Electrician Math: Ohm's Law, Load Calculations, Voltage Drop & Conduit Fill

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Turn the nameplate watts of six plug-in loads into amps and ohms, work out current and power of four 240 V heating elements and check whether the whole circuit stays under an illustrative 80 % continuous-load limit.
• Solve a 24 V series string of three lamps (total resistance, current, voltage drop on each lamp) and a 120 V circuit with four parallel loads (branch currents, total current and equivalent resistance).
• Calculate kVA and kW for six single- and three-phase loads with the √3 factor and the power factor, find the overall power factor of the building and the line current of a new 15 kW three-phase motor.
• Build the general lighting and receptacle load of a 2,400 ft² house, apply illustrative demand tiers, add the fixed appliances and pick the smallest standard service size that covers the calculated current.
• Look up an ambient temperature factor and a bundling factor for six circuits, work out the ampacity each conductor needs before derating and pick the smallest copper size from an illustrative ampacity table.
• Look up the circular mils of six runs, calculate their voltage drop in volts and percent with the single- and three-phase formulas, and size the long barn feeder so it stays within an illustrative 3 % limit.
• Add up the cross-section of 14 conductors, find the smallest conduit that keeps them within an illustrative 40 % fill, and check whether a device box is big enough for its conductors, ground, device and clamps.
• Calculate the full-load current of six three-phase motors from hp, voltage, efficiency and power factor, set the overloads and the breaker limit with illustrative multipliers, pick standard breaker sizes and chart current against breaker size.