Commercial Electrical Fit-Out: Planning Your Next Project

Whether you're fitting out a new office in Canary Wharf, refurbishing a retail unit in Bromley, or converting a warehouse in Maidstone into a commercial workspace, the electrical installation is one of the most critical elements of the project. Get it right and everything else follows. Get it wrong and you're looking at costly remedial work, delays, and potentially a failed inspection.

A commercial electrical fit out in London and the wider South East typically involves far more complexity than a domestic job — different regulations apply, the loads are higher, the consequences of poor design are greater, and the expectations of building control and end users are more demanding. This guide walks you through what's actually involved so you can plan your project properly.

What Does a Commercial Electrical Fit-Out Actually Involve?

A commercial fit-out isn't just wiring some sockets and hanging a few light fittings. Depending on the size and nature of the premises, a full electrical fit-out can include:

• Distribution board (consumer unit) design and installation — specifying the correct board for the load requirements and future expansion
• Cable containment systems — trunking, conduit, cable trays installed before walls are finished
• Power circuits — dedicated circuits for equipment, kitchen facilities, server rooms, and machinery
• Lighting design and installation — including emergency lighting to BS 5266-1
• Data and communication infrastructure — Cat 6 cabling, server room power, structured cabling systems
• Fire alarm systems — to BS 5839-1, often coordinated with the fit-out programme
• Access control and security systems
• EV charging points — increasingly common in commercial car parks and business parks
• Testing and certification — all work certified to BS 7671 (the 18th Edition Wiring Regulations)

For a commercial electrical fit out in London, you'll also often need to coordinate with the landlord's appointed engineer, the building's existing supply infrastructure, and sometimes the Distribution Network Operator (DNO) if you're increasing the incoming supply capacity.

Regulations and Compliance: What Applies to Commercial Premises

BS 7671 — The Wiring Regulations

All electrical installation work in commercial premises must comply with BS 7671, the IET Wiring Regulations (currently the 18th Edition, with Amendment 2 in force). This covers everything from cable sizing and protective devices to earthing arrangements and inspection and testing.

Unlike domestic work, commercial installations are not covered by Part P of the Building Regulations — that applies to dwellings only. However, commercial electrical work does fall under other parts of the Building Regulations, particularly Part L (energy efficiency) and Part B (fire safety), and must comply with the Electricity at Work Regulations 1989.

NICEIC Certification

Working with a NICEIC-approved contractor matters here. NICEIC approval isn't just a badge — it means the contractor has been assessed against BS 7671, carries appropriate insurance, and can issue the correct electrical certificates (Electrical Installation Certificates, or EICs) for your project. Many commercial leases and building warranties require work to be carried out and certified by an approved contractor.

If you're working in a managed building in central London or a business park in Surrey, the building management company will almost certainly ask for evidence of NICEIC or equivalent approval before allowing contractors on site.

Local Authority and Landlord Requirements

In some cases — particularly for larger fit-outs or where planning permission is involved — you may need to notify the local authority building control department. For tenanted commercial premises, always check the lease carefully. Many leases require landlord's consent for electrical alterations and stipulate that all work be carried out by approved contractors and certified accordingly.

Planning the Electrical Design

Start Early

One of the most common and costly mistakes on commercial fit-outs is bringing the electrician in too late. Electrical cable routes, containment systems, and distribution board positions all need to be agreed before partitions go up and ceilings are closed. Once the fit-out is at first-fix stage, significant changes become expensive.

Ideally, the electrical contractor should be involved at the design stage — working alongside the architect, mechanical engineer, and fit-out contractor to agree routes, load schedules, and the position of the incoming supply.

Load Assessment and Diversity

A proper commercial electrical design starts with a load schedule — a document that lists every piece of electrical equipment in the building, its rated load, and how often it's likely to run simultaneously. This determines the size of the distribution board, the incoming supply requirement, and the cable sizes throughout the installation.

Don't underestimate future load. A fit-out that's tight on capacity the day it's completed will cause problems within a year or two as IT equipment, additional kitchen facilities, or EV chargers are added.

Emergency Lighting and Fire Alarms

Emergency lighting is a legal requirement under the Regulatory Reform (Fire Safety) Order 2005, and must be designed and installed to BS 5266-1. In practice, this means a risk-assessed design that ensures adequate illumination of escape routes when the main supply fails.

Fire alarm systems in commercial premises must meet BS 5839-1. These are categorised by system type (L1–L5 for life protection, P1–P2 for property protection) and the correct category for your building will be determined by the fire risk assessment.

What Does a Commercial Electrical Fit-Out Cost?

Costs vary significantly depending on the size and specification of the project, but here are some realistic benchmarks for commercial electrical work in the South East:

• Small office fit-out (up to 500 sq ft): £3,000–£8,000
• Medium commercial office (500–2,000 sq ft): £8,000–£25,000
• Large commercial fit-out (2,000 sq ft+): £25,000–£100,000+
• Data infrastructure (Cat 6 structured cabling): £40–£80 per outlet installed
• Emergency lighting design and installation: £1,500–£8,000 depending on complexity
• Three-phase supply upgrade (coordinating with DNO): £2,000–£10,000+ depending on location and network capacity

These figures cover labour and materials for a qualified electrical contractor working to BS 7671. London pricing is typically 15–25% higher than equivalent work in Kent or Surrey, reflecting higher labour rates and parking/logistics costs.

Timelines: How Long Does a Commercial Fit-Out Take?

For a small-to-medium office fit-out, allow four to eight weeks from design sign-off to completion and certification. Larger or more complex projects — say, a full floor fit-out in a multi-storey office block in central London — can take three to six months.

Key milestones in the programme typically include:

1. Design and load schedule sign-off
2. Landlord and building management approval (if applicable)
3. First fix (cable containment, cabling, back boxes)
4. Coordination with other trades (mechanical, AV, partitions)
5. Second fix (fitting accessories, luminaires, distribution board)
6. Testing, inspection, and certification
7. Snagging and handover

When to Call a Qualified Electrician

Don't rely on a general builder for electrical work on a commercial fit-out. Beyond the technical complexity of a properly designed commercial installation, there are real legal and insurance implications if work isn't carried out and certified correctly. If an incident occurs in premises where electrical work wasn't properly certified, your building insurance and employer's liability cover may be void.

For any commercial electrical fit out — whether in London, Rochester, Sidcup, or anywhere across the South East — instruct a qualified, NICEIC-approved electrical contractor from the outset. Get them involved at design stage, not once the plastering is done.

Planning a Commercial Fit-Out in the South East?

Cleary Electrical is a NICEIC-approved electrical contractor based in Rochester, Kent, working across Greater London, Surrey, Essex, Sussex, Hertfordshire, Berkshire, Buckinghamshire, and Hampshire. We carry out commercial electrical fit-outs of all sizes, from small office refurbishments to large-scale multi-floor installations.

If you'd like to discuss your project, we offer free, no-obligation quotes. Get in touch with the team here.