Practical takeaway
A voltmeter goes across two points, an ammeter goes in series with the current path, and an ohmmeter is used on a de-energized circuit or component.
Electricity & Electronics
Test Instruments
Choose the right meter, then use it on an actual circuit. The goal is not just to know the name of the instrument — it is to know how to connect it correctly.
TECHNICIAN FOUNDATION15 of 16
Technician exam focus
Recognize what the three common meters measure and how each one is connected. Those connection rules matter just as much as the instrument names.
Three meters, three different jobs
Voltmeter
Measures electrical potential difference between two points. To measure the voltage across a component, place the meter leads on the two ends of that component. The voltmeter is connected in parallel with what you are measuring.
Ammeter
Measures current. The current being measured must pass through the meter, so the circuit path is opened and the ammeter is inserted in series.
Ohmmeter
Measures resistance using its own internal test source. Do not use it on an energized circuit. For a clean measurement, other circuit paths may also need to be isolated from the component.
One useful mental check: voltage is measured across, current is measured through, and resistance is measured with circuit power off.
STEMulation
Hands-on measurement lab
Measurement 1 of 3
First: which instrument should you use?