User's Guide
True RMS AC / DC Power Clamp Meter
Model 380940
380940-EU-EN-V4.1-4/12
2
Introduction
Congratulations on your purchase of the Extech 380940 True RMS Watt Clamp DMM. This meter
combines multimeter and clamp meter functionality in one convenient meter. Careful use of this
meter will provide years of reliable service.
Safety
1. NEVER exceed the specified voltage/current maximum
2. USE EXTREME CAUTION when working with high voltages.
3. DO NOT measure voltage if the voltage on the "COM" input jack exceeds 500V above earth
ground.
4. NEVER connect the meter leads across a voltage source while the function switch is in the
current mode. Doing so can damage the meter.
5. ALWAYS discharge filter capacitors in power supplies and disconnect the power when
measuring.
6. ALWAYS turn off the power and disconnect the test leads before opening the back to replace
the fuse or batteries.
7. NEVER operate the meter unless the back cover and the battery/fuse door are in place and
fastened securely.
International Safety Symbols
380940-EU-EN-V4.1-4/12
3
Meter Description
1. Conductor under test
2. Clamp Jaws
3. Jaw trigger – Opens the meter jaws
4. ZERO button – Zeroes the DCA reading
5. Positive input jack (for red test lead)
6. Function select dial
7. HOD button freezes the displayed reading
8. MAX/MIN button – Press to track and view highest and lowest readings
9. LCD Display with function indicators and bargraph
10. COM input jack (for black test lead)
Function Select Switch
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