Flexible Cords & Flexible Cables

Article 400 covers the flexible cords and cables that connect movable equipment — the SO, SJO, SPT and similar types, with a big table of constructions, insulations and ampacities. It tells you which cord is rated for hard usage, wet locations or extra-hard service.

Its most important message is what cord may NOT do: it can't substitute for the fixed wiring of a structure, can't run through walls, ceilings or floors, and can't be concealed or attached to building surfaces as permanent wiring. Cord is for flexibility and disconnection, not to save the cost of a proper circuit.

When it applies

Article 400 covers flexible cords and cables like SO, SJ, and SPT. The core idea is that flexible cord is for things that move, vibrate, or need frequent disconnection, not as a substitute for fixed building wiring.

Common mistakes

• Using cord as permanent wiring, running it through walls or ceilings in place of a raceway. That is a classic violation.
• Sizing the cord for the load but ignoring the ampacity reduction when conductors are bundled or the cord is long.
• Leaving a cord unprotected where it passes through an opening and letting the edge chafe the jacket.

In the field

In a plant I found extension cord stapled along a wall feeding a permanently mounted machine, run right through a knockout. That cord was doing a raceway's job and the jacket was already worn at the metal edge. I pulled it out and ran proper conduit to the machine. Flexible cord earns its place where equipment actually flexes or gets unplugged; bolt something down and it deserves real wiring.