Office Electrical Requirements — Commercial Fit-Out Guide

Distribution Strategies

• Perimeter distribution: Dado trunking or skirting trunking around the perimeter walls feeds desks near walls. Simple and cost-effective for cellular or semi-open layouts. Not suitable for central island desks.
• Underfloor distribution: Raised access floors allow power and data cables to be routed under the floor to floor boxes positioned anywhere in the space. Maximum flexibility — outlet positions can be changed by moving floor boxes. Higher initial cost due to raised floor system.
• Overhead busbar trunking: Power distributed via busbar trunking suspended from the ceiling structure. Tap-off boxes can be added or moved to suit desk layout changes. Used in large open floors, particularly industrial office environments.

Floor Boxes

• Recessed into the floor — either a solid concrete slab with conduit routes cast in, or a raised access floor. Floor boxes typically contain two to four double sockets plus two to six data outlets. Specify flush-fit lids rated for the floor loading category (typically Class B for offices, Class C for industrial areas per EN 1433).
• Position floor boxes based on the desk layout drawing — typically one box per two workstations, at 1,200mm to 1,500mm centres for standard 1,400mm desks. Feed from a sub-distribution board (SDB) in a riser or comms room on the floor.

Dado and Skirting Trunking

• Dado trunking mounts at desk height (approximately 900mm to 1,100mm from floor) and contains separate compartments for power, data, and sometimes voice circuits. Compartment separation maintains segregation between Category 1 (power) and Category 2 (data) wiring per BS 7671 Section 528.
• Outlets can be spaced at any interval along the trunking. Minimum outlet spacing for a busy perimeter run is 1,200mm to ensure desk users can reach power without trailing leads. Universal or brand-specific faceplates accept standard MK, Legrand, or Hager socket modules.

• Dedicated sub-distribution board: The server room should have its own consumer unit or distribution board, fed from the main distribution board via a dedicated circuit. This enables isolation of server room power without affecting the rest of the office.
• UPS provision: An uninterruptible power supply (UPS) protects critical IT equipment from power interruption and quality issues (voltage sags, surges, harmonics). Size the UPS to cover the full server room load at 80% capacity for the required runtime. Specify bypass switching for maintenance.
• Cooling supply: Dedicated circuit for precision air conditioning units. Cooling typically accounts for 30% to 50% of total server room electrical load. Size the cooling circuit independently of the IT equipment circuits.
• Cable management: Overhead cable ladders or under-floor cable runs for power and data. Maintain segregation between power and data cables per BS 7671 Section 528. Label all circuits clearly at both ends.

• HSE risk-based approach: The Health and Safety Executive recommends that PAT frequency be determined by risk assessment. Low-risk environments (offices) with low-use Class II double-insulated equipment may only need testing every four years. High-risk environments (construction, catering) require testing every three to six months for portable tools.
• Visual inspection: Every PAT test should begin with a visual check of the plug, cable, and appliance for physical damage, burns, ingress of liquid, or signs of overheating. Many defects are found at this stage without requiring electrical testing.
• Record keeping: A PAT register recording appliance ID, test date, tester name, and pass/fail result is essential evidence of compliance. Failed appliances must be quarantined, labelled, and removed from use until repaired or disposed of.

• Five-year EICR cycle: BS 7671 and IET Guidance Note 3 recommend a maximum five-year EICR interval for commercial premises, or on change of occupancy whichever is sooner.
• Change of occupancy: When a new tenant takes occupation of an office, an EICR should be obtained regardless of when the previous one was carried out. The new occupier should not rely on records from a previous tenant.
• C1 and C2 observations: Danger present (C1) and potentially dangerous (C2) observations must be remedied before the EICR can be marked as Satisfactory. Landlords and building owners are legally responsible for ensuring remedial works are completed promptly.

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