Double square (Class II, double insulated)
Class II equipment: the maker says the live parts are protected by extra (double or reinforced) insulation instead of an earth connection, so the appliance does not need an earth to remain safe. The HSE gives hand-held equipment such as hair-dryers as items that are usually built this way.
Symbol reference: IEC 60417-5172
A mark tells you what the maker declares, never that the product is safe.
- What it looks like
- A small square centred inside a larger square, drawn in outline. It sits among the technical data, not beside the brand name.
- Who may apply it
- The manufacturer, for equipment built to the Class II requirements of IEC 61140. The IEC entry says the symbol must be placed so it is obviously part of the technical information and cannot be confused with the maker’s name.
What it does not promise
It does not make damaged equipment safe: the UK Health and Safety Executive points out that the casing is a key safety feature, so cracks and damage still matter. It is not a lab listing either. OSHA, for example, also wants a recognised testing laboratory’s mark on double-insulated power tools. If the symbol is missing, the HSE says to assume the item is Class I (earthed).
Other marks with the same shapes
Sources
Each page below was fetched and read on the date shown. Where a symbol’s IEC 60417 or ISO 7000 number is given, a public page listing that number is among them.
- Wikimedia Commons: File page transcribing IEC 60417 entry 5172 (title, function, publication) — Symbol 5172 from IEC 60417, “Class II equipment”: to identify equipment meeting the safety requirements for Class II according to IEC 61140; the double-square must be positioned so it is part of the technical information. Checked 2026-09-24.
- Health and Safety Executive (UK): INDG236 — Maintaining portable electrical equipment in low-risk environments (PDF) — Class II (double insulated) has extra insulation “to prevent accidental contact with live parts, even if there is a fault” and “does not need an earth connection”; casing integrity is key; “If you cannot see this symbol, you should assume that the item is a Class I appliance”. Checked 2026-09-24.
- US Occupational Safety and Health Administration: Letter of interpretation: marking recognition, regulations and policy of double insulated power tools (1985) — Double-insulated tools use “a special insulating system in lieu of a grounding means”, marked with “a square within a square”; OSHA also expects the listing mark of a nationally recognised laboratory. Checked 2026-09-24.
Written in our own words; quotations are the sources’ wording.