32A require 30mA RCD protection.

• All circuits in bathrooms.

• All cables concealed in walls at depths less than 50mm without earthed metallic protection require an RCD.

• All lighting circuits in domestic premises now require RCD protection. [1, 2]

Because most domestic cables are buried in walls and lighting circuits require protection, modern consumer units (like those using RCBOs on every circuit) are nearly completely RCD-protected. Furthermore, BS 7671 strictly requires the use of modern Type A RCDs, as older Type AC devices are no longer permitted for new installations.Regulation number(s):411.3.3

BS 7671 requires most if not all circuits in domestic premises to be RCD-protected. There have been a number of suggestions as to how the consumer unit may best be configured to comply with the Regulations, the best and most common being a main switch with RCBOs protecting each individual circuit.

Why don't you fit RCD or recommend protected split main boards considering that they are cheaper?

We don't fit RCD split main boards as often as before because they can cause nuisance tripping and lack circuit discrimination, which can lead to the loss of power to several circuits if one RCD trips. Modern installations typically use RCBOs(Residual Current Breakers with Overcurrent protection) because they offer better individual circuit protection, reducing the risk of a single fault affecting the entire property.

Disadvantages of split-load boards

• Nuisance tripping:

  In a split-load board, each RCD protects a group of circuits. If the total earth leakage from all the circuits under one RCD's protection exceeds a certain threshold (e.g., 9mA) for a 30mA RCD

  it can trip unnecessarily.

• Lack of discrimination:

  When an RCD trips, it cuts power to all the circuits it protects, which can cause a complete loss of power to a significant part of the house.

• Safety risk:

  If one RCD trips, it can lead to a loss of light in multiple areas, which can be dangerous, especially for vulnerable individuals.

Why RCBOs are preferred

• Individual circuit protection:

  An RCBO protects a single circuit from both earth leakage and overcurrent. This means if one circuit has a fault, only that specific circuit will lose power, and the rest of the house will remain live.

• Improved safety:

  By isolating faults to individual circuits, RCBOs provide better protection against electric shock and fire.

• Better control:

  RCBOs offer more control, allowing for better isolation of faults without affecting other parts of the installation.

Is there a specific regulation that requires consumer unit ( fusebox ) design not to disconnect all circuits in the event of one fault?

Yes

The primary rule that prevents a single fault from cutting off power to your entire home is Regulation 314.1of BS 7671, which is heavily reinforced by Regulation 531.3.2.

While split-load boards can be a cost-effective option, especially in smaller properties, they are being phased out in favour of RCBOs due to the safety and inconvenience concerns associated with nuisance tripping and the lack of individual circuit protection.

Are Surge Protection Devices required for new installations under BS7671?

Yes, surge protective devices (SPDs) are required for new electrical installations in the UK under the 18th Edition Wiring Regulations (BS7671), unless a risk assessment proves they are not needed. This requirement applies to virtually all new installations, including those in homes and commercial buildings, particularly when overvoltage could lead to injury, failure of safety services, or significant financial/data loss.

Key requirements for SPDs

• Mandatory for new installations:

  SPDs are now mandatory for new installations unless a risk assessment can justify their omission.

• Exceptions:

  An SPD is not required if a formal risk assessment concludes that the risks from overvoltage are negligible. Examples of when SPDs would be required even without a formal risk assessment include installations where overvoltage could cause serious injury, failure of a safety service, or significant financial or data loss.

• Domestic and commercial:

  The requirement applies to both domestic and commercial properties.

• Risk assessment default:

  If an electrician does not carry out a risk assessment, SPDs must be installed by default.

• Consequence of non-compliance:

  A lack of SPDs in an installation that requires them will result in a "C2" (urgent remedial work needed) code on an Electrical Installation Condition Report(EICR).

• Information notice:

  Installers must provide an information notice at or near the distribution board, explaining the presence or absence of surge protection.

• retrofit:

  While SPDs are mandatory for new installations, they can also be retrofitted into existing systems.

