Replacing the fuse board — or consumer unit, to give it its proper modern name — is one of those jobs most homeowners only think about when something has already gone wrong. A circuit keeps tripping, an EICR flags the installation as “unsatisfactory”, or a surveyor’s report mentions it during a house sale. For a lot of Portsmouth homes — particularly the Victorian and Edwardian terraces in Southsea, the post-war semis around Cosham and Paulsgrove, and the older flats in Old Portsmouth and Fratton — the fuse board is the single oldest piece of electrical kit in the building, and an upgrade is usually long overdue.
The good news is that a fuse board replacement is a well-defined, single-day job in the vast majority of cases. It’s far less disruptive than a full rewire, you won’t lose your kitchen for a week, and once it’s done your home is genuinely safer and easier to live with. This guide walks you through what actually happens on the day, what sits behind the bigger steps, and what to expect on cost, paperwork and timing in 2026.
Why You Might Need a New Fuse Board
Your fuse board is the central control point for the home’s electrics. Power comes in from the street, passes through the main switch, and then splits out into the individual circuits — ring final sockets, lighting circuits, oven, shower, immersion, and these days an EV charger or solar inverter as well. Each circuit is protected by a fuse or breaker that’s supposed to cut the power quickly if something goes wrong.
Consumer units have come a long way over the last twenty years because the protection itself has improved. Older Portsmouth properties often still have rewireable fuse boxes (sometimes called BS 3036 boards), early plastic-cased units with very limited RCD protection, or split-load boards that only protect some circuits and not others. These can still carry current, but they’re slow to react to faults and offer poor protection against electric shock. Modern consumer units use RCBOs — devices that combine overcurrent and earth-leakage protection on every circuit independently — and are housed in metal enclosures to contain any internal arcing.
Common signs you might be due for a replacement include circuits that trip with no obvious cause, a fuse board that buzzes, gets warm or has visible scorching, lights that flicker when high-draw appliances kick in, the absence of any RCD protection, or simply an “unsatisfactory” outcome on a recent EICR. If you’ve just bought an older home in Portsmouth and you’re planning an EV charger, a kitchen renovation or a loft conversion, the electrician will almost certainly recommend upgrading the consumer unit at the same time.
Before the Job Starts: The Survey
A reputable Portsmouth electrician won’t quote for a fuse board replacement sight unseen. The survey is normally free, takes around 20–30 minutes, and is when they confirm what you’ve actually got, what you actually need, and what surprises might come up mid-job.
During the survey they’ll inspect the existing board, look at the main tails and meter arrangement, count and identify each circuit, check for obvious wiring issues (older PVC cable, signs of overheating, missing earths), and confirm whether you’ll need an 80A or 100A main switch. They’ll also check whether the property has a TN-C-S, TN-S or TT earthing system, which affects the configuration of the new unit. If you’re in a flat with a shared meter cupboard, they’ll discuss timing for power isolation with the freeholder or the network operator if needed.
Out of this you’ll get a written quote that breaks down labour, materials, certification and any likely extras. In Portsmouth, expect a straightforward like-for-like replacement to come in somewhere around £550–£900 for a typical domestic property in 2026, with more complex jobs going higher (see the cost section below).
Step by Step: What Actually Happens on the Day
Here’s the process a qualified electrician will follow on the day itself. It’s broadly the same whether you’re in a two-bed terrace in Eastney or a four-bed detached in Drayton — the only real variable is how messy the existing wiring turns out to be.
1. Power isolation
The first thing the electrician will do is isolate the property from the incoming supply. For most Portsmouth homes that means pulling the main fuse at the meter — the big sealed cartridge fuse owned by the network operator (in our area that’s SSEN). Strictly speaking the network operator owns these fuses and only their staff are meant to remove them, but in practice most established electrical contractors break the seal as part of a consumer unit swap, log the time and reseal afterwards. Some installers will instead arrange a formal isolation appointment with SSEN where the meter arrangement is unusual or a smart meter has been recently fitted.
Once the supply is isolated, every circuit is proved dead with a verified voltage tester before any work starts.
2. Removing the old unit
The old fuse board is unscrewed from the wall, and each circuit cable is carefully labelled before being disconnected. This is one of the steps where experience really shows — a tidy electrician will photograph the existing arrangement, label every cable clearly, and make notes on each circuit’s destination. A rushed one will just yank cables out, and you end up with a “guess which circuit this is” exercise later.
The old enclosure comes off the wall, and any redundant cabling, sleeving or junction boxes inside the box are tidied up.
3. Installing the new consumer unit
The new unit — a metal-clad, dual-RCD or full-RCBO board with built-in surge protection (SPD) — is fixed to the wall in roughly the same position. Modern units are physically larger than older fuse boxes because they have more components inside, so occasionally a little extra wall space is needed.
The main switch and bus-bar are fitted first, then each RCBO is clipped into position. Surge protection devices became a near-default requirement under the latest amendments to BS 7671 and are particularly worth having in coastal areas like Portsmouth, where summer storms can produce significant transient voltages on the network.
