Do Consumer Units Have to Be Metal? UK Regulations Explained
Metal consumer units are now the standard choice for new domestic electrical installations, but the actual regulation is slightly more precise than saying “all consumer units must be metal”.
For consumer units and similar switchgear assemblies installed within domestic premises, BS 7671 requires the enclosure to be manufactured from non-combustible material, or for the assembly to be enclosed within a suitable cabinet or enclosure constructed from non-combustible material.
Quick answer: New consumer units installed within domestic premises are normally metal because steel provides a straightforward way of meeting the BS 7671 requirement for a non-combustible enclosure. However, the regulation does not literally state that every consumer unit everywhere must be metal.
The rule was originally introduced under Amendment 3 of the 17th Edition and was subsequently carried forward into the 18th Edition.
👉 Replacing or specifying a domestic board? Browse our metal consumer units or compare the wider consumer unit range.
| Question | Short Answer |
|---|---|
| Do new domestic consumer units have to be metal? | They must use a non-combustible enclosure or be enclosed within a suitable non-combustible cabinet. Metal is the normal solution. |
| When did the rule change? | The requirement originated with Amendment 3 of the 17th Edition in 2015. |
| Are existing plastic consumer units illegal? | No. Their presence alone does not automatically make an existing installation unsafe or require replacement. |
| Do outdoor consumer units have to be metal? | Not automatically. The domestic non-combustible enclosure requirement applies within domestic premises. |
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When Did Metal Consumer Units Become Mandatory?
The requirement did not originate with the 18th Edition.
The change was introduced through Amendment 3 to BS 7671:2008, the 17th Edition Wiring Regulations.
Amendment 3 was published in 2015 and introduced the requirement for consumer units and similar switchgear assemblies within domestic premises to:
- Have an enclosure manufactured from non-combustible material, or
- Be enclosed within a cabinet or enclosure made from non-combustible material.
The requirement was subsequently carried forward into the 18th Edition.
Useful distinction: If someone asks “when did metal consumer units become mandatory?”, the industry change dates back to the 17th Edition Amendment 3, not the original publication of the 18th Edition.
What Do the Metal Consumer Unit Regulations Actually Say?
The relevant BS 7671 requirement applies to consumer units and similar switchgear assemblies within domestic premises.
The enclosure must either:
- Be manufactured from non-combustible material, or
- Be installed within an additional cabinet or enclosure constructed from non-combustible material.
In practice, manufacturers overwhelmingly meet this requirement using steel consumer-unit enclosures.
That is why electricians and wholesalers normally refer to the requirement simply as the “metal consumer unit rule”.
However, that shorthand can create three misconceptions:
- It does not mean every distribution board in every location has to be metal.
- It does not mean every existing plastic consumer unit must immediately be replaced.
- It does not mean an external domestic consumer unit automatically needs a steel enclosure.
Always apply the requirement to the actual location and installation rather than treating “metal” as a universal rule for every enclosure.
Why Was the Non-Combustible Consumer Unit Rule Introduced?
The change was introduced in response to concerns over fires originating around domestic consumer units and similar switchgear assemblies.
Electrical connections inside a consumer unit can generate significant heat if something goes wrong.
Potential causes include:
- Loose terminations
- Poor connections
- Damaged conductors
- Arcing
- Overheating terminals
- Incorrectly installed devices
Where the surrounding enclosure itself is combustible, a local electrical fault has more opportunity to contribute to fire spread.
A non-combustible enclosure provides an additional level of containment around the switchgear assembly.
It does not prevent electrical faults from occurring and does not replace correct:
- Termination
- Torque settings
- Circuit design
- Protective-device selection
- Inspection
- Testing
Instead, it reduces the ability of the consumer-unit enclosure itself to contribute combustible material if an internal fault occurs.
What Is a Metal Consumer Unit?
A metal consumer unit is a domestic distribution board with an enclosure constructed from non-combustible metal, normally steel.
