Which UL Standard is required to be used by qualified electrical testing laboratories to evaluate snap switches for electrical safety?

• A. UL 20
• B. UL 50
• C. UL 489
• D. UL 105

Answer: (A)

Evaluating snap switches for electrical safety relies on a standard that specifically covers switches. UL 20 defines safety requirements for electrical switches and provides the testing criteria labs use to verify performance, insulation, mechanical endurance, and electrical ratings so the switches operate safely in their intended applications. The other standards address different equipment: UL 50 deals with enclosures for electrical equipment, UL 489 covers industrial control equipment like circuit breakers and controllers, and UL 105 covers other kinds of electrical devices not specific to general switches. So UL 20 is the appropriate standard because it directly targets switches such as snap-action types and the safety tests they must pass.