Compliant on paper. Buildable on site.
CurrentProof is the BS 7671 design platform built around a question the others do not ask: can this actually be installed? Whole network design checking today, with the constructability family shipping check by check.
Public beta: every calculator, Circuit and Infrastructure included, is free until 28 February 2027. No card needed. Create an account
Compliance is the price of entry. Constructability is the reason to buy.
Every tool in this market checks a design against BS 7671. None of them checks whether the thing you have drawn can be installed in the building it is going into. That gap is where the phone calls come from, and it is the gap CurrentProof is built to close.
Live today
- Terminal capacity advisory, on the Circuit calculator. Select an MCB with a cable above 35 mm² and it warns you the cable may not fit the breaker terminal. It works from a typical device rating rather than the specific device, and the product labels it as an advisory.
In build
Not yet available- Cable type against the premises. Standard cable where low smoke zero halogen is required.
- Bending radius and containment capacity. The bend that cannot be achieved in the space it was drawn into.
- Switchboard access. The board that cannot get into the room.
What you get, before you sign up
The three free calculators work without an account. These are the screens you'll use, with real numbers from the engine.
The working, not just the answer
Every input, factor and equation, with the table each value came from.
A fail is shown as a fail
Run the cable past the Table 4Ab limit and the result turns red, with the limit beside it.
Every board on one schedule
Connected and diversified load per phase, with the phase imbalance worked out for you.
In the subscription
Infrastructure. Whole network design.
Draw the network, supply to final circuit, and have every circuit checked against BS 7671 with the result sourced to the regulation it came from. One subscription, no limit on the size of the design.
Circuit
Full circuit design: OCPD selection, fault current, and disconnection times checked against Chapter 41.
The free calculators
Volt Drop
Voltage drop for every Appendix 4 cable type, with temperature correction (Ct), power factor, and a pass or fail against Table 4Ab.
Maximum Demand & Diversity
Maximum demand with diversity applied load by load, using the IET Design Guide allowances that Reg 311.1 permits.
Load
Build a load schedule and check total equipment load against supply capacity.
Every value, traced to its table.
A spreadsheet won't tell you when a lookup came from the wrong table. CurrentProof cites every one, and if a check can't be evaluated, the result says so. It never reports a pass in its place. Got a result from another tool you can't verify? Run it here and see every factor.
Define your circuit and cable
Choose installation method, conductor material, and cable reference from the A4:2026 tables, with buried cables split into Methods D1 and D2.
Table 4A1 · Table 4A2 · Table 4A3
Enter installation conditions
Provide ambient temperature, grouping arrangements and circuit length. Correction factors are applied automatically.
Appendix 4 Eq 6 (Ct) · Table 4B1 (Ca) · Table 4C1 (Cg)
The result, with the working
A pass or fail against Table 4Ab, with every intermediate value and the reference it came from.
Table 4Ab · BS 7671:2018+A4:2026 Appendix 4
Start free. Upgrade when you need more.
Starter
- Volt Drop calculator
- Demand calculator
- Load calculator
- Unlimited calculations
- Full working shown
- Tables from BS 7671:2018+A4:2026
- – PDF export
- – Advanced calculators
Professional
or £59 per seat per month · further seats cost less
- Everything in Starter
- Circuit and Infrastructure calculators
- PDF reports with the full working, ready for checking
- Calculation history
- Saved projects
- Priority support
Cancel anytime: you move to Starter and keep every calculation and project. The free calculators stay free, with no ads. Full pricing details →
Check your next volt drop here.
Volt Drop, Demand and Load are free, with unlimited calculations and no account needed.