Proving unit
Updated 2026-10-27
Data records
- A proving unit of this kind generates an alternating output at the power frequency that simulates the mains supply a voltage tester meets in service.
- A proving unit is a portable battery-operated source that generates a known voltage at its output terminals, so that a two-pole voltage tester can be shown to be working.
- A proving unit gives the worker a known source to test against wherever the work is, so that proving the tester does not depend on finding and touching a live part of the installation.
- Proving units are powered by alkaline batteries or an external low-voltage supply, and a low-battery indicator warns when the output may fall below nominal, so that a good tester is not failed because of a weak source.
- A stepped proving unit switches on when the tester probes are inserted, generates its highest nominal voltage and then ramps down through each lower step, each step indicated by a light, so that each voltage threshold of a two-pole tester can be checked in turn.
- A proving unit with a high output power rating and widely spaced terminals can also prove voltage indicators that use a filament test lamp, which draws more current than an electronic tester; a proving unit built for voltage detectors is not necessarily suitable for proving a multimeter.
Elsewhere in the family
- Energization Checks related entry on Electrical Testing Reference
- Osha qualified person related entry on Electrical Testing Reference
Sources
- Martindale product page, Martindale VT28PD Voltage Indicator and Proving Unit Kit, web page edition, Martindale Electric. Held as: Public page. Publisher page
- Martindale product page, Martindale PD440 440V AC Proving Unit, web page edition, Martindale Electric. Held as: Public page. Publisher page
- Megger product page, MPU690 Proving Unit, web page edition, Megger. Held as: Public page. Publisher page
Changelog (16 entries)
| Date | Revision | Change |
|---|---|---|
| 2026-10-27 | created (instr.proving-unit.alternating-output) | |
| 2026-10-27 | revised (instr.proving-unit.alternating-output) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (instr.proving-unit.alternating-output) | |
| 2026-10-27 | created (instr.proving-unit.definition) | |
| 2026-10-27 | revised (instr.proving-unit.definition) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (instr.proving-unit.definition) | |
| 2026-10-27 | created (instr.proving-unit.known-source-at-the-point-of-work) | |
| 2026-10-27 | revised (instr.proving-unit.known-source-at-the-point-of-work) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (instr.proving-unit.known-source-at-the-point-of-work) | |
| 2026-10-27 | created (instr.proving-unit.power-and-low-battery) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (instr.proving-unit.power-and-low-battery) | |
| 2026-10-27 | created (instr.proving-unit.stepped-output) | |
| 2026-10-27 | revised (instr.proving-unit.stepped-output) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (instr.proving-unit.stepped-output) | |
| 2026-10-27 | created (instr.proving-unit.test-lamps-and-multimeters) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (instr.proving-unit.test-lamps-and-multimeters) |
Cite this page
Cite the governing standard for the fact itself; cite this page as the finding aid.
"Proving unit." Test Instrument Reference. 2026-10-27. https://www.testinstrumentreference.com/instruments/proving-unit/.
Test Instrument Reference, Proving unit (Oct. 27, 2026), https://www.testinstrumentreference.com/instruments/proving-unit/.
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title = {Proving unit},
howpublished = {\url{https://www.testinstrumentreference.com/instruments/proving-unit/}},
organization = {Test Instrument Reference},
publisher = {Test Instrument Reference},
year = {2026},
note = {last substantive change 2026-10-27}
}{{cite web |title=Proving unit |website=Test Instrument Reference |publisher=Test Instrument Reference |url=https://www.testinstrumentreference.com/instruments/proving-unit/ |date=2026-10-27 |access-date=}}