What is a Proving Unit?

An electrical proving unit is a device that can be used to verify the measurements taken by voltage testers such as digital multimeters or clamp meters. Made up of two poles, proving units complete this function by testing the instruments against a known voltage, hence proving units are sometimes referred to as known voltage sources.

By using proving units to test both AC and DC instruments, electricians and engineers won’t just verify the accuracy of their measurements but ensure they’re working safely by ensuring no dangerous voltages are passing through circuits or equipment.

This article will explain exactly how proving units work, what their applications are and the advantages of using them for electrical testing.

Each type of proving unit will work in slightly different ways. However, the typical steps for testing a piece of equipment are as follows:

• Plug the testing probes into the device you’re using
• Set the proving unit to AC or DC depending on the device type
• Set the test voltage on the proving unit
• Put the black probe onto the negative terminal and the red probe onto the positive one
• Check the device to see if the voltage matches that on the proving unit
• Depending on the type of device, you may want to test both AC and DC function

By performing this check, you can make sure the device is accurate in measuring voltage. Depending on the specific way you’re using a device, you might want to perform this check multiple times.

Voltage Tester Proving Unit

Otherwise known as a voltage indicator or detector, proving units are mainly used to test electrical devices that measure the power running through circuits. To ensure the tools are measuring voltage accurately and meeting electrical performance standards, calibrating them with proving units is key.

To do this, the proving unit needs to be set to a test voltage and probes need to be placed firmly onto the terminals of the voltage testing device. If the reading is consistent with what has been sent from the proving unit, then that device is working accurately.

The benefits of proving units are that they are lightweight and sturdy enough to be used in a variety of challenging conditions, including as a voltage source up in towers or at junction boxes.

Safe Isolation Proving Unit

Proving units can also be used in combination with electrical testing devices to make sure circuits are actually dead and safe to work on. Once a circuit has been locked off, it’s important that a proving unit is used to calibrate the voltage testing device before it is used to check that there’s no power running through the system.

Then, after the voltage testing device is used to check the circuit, the device should be rechecked with a proving unit. This will ensure that the device hasn’t malfunctioned during testing. By completing this process, electricians or engineers can be sure that the circuit isolation has been done safely and that there’s truly no voltage running through it. This will prevent any arcs or shocks from happening during repairs or installations.

The HSE recommends using voltage indicators rather than multimeters or non-contact voltage detectors, as indicators aren’t as susceptible to human error (such as an electrician selecting the wrong range on a multimeter) or sensitive to other signals (such as non-contact detectors which pick up static).

Proving Unit Calibration

To calibrate a proving unit, it should be taken to a professional. Accredited calibration services will fully reset the device to make sure it’s working as accurately as possible and conforms to the required standards.