A typical part of an engineer’s job is to perform measurements with a multimeter. For example, if you are working as a building maintenance engineer or electrician, your daily routine may require you to measure power from AC mains or other high voltages. Before you start performing a measurement, what is the first thing that comes to your mind? Should you just grab the nearest handheld multimeter available? No!
Imagine you need to select a helmet. You need to select one with high quality to protect your head. But a helmet’s structure, design, and protective ability vary for different kinds of activities. A helmet designed for rock climbing needs to protect you against small rocks, falling objects, and sharp faces. A bicycle helmet needs to protect your head during impact to reduce the likelihood of injury in the event of an accident. A motorcycle helmet needs to protect you against high-speed impacts with the road and other vehicles. It’s important to choose the right helmet for your activity.
Likewise, different multimeters are designed with different levels of protection against common electrical hazards.
For your own safety and the safety of those near you, you must choose a multimeter that is designed and tested to protect you against electrical hazards you might encounter. Remember you only have one life, and there are no second chances. Here are some safety considerations that you need to take note of before you start making measurements with a multimeter.
1. Understand your multimeter’s safety indicators
Safety certification is important to ensure the multimeter is compliant with the relevant safety standards. Usually, the manufacturer of the multimeter will obtain safety certifications from third-party independent testing agencies, such as the Canadian Standard Association (CSA), to ensure the product has been tested and complied to the relevant safety standard.
Products that successfully pass the independent testing are labeled with the logo of the independent testing agency on the back of the multimeter.
The accessories used with a multimeter ─ like probes ─ should also be tested and marked with a third-party safety agency logo. Before you start measuring, be sure to select a multimeter and accessories that have passed these tests.
Some independent testing agency logos are as follows:
Be cautious of the CE marking:
The “CE” marking is an abbreviation for "European Conformity" (from the French phrase “Conformité Européene”). The CE marking indicates the product's conformity to the applicable European Union safety, health, and environmental requirements, a mandatory conformity mark on all products sold in the European Union.
Manufacturers are permitted to self-certify. They must meet the standards, issue their own Declaration of Conformity, and mark the product “CE.” Therefore, the CE marking is not a guarantee of independent testing.
For safety purposes, you should not accept a multimeter that has only a CE mark unless you know the manufacturer to be trustworthy and you have reviewed the manufacturer’s Declaration of Conformity.
2. Pay attention to voltage rating of the measurement circuit and measurement limit of your multimeter
Before you start to perform a measurement, you need to understand the maximum voltage rating of your circuit. Use a multimeter that will be able to withstand the maximum voltage of the circuit. In general, manufacturers label the multimeter’s measurement limits on the front panel. A multimeter provides protection circuitry to prevent damage to the instrument and protect against the danger of electric shock, provided the measurement limits are not exceeded.
To ensure safe operations of the instrument, do not exceed the measurement limits shown on the front panel of the multimeter.
3. Take precautions when performing live measurements
Here are a few safety precautions you should take when making live measurements with a multimeter:
- When measuring a live circuit, use insulated tools like safety glasses, insulated mats, and insulated gloves.
Figure 1. Wear insulated gloves when using a multimeter.
- Inspect the test leads for damaged insulation or exposed metal. Check the test leads for continuity. If the test leads are damaged, replace them before you use the multimeter.
- It is recommended that you disconnect circuit power and discharge all high-voltage capacitors before testing resistance, continuity, diodes, or capacitance.
- When making measurements, always connect the common test lead before you connect the live test lead. When you disconnect the leads, disconnect the live test lead first. Avoid holding the test lead in your hands to minimize personal exposure if transients occur. Before use, verify the multimeter’s operation by measuring a known voltage.
Conclusion – Safety First!
Safety is always the top priority no matter what you are measuring, so there are a few precautions you should take. Always choose a multimeter with a voltage rating higher than the circuit you are measuring. Remember to check that the multimeters and probes you are going to use are marked with third-party safety agency logos such as CSA, ETL, TÜV, or VDE. Do not overlook the safety of the probes! With safety in mind, you will be assured that the high voltage goes into your measurement instrument instead of you!
To learn more, download the Think SAFETY when Selecting a Handheld Multimeter application note.
For more info about Keysight’s DMMs, visit www.keysight.com/find/dmm