Low-voltage power: Ohm's law, voltage drop, wire gauge and safe meter use

Skills you'll practise

• Use Ohm's law and P = V × I to work out a device's current and a supply's total load
• Calculate voltage drop on a two-conductor run using the loop length and the cable's resistance per length
• Choose a fix for low voltage at a device: thicker gauge, shorter run, a higher-voltage option or a local supply
• Pick a meter and leads with a CAT rating that matches where you are measuring, and keep their protection intact
• Measure voltage at the device under load and record readings that prove the install

Course outline

1. 1.Low-voltage power: voltage drop and safe meter useVideo · 2 min
2. 2.Ohm's law and power for low-voltage devicesLesson · 18 min
3. 3.Voltage drop and wire gaugeLesson · 22 min
4. 4.Using a meter safelyLesson · 20 min
5. 5.Low-voltage power: Ohm's law, voltage drop, wire gauge and safe meter use: knowledge checkKnowledge check · 19 questions
6. 6.Final exam10 questions · passing it completes the course, so people who already know the material can test out

Sources it draws on

The lessons and questions are written from these references, so learners can go back to the original.

• Wikipedia: American wire gauge (copper resistance per 1000 ft and per km, e.g. 22 AWG 16.14 Ω/kft, 18 AWG 6.385 Ω/kft, 16 AWG 4.016 Ω/kft)
• Fluke: IEC category ratings, use the right tools for the job (CAT I to CAT IV per IEC 61010-1)
• Fluke: 10 dumb things smart people do when testing electricity (CAT-rated meters and leads, authorised fuses, de-energize, lockout/tagout)
• Device and power supply manufacturers' installation instructions and cable datasheets (operating voltage range, current draw, wire gauge tables)