Metal vs Plastic Enclosures — Which Should You Use?

Metal enclosures (typically IP40 steel) are the standard for indoor domestic consumer units. Plastic/polycarbonate enclosures (typically IP65) are used for outdoor and damp locations. The choice is driven by location, IP rating requirement, and fire resistance — not personal preference.

Metal and plastic electrical enclosures are not interchangeable — they are designed for different environments and have different performance characteristics. Understanding the key differences helps you specify correctly, comply with BS 7671, and ensure the installation remains safe and serviceable over its lifetime.

Key differences at a glance

Property	Metal (steel, IP40)	Plastic/polycarbonate (IP65)
Typical IP rating	IP40	IP65
Fire resistance	Non-combustible — will not contribute to fire spread	Polycarbonate is self-extinguishing but not non-combustible
Water protection	None (IP40)	Protected against water jets (IP65)
Mounting	Wall-mounted, surface or flush	Wall-mounted, surface only
Cable entry	Knockouts — standard sizes	Cable glands required — maintains IP65 rating
Typical locations	Indoor domestic, commercial switchrooms	Outdoor, garage, EV charging, solar sub-boards
WCED range	WME series (consumer units and sub-boards)	WP series (IP65 enclosures)

When metal is required or preferred

Metal consumer units are required in domestic properties in England and Wales under BS 7671 — the 17th Edition Amendment 3 (now incorporated into the 18th Edition) requires that consumer units in domestic premises be enclosed in non-combustible material. Steel meets this requirement; standard plastic does not. This is why virtually all domestic consumer units installed since 2016 are metal-clad.

In commercial and industrial settings, metal distribution boards are preferred for their rigidity, earth bonding capability (the metal enclosure itself provides an equipotential surface), and resistance to mechanical damage in high-traffic areas.

When plastic/polycarbonate is required or preferred

IP65 polycarbonate enclosures are the correct choice for any outdoor or damp location — outdoor EV charging sub-boards, solar string combiner boxes, garden outbuilding distribution boards, and any location where water ingress is a risk. Polycarbonate is inherently non-conductive, which simplifies earthing requirements in some configurations and eliminates any risk of the enclosure body becoming live through insulation failure.

The WCED WP series provides IP65 enclosures in 4-way, 8-way, 12-way, and 16-way configurations, with matching IP65 EV connection units (WPEVCU series) for complete outdoor EV installations.

Shop WCED Metal and IP65 Plastic Enclosures

WME series metal consumer units (IP40) and WP series IP65 polycarbonate enclosures — fully assembled options available. In stock.

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Frequently Asked Questions

Can I install a plastic consumer unit in a domestic property?

Not for the main consumer unit in domestic premises in England and Wales — BS 7671 requires non-combustible enclosures (i.e. metal) for domestic consumer units. Plastic enclosures can be used for sub-boards, EV connection units, and outdoor installations where IP65 protection is required, but the main consumer unit must be metal-clad.

Does a metal enclosure need to be earthed?

Yes — the metal enclosure of a consumer unit or distribution board must be connected to the protective earth (PE) via the main earth bar. This ensures the enclosure is at earth potential and will cause an RCD or MCB to trip immediately if the enclosure becomes live due to an internal fault. Most metal WCED consumer units include a dedicated earth stud on the enclosure body for this connection.

Is polycarbonate UV-resistant for outdoor use?

WCED WP series enclosures use UV-stabilised polycarbonate that resists degradation from sunlight exposure over time. Standard polycarbonate without UV stabilisation will yellow and become brittle when exposed to prolonged direct sunlight — always confirm UV resistance when specifying outdoor enclosures.

Further reading:
IP40 vs IP65 enclosures explained
Fully assembled consumer units explained
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