Why a SPD is required

• Legal requirement:

  Since January 2019, BS 7671 requires SPDs for new installations unless a risk assessment proves they are not needed. This requirement was reinforced in the 2022 Amendment 2 update.

• Risk assessment:

  The regulations have removed previous exemptions for many types of buildings, including single-dwelling units. For an installation to be compliant without an SPD, a formal risk assessment must be conducted and agreed upon by the client, who must then accept responsibility for any potential loss or damage.

• Insurance implications:

  Homeowners who decline an SPD may find that their insurance policy will not cover damage caused by power surges.

• Classification:

  The lack of a required SPD will be noted in the EICR, likely with a C2 code, indicating an urgent need for improvement to enhance safety.

What this means for you

• For a new installation:

  The installer is now legally required to fit an SPD unless you formally opt out by signing a waiver and accepting the responsibility.

• For an existing installation:

  If you are having an EICR on an existing installation, the absence of an SPD may lead to a C2 code if one is deemed necessary based on the risk assessment or location.

• For your safety:

  SPDs are a cost-effective way to protect sensitive and expensive electronic equipment from damage caused by power surges, which can be a result of lightning strikes or other events.

How We Change A Consumer Unit (Fusebox) Job Description Summary

Replacement of an existing, non-compliant plastic 8-way Miniature Circuit Breaker (MCB) consumer unit with a fully compliant, fire-rated metal 8-way consumer unit. The new board will feature Individual Residual Current Circuit Breakers with Overcurrent protection (RCBOs) and an integrated Surge Protection Device (SPD). The project will conclude with full system testing, verification, and the issuance of an Electrical Installation Condition Report (EICR) and an Electrical Installation Certificate (EIC).

Scope of Work

Phase 1: Pre-Work Assessment & Isolation

• Perform initial site visual checks and safe isolation protocols at the main incoming supply.

• Identify, trace, and clearly label all 8 existing final circuits.

• Verify the adequacy of the existing main earthing and bonding arrangements (gas and water supplies).

Phase 2: Removal & Installation

• Carefully dismantle and remove the existing plastic consumer unit.

• Supply and securely mount a new, amendment-compliant metal consumer unit enclosure.

• Install a high-quality, integrated Type 2 Surge Protection Device (SPD) to safeguard household electronics against voltage spikes.

• Install 8 individual Type A RCBOs to ensure total circuit separation and protect against AC and pulsating DC earth leakage.

• Terminate all existing final circuits into the new board, ensuring neat cable management and correct torque settings on all terminal screws.

Phase 3: Testing & Commissioning

• Conduct comprehensive dead testing (continuity, insulation resistance, and polarity) on all 8 circuits.

• Re-energise the system safely and perform live testing (earth fault loop impedance, RCD/RCBO trip times, and SPD verification).

• Verify that any cumulative background earth leakage does not cause unwanted tripping.

Phase 4: Certification & Handover

• Provide a comprehensive Electrical Installation Condition Report (EICR) detailing the state of the property’s fixed wiring.

• Issue an Electrical Installation Certificate (EIC) for the new consumer unit installation.

• Provide the homeowner with the compliance certificate.

• Affix all mandatory safety labels, circuit schedules, and testing indicators to the new consumer unit faceplate.

Key Technical Specifications

• Standards Compliance: Fully compliant with BS 7671 (IEE Wiring Regulations, latest amendments).

• Enclosure Material: Non-combustible steel (designed to contain fire).

• Circuit Protection: Type A RCBOs on every final circuit to eliminate total power loss from a single fault.

• Surge Protection: Integrated Type 2 SPD, correctly fused and bonded.

Typically you would expect to pay

In Edinburgh, the typical combined cost for replacing an 8-circuit consumer unit with a metal RCBO + SPD board and providing a full Electrical Installation Condition Report (EICR) from other Edinburgh contractors typically ranges between £850 and £1,200 + VAT

Call 07525364945 to arrange a competitive quote or you can use the contact form below.

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