Welcome to Klein MM720 Digital Multimeter Training
Course Duration: 45–60 minutes
Learn to use the Klein Tools MM720 — an auto-ranging, True RMS digital multimeter rated CAT IV 600V / CAT III 1000V — for accurate, safe measurements on the circuits a low-voltage technician works on every day. This course follows Klein’s MM720 instruction manual.
What You’ll Learn:
- Explain the MM720’s specifications, safety ratings, and warnings
- Use SEL, HOLD, RANGE, REL, and MAX/MIN, and measure AC/DC voltage — including Lo Z for ghost voltage
- Measure current safely in series, and know when to use a clamp meter instead
- Test resistance, continuity, and diodes
- Measure capacitance, frequency, duty cycle, and temperature
- Replace batteries and fuses, and care for the meter
How This Course Works
- Five modules, each ending with a knowledge check. You get two attempts, and a first miss gives you a hint rather than the answer.
- Finish each knowledge check to unlock the next module.
- Final assessment: 15 questions. You need 80% (12 of 15) to pass and receive your certificate.
- Your results are emailed automatically to the training administrator, and a copy goes to you, whether you pass or not.
Module 1: Meet the MM720: Specs and Safety
What the MM720 Is
The Klein Tools MM720 is an auto-ranging, True RMS (TRMS) digital multimeter. It measures AC/DC voltage, AC/DC current, and resistance, and it also measures temperature, capacitance, frequency, and duty cycle, tests diodes, and checks continuity. It replaces Klein’s MM600 and adds True RMS, a Low Impedance (Lo Z) voltage setting, a 6000-count display, and an automatic backlight.
| Specification | MM720 |
|---|---|
| Display | 6000-count, reverse-contrast LCD, with an optical sensor that adjusts the backlight automatically |
| Voltage | Up to 1000V AC/DC (input impedance 10MΩ); Lo Z setting up to 600V |
| Current | 600.0µA to 10.00A, AC and DC |
| Resistance | 600.0Ω to 60.00MΩ |
| Capacitance | 60.00nF to 6000µF |
| Frequency / duty cycle | 9.999Hz to 500.0kHz / 1.0% to 99.9% |
| Temperature | −40°F to 1832°F (−40°C to 1000°C) with a K-type thermocouple |
| Safety rating | CAT IV 600V, CAT III 1000V, double insulated |
| Durability | IP42 dust and water resistance; 6.6 ft (2 m) drop protection |
| Power | 2 × AAA batteries; auto power-off after about 5 minutes |
| Calibration | Accurate for one year |
Why True RMS Matters
An average-responding meter assumes a clean sine wave. The loads you work on every day — LED drivers, switch-mode power supplies, PoE equipment, computers, and variable-frequency drives — draw distorted, non-sinusoidal current. A True RMS meter calculates the real effective value of whatever waveform is present, so its AC readings stay accurate on those loads. (The MM720’s AC accuracy is specified from 50 to 400Hz.)
Measurement Categories
The CAT rating tells you where in the electrical system the meter can safely survive a voltage transient:
- CAT IV 600V: Circuits at the source of the building’s low-voltage mains installation — the service entrance, utility meter, and service conductors.
- CAT III 1000V: The distribution part of the building’s mains — panelboards, feeders, and branch circuits.
- CAT II: Receptacle-connected loads, such as equipment plugged into a wall outlet.
⚠️ Klein’s Key Warnings
- Before each use, verify the meter works by measuring a known voltage or current.
- Never use the meter on a circuit that exceeds its category rating.
- Use only CAT IV-rated test leads, and don’t use damaged leads or a damaged meter.
- Keep fingers behind the probe guards, away from the metal tips.
- Use caution above 25V AC RMS or 60V DC — these voltages pose a shock hazard.
- Don’t use the meter in electrical storms or wet weather. If it gets wet, dry the meter and jacks thoroughly before the next use.
- Replace the batteries as soon as the low-battery indicator appears — low batteries cause false readings that can lead to shock.
