A conduit run needs to be installed in a hazardous location where ignitable concentrations of flammable gases or vapours are present continuously, intermittently, or periodically. Assuming the location is indoors and subject to chemical fumes, what is the minimum trade size (metric designator) of rigid metal conduit (RMC) that must be used for a new 120 V, 10 A motor circuit, if the conduit is to be sealed within 450 mm (18 in) of an enclosure containing arcing parts, according to CEC Rule 18-102(1)?

Question: A conduit run needs to be installed in a hazardous location where ignitable concentrations of flammable gases or vapours are present continuously, intermittently, or periodically. Assuming the location is indoors and subject to chemical fumes, what is the minimum trade size (metric designator) of rigid metal conduit (RMC) that must be used for a new 120 V, 10 A motor circuit, if the conduit is to be sealed within 450 mm (18 in) of an enclosure containing arcing parts, according to CEC Rule 18-102(1)?

Answer options:

• Metric Designator 16 (1/2 in) ✅ Metric Designator 21 (3/4 in)
• Metric Designator 27 (1 in)
• Metric Designator 35 (1 1/4 in)

Correct answer: Metric Designator 21 (3/4 in)

Explanation: Rule 18-102(1) specifies that fixed wiring shall be installed in rigid metal conduit of a minimum trade size Metric Designator 21 (3/4 in) in Class I, Zone 1 hazardous locations, even for circuits that might otherwise permit smaller conduit sizes. This rule prioritizes the integrity and explosion-proof nature of the wiring method in such environments.