Martindale Electric recently introduced four new proving units into its industry-leading range. The company now offers the widest range of proving units on the market. One key model, the PD440SRDX, features two important tools for both electricians and electrical contractors combined in a single unit. Firstly, a fully functioned 440V proving unit and, in addition, a checkbox tool for use when checking insulation and continuity ranges on installation testers.

In accordance with the electricity at work regulations, safe electrical working requires the use of a voltage indicator that has been proven with a suitable proving device before and after use, to ensure the indicating instrument is working correctly. The PD440SRDX is an ideal solution, fast and easy to use, instantly supplying the test voltage for both high and low-impedance voltage indicators, test lamps and meters. The unit has both AC & DC outputs selectable by a push button switch for maximum flexibility and stepped voltage output, which is matched to two-pole tester thresholds up to 440V.

For the checkbox type function, the PD440SRDX includes the unique CALCHECK feature, offering a quick and simple method to ensure the ongoing accuracy of your installation testers in between the standard, usually yearly, calibration.

The CALCHECK feature is used to check that a multifunction tester, insulation tester or continuity tester is maintaining ongoing accuracy. There are two insulation test resistance values, 0.5MΩ and 1MΩ, and two continuity test resistance values, 0.5Ω and 1Ω. Checking is easy, and the user simply places one probe of the tester being checked on the desired resistance value and the other probe on the common terminal, and a measurement is taken (following the installation tester’s instruction manual).

The PD440SRDX can, therefore, be used to regularly check that instruments are not drifting in between the yearly calibration cycle. Initial resistance measurements need to be taken as soon as possible after a standard calibration and record these results. Further checks can then be made periodically, for example, every month, and the results recorded to check for drift from the initial measurements. Martindale supplies a CALCHECK verification measurement sheet, so records can easily be kept of the values. Extra copies of the sheet can be downloaded from

With all the benefits of the industry standard Martindale proving units, the PD440SRDX is fast and easy to use with long battery life, low battery indicator, auto power off and an over-moulded low-profile case with magnetic hanger. In addition, it can help verify insulation and low resistance ranges on 18th Edition multifunction and single-function testers. Wherever you are working, the PD440SRDX is ideal for identifying potential calibration issues 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 protect the installation tester, the 440V maximum output from the proving unit ensures that the installation tester cannot be damaged by “over proving”, as most testers have a 500V maximum input voltage specification and the use of 690V proving units is not recommended.