Ever needed to check the voltage, AC DC current or resistance of your appliances or other electrical components? Most of us have called an electrician at some point to do just that, but you can do it yourself with a multimeter if you know how to use a multimeter.
A multimeter is a device that measures circuit currents. With this device you’ll be able to see if a circuit has voltage and if there is an electrical problem.
A multimeter is designed mainly for voltage metering but newer models have other features built in that automate a lot of tasks. It has a lot of functions but that does not mean it is difficult to use. The following step by step guide shows how to use it.
How to Measure Resistance
Step 1. Adjust the multimeter setting to resistance or ohms
Turn your multimeter on. Locate the ohm scale, typically it is at the uppermost scale with the highest values along the dial’s left side, going down to zero to the right. This is the opposite of the other measurements that have the lowest values along the left and go up to the right.
Step 2. Check the meter indicator
If the test leads don’t touch anything, an analog meter’s pointer should be at the left most area. This indicates resistance is infinite and the circuit is open. It also means there is no path between the black and red probes and no continuity.
Step 3. Hook the test leads.
Link up the black test lead on the jack labeled “-” or “common”. Connect the red test lead on the jack with the ohm symbol or omega / R sign. Adjust the range to R x 100 if the option is available.
Step 4. Grab the test lead probe ends and set them together
The pointer will now move to the right. Find the knob labeled zero adjust and turn it so the meter is as near 0 as possible.
Make sure to zero your multimeter after the resistance has been changed or the next reading will come out wrong.
Step 5. Measure resistance
- To try out the multimeter, get a light bulb and find its two electrical contact points. They are the bottom base center and the threaded base.
- Hold the bulb or have a friend hold it for you. Set the red probe against the base bottom center and the black probe on the threaded base.
- Observe the needle as it goes from left to right.
How to Measure Voltage
Step 1. Set your multimeter to the maximum AC volt range allowed
Often the voltage to be tested has an unknown value. By choosing the highest setting your multimeter ensures you don’t risk damaging the device.
Step 2. Put the probes in the jacks
Put the black probe in the jack marked “-” or COM. Put the red probe in the jack marked “+” or V.
Step 3. Find the voltage scales
The range selected by the knob decides what scale is evaluated. The max value scale needs to match the selector ranges on the knob.
Step 4. Test a power outlet
- In the US and other nations, the volts are either 120 or 240, though in other countries it might be 380 volts.
- Set the black probe in one of the electrical outlet’s slots. The outlet’s contact grabs hold of the probe so you can let it go.
- Put the red probe in the other slot.
- Check your multimeter. It should signify voltage close to 120 or 240.
Step 5. Take off the probes
Turn the selector knob to the lowest range available that is higher than the voltage measurement you got.
Step 6. Put the probes back in
Insert the probes the same way you did before. This time the meter may read 125 or 110 volts. Keep in mind the meter range is critical in getting an accurate reading.
If the pointer doesn’t move it means DC was selected rather than AC. Double check and make certain AC is selected.
When testing voltage, do it in a way that won’t require you to hold them at the same time. Fortunately a lot of multimeters have alligator clips to help with this.
How to Measure Amperes
Step 1. Ensure the voltage measurement has been taken
You have to check if it’s an AC or DC circuit. Measure the voltage the same way as described above.
Step 2. Adjust the multimeter to the maximum AC or DC amp range
Bear in mind that some multimeters only measure small levels of current along the mA and uA range. 1 mA is equal to. .001 amp and 1 uA is 000001.
Those are current values which flow in intricate electronic circuits. That is smaller than the typical flow in household appliance and car circuits. Just for reference a typical 120 volt light bulb pulls in .833 amperes.
How to Use a Clamp on ammeter
This device is ideal for measuring current thru an ohm resistor (4700) at 9V DC. This is more suited for homeowners who want to check appliances and fixtures. Here’s how you use one.
- Put the black probe in the COM jack.
- Look for the A jack and put the red probe there.
- Turn off the power circuit.
- Open the part of the circuit that you will test.
- Put the meter in the circuit in such a way the circuit is completed. You have to put an ammeter in series rather than across as it won’t work.
- Check the polarity. The current should move from the positive to the negative. Adjust the current range to the maximum value.
- Apply power and make range adjustments downward to get a better reading.
How to Measure Battery Voltage
Follow these steps.
Step 1. Insert the probes
Insert the black probe in the COM and the red probe at the jack labeled A or mAV. Adjust the multimeter to 2V DC.
Step 2. Connect the probe and battery
Link the black probe with the battery’s – sign and the red probe to the plus sign. Squeeze the probes a bit.
