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Class III construction symbol: a square standing on one corner (diamond) with the Roman numeral III in the middle
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Chargers and power adaptersConsumer electronics

Class III construction

A square standing on one corner (diamond) with the Roman numeral III in the middle. · also called “III in a diamond”, “class III”, “protection class III”, “safety class III”

What the Class III construction symbol means

Protection class III construction

Marks a transformer or appliance built to protection class III, as classified in the transformer safety standard EN 61558-1. It is one of the three construction-class marks printed on transformers and power supplies, next to class I (earth symbol in a circle, needs a protective earth) and class II (double square, double insulation).

Source · Official website Noratel transformer symbols and standards reference sheet · checked

Where it appears

Chargers and power adapters
  • EN 61558
    —This meaning

Questions about the Class III construction symbol

What does the Class III construction symbol mean?
Marks a transformer or appliance built to protection class III, as classified in the transformer safety standard EN 61558-1. It is one of the three construction-class marks printed on transformers and power supplies, next to class I (earth symbol in a circle, needs a protective earth) and class II (double square, double insulation).
What does the Class III construction symbol look like?
A square standing on one corner (diamond) with the Roman numeral III in the middle. It is also called “III in a diamond”, “class III”, “protection class III” and “safety class III”.
Which standard defines the Class III construction symbol?
It follows EN 61558.

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