Commercial Rewire Timeline: What to Expect from a Small Business Rewire

Commercial rewires are less mysterious than they look. The sequencing is similar to a domestic rewire; the compliance overhead is not. You have a business that has to keep trading, staff who need somewhere to work, a landlord or a lease clause with an opinion about how long the works take, and a stack of statutory duties that sit with the client, not the contractor.

Here’s a realistic breakdown of what a commercial rewire looks like for a small business, from first survey to final certificate.

What compliance paperwork does the client own?

These are the client’s responsibility, not the electrician’s, and they routinely stall projects that skip them:

• CDM 2015 (Construction Design and Management Regulations). Any project with more than one contractor triggers CDM. As the client, you must appoint a Principal Designer and Principal Contractor, provide pre-construction information, and allow adequate time in the programme.
• Asbestos Refurbishment and Demolition survey. For any building constructed before 2000, an R&D survey is required by the Control of Asbestos Regulations 2012 before invasive works, including cutting cable routes, stripping ceilings, or opening risers. Expect 1 to 2 weeks lead time.
• Landlord consent. Most commercial leases require written landlord approval for alterations to fabric, risers, or the incoming supply. Ask early; it takes weeks.
• Regulatory Reform (Fire Safety) Order 2005. If your building has fire detection, alarm, or emergency lighting, you cannot compromise cover during works. This drives phasing and interim arrangements.
• Public liability and business interruption insurance. Check both cover the works before day one.
• Risk assessments and method statements (RAMS). Standard on any commercial site, and part of any competent contractor’s tender pack.

Stage 1: How long does the survey and estimate take?

Every commercial rewire starts with an on-site survey. The electrician walks the property, records the existing distribution, checks the incoming supply capacity, and identifies constraints:

• Where are the risers and containment routes?
• Is the existing consumer unit or distribution board oversized for the current load?
• Are there tenanted floors above or below that need coordination?
• Is there a fire alarm, emergency lighting, or security system that needs to stay live throughout?

The survey feeds into a written estimate with a phased plan. A useful estimate breaks out labour, materials, containment, testing, and any expected out-of-hours work as separate lines, so you can see what you’re paying for.

Stage 2: What are the material lead times in 2026?

Once the estimate is accepted, the electrician prepares circuit designs and orders long-lead items. Lead times in 2026 vary sharply by item:

• Cable: 2 to 4 weeks for standard singles and multicore
• TP&N distribution boards and specified LV switchgear: 6 to 12 weeks, sometimes longer
• Specialist items (surge protection, arc fault protection, sub-metering): variable

Board lead times have stretched significantly since 2024 because data-centre construction is crowding out standard commercial stock at Schneider, Eaton, ABB, Siemens, and GE Vernova. The board often drives the programme; if the boards will arrive in week 10, the first-fix phase cannot start in week 4. Skipping this stage and starting work “on the fly” is a false economy: the job stalls when materials run out.

Stage 3: What happens during first fix?

First fix is the phase where new cabling, containment, back boxes, and distribution equipment go in, before ceilings and walls are closed up. For a small retail unit or a two-floor office, this is usually 1 to 3 weeks depending on the extent of the works.

Typical first-fix activities:

• Isolating and removing existing circuits, section by section
• Installing trunking, tray, and conduit for new cabling
• Pulling in new cable to all outlets and lights
• Fitting new distribution boards
• Coordinating with the building’s fire alarm and emergency lighting where required

Where possible, we phase this so one area of the business stays trading while another is under works. Retail units often phase by floor or by trading zone. Offices phase by department.

Stage 4: What happens during second fix?

Second fix is the visible half of the job: sockets, switches, light fittings, wall plates. It’s quicker than first fix and it’s the phase that makes the site look finished.

Which other systems are affected by a rewire?

A commercial rewire rarely touches only the power circuits.

