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A small square inside a larger square — IEC 60417-5172, marking equipment protected by double or reinforced insulation rather than an earth connection.
Also known as: Double insulation symbol, Double square symbol, IEC 60417-5172, Double insulated symbol
Marks Class II equipment: protection against electric shock comes from double or reinforced insulation, so the appliance needs no protective earth connection. Commonly seen on power tools and small appliances with two-pin plugs.
Marks Class II equipment, in which protection against electric shock relies on double or reinforced insulation rather than on a protective earth connection — which is why such appliances may be supplied with a two-pin plug.
Contexts: Electrical equipment
The outer square is conventionally about twice the side length of the inner square, with a stated minimum size so the marking stays legible on small appliances.
Proportions and minimum dimensions come from a manufacturer's technical explainer summarising the standard, not from the paywalled standard text itself.
Contexts: Electrical equipment
Two concentric squares: a smaller square centred inside a larger one, with a clear gap between them.
Opposite protection strategies on the same rating plate: the double square means no earth connection is needed, while the earth symbol marks the terminal that must be connected.