The enclosure contains components such as:
- Main switch
- RCCBs
- RCBOs
- MCBs
- AFDDs
- Surge protective devices
- Neutral bars
- Earth bars
- Busbars
The requirement for the enclosure to be non-combustible does not mean that every component inside the consumer unit must itself be metal.
Modern protective devices still contain insulating and polymer components appropriate to their product design.
👉 Browse metal consumer units.
Are Plastic Consumer Units Still Legal?
Yes. The presence of a plastic consumer unit in an existing installation does not automatically make that installation illegal.
Thousands of plastic consumer units were correctly installed before the non-combustible enclosure requirement came into effect.
A change to the Wiring Regulations does not automatically mean every existing installation has to be retrospectively brought up to the latest edition.
An older plastic board should instead be assessed on its actual condition and installation.
Check for:
- Signs of overheating
- Thermal damage
- Loose or damaged covers
- Missing blanks
- Accessible live parts
- Damage around cable entries
- Evidence of arcing
- Location on or near combustible materials
- Its position relative to an escape route
A plastic consumer unit may therefore remain in service where it is otherwise safe and suitable.
Does a Plastic Consumer Unit Fail an EICR?
No. A plastic consumer unit does not automatically result in an unsatisfactory EICR.
The inspector assesses the condition and circumstances of the installation rather than simply failing every pre-metal consumer unit.
The location is particularly important.
For example, greater concern may arise where a combustible consumer unit is:
- Under a wooden staircase
- Within the sole escape route from the property
- Showing evidence of thermal damage
- Installed in a way that increases the risk of fire spreading
Conversely, the mere fact that the enclosure is plastic does not mean the board is immediately dangerous.
EICR point: Assess the actual condition, location and fire risk. “Plastic consumer unit present” is not by itself an automatic failure.
Should You Replace an Existing Plastic Consumer Unit?
Not purely because the enclosure is plastic.
Replacement may make sense where:
- The board is damaged or deteriorated.
- Signs of overheating are present.
- The installation requires significant upgrading.
- Existing RCD protection is inadequate.
- Additional ways are needed.
- Modern RCBO protection is being introduced.
- Surge protection needs to be added and cannot practically be accommodated.
- The location creates an increased fire risk.
- The board is being replaced as part of wider electrical work.
Where replacement is being carried out, a modern non-combustible consumer unit allows the new installation to be designed around the current protection requirements rather than simply swapping like-for-like.
Does a Consumer Unit Need to Be in a Fire-Rated Cupboard?
Not as a general rule simply because it is a consumer unit.
For domestic installations covered by the non-combustible enclosure requirement, one permitted route is for the consumer unit or similar assembly to be installed within a cabinet or enclosure constructed from non-combustible material.
However, that should not be confused with a blanket requirement saying every domestic consumer unit must be installed in a separate “fire-rated cupboard”.
A modern metal consumer unit normally provides the non-combustible enclosure itself.
Separate building fire-safety requirements may still apply depending on:
- The type of building
- Escape routes
- Compartmentation
- Building Regulations
- The fire strategy
- The location of the switchgear
Those are separate considerations from simply complying with the domestic consumer-unit enclosure requirement.
Do Outdoor Consumer Units Have to Be Metal?
No, not automatically.
The BS 7671 requirement for non-combustible consumer-unit enclosures applies to consumer units and similar switchgear assemblies within domestic premises.
An external consumer unit therefore does not automatically have to use a metallic enclosure solely because it serves a house.
For an outdoor board, other factors become particularly important:
- Weather resistance
- Declared IP rating
- Condensation
- Temperature
- Direct sunlight
- UV exposure
- Mechanical impact
- Tampering
- Earthing arrangement
- Manufacturer verification of the complete assembly
A suitably designed insulated external enclosure may therefore be appropriate in circumstances where the equipment manufacturer and installation design support its use.
This is especially relevant to external EV and specialist distribution equipment, where automatically choosing a metal enclosure can introduce additional considerations on PME supplies.
Do Garage Consumer Units Have to Be Metal?
