Several Type NM cables enter a flush-mounted panelboard cabinet through knockouts in its side. What does the Code require of those cables at the cabinet?
- ACables may enter through open knockouts provided each one is stapled within 12 inches of the cabinet
Stapling the cable nearby does not satisfy a rule that requires the cable to be secured to the enclosure. An open knockout also leaves an unclosed opening in the cabinet.
- BOne connector may serve as many cables as the knockout will physically allow to pass through it
Connectors are listed for a stated number and size of cables. Forcing extra cables through one fitting voids the listing and crushes the cable jackets.
- Each cable must be secured to the cabinet with a fitting identified for use with that cable type
- DCables need to be secured only where the cabinet is surface mounted rather than flush mounted
The general rule applies to flush and surface enclosures alike. The narrow exception that mentions surface mounting has several further conditions and is not a blanket relief.
Why C is correct
The rule ties the cable to the enclosure itself, not merely to nearby framing. Securing the cable at the cabinet keeps mechanical strain off the terminations inside and keeps the cable from moving through a sharp-edged knockout. Connectors are listed by cable type and by the number of cables they accept, so a fitting rated for one cable holds one cable.
What this question is testing
The item tests whether the candidate knows that the securing obligation runs to the enclosure itself, and whether a commonly quoted exception is being over-applied.
On the job
Old panels routinely have three or four cables jammed into one connector, or cables run through bare knockouts with no fitting at all. Both are cited on service change inspections. The practical fix is either one listed connector per cable or a fitting listed for multiple cables, and there are plenty of the latter. The rule also matters for cable movement: a cable that can slide in and out of the cabinet eventually wears through its jacket on the knockout edge.
Memory technique
Every cable gets a fitting, and the fitting grabs the cabinet.
Exam tip
When an exception mentions surface mounting, check every other condition attached to it before relying on it.
Where to look it up
Look at the cabinets and cutout boxes article, in the section on cables entering enclosures.