4. Reconnecting and labelling circuits
Each circuit is then terminated into its new RCBO, with the cable correctly stripped, sleeved and torqued to the manufacturer’s specification. The board is labelled clearly — kitchen ring, upstairs lights, oven, shower, EV charger, and so on — so anyone looking at it in future can identify what’s what at a glance. A clean, well-labelled board is also the first thing a future EICR inspector will look for.
5. Testing
This is the part of the job that takes the longest, and it’s the bit you really want done properly. Before the supply is restored, the electrician carries out a full set of dead tests on every circuit:
- Continuity of protective conductors (CPCs)
- Continuity of ring final circuit conductors
- Insulation resistance
- Polarity
The supply is then re-energised, and a set of live tests is performed: earth fault loop impedance (Zs) at the furthest point of each circuit, prospective fault current, and RCD trip times against the regulation thresholds. Any deviations are investigated and corrected before the certificate is issued.
6. Certification and notification
Once everything passes, the electrician issues an Electrical Installation Certificate (EIC) for the new consumer unit — the legal document confirming the installation complies with BS 7671. Because a consumer unit replacement is “notifiable work” under Part P of the Building Regulations, the installation must also be registered with Building Control. If your electrician is registered with a Competent Persons Scheme (NICEIC, NAPIT, ELECSA or similar), they’ll self-certify and you’ll receive a Building Regulations Compliance Certificate in the post within a few weeks. If they’re not registered, they’ll need to submit a Building Notice to Portsmouth City Council before starting work, which is slower and more expensive — so always check an installer’s scheme membership before booking.
How Long Does It Take?
A straightforward consumer unit replacement in a standard Portsmouth home takes between four and six hours of on-site work. You’ll be without power for most of that time, but a considerate installer will discuss timing in advance — fridges and freezers stay shut, work-from-home calls get moved, and most people pop out for a few hours during the bulk of the job. We aim to start by 8.30am where possible so the property is back on power by mid-afternoon.
More involved replacements — older properties with poor existing cabling, no main earth, or a TT installation needing new earth electrodes — can stretch into a second day. The survey should flag any of this before you book.
Cost of a Fuse Board Replacement in Portsmouth in 2026
For most domestic properties in the city, typical 2026 pricing looks like this:
- Like-for-like replacement, 10–12 circuits, modern wiring: £550–£800
- Full-RCBO board with SPD, 10–12 circuits: £700–£950
- Larger property, 14+ circuits, or three-phase: £950–£1,400+
- Replacement plus remedial works (new main earthing arrangement, supplementary bonding, fault-finding): case-by-case.
These figures are typical for NICEIC or NAPIT-registered electricians working across Portsmouth, Southsea, Cosham, Fareham and Havant in 2026. Materials make up a smaller share of the total than people often assume — most of the cost is skilled labour and certification. Cheaper quotes from non-registered tradespeople usually exclude the Building Regulations notification, which costs significantly more to arrange retrospectively if you ever sell the property.
Common Issues That Crop Up Mid-Job
A fair number of fuse board replacements throw up at least one surprise once the old board is off the wall. The most common in Portsmouth homes are:
- No main earth — very common in older flats and Victorian terraces; needs a new earth conductor run back to the cut-out, or in some cases an earth rod installation.
- Borrowed neutrals between circuits — these were common in 1960s and 70s lighting and have to be untangled before RCBOs will hold in.
- Missing supplementary bonding to bathrooms and kitchens — often added at the time of the upgrade for a small extra cost.
- Failing insulation resistance on the existing fixed wiring — at which point a partial rewire may be recommended before the new board is signed off.
A good electrician will flag these in writing, give you a clear additional quote, and let you decide whether to proceed.
Frequently Asked Questions
Can I just replace the fuses inside the old board instead?
On older BS 3036 rewireable boards, no — the right move is to replace the whole unit so you get RCD/RCBO protection and a metal enclosure. Swapping individual fuses doesn’t bring the installation up to modern standards.
Will my circuits be the same afterwards?
Yes — your sockets, lights and appliances continue to work exactly as before. The change is internal to the consumer unit. The only difference you might notice is that an RCBO will now trip a single circuit rather than taking out half the house when there’s a fault.
Do I need a Building Regulations certificate?
Yes — consumer unit replacement is notifiable work under Part P. Your electrician should handle this through their Competent Persons Scheme and post you the certificate within a few weeks.
How long does a modern consumer unit last?
Properly installed and undisturbed, a modern metal-clad consumer unit should last 25 years or more. The RCBOs themselves are usually rated for 10,000+ operations.
Is it worth upgrading before getting an EV charger?
Often yes. A modern EV charger needs its own RCBO-protected circuit and a healthy main earth, and many older Portsmouth fuse boards simply don’t have spare ways or the protection arrangement to take it cleanly. Doing both jobs together usually saves money compared with doing them six months apart.
Book a Fuse Board Replacement in Portsmouth
If your fuse board is over 20 years old, has no RCD protection, or has been flagged in a recent EICR, it’s worth getting a survey booked in. Our Portsmouth-based electricians cover the whole city and surrounding area — Southsea, Cosham, Drayton, Portchester, Fareham, Havant and beyond — and we’ll give you a clear, fixed-price quote for the job, including testing, certification and Building Regulations notification. Get in touch for a free no-obligation survey.