CEA Wiring Methods & Installation Practices 5 — Questions and Answers
Question 1: What must be done when Type NM cable passes through a metal knockout in a box?
- No special treatment is required
- A cable clamp or connector listed for NM cable must be used (Correct answer)
- The knockout must be covered with electrical tape
- The cable must be converted to conduit at the box
Correct answer: A cable clamp or connector listed for NM cable must be used
A listed cable clamp or connector must be used when Type NM cable passes through a metal knockout to prevent the sharp metal edges from damaging the insulation.
Question 2: Intermediate metal conduit (IMC) offers which advantage over rigid metal conduit (RMC)?
- IMC has greater corrosion resistance than RMC
- IMC is lighter and thinner-walled than RMC while still being suitable for most applications (Correct answer)
- IMC allows higher fill percentages than RMC
- IMC is listed for direct burial without corrosion protection
Correct answer: IMC is lighter and thinner-walled than RMC while still being suitable for most applications
IMC has thinner walls than RMC, making it lighter and easier to handle while still approved for use in most locations where RMC is required.
Question 3: Where is Type NM cable specifically prohibited by the NEC?
- In one-family dwellings built before 1978
- In structures over three floors above grade or in commercial/industrial occupancies where exposed (Correct answer)
- In garages and attics of residential buildings
- Where more than three circuits share the same cable path
Correct answer: In structures over three floors above grade or in commercial/industrial occupancies where exposed
Type NM cable is prohibited in structures exceeding three floors above grade and in most commercial or industrial occupancies, where it would be exposed.
Question 4: When pulling wire through conduit, what substance is approved as a pulling lubricant?
- Petroleum-based grease
- Wire-pulling compound specifically listed for use with conductor insulation (Correct answer)
- WD-40 or similar penetrating oil
- Vegetable oil
Correct answer: Wire-pulling compound specifically listed for use with conductor insulation
Only listed wire-pulling compounds (wire lubricants) that are compatible with conductor insulation should be used; petroleum products can degrade thermoplastic insulation.
Question 5: What is the minimum radius for a bend in 2-inch rigid metal conduit (RMC)?
- 8 inches
- 12 inches (Correct answer)
- 15 inches
- 20 inches
Correct answer: 12 inches
NEC Table 2 specifies that 2-inch RMC requires a minimum inner edge bend radius of 12 inches to prevent conductor insulation damage during installation.
Question 6: Electrical metallic tubing (EMT) is not permitted in which location?
- Dry indoor locations
- Where subject to severe physical damage (Correct answer)
- Exposed in commercial buildings
- In concrete that is not subject to permanent moisture
Correct answer: Where subject to severe physical damage
EMT is not permitted where it is subject to severe physical damage because its thin walls do not provide adequate protection for conductors.
Question 7: When installing conduit in a hazardous location, sealing fittings (seals) must be installed within how many inches of an enclosure boundary?
- 12 inches
- 18 inches (Correct answer)
- 24 inches
- 36 inches
Correct answer: 18 inches
In Class I hazardous locations, conduit seals must be installed within 18 inches of enclosures to prevent flammable gases from traveling through the conduit system.
CEA Wiring Methods & Installation Practices 5
What must be done when Type NM cable passes through a metal knockout in a box?