Step 3. Read the results
If the battery is new, the reading should be 1.5V or thereabouts. For DC voltage, make sure the knob is set where the V line is straight.
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Tips and Warnings
Whether it is your first time to use a multimeter or have been using it for years, always practice safety.
Choose the Right Multimeter
- Make sure the multimeter has the specs and capabilities you need. The multimeter should also be designed for the environment where you intend to use it.
- The multimeter must have sufficient overload protection.
- The category rating (CAT II, CAT III, CAT IV) needs to be appropriate for the tasks you have in mind.
- Always select a multimeter that’s rated for the highest category that it can be utilized. If you’re going to measure 4880 volts, your multimeter should have a CAT III 600V rating, CAT IV 600V or CAT III 1000V.
Always Check the Multimeter before Use
- Inspect your multimeter before using it. Do not use if there are indications of physical damage.
- Use a proving unit or known voltage source before using a multimeter on a live circuit.
- Store the multimeter and probes in a carry case to avoid damage.
How to Check the Test Probes
- Remove the test probes from the jacks. Look for signs of damage or wear and tear.
- The probes should feel secure when inserted in the jacks.
- Run your fingers on the test probe. Check for signs of worn out insulation.
- For protection against electrical shorting, use only test leads with as little as exposed metal tip as possible.
- Do not use broken test probes. Replace, don’t repair them.
Electric Shock Prevention Tips
- Always proceed on the assumption a circuit is live until has been discharged.
- Wear protective gear like headgear, gloves and rubber mats with insulation. These are needed if you’re going to be close to circuits that are exposed and stronger than 50 V.
- Keep an eye on the safety indicators on your multimeter. They will notify you of potential hazards.
- Do not test electrical circuits when you’re near vapor or any flammable material.
- Do not take measurements in damp and humid locations.
The effects of electric shock depends on several factors such as:
- The body areas affected
- The path the current went through
- How long your body was exposed
- Condition of your body
You should always be aware of the potential hazards of using a multimeter. Aside from those described above, be aware of the following.
Overvoltage
A transient overvoltage is a short voltage surge. It might reach thousands of volts, and the most common causes are power being switched on and off repeatedly, unfiltered electrical components, lightning and motors.
Arc Blasts and Flashes
These are electric currents that have been discharged in a gap of air. This is due to two conductors accidentally making contact. It could also be due to too much voltage that it ionizes the air.
An arc flash can also happen if you use a multimeter and a power surge or lightning strike occurs. This could reach the electrical system you’re working on, and that’s why it is important to use only multimeters with CAT ratings to prevent damage.
CAT Ratings and Voltage
There is a voltage rating in each category that determines its capacity to handle a higher transient.
For instance, a CAT III 1000 V multimeter provides better protection than a CAT III 600 V. However, a CAT II 1000 V does not provide additional protection compared to a CAT III 6000 V.
Bottom line: the higher the category, the more protection provided.
CAT II
These multimeters are for portable tools, household appliances and other devices with the same loads.
CAT III
These are for fixed installation equipment like polyphase motors and switchgear. Other examples are appliances with short service entrance connectors, commercial lighting systems, short branch circuits and feeders.
CAT III rated multimeters are also good for industrial plant feeders and devices which feed from the distribution panels directly.
CAT IV
These are often used for origin of installation, underground lines, overhead lines, service and outside entrance, over current protection gear and more.
Other Considerations
- Read the user guide and follow the directions indicated there.
- Do not use a multimeter for something that it is not designed to handle.
- Discharge and de-energize the circuit prior to connecting and disconnecting your multimeter.
- The circuit should never be powered when you measure resistance.
- Your multimeter should always be connected in series when measuring circuits. Voltage measurements must also be parallel.
- Make certain the multimeter is set to AC mode if you’re going measure AC, or DC mode if you will be checking DC.
- Keep an eye on polarity during DC measurements.
- Turn your multimeter off when you’re done. If there is no off switch, just set it to the maximum AC value.
- No matter the brand or design, always begin your AC and voltage measurement at the highest range your multimeter allows.
- Once you have changed resistance, make adjustments to 0 ohms. Do this also after checking resistance.
- Never use a multimeter if it is malfunctioning.
- Don’t use a multimeter on any electrical outlet or equipment with signs of damage.
Conclusion
So there you have it, the many ways you can use a multimeter. The steps provided above are meant as a general guideline only, as your multimeter may have other features and function differently.
For instance, some multimeters can automatically detect if you’re measuring current, voltage or resistance. The unit automatically adjusts so you don’t have to do a lot of tinkering.
The important thing to remember is to get a quality multimeter and use it as directed. Do that and you won’t go wrong.