• Emergency lighting (BS 5266). Any change to fittings usually puts the system in scope for re-commissioning and a fresh commissioning certificate.
• Fire alarm (BS 5839-1:2025). Detection coverage must be maintained through the works. On a phased rewire this often means temporary detection in areas being worked on. See our fire alarm testing frequency post for the servicing rhythm you inherit at handover.
• IT and network cabling. The most common modern-rewire failure is running power before the network cabling contractor has set out Cat6A routes, cabinet locations, and power feeds for network kit. Coordinate at design stage, not first fix.

Stage 5: What certificates do you receive?

Every new circuit is tested to BS 7671 and the results are logged on an Electrical Installation Certificate (EIC). Where the rewire has touched linked systems, expect additional deliverables:

• BS 5266 Commissioning Certificate for emergency lighting
• BS 5839 Design / Install / Commission Certificate for fire alarm changes
• Manufacturer O&M documentation for new distribution boards and switchgear

For a full commercial rewire the paperwork is substantial, and the electrician often needs half a day to a day at the desk after the on-site testing is complete to write it up cleanly.

How long does a commercial rewire take in total?

For a typical small business commercial rewire:

• Small retail unit (up to 100 sqm): 2 to 4 weeks on site
• Mid-size office (100 to 400 sqm): 4 to 8 weeks on site
• Multi-floor building (400 to 1,000 sqm): 8 to 16 weeks, usually phased

Add the pre-work stages (survey, design, materials) and you’re looking at 2 to 6 months from first conversation to final certificate for a small to mid-size job, with board lead times potentially adding another 6 to 8 weeks.

Durations assume no asbestos remediation and standard switchgear availability. Add 6 to 8 weeks where specified boards carry extended lead times.

Can the business keep trading during a rewire?

The biggest question we hear on a first survey is whether the business can keep trading during the works. In most cases the answer is yes, with some planning. Options include:

• Phased works, one area or floor at a time
• Temporary sub-mains to keep essential systems live (tills, POS, fridge/freezer, security)
• Out-of-hours works for the noisy and disruptive sections
• Weekend and evening shifts to compress the on-site duration

Out-of-hours labour is charged at a premium, so it’s worth being deliberate about which sections of the job justify it and which don’t.

What about VAT, warranties, and aftercare?

• VAT: commercial rewires on existing buildings are standard-rated at 20%. Zero-rating applies only to genuinely new residential builds, not to commercial refurbs.
• Warranty: an EIC-backed installation, plus the manufacturer warranty on switchgear (typically 12 months labour, 1 to 5 years parts). Ask your contractor to schedule six-monthly emergency lighting duration tests and annual EICR of the new installation as part of a planned maintenance contract if the site warrants it.
• Post-completion snagging: agree in writing what the snagging window is and how it will be handled.

What causes commercial rewires to run late?

The three most common causes of a commercial rewire running late are:

1. Undiscovered condition. The pre-works survey missed something, usually because access wasn’t possible until sections were opened up. Reduce this with a thorough survey and by lifting a sample of floor panels or ceiling tiles as part of the estimate stage.
2. Landlord and neighbour coordination. Shared risers, party walls, and lift shafts often require permission to work in, and permission takes weeks. Start these conversations early.
3. Late variations from the client. “While you’re here, can you also do…” is fine, but variations after first fix nearly always push the finish date out. If you know a variation is coming, get it into the schedule at the design stage.

Why use one contractor for all three trades?

Because Nulectrics also covers mechanical (M&E) and fire & security, a single contractor can carry the rewire, the associated M&E works, and the fire alarm re-commissioning under one programme. That removes the interface risk between trades that typically causes the messiest delays on a commercial refurbishment.

Booking a survey

See our commercial electrical page for the full scope of what we cover, our recent case studies including the Kennet & Avon Canal Trust rewire in Devizes, KFC & Costa in Chippenham, and Northwick Park in Harrow, or our rewire page for domestic rewires. For a commercial rewire survey and estimate, get in touch.