How to Safely Operate a Multimeter

The most common item of electrical test equipment is multimeters, which are able to measure a wide array of variables including current, resistance and voltage, but use by inexperienced or careless users could result in electrical accidents.

The efficient and safe use of a multimeter is one of the most important skills that an electrician or technician can have.

The main cause of electrical accidents is carelessness, and multimeter safety precautions need to be followed by all users, no matter how skilled or experienced.

For a great range of multimeters, see RS Components.

Voltage measuring

It is important to know the quantity you intend to measure and to avoid placing the test lead in the wrong socket to prevent electric shock. You should also be aware of the voltage you intend to measure.

If you measure AC voltage the probe tips should not touch each other while they remain connected to their respective electrical circuit points in order to avoid the circuit shorting out, which could result in fire.

Test leads should not be used if the probes or leads come with protective insulation that appears worn or cracked. The probe conductor may touch your fingers and cause a bad shock.

When an electric shock happens, the most dangerous moment is when current moves from one hand to another. Use just one hand when possible to hold onto the probe or latch its tip to the circuit’s test point so the other can be held and set in place by your other hand.

AC and DC voltage are both dangerous, and a multimeter should be used to check for both.

Resistance measuring

It is much easier to use a multimeter to measure resistance. The probes need to be placed in the right sockets, after which you just turn the selector switch to Ω and have the probes touched across the electrical device you are measuring to display the meter readings.

Keep in mind that measuring resistance should only be done with a de-energized component as a small internal battery is used by a meter in resistant mode in order to move small current through the very components you want to measure. The meter will record and display the difficulty of that current movement through the component as resistance.

Faulty readings could result from an energized circuit or extra source of voltage, but only the meter would risk damage.

Current measurement

This is the most complicated and dangerous way to use a multimeter, as the current that needs to be read has to be forced through it, making it part of the current circuit path.

To do this the original circuit has to be broken and the meter connected via the two open break points. Use the selector switch to set the meter to either AC or DC and plug the red test lead into the A socket. The circuit then needs to be broken and the multimeter probes connected to those broken ends.

This can be very dangerous with high power circuits, and even low voltage can cause sparks.

Failing to remove the multimeter from current measuring mode before trying to measure voltage can also cause electrical accidents.

Clear thinking and obeying the required safety precautions are crucial for the safe operation of a digital multimeter.