The proving unit: an essential tool for safer working 

Recent industry research revealed that 86% of electrical professionals have experienced an ‘electrical incident’ at work and it’s just part of a wider picture of many electrical incidents and near misses among UK electrical professionals. Because electricity can be an unseen danger, a proper safe isolation procedure is essential for anyone working on or near electrical systems. From the survey, over 86% of the participants stated they were very familiar with safe isolation procedures but only 55% always follow the full procedure before starting work.

Effective safe isolation prevents accidental contact with live parts, protecting both workers and anyone else nearby, by ensuring all relevant circuits and equipment are fully de-energised before work begins. Correct safe isolation procedures are critical to ensure the protection of you, your teams and others.

Proving dead 

Part of the safe isolation process includes proving the conductors are dead where the work is taking place, before the task starts. A fully compliant voltage indicator should be used and should itself be proved, before and immediately after testing the conductor.

The established procedure for proving dead is to take the voltage indicator or tester being used to prove dead, check it against a known source, then test the circuit, and then test the voltage indicator against the known source again to prove the tester has not failed during testing.

Live source or proving unit?

Whilst it is possible to use a known live source to test a voltage indicator, a much safer method is to use a dedicated proving unit matched to the indicator being used. The reasons for this are twofold. Firstly, there may not be a suitable known source available at the point where the work is being undertaken, which could potentially encourage shortcuts to be made on safety. Secondly, a live source may only light some of the LEDs on a voltage indicator, whereas a proving unit will ensure that all LEDs on all ranges are working, safeguarding against incorrect readings due to a fault.

Growing need for DC

Additionally, electrical workers are encountering more and more DC systems, particularly when working within renewable industries, solar installations, battery systems and electric vehicle charging, to name a few. The need to check the correct DC operation of measurement and indication testing devices used in these applications is therefore increasing. Confirming the correct operation not only helps reassure the user of correct functionality but can also assist with implementing safe working practices within a DC environment.

Advanced proving units – AC & DC

Historically, standard proving units were simple single output AC or DC sources. Whilst useable for simple indicators, the flexibility of range checking indication or the ability to switch between AC and DC were not available. The latest advanced proving devices provide a higher level of output to thoroughly check a wide range of safe isolation applications.

The Martindale SRD series, for example, are fast and easy to use; they instantly supply the test voltage for both high and low impedance voltage indicators, test lamps and meters. The units have AC/DC outputs selectable by a push button switch and stepped voltage output, matched to two-pole tester thresholds with three maximum output voltages across the range: 230V, 440V and 690V. It’s good practice to match the output voltage of the proving unit with the voltage range of the instrument to be proved so as not to ‘over prove’ with too high a voltage.

In addition, the Martindale PD440SRDX has a unique CALCHECK feature, making it easy to verify insulation and low-resistance ranges on 18th Edition multifunction testers wherever you are working. This makes it ideal for identifying potential calibration issues with a multifunction tester prior to certifying a new wiring installation or carrying out a condition report. It is also a valuable procedure recognised by electrical contractor assessment bodies.

Keeping safe

By incorporating a proving device into an electrical safety process, that process becomes inherently more robust and reliable. Although a relatively straightforward addition, when working with or near electrical systems and equipment, a proving device can significantly reduce the risk of electrical injury.

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