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ApprenticeDojo

In the trades, the maths isn’t homework — it’s the difference between a job that’s safe and one that isn’t.

Three trades, one habit: get the number right

Electricians, HVAC techs and plumbers do proportional reasoning, formula rearrangement and unit conversion all day — and unlike a worksheet, a wrong answer overheats a wire, floods a floor, or fails an inspection. Here’s the maths that keeps a job to code.

⚡ Electrical. Amps = volts ÷ ohms, watts = volts × amps. A wire has an ampacity, and the breaker protecting it must never exceed it — 12-gauge copper is good for 20 A, and continuous loads cap at 80%.
❄️ HVAC. A room’s cooling load is roughly area × 25 BTU per square foot, and air conditioners are sized in tons — 12,000 BTU each.
🚰 Plumbing. A drain slopes ¼ inch per foot: enough to drain, not so much the water outruns the solids and clogs.

Everything runs on your device — no internet, no accounts.

The four rules of a job that passes

Ohm. Volts push, ohms resist, amps flow — and amps are what the wire has to survive.
The breaker protects the wire, not the appliance: its rating can never exceed what the wire can safely carry.
The 80% rule. Rated for a sprint, sized for a marathon — never load a circuit to its full number for hours.
Slope and size. A drain is a ramp for gravity; an AC is sized to the load — the number has to fit the job.

ApprenticeDojo is text-forward (ages 15–18) — the trades’ own rules are the cast.