Smaller, lighter and with new options for calibration checking test equipment, Martindale’s PDSX proving units not only give your confidence in safety critical voltage measurements, they can also be used to validate the performance of 18th Edition multifunction testers.

The added CALCHECK functionality of the SX models is ideal for identifying potential calibration issues with test equipment prior to certifying a new wiring installation or carrying out a condition report. This is a valuable procedure recognised by electrical contractor assessment bodies to ensure reliable results and avoid unnecessary and expensive retests.

Easily accessible low Ohm and insulation resistance test pads

The four nominal resistance values of 0.5Ω, 1.0Ω, 0.5MΩ, 1.0MΩ built-in to the new design make it easy to check the calibration consistency of insulation and low resistance ranges on installation testers at any time between annual calibrations. The resistance values have been set to identify potential calibration issues in the ranges which could lead to an incorrect pass or fail result when certifying an installation. The resistance pads on top of the proving units are clearly labelled and easily accessible with standard test leads, ideal for on-site use.

There’s a handy table supplied with the proving unit too, making it easy to record CALCHECK results on a regular basis and identify any changes. This can provide an early warning that it may be time for a recalibration of the tester before it’s too late.

Proving a Martindale VT25 two pole voltage tester


When carrying out safe isolation procedures, the proving unit functionality of the PDSX Series makes it easy to prove that voltage indicators, two pole testers and test lamps are functioning correctly before and after being used to prove circuits are dead, essential for compliance with Electricity at Work Regulations. Fast and easy to use, the proving units immediately supply the full test voltage on contact and then step down through common two pole tester LED voltage thresholds from 690V to 50V, ideal for identifying potential voltage tester calibration issues. On completion of the voltage test the PDSX Series also carries out a continuity test for two pole testers, by presenting a low resistance across the terminals.

The unique combination of proving unit and calibration checker in a new compact design now means it’s easy to stay safe and have confidence in all your essential test equipment wherever you are working.

Click here to see the full range of proving units.