Singer 3333 Instruction Manual page 5

INTRODUCTION
Important Safety Instructions
SERVICING OF DOUBLE INSULATED
PRODUCTS
In a double-insulated product, two systems of insulation are provided instead
of grounding. No ground means is provided on a double-insulated product, nor
should a means for grounding be added to the product. Servicing of a double-
insulated product requires extreme care and knowledge of the system and
a double-insulated product must be identical to those parts in the product. A
double-insulated product is marked with the words "DOUBLE INSULATION" or
"DOUBLE INSULATED".
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