Special Occupancies & Hazardous Locations Flashcards

Under the NEC zone system, which zone describes a location where ignitable gas concentrations are present continuously or for long periods?

Answer: Zone 0

Zone 0 covers ignitable concentrations of flammable gases or vapors present continuously or for long periods (Article 505).

In a Class I, Division 1 location, a conduit seal for an enclosure containing arcing devices must be located no more than what distance from the enclosure?

Answer: 18 in. (450 mm)

NEC 501.15(A)(1) requires the seal within 18 in. (450 mm) of the enclosure.

Threaded rigid metal conduit joints in Class I, Division 1 locations must be made up wrenchtight with at least how many fully engaged threads?

Answer: Five

NEC 500.8(E) requires NPT threaded entries and conduit to have at least five full threads fully engaged.

Which Class II group covers atmospheres containing combustible metal dusts such as aluminum or magnesium?

Answer: Group E

Group E is assigned to combustible metal dusts in Class II locations.

A cotton gin where easily ignitible fibers are handled would most likely be classified as which class?

Answer: Class III

Class III locations involve ignitible fibers or flyings, such as those in textile mills and cotton gins.

The thickness of sealing compound in a completed Class I seal must be at least the trade size of the fitting but never less than what minimum?

Answer: 5/8 in. (16 mm)

NEC 501.15(C)(3) sets a 16 mm (5/8 in.) minimum compound thickness.

In a major repair garage where Class I liquids are transferred, the floor area is generally classified Class I, Division 2 up to what height above the floor?

Answer: 18 in. (450 mm)

NEC 511.3 classifies the area up to 450 mm (18 in.) above the floor as Class I, Division 2.