Guide to digital multimeter safety

• What are electrical parameters?
• What are multimeter CAT ratings?
• What are multimeter safety precautions?

In a recent survey, more than 30% of electricians admitted to not using test tools accurately rated for their work environment. It’s the cold truth that a well-built digital multimeter will perform better in demanding conditions than a second-tier model. Not only will a top-tier tool be able to stand up to your work environment, but it will help keep you safe. Once you’ve got your multimeter, it’s important to continue to stay safe in every environment you work in—always check to make sure your multimeter is safe to use.

What are electrical parameters?

Any asset that uses or moves electricity has a set of electrical parameters. These are ratings and codes, like CAT ratings and Ingress Protection codes (IP codes), that align with standards determined by designated teams of professionals. Understanding the electrical parameters of an asset will help you understand how to test that asset for performance and how to keep the asset and yourself (and those around you) safe. Some examples of electrical parameters include impedance, inrush current, power factor, and voltage drop.

What are multimeter CAT ratings?

Digital multimeters come rated for different electrical parameters, so you’ll need to check for appropriate CAT ratings, IP codes and independent verification symbols to be sure the meter you select has been tested by an independent lab and is safe for your measurements.

While you’re determining the correct Overvoltage Installation Category rating (CAT II, CAT III, or CAT IV), you’ll want to remember to always choose a tool rated for the highest category you could potentially use it in and select a voltage rating to match, or exceed, those situations. CAT-rated meters are designed to minimize or reduce the possibility of an arc flash occurring inside the meter. The ratings are usually located near the input jacks.

To break that down, if you’re preparing to measure a 480-V electrical distribution feeder panel, you need to use a meter that’s at least CAT III-600 V rated. Meaning a CAT III-1000 V or CAT IV-600 V could also work for this situation.

Measurement Category	Description	Examples
CAT IV	Three-phase at utility connection, any outdoor conductors Limited only by the utility transformer feeding the circuit ››50 kA short circuit current	The "origin of installation"—where low-voltage connection (service entrenc cables) is made to utility power. Electricity meters, primary overcurrent protection equipment. Outside and service entrance, service drop from pole to building, run between meter and panel Overhead line to detached building, underground line to well pump.
CAT III	Three-phase distribution, including single-phase commercial lighting ‹50 kA short circuit current	Equipment in fixed installations, such as switchgear and polyphase motors. Bus and feeders in industrial plants. Feeders and short branch circuits, devices fed directly from distribution panels. Lighting systems in larger buildings. Appliance outlets with short connections to service entrance
CAT II	Single-phase receptacle connected loads. ‹10 kA short circuit current.	Appliances, portable tools, and other household and similar loads. Outlet and long branch circuits. Outlets at more than 10 meters (30 feet) from CAT III source. Outlets at more than 20 meters (60 feet) from CAT IV source.

The two-digit IP codes tell you what level of resistance to dust and water your meter can withstand. It details what size of dust particles will be kept out and to what water depth your multimeter can be submerged and continue functioning.

Ingress protection levels for solids

Level	Object Size	Effective Against
0	Object size	No protection
1	>50mm	Any large surface of the body
2	>12.5mm	Fingers or similar objects
3	>2.5mm	Tools, thick wires
4	>1mm	Granular objects. Most wires, screws etc
5	Dust protected	Not entirely prevented but must not interfere with satisfactory operation
6	Dust tight	No ingress of dust. Dustproof

The second digit of an IP rating specifies the level of protection against water.

Ingress protection levels for water

Level	Protected Against	Detail
0	Not protected
1	Dripping water	Vertically falling water. No harmful effect
2	Dripping water, 15 ° tilt	Vertically falling water. No harmful effect when unit tilted up to 15 ° from its normal position
3	Spraying water	Water falling as a spray at up to 60 °. No harmful effect
4	Splashing water	Water splashing from any direction. No harmful effect
5	Water jets	Water projected by a nozzle from any direction. No harmful effect
6	Powerful water jets	Water projected in powerful jets by a nozzle from any direction. No harmful effect
7	Immersion up to 1m	Immersion in water up to 1m for 30 minutes Waterproof to 1m for 30 minutes
8	Immersion beyond 1m	Continuous immersion

At Fluke, we safety test our products, pushing them to the limit. It’s only when the test team can no longer get a unit to fail that it can be released into production. The goal is to ensure a Fluke digital multimeter can repeatedly withstand the most demanding real-world conditions and keep you, the user, safe and heading home every single day. We also make sure our products are independently tested to ensure our claims.

What are multimeter safety precautions?

Before you take a measurement with your multimeter, you should visually inspect it first. Check the meter, test probes and accessories over for signs of physical damage. Make sure all plugs fit securely and keep an eye out for exposed metal or any cracks in the casing. You should never use a damaged meter or damaged test probes.

After the visual inspection is done, check to make sure your multimeter is working properly. Never just assume it is. Use a known voltage source or a proving unit, such as the Fluke PRV240, to verify your meter is working properly. This is an NFPA70E (U.S.) and GS38 (Europe) requirement.

Working with electricity always carries a risk. Know what those hazards are and take the appropriate precautions before you begin taking any measurements. Be aware of the possibility of spikes like transient overvoltage and arc flashes or arc blasts.

1. Always assume every electrical component in a circuit is energized until you’ve taken the steps to positively discharge it. Shock occurs when the human body becomes part of an electrical circuit; be cognizant of body positioning when working in electrical environments.
2. Be sure to use the correct personal protective equipment (PPE) in each and every situation. This means both on-body (i.e. gloves, headwear) and near-body (i.e. insulated rubber mats). They’re required when working on, or near, energized and exposed electrical circuits greater than 50 V.
3. Never work alone when working on, or near, exposed and energized equipment. Stay safe and make sure you and your partner are aware of your environment, as well. If possible, don’t take measurements in humid or damp environments and make sure there are no atmospheric hazards around you (i.e. flammable dust or vapor).
4. Finally, watch your digital multimeter’s display for any visual warnings. It can alert users to irregularities such as unsafe voltages (30 V or greater) at the test probes.

Related Resources

• 7 Essential tools for Electricians
• Safe Isolation Procedures for Low-Voltage Installations
• Preparing Fluke Tools for Real-World use
• How a few good test tools saved motor replacements at a pulp and paper company

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