Quick Hits

Episode 6 — Standard Ratings and Adjustable-Trip Breakers

Covers: 240.6

Hook: Ever wonder why breakers come in 15, 20, 30, 40, 50... and not, say, 37? Here's the standard sizing table and the rules for adjustable ones.

Slide 2: Standard fuse/inverse-time breaker sizes run from 10A up through 6000A in fixed steps (with 1, 3, 6, and 601A as extra standard fuse sizes) — nonstandard sizes are still allowed too. Adjustable-trip breakers with external adjustment access are rated at their maximum possible setting by default.

Slide 3: That changes if access to the adjustment is restricted — behind sealable covers, bolted doors, locked doors for qualified personnel only, or password protection — in which case the breaker can be rated at its actual set point instead of its max. Remotely adjustable breakers get the same allowance, but only with both local restricted access AND a secure remote connection method (direct nonnetworked interface, or a networked interface with documented cybersecurity evaluation).

Quiz: By default, what's the ampere rating of an adjustable-trip circuit breaker with unrestricted access to its adjustment?
Answer: Its maximum possible setting.

CTA: Follow — OCPD types, parallel fuses, and supplementary protection are next.

← View Chapter 2 Home

← Back To Article 240 Home

← Back To Quick Hits Home