It depends on where the garage and consumer unit sit in relation to the domestic premises and how the installation is classified.
Do not simply assume every garage board requires metal because it supplies a domestic property.
The installer should establish:
- Whether the board is within the domestic premises
- Whether it is internal or external
- The construction and use of the building
- Environmental conditions
- Fire risk
- Manufacturer requirements
Metal garage consumer units are widely used and provide a straightforward robust option, but enclosure material still needs to be selected from the actual installation conditions.
👉 Browse garage consumer units.
What Are the Rules for Cable Entries in Metal Consumer Units?
A steel enclosure is only one part of maintaining the required level of safety.
Cable entries need to be completed properly so that the finished consumer unit maintains:
- Protection against access to live parts
- The required IP characteristics
- Mechanical protection around conductors
- The integrity of the enclosure
Sharp metal edges must not be allowed to damage cable insulation.
Depending on the enclosure and cable-entry method, this may involve:
- Suitable glands
- Grommets
- Bushes
- Manufacturer-provided entry systems
- Appropriate trunking interfaces
There is not a universal requirement to fill every consumer-unit cable entry with fire-rated or intumescent sealing products simply because the enclosure is metal.
Follow the consumer-unit manufacturer’s instructions and maintain the required enclosure characteristics.
What Does an 18th Edition Consumer Unit Need?
A compliant modern consumer unit involves considerably more than simply having a metal box.
Depending on the installation, the designer may need to consider:
- Main switch configuration
- RCD or RCBO protection
- Type A, Type F or Type B residual-current requirements
- Surge protection
- Arc fault detection where required
- Breaking capacity
- Circuit separation
- Maximum demand
- Earthing and bonding
- Labelling
- Accessibility
- Manufacturer compatibility between devices and enclosure
This means a product being advertised as an “18th Edition consumer unit” does not remove the need to design the protective arrangement around the actual circuits.
Modern installations increasingly use individual RCBO protection because it can reduce the number of circuits lost during a residual-current fault compared with older split-load arrangements.
👉 Compare consumer units, RCBOs and surge protection devices.
Does an 18th Edition Consumer Unit Need an SPD?
The metal enclosure requirement and the surge-protection requirements are separate parts of BS 7671.
A metal enclosure does not provide surge protection.
Where the installation requires surge protective devices, these may be incorporated:
- Within the main consumer unit
- At the origin in another suitable enclosure
- At downstream distribution equipment where coordinated supplementary protection is required
The need for an SPD should therefore be assessed separately from whether the consumer unit is metal.
What to Check When Choosing a New Consumer Unit
- Location: domestic, commercial, internal or external.
- Enclosure requirement: confirm the applicable fire and environmental requirements.
- Number of ways: allow adequate capacity for current and expected circuits.
- Main switch rating: coordinate with the incoming supply.
- Protective-device arrangement: decide between individual RCBOs or another suitable configuration.
- RCD types: match the connected loads.
- Surge protection: assess SPD requirements.
- AFDD requirements: check whether any circuits require arc-fault protection.
- Breaking capacity: ensure devices suit prospective fault current.
- Device compatibility: use equipment approved for the consumer-unit assembly.
- Cable entries: maintain IP and mechanical protection.
- Future capacity: allow for EV charging, heat pumps, solar PV or additional circuits where appropriate.
Installer summary: “Metal consumer unit” is only the starting point. A modern board still needs the correct RCBO/RCD arrangement, SPD provision, circuit capacity and compatible protective devices for the installation.
Consumer Units & Related Protection
Metal Consumer Unit Regulation FAQs
Do consumer units have to be metal?
Within domestic premises, consumer units and similar assemblies must use a non-combustible enclosure or be enclosed within a suitable non-combustible cabinet. Steel consumer units are the normal way manufacturers satisfy this requirement.
When did metal consumer units become mandatory?
The non-combustible enclosure requirement was introduced through Amendment 3 of the 17th Edition in 2015 and was subsequently carried forward into the 18th Edition.
Did the 18th Edition introduce metal consumer units?
