Martindale PD440S Proving Unit

Martindale PD440S Proving Unit

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Martindale PD440SX 440V Proving Unit with CALCHECK

£123.60 £103.00
Availability: In stock
Martindale PD440SX 440V Proving Unit with CALCHECK

Ideal for proving low and high impedance voltage indicators, test lamps and two pole testers for safe isolation and calibration checking.

Comes complete with a calibration Certificate Traceable to National Standards when purchased new.

Martindale PD440SX 50V/120V/230V/440V AC Proving Unit with CALCHECK

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 instrument is working correctly in accordance with the Electricity at Work Regulations.

The PD440SX proving unit output voltages are stepped with individual LED indicators for each voltage threshold from 50V to 440V matched to common two pole tester thresholds, ideal for identifying potential voltage tester calibration issues. On contact, it outputs the highest voltage first instantaneously checking all LEDs up to 440V and confirming the tester for safe isolation use, it then steps down through each level automatically. At the end of the test, a low resistance appears across the terminals to verify the continuity function of two pole testers.

It’s good practice to match the output voltage of the proving unit with the voltage range of the instrument to be proved.

The PD440SX has a CALCHECK feature for use to verify the insulation and low resistance ranges on 18th Edition multifunction instruments and single function insulation testers on-site, making 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’s also a valuable procedure recognised by electrical contractor assessment bodies.

It’s easy to keep a record of periodic CALCHECK results and equipment serial numbers for assessments using the form in the user guide or downloading copies from this page.  The individual reference resistance test pads with nominal values of 0.5Ωand 1.0Ω for continuity measurements and 0.5MΩ and 1.0MΩ for insulation resistance make it simple to check and identify calibration drift and remain confident in your test results wherever you are working.


  • Maximum voltage output 440V AC
  • Stepped voltage output to match two pole tester thresholds
  • LED voltage thresholds 50V, 120V, 230V,440V
  • CALCHECK feature, verify insulation and low resistance ranges on insulation testers
  • High voltage LED
  • Low battery LED
  • Compatible low / high impedance
  • Suitable for multimeters, voltage testers & Drummond test lamps


Output voltage

440/230/100/50V nominal

Output frequency

50Hz nominal

Output loading

See datasheet

CALCHECK insulation test resistance

0.5MΩ (max test voltage 1kV)
1.0MΩ (max test voltage 1kV)

CALCHECK continuity test resistance

0.5Ω (max test current 200mA)
1.0Ω (max test current 200mA)

Temperature (Operating & Storage)

-10°C to 40°C

Humidity (Operating & Storage)

max. 70% R.H.


up to 2000m

Pollution Degree



6 x 1.5V, AA alkaline batteries (IEC LR6, NEDA 15A)


150 x 80 x 35mm


350g approx. with batteries



  • MG3 magnetic hanger
  • 6 x 1.5V AA alkaline batteries
  • Instruction manual

PD440SX proving unit comes complete with a Calibration Certificate Traceable to National Standards when purchased new.

Contact us for further information regarding PD440SX proving unit.

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