Cable Ampacity Calculator

Cable sizing decisions outlive the project that ships them. A run installed for the original 250 A demand of a manufacturing line becomes the bottleneck when production grows, when a new EV charging bank lands in the car park, or when an additional chiller goes in on the back of a heat-pump refit. Getting the headroom right at design stage is materially cheaper than re-cabling a live site three years later.

Commercial EV rollouts have made cable ampacity a board-level question. A 22 kW charger draws around 32 A at 400 V three-phase, and a bank of eight chargers on a single sub-distribution feed is already pushing 256 A before diversity. Add the next phase, add the cargo van fleet, and the cable that was generous in year one is the constraint in year three. Sizing for the destination state, not just the day-one load, is the cheapest decision the project will make.

These figures are indicative; commission a competent electrical designer for BS 7671 compliance and the final installation drawings. Purely Energy sits on the contract side: we will tell you whether the supply capacity you are paying for matches the load profile the new cabling will carry, and whether the MIC needs uplifting with the DNO before the cables are even pulled. The two conversations belong together at the design stage, and most sites end up doing them six months apart and paying for the gap.