Blanking Plug
A blanking plug is the element that closes an unused hole in an enclosure or connector housing together with its gasket. A single hole left open effectively cancels the dust and water protection of the enclosure; the moisture that gets in condenses and creates corrosion and leakage paths on the board.
The protection rating is set by the weakest point of the housing. An enclosure in which five of six entries are perfectly glanded and one is left empty has the same protection as an enclosure with no glands at all. Tape, a bung or silicone sealant is not a permanent solution; thermal cycling and vibration open them up in a short time.
- The right plug: a gasketed plug matching the thread size of the hole and compatible with the housing material is selected.
- Metal and plastic: a metal plug in a metal housing provides both sealing and electrical continuity.
- Holes drilled later: every hole opened during field installation is either glanded or plugged; burrs are removed and the edge is cleaned.
Before handing over the installation, inspect the enclosures from below and from the sides and confirm that no empty hole is left. The same rule applies to connectors: when unused pin cavities are not closed with blanking plugs, water gets inside the housing and creates leakage between neighbouring pins.
Context in which this term is used: Installation, redundancy and field continuity