I'm a platform engineer. Kubernetes, Java, AWS, that kind of work. I am not an electrician, and for the last few weeks I've been building a calculator for electricians. This post is about the mistake that taught me the most. It was not in the math.

What the app does

Electrician Calc picks the wire and the breaker for a circuit, checks the voltage drop and shows every step of the working, so you can show it to an inspector or a client.

It started as an IEC app: mm², metres, 230/400 V, the standard used in Ukraine and most of Europe. Then I added the NEC for the US: AWG, feet, 120/240 V, Table 310.16. The app picks one by the phone's region and you can switch with one tap.

I thought the NEC part was mostly tables. Type in the ampacity table, the standard breaker sizes and the grounding table, write tests against worked examples, done. The tests were green and I was happy.

A 40 A range

I didn't have an American electrician to ask, so I ran a user test with an AI agent in that role.…