During an inspection, a journeyperson notes that a 20 A branch circuit supplying a lighting load in a suspended ceiling space of a commercial building is installed using open wiring methods. The conductors are 12 AWG T90 nylon, neatly run and strapped, but not enclosed in conduit or cable. Under what conditions is this wiring method generally NOT permitted in a commercial building according to the CEC?

Question: During an inspection, a journeyperson notes that a 20 A branch circuit supplying a lighting load in a suspended ceiling space of a commercial building is installed using open wiring methods. The conductors are 12 AWG T90 nylon, neatly run and strapped, but not enclosed in conduit or cable. Under what conditions is this wiring method generally NOT permitted in a commercial building according to the CEC?

Answer options:

• When the conductors are copper
• When the ceiling space is not used as a plenum
• When the voltage is 120 V ✅ As a rule, open wiring is not permitted for branch circuits in commercial suspended ceiling spaces.

Correct answer: As a rule, open wiring is not permitted for branch circuits in commercial suspended ceiling spaces.

Explanation: CEC Rule 12-100 states that open wiring is not permitted in commercial, industrial, or institutional buildings, except in certain specific, usually temporary, agricultural, or exposed industrial applications. For typical branch circuits in commercial suspended ceiling spaces, enclosed wiring methods like EMT, AC90, or conduit systems are mandatory.