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I need to replace a damaged 120V-12V transformer that is a European sourced Comelit Model 542012/A, also marked as "Class 2 Transformer" supplying power to a halogen table lamp. My question is what is the meaning/importance of the "Class 2" designation?

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Class 2 refers to a transformer that delivers 100VA or less with a maximum output voltage of \$30\text{V}_\text{AC}\text{ }\$ or less. Class 2 transformers are limited, either by inherent winding impedance or external fusing, to power levels considered safe enough to receive special consideration in safety requirement compliance.

They are covered by standard UL 5085-3, for which UL will be glad to take your money (link is summary only).

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Class II transformers are specifically different in the sense that it's a low energy device - its secondary windings impedance is inherently higher thus its inductive reactance limits available current to its load.

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Class 2 devices are also called "double-insulated"; it is safe to use equipment with such transformers even if a protective ground is not also present. So, most two-prong plug power bricks are Class 2. This allows a two-wire cord from the power brick to the desk lamp, and the desk lamp need not have a ground connection either.

A Class 2 electric drill might completely lack metal enclosure parts, and have a two-prong AC power plug, while a three-prong AC power plug is used for a non-Class 2 drill.

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