Using a Multimeter: Chapter 9
In this module, we will teach you about multimeter safety, CAT ratings, and arc flashes. Skip to quiz!
1. CAT Ratings
The CAT rating determines what equipment the multimeter can safely be used on. Multimeters and multimeter leads are given a CAT rating. CAT Ratings are only approved for “low voltage” applications, meaning 1000V or less.
Using a meter with a higher CAT rating can reduce the risk of shock, explosion, or injury. A higher CAT multimeter can also reduce your risk if the multimeter is used incorrectly.
There are four levels of CAT ratings:
CAT I
CAT II
CAT III
CAT IV
A multimeter with a higher CAT rating, like CAT IV, can be safely used on more dangerous equipment.
A multimeter with a higher CAT rating can safely work on all CAT equipment beneath it. For example, a CAT III multimeter can safely be used on CAT II and CAT I equipment. A CAT III multimeter would not be safe to use on CAT IV equipment.
CAT I is the lowest level of CAT rating a multimeter can be given. A CAT I multimeter is approved to handle low energy equipment. Low energy equipment includes protected electronic equipment and standard circuit boards.
A CAT II rating is the second lowest rating that a multimeter can be given. CAT II multimeters are approved to handle appliances, portable tools, and other household loads.
A CAT III rating is the second highest rating a multimeter can receive. CAT III meters are approved for use on distribution circuits. Distribution circuits include distribution panels, load centers, and feeder circuits.
A CAT IV rating is the highest rating that a multimeter can receive. CAT IV meters are approved for handling outside service work. Outside service work includes working on lines from a street pole to the meter.
All CAT ratings will also come with a number in front of the rating such as CAT III 600V. The number is the maximum amount of voltage the meter can handle. Do not measure voltage above the maximum voltage. This can be very dangerous.
2. General Safety
When handling any type of wire or circuit, act as if the power is on. Electricity is incredibly dangerous. Before handling any electronic equipment, always turn off the power. Once the power is off, check the voltage to confirm that there is no power.
In some cases, the power can be turned off but the circuit will remain energized. A common cause of this can be a capacitor. Recall that capacitors store electrical energy. Checking the voltage of the wire prevents you from being shocked or killed.
When you use a multimeter, It is important to take measurements in a safe space. A mistake due to a bad environment can damage equipment or kill you.
When using a multimeter, make sure that there is enough lighting to see the components. With bad lighting, you may accidentally touch a live component or damage equipment.
Before using your multimeter, scan the area for environmental hazards which could injure you. Look for standing or running water near you or the electrical components.
When using a multimeter, it is important to keep your hands free. Holding a multimeter and two leads at one time can result in injury. A good way to free up a hand is to hang your multimeter. You can also use alligator clips.
A common safety problem is the metal section of your multimeter leads touching while measuring a component. Some brands prevent leads from touching by only exposing the metal at the tip of the probe.
If your multimeter leads touch while you are touching an active component, it can short the circuit. Generally, this will create sparks or even an arc flash. We recommend getting leads where the metal tip is barely exposed.
It is important to wear the appropriate safety gear when working with electrical equipment. In general, you should always wear safety glasses, insulated gloves, and insulated boots when using a multimeter. The safety gear you need will change depending on the equipment you are working with.
3. Arc Flashes
Arc flashes are an explosion caused by an arc of electricity superheating the air. Arc flashes are incredibly dangerous. Technicians die every year due to arc flashes.
When you are using your multimeter, there are rapid and large spikes in current/voltage. Arc flashes are caused by the current moving from the circuit to another conductive material, like your meter leads.
As the current moves from the circuit to your leads, it creates a bright blue arc as the air superheats. The arc melts the tips of your leads, and if your second lead is close it can create an arc flash. An arc flash can create a large explosion that destroys the equipment and can kill you.
4. Conclusion
In this section, you learned about some common safety practices. Be extremely careful when using a multimeter.
Question #1: A CAT IV multimeter has the highest CAT rating.
True
False
Scroll down for the answer...
Answer: True
True, a CAT IV meter is the highest rating a multimeter can receive.
Question #2: Always choose a multimeter based on the highest category of equipment you will be working on.
True
False
Scroll down for the answer...
Answer: True
True, the multimeter should be rated to work with all equipment you work on. Even if only one item you work on is rated CAT IV, you need a CAT IV multimeter.
Question #3: The number next to the CAT rating represents the maximum amount of ____ the meter can be used to measure.
Current
Voltage
Resistance
Capacitance
Scroll down for the answer...
Answer: Voltage
The number next to the CAT rating is the maximum amount of voltage the meter can safely measure. If it is a CAT II 300V meter, then you can safely measure up to 300V.
Question #4: Using the proper CAT rated multimeter can reduce the risk of injury.
True
False
Scroll down for the answer...
Answer: True
True, a multimeter that has the CAT rating for what you are working on will reduce the chance of an accident.
Question #5: If you turned the power off to a circuit, you can touch the components.
True
False
Scroll down for the answer...
Answer: False
False, just turning off a circuit does not mean you can touch a component. You must check the voltage or current of the circuit to ensure that there is no power.
Question #6: Before using your multimeter you should:
Set up adequate lighting
Hang your multimeter
Check the environment for hazards
All of the above
Scroll down for the answer...
Answer: All of the above
All of these are important steps before using your multimeter.