No. The requirement predates the 18th Edition. It originated with the third amendment to the 17th Edition Wiring Regulations.
Are metal consumer units a legal requirement?
BS 7671 itself is a technical standard rather than a standalone Act of Parliament. However, its requirements are widely used as the recognised standard for electrical installation work. The exact requirement is for a non-combustible enclosure or suitable non-combustible cabinet within domestic premises.
Are plastic consumer units illegal?
No. Existing plastic consumer units are not automatically illegal or unsafe simply because regulations for new work have changed.
Does a plastic consumer unit fail an EICR?
No. The presence of a plastic enclosure alone does not automatically result in an unsatisfactory EICR. The inspector considers its condition, location and the associated risk.
Do I have to replace my plastic fuse box?
Not simply because it is plastic. Replacement should be based on the condition of the installation, identified defects, required upgrades and the scope of any new electrical work.
Can a new plastic consumer unit be installed in a house?
Within domestic premises, the assembly must meet the non-combustible enclosure requirement. One permitted route is placing the consumer unit within a suitable cabinet or enclosure constructed from non-combustible material.
Do fuse boxes have to be metal?
For modern domestic consumer units installed within the premises, steel is the usual enclosure material used to satisfy the non-combustible requirement. “Fuse box” is commonly used informally to describe the consumer unit.
Does a consumer unit need a fire-rated enclosure?
A modern non-combustible consumer-unit enclosure normally satisfies the specific BS 7671 enclosure requirement without automatically needing another cupboard around it. Separate building fire-safety requirements may apply in particular locations.
Do electrical distribution boards need to be in a fire-rated cupboard?
Not as a universal rule. Requirements depend on the type of board, location, building fire strategy and applicable regulations. The domestic consumer-unit rule specifically provides for either a non-combustible consumer-unit enclosure or an appropriate non-combustible cabinet.
Do outdoor consumer units have to be metal?
No. The specific domestic non-combustible consumer-unit requirement applies within domestic premises. External boards need to be selected for their actual environmental and electrical conditions.
Do garage consumer units have to be metal?
Not simply because the board is in a garage. Its location, whether it is within the domestic premises, environmental conditions and applicable enclosure requirements need to be assessed.
Do metal consumer units need to be earthed?
Metallic enclosures and exposed-conductive-parts need the appropriate protective earthing arrangement. Follow the consumer-unit manufacturer’s installation instructions and applicable BS 7671 requirements.
Do holes in a metal consumer unit need fire sealing?
There is no universal requirement to apply intumescent or fire-rated sealants to every cable entry. The finished installation must maintain the required enclosure protection and follow the manufacturer’s instructions.
Does an 18th Edition consumer unit need surge protection?
Surge protection is a separate requirement from the metal enclosure rule. The installation should be assessed to determine the required SPD arrangement.
Are RCBO consumer units required by the 18th Edition?
RCBOs are not universally mandatory simply because a board is installed to the 18th Edition, but individual RCBO protection is increasingly common because it provides circuit-level residual-current protection and limits disruption when a fault occurs.
What is a metal-clad consumer unit?
It is another term commonly used for a consumer unit or distribution enclosure manufactured with a metal outer casing.
Do You Need a Metal Consumer Unit?
For a new consumer unit installed within domestic premises, the enclosure must meet the BS 7671 requirement for non-combustible construction or be enclosed within an appropriate non-combustible cabinet.
In practice, that normally means installing a steel consumer unit.
But remember:
- The requirement originated under 17th Edition Amendment 3, not the original 18th Edition.
- Existing plastic consumer units are not automatically illegal.
- A plastic board does not automatically fail an EICR.
- An outdoor consumer unit does not automatically have to be metal.
- A metal enclosure alone does not make an entire consumer-unit installation compliant.
For a new board, the complete specification still needs to address circuit protection, RCD/RCBO selection, surge protection, capacity, device compatibility and the requirements of the particular installation.
👉 Browse our metal consumer units, compare all consumer units or build out the board with RCBOs and surge protection.