Online numbers are a best-case guide. The calculator cannot see awkward cable runs, damaged accessories, DNO or building limits, or extra work hidden in the fabric. We can only account for the full job once we have attended and seen the installation for ourselves — that is when you get a firm, responsible quote.
Fixed sizes, spare ways, and “20%”
Consumer units are sold in fixed way counts (manufacturing sizes, not custom-cut boxes for every job). Spare ways (empty ways or unused capacity) matter because you are not only protecting today’s circuits — you are leaving a realistic path to add, for example, a kitchen reconfiguration, a loft circuit, or an EV supply later without a full re-board the moment something changes.
BS 7671 / IET guidance talks about spare capacity in design terms. In practice, many specifiers and tutors talk in terms of roughly 20% headroom as good design practice — it is not a personal policy we invented and it is not a substitute for a proper on-site design check, but it is why we do not squeeze a board to the last millimetre if we can help it.
Surge protection (SPD) — not always the law, but we think it’s the future
SPD is not a blanket legal requirement in every single domestic case today the way a smoke alarm in a new build might be — the exact requirement depends on the installation, supply, and current regulations at the time of the work. Our position is simple: we include SPD in our default domestic board upgrade because (a) where it is required, you are covered, and (b) where it is not yet strictly mandated in your exact scenario, it is a cheap insurance policy against a problem that is only getting more common as homes fill with electronics and the grid and nearby kit throw transients at the installation.
We are not claiming to know the exact year SPD becomes mandatory in every case — but we are future-proofing you for the way the industry is moving, not building to yesterday’s “just pass” minimum in order to undercut a softer quote.
Our standard vs “budget board” routes
On a typical home we work to a current, durable layout: a metal consumer unit, an RCBO on each final circuit (one fault does not drop half the house on a group RCD), SPD as above, and spare headroom for what comes next. That is a different value proposition to a split-load / RCD + MCB board that can still be quoted as “compliant” in the right context but is a worse experience in day-to-day life and often a shorter “comfortable” life before the next change.
When another price is far below ours, it is very often a softer spec, not a secret discount. Like-for-like with the way we work, a lot of reputable firms in the area are more expensive than we are — not less. We would rather you knew that up front, on an advanced page, than feel surprised after a visit.
How the upgrade calculator is built (line items)
The upgrade calculator is built the same way as we invoice in principle: the enclosure and installation labour are in bands by circuit count (labels such as 1–3, 4–6, 7–10, 10–14, 14+ as appropriate to the way-count names). RCBOs and SPD are listed so you can see where the money goes. Testing uses the same £49.95 per board + £19.95 per testable domestic circuit “EICR test build” as our EICR pricing, with 25% off that testing when it is part of the same changeover.
Main / home uses the full main enclosure band for the property’s main board. Secondary is a separate, lower band for a single small sub-board; the public tool is deliberately capped at 1–3 circuits (under four) — 4+ on a sub-board, or many boards, needs a site visit to quote, including older houses with original, extension, garage, and outhouse boards. A full EICR is the correct route for a certificated, whole-picture assessment. By-the-hour spot tests are advice only and not a “pass” certificate — they often show why a full report is the next step.
If the main and one sub-board (1–3 circuits) are done the same visit, the calculator’s same-visit toggle on the secondary run applies the published % off that sub-board (see the live build on the calculator; currently 10% in the default script).
Knowledge Hub & service pages
Installation detail and what you receive on completion: Consumer unit (fuse box) upgrades service page.