Test Leads and Shields
Press each lead fully into its jack — a partly seated lead causes intermittent readings. When you turn the meter on, “LEAD” flashes as a reminder to check that the leads are in the right jacks for that function.
- CAT III and CAT IV locations: Keep the probe-tip shields pressed firmly in place. Leaving them off increases arc-flash risk.
- CAT II locations: You may remove the shields so the probe tips reach recessed contacts, such as a standard wall outlet. Don’t lose them.
Knowledge Check
You're checking voltage at a standard wall receptacle (a CAT II location). What may you do with the CAT III/CAT IV shields on the test probes?
Module 2: Controls and Voltage Measurement
The Function Selector and Buttons
Turning the selector from OFF to any function powers the meter on. The dial positions are: V, Continuity/Ω/Diode/Capacitance, Hz/%, Lo Z, Temperature, µA, mA, and 10A. Default functions are printed on the meter in white; secondary functions are printed in orange.
| Button | What it does |
|---|---|
| SEL | Selects the secondary function: AC/DC for voltage, Lo Z, and current; continuity → resistance → diode → capacitance on the Ω position; Hz/% and °F/°C |
| HOLD / Backlight | Press to freeze the reading; press again to resume. Hold for over 1 second to step the backlight through high, low, and automatic (“A” = automatic, “M” = manual) |
| RANGE | Press to leave auto-ranging and step through manual ranges; hold for over 1 second to return to auto-ranging |
| REL | With the leads connected, press to store a reference; the display then shows the difference. Works on voltage, current, resistance, temperature, capacitance, and Lo Z |
| MAX/MIN | Press to show the maximum reading (it updates if a new maximum occurs); press again for the minimum; hold for over 1 second to return to normal |
Measuring AC or DC Voltage (up to 1000V)
- Insert the red lead into the VΩ jack and the black lead into COM.
- Turn the selector to V. The meter defaults to AC; press SEL to switch to DC. The AC or DC icon shows which mode is active.
- Touch the probes to the circuit. The meter auto-ranges to the best range.
- A “–” on a DC reading means the leads are reversed. Swap them (or note the polarity).
- The hazardous voltage indicator appears for voltages above 30V.
- With the leads open, a few millivolts may appear. That’s normal noise — touch the leads together and the meter reads zero.
Lo Z: Finding Ghost Voltage
A high-impedance (10MΩ) meter can read “ghost” or stray voltage that’s capacitively coupled onto an open or de-energized conductor from nearby live wiring — common in long conduit runs and bundled cable. The Lo Z setting loads the circuit with a much lower input impedance (above 3kΩ), so coupled voltage collapses while a real source holds steady.
- Use the same lead connections as for voltage, and turn the selector to Lo Z. Press SEL for AC or DC.
- If a reading that appeared on V drops to near zero on Lo Z, it was ghost voltage. If it stays, the conductor is truly energized.
⚠️ Lo Z Limit
Never measure more than 600V in the Lo Z setting. Use the V setting for anything higher.
Common Low-Voltage Readings
| Circuit | Expected | Notes |
|---|---|---|
| Class 2 transformer (access control, HVAC controls) | About 24V AC | Read with no load and under load |
| 12V / 24V DC power supply | 12–13.8V / 24–28V DC | Check regulation under load |
| PoE port | 44–57V DC (802.3af); 50–57V (802.3at/bt) | Measure with the powered device connected, through a PoE tester or breakout |
Why a PoE Port Can Read 0V
Standards-based PoE equipment applies its 44–57V only after it detects a valid powered device. With only your meter connected, it sees no device and keeps the power off, so you’ll typically read about 0V on a working port. Passive PoE injectors are the exception — they apply voltage all the time.
Knowledge Check
A conductor you've disconnected at both ends still reads 38V AC on the V setting. It runs in a conduit with live circuits. Which setting helps you tell whether that's ghost voltage?
Module 3: Current Measurement
Current Is Measured in Series
To measure current, the current has to flow through the meter, so you open the circuit and insert the meter in series. In a current setting, the meter’s internal resistance is very low — if you place the leads across a voltage source, you create a short circuit that blows the fuse and can cause an arc flash.
