Guard terminal
Updated 2026-10-27
Data records
- A guard terminal is a third connection on an insulation resistance tester that provides a return path for surface leakage current which bypasses the measuring circuit, so that the reading reflects the current through the insulating material alone. It is connected to a conductive band or bare wire wrapped around the insulation between the two measuring connections.
- A maker's article on insulation testing describes the guard terminal as a third connection to the asset under test that provides a return path for surface leakage current, so that the instrument measures only the leakage current through the insulating material rather than the sum of the two. It notes that a test made with the guard and one made without it, when the readings differ greatly, show that surface contamination rather than degradation of the insulation is the cause of a low reading.
Sources
- Electrical Testing Reference editorial taxonomy, Electrical Testing Reference editorial taxonomy of test methods, 2026-10 edition, Electrical Testing Reference. Held as: Own observation.
- Megger Electrical Tester article, The importance of the guard terminal in insulation testing, Electrical Tester, 1 April 2019 edition, Megger. Held as: Public page. Publisher page
Changelog (4 entries)
| Date | Revision | Change |
|---|---|---|
| 2026-10-27 | created (gloss.guard-terminal.definition) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (gloss.guard-terminal.definition) | |
| 2026-10-27 | created (gloss.guard-terminal.usage) | |
| 2026-10-27 | review_status unreviewed -> software_reviewed (gloss.guard-terminal.usage) |
Cite this page
Cite the governing standard for the fact itself; cite this page as the finding aid.
"Guard terminal." Test Instrument Reference. 2026-10-27. https://www.testinstrumentreference.com/glossary/guard-terminal/.
Test Instrument Reference, Guard terminal (Oct. 27, 2026), https://www.testinstrumentreference.com/glossary/guard-terminal/.
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title = {Guard terminal},
howpublished = {\url{https://www.testinstrumentreference.com/glossary/guard-terminal/}},
organization = {Test Instrument Reference},
publisher = {Test Instrument Reference},
year = {2026},
note = {last substantive change 2026-10-27}
}{{cite web |title=Guard terminal |website=Test Instrument Reference |publisher=Test Instrument Reference |url=https://www.testinstrumentreference.com/glossary/guard-terminal/ |date=2026-10-27 |access-date=}}