Cable Management Systems — UK Electrician Guide

Main Conduit Types

• Heavy gauge screwed steel conduit (BS EN 61386-21): The highest mechanical protection class. Standard for industrial and commercial premises, plant rooms, and exposed locations. Can serve as CPC if correctly installed and bonded. Hot-dip galvanised for corrosion resistance.
• Rigid PVC conduit (BS EN 61386-22): Used in domestic and light commercial surface-mounted installations. Lighter and corrosion-resistant but lower impact resistance than steel. Cannot serve as CPC — a separate earth conductor is always required.
• Pliable (corrugated) conduit: Used almost exclusively concealed in plaster, screed, or concrete. Not for surface-mounted or exposed use. Available in grey (non-corrugated outer, corrugated inner) or orange (standard for underground).
• Flexible conduit (BS EN 61386-23): Final connections to motors, pumps, and vibrating equipment. Metal or PVC construction. Must not be used as fixed wiring routes — keep runs as short as practicable.

Common Trunking Types

• Steel trunking (BS EN 50085-1): The standard for industrial and heavy commercial premises. Available in galvanised and powder-coated finishes. Can serve as CPC where continuity joints are earth-bonded. Common sizes: 50×50mm to 300×150mm.
• PVC trunking (BS EN 50085-2): Used in offices, schools, and domestic surface-mounted installations. Available in white, grey, and woodgrain finishes. Lighter and corrosion-resistant. Cannot serve as CPC.
• Multi-compartment trunking: Divided internally into two or three compartments for segregation of power, data, and telecommunications cables. Required where BS 7671 Regulation 528 separation must be maintained within a single trunking route.
• Skirting trunking and dado trunking: Perimeter trunking systems integrated into skirting boards and mid-wall dado positions in offices and commercial fit-outs. Provide power, data, and AV cable routes with access every 600mm via snap-in faceplates.

• Perforated cable tray: The standard in UK industrial and commercial installations — plant rooms, distribution risers, external cable routes. Available in hot-dip galvanised (standard), stainless steel (for food processing and corrosive environments), and PVC-coated. Width 50mm to 900mm, standard load classifications to BS EN 61537.
• Cable ladder: Used for heavy cable loads and long spans. Ladder rungs at typically 300mm centres allow heat dissipation and give good support to large cables. Standard in power station, process plant, and large industrial installations.
• Wire basket tray: Lightweight, flexible, and quick to install. Widely used in data centres, commercial offices, and suspended ceiling spaces. Easily cut and bent on site. Cannot serve as CPC — a separate earth conductor must be installed.

BS 7671 Appendix 5 Fill Ratios

• Conduit (wired during installation): 45% of internal cross-sectional area. For a 20mm conduit with 201mm² internal area, maximum cable area = 90mm².
• Conduit (cables drawn in after installation): 40% of internal cross-sectional area.
• Trunking: 45% of internal cross-sectional area (same as conduit for wired installations). Multi-compartment trunking — apply 45% to each compartment separately.
• Cable tray (open): No specific BS 7671 fill ratio prescribed. Good practice limits fill to 70% of tray width for single-layer installation, with multi-layer installations using grouping derating from BS 7671 Appendix 4.

• Requirement: Every penetration of a fire-resistant compartment wall or floor by a conduit, trunking, or tray run — or by individual cables — must be sealed to restore the fire resistance of the compartment element. The seal must achieve the same fire resistance period as the element penetrated (E = integrity, I = insulation, R = resistance).
• Approved products: Intumescent putty and sealant, intumescent pillow and block systems, intumescent cable transit frames, and cementitious mortar systems. All must be third-party tested and certified to BS EN 1366-3 (penetration seals) and marked with the achieved FRL.
• Steel conduit penetrations: Pack the inside of the conduit with certified intumescent putty at the wall face. Also seal around the outside of the conduit in the wall aperture. Sealing conduit with ordinary caulk or foam is not acceptable — it must be tested fire-stopping product.
• Documentation: Retain the product data sheet and the installer's declaration for all fire barrier installations with the building records. These are required by the Building Safety Act 2022 for higher-risk buildings (7 storeys or 18 metres+).

• Segregation in trunking: Power and data cables may share a trunking if a metallic divider is installed between the two groups. Multi-compartment trunking systems designed for this purpose are available from most manufacturers.
• Separation distances on cable tray: CENELEC EN 50174-2 specifies minimum separation distances for parallel cable runs: 200mm between unscreened power cables and Cat 5e/6 data cables (unscreened); 100mm where one or both are screened; 50mm where both are in metallic conduit or trunking.
• Fire alarm and emergency lighting segregation: BS 5839-1 (fire detection) and BS 5266 (emergency lighting) require their respective cable systems to be segregated from other services to prevent common-cause failure. Fire alarm cables in fire-resistant containment must not share containment with general power or lighting circuits.

• BS 7671 Regulation 411.3: All metallic cable management not used as a CPC must be bonded to the protective earth. The bonding conductor cross-section is determined by BS 7671 Table 54.8 — minimum 4mm² copper where the bonding conductor is not mechanically protected.
• Trunking and tray earth continuity: Metallic trunking and tray joints must maintain earth continuity throughout the run. Trunking manufacturers supply earth continuity link straps to bridge each joint. Where earth continuity link straps are not fitted, a separate earth conductor must be bonded at each end of the run and at regular intervals.
• Testing: Earth continuity of metallic cable management must be verified as part of the initial verification test under BS 7671 Regulation 643.2. The resistance must be low enough that a fault to the metalwork would operate the protective device within the required disconnection time.