Choosing the Jack and Setting
| Expected current | Red lead jack | Selector | Fuse |
|---|---|---|---|
| Less than 600µA | mA/µA | µA | 800mA / 1000V fast-blow |
| Less than 600mA | mA/µA | mA | 800mA / 1000V fast-blow |
| 600mA to 10A (or unknown) | 10A | 10A | 10A / 1000V fast-blow |
The black lead always goes in COM. The current settings default to AC; press SEL for DC. When you don’t know the current, start on the 10A jack and setting, then move down for better resolution.
Procedure
- Insert the leads into the correct jacks and set the selector.
- Remove power from the circuit.
- Open the circuit at the measurement point.
- Connect the meter in series using the test leads.
- Apply power and read the display. The meter auto-ranges.
Current Limits
- Never attempt to measure more than 10A.
- For currents above 6A, Klein recommends measuring for no more than 30 seconds, followed by 10 minutes of recovery time.
- More than 800mA into the mA/µA jack, or more than 10A into the 10A jack, can blow that jack’s fuse.
Typical Low-Voltage Current Checks
- Door strikes and maglocks: Confirm the draw is within the power supply’s rating
- Sensors and keypads: Small loads on the mA or µA setting
- Panel standby current: Use it to size backup batteries
- LED lighting: Driver output current (True RMS keeps AC readings accurate)
Above 10A, or Without Breaking the Circuit
The MM720 has no clamp input. For currents above 10A, or when you can’t open the circuit, use a separate clamp meter around one conductor.
Knowledge Check
What is the correct order of steps once the leads and selector are set for a current measurement?
Module 4: Continuity, Resistance, Diodes, and Capacitance
One Dial Position, Four Functions
Continuity, resistance, diode test, and capacitance share one selector position. Leads go in VΩ (red) and COM (black). The meter starts in continuity; each press of SEL moves to the next function:
| SEL presses | Function | Display icon |
|---|---|---|
| 0 (default) | Continuity | Speaker/continuity symbol |
| 1 | Resistance | Ω |
| 2 | Diode test | Diode symbol |
| 3 | Capacitance | nF or µF |
⚠️ Power Off First
Never measure continuity, resistance, or capacitance on a live circuit. These functions use the meter’s own small test current, so circuit voltage gives false readings and can damage the meter (inputs are protected to 600V in these settings). Discharge capacitors before testing.
Continuity
- Confirm the continuity icon is showing (press SEL if not).
- Remove power from the circuit.
- Connect the leads across the conductor or circuit. Below 50Ω, the meter beeps and shows the resistance. An open circuit shows “OL”.
Use continuity to verify conductors and pairs end to end, check fuses and switches, and find shorts between conductors.
Resistance
- Press SEL once for Ω, and remove power from the circuit.
- Connect the leads. The meter auto-ranges from 600.0Ω to 60.00MΩ.
“OL” with the leads open, or on a failed (open) resistor, is normal — the resistance is beyond the meter’s range. For low-ohm readings, touch the leads together and press REL to subtract the test-lead resistance.
Diode Test
- Press SEL twice for the diode icon.
- Touch the red lead to the anode and the black to the cathode. A reading of 200–700mV means the diode is forward biased and conducting; reversed, it should show “OL”.
- “OL” in both directions: the diode is open.
- About 0mV: the diode is shorted.
- The test uses up to 1.5mA at 3.2V open-circuit, so LEDs (forward drop roughly 1.6–3V) may read high or glow faintly.
Capacitance
- Press SEL three times until nF or µF appears.
- Remove power and discharge the capacitor — with a resistive discharge tool, never a screwdriver — and verify 0V.
- Connect the leads across the capacitor. The meter auto-ranges from 60.00nF to 6000µF; large values take a few seconds to settle.
Knowledge Check
In resistance mode, the display shows "OL" while the test leads are not touching anything. What does that mean?
Module 5: Frequency, Temperature, and Maintenance
Frequency and Duty Cycle
- Red lead in VΩ, black in COM; turn the selector to Hz/%.
