Volts, Amps, Ohms, Watts: Sean White on Ohm’s Law and How to Measure Each One

Ohm’s Law describes the relationship between voltage, current, and resistance in an electrical circuit: voltage equals current multiplied by resistance (V = IR). Pair that with the power equation – power equals current multiplied by voltage (P = IV) – and you get the four values that come up constantly in PV work: volts, amps, ohms, and watts. Each one is a different measurement, taken with a different technique, and knowing which is which is foundational to working with electrical systems.

We sat down with Sean White, one of the most respected voices in solar education and a lead instructor for HeatSpring’s PV Associate (PVA) and O&M Associate Technician (OMAT) courses, to get his practical breakdown of Ohm’s Law and how each of these values is measured.

In this excerpt from our conversation, Sean walks through volts, amps, ohms, and watts, and the technique behind measuring each one. 

Ready to build your confidence across every topic on the exam? Sean’s full PVA and OMAT courses cover concepts like this in depth, with the same clear and entertaining approach.

Tune into the video excerpt or the transcript below. 

Transcript

When you’re using a clamp meter to measure the output of a PV string, what units would you be measuring in? What would be displayed on your digital multimeter?

Of course, we’re probably not going to have “miles” as one of the answers on the test — but it might be something like volts, ohms, watts, and amps. Which one of these units are you going to measure with the clamp?

If we could, we’d play the Jeopardy! theme song right now — but instead, I’ll just give you the answer: amps. That’s what you measure through the clamp.

When you want to measure volts, you need two different probes, and you touch two different points — that’s how you measure volts. When you measure resistance, you also need to test both sides of the circuit. And to measure watts, you have to measure both amps and volts, because amps times volts equals watts.

But here’s the thing about the Associate exam — and all the associate-level exams — it’s not the kind of test where you need to bring a big, thick reference book to answer the questions. You need to have this stuff in your head. So there you go: the clamp measures amps. That’s what you need to know. Put it on your flashcard.