- The meter starts in frequency (Hz). Press SEL once for duty cycle (%).
- Connect the leads across the circuit.
- Frequency: 9.999Hz to 500.0kHz.
- Duty cycle: 1.0% to 99.9%, for signals from 5Hz to 10kHz — useful for PWM dimming and motor-control signals.
- Both functions need a signal between 2V and 220V RMS to read reliably.
Temperature
- Plug the K-type thermocouple and its adapter into the VΩ and COM jacks, matching the polarity markings.
- Turn the selector to temperature. The meter defaults to °F; press SEL once for °C.
- Hold the thermocouple tip against the object. The reading settles when the tip reaches the object’s temperature.
Thermocouple Rules
- The meter reads −40°F to 1832°F, but the thermocouple included with the meter is rated only below 356°F (180°C). Use a K-type probe rated for the range you need.
- Remove the thermocouple before switching to any other function.
Power and Backlight
- Auto power-off: After about 5 minutes of inactivity. Press any button to wake the meter. To disable auto power-off, turn the meter on while holding SEL — the auto power-off icon disappears.
- Backlight: Automatic by default, using the optical sensor. Hold HOLD for over 1 second to switch to manual high or low.
Batteries and Fuses
When the low-battery indicator appears, replace the batteries right away. Disconnect the leads from any voltage source before opening the battery/fuse door, and never operate the meter with the door removed.
| Part | Replacement |
|---|---|
| Batteries | 2 × AAA (observe polarity) |
| mA/µA jack fuse | 800mA / 1000V fast-blow — Klein Cat. No. 69399 |
| 10A jack fuse | 10A / 1000V fast-blow — Klein Cat. No. 69034 |
Use only fuses of the exact rating — a lower-rated or slow-blow fuse can fail to protect you during an overload. There are no user-serviceable parts inside the meter.
Care and Storage
- Cleaning: Turn the meter off and wipe it with a clean, dry, lint-free cloth. No abrasives or solvents.
- Storage: Remove the batteries if the meter won’t be used for a long time. Avoid high heat and humidity, and let the meter return to normal operating conditions after storage in extreme conditions.
- Operating conditions: Indoor use, 14°F to 122°F (−10°C to 50°C), below 90% non-condensing humidity, up to 6,562 ft (2,000 m).
- Calibration: Klein specifies accuracy for one year — follow your company’s calibration schedule.
Knowledge Check
You've finished a temperature reading and want to switch to voltage. What should you do first?
Final Assessment
Assessment Information
- Questions: 15, different from the module knowledge checks
- Passing score: 80% (12 of 15)
- Time limit: None — take your time
- Attempts: You can retake it if needed
Question 1: What does the MM720's True RMS capability provide?
Question 2: The MM720 is rated CAT IV 600V. Where does CAT IV apply?
Question 3: According to Klein, what should you do before each use of the meter?
Question 4: You turn the selector to V. Which mode does it start in, and how do you change it?
Question 5: What is the maximum voltage you may measure in the Lo Z setting?
Question 6: Above what voltage does the MM720's hazardous voltage indicator appear?
Question 7: On the V setting with the leads not connected to anything, the display shows a few millivolts. What does that mean?
Question 8: You need to measure a sensor that draws about 300mA. Where do the red lead and selector go?
Question 9: What fuse protects the mA/µA jack?
Question 10: When measuring currents above 6A, what does Klein recommend?
Question 11: Below what resistance does the MM720 beep in continuity mode?
Question 12: Starting from continuity on the Ω position, how many presses of SEL bring you to capacitance?
Question 13: In diode test, a component reads about 0mV in both directions. What does that indicate?
Question 14: How long does the MM720 wait before powering off automatically, and how can you disable that?
Question 15: The MM720 reads temperature up to 1832°F. What limits the thermocouple included with the meter?
Your Information
When you submit, your results are emailed automatically to the Five 9s Communications training team, and a copy is sent to the email address you enter here — whether or not you pass.
Assessment Results
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