National Electrical Code Top Ten Tips: Article 240 -- Overcurrent Protection
by Mark Lamendola
Based on the 2020 NEC.
Please note, we do quote from copyrighted material. While the NFPA
does allow such quotes, it does so only for the purposes of education
regarding the National Electrical Code. This article is not a substitute
for the NEC.
These are the 10 NEC Article 240 items we deem most important, based
on the pervasiveness of confusion and the potential costs of same.
- General philosophy: Providing overcurrent
protection isn't just a matter of selecting a fuse or breaker from a
table. When current exceeds the rating of conductors or
equipment—due to overload, short circuit, or ground fault—you
have overcurrent. This is what you must protect conductors and
equipment and equipment against, and to to that you use Overcurrent Protection
- General background: Article 240, consisting of
nine parts, provides the requirements for selecting and installing
- General concept of equipment protection. To
protect equipment, an OCPD opens when it detects a short-circuit or
- General concept of circuit protection. To
protect a circuit, an OCPD opens when current reaches a value that
will cause an excessive temperature rise in conductors.
- The Tables in Chapter 3 provide the ampacities you must
use for selecting conductors for a given load. Please note the
- Motor overload protection and motor circuit
protection are not the same thing. See the table at the beginning of
Article 430. To size motor branch-circuit conductors, see Table
310.16, 430.22, and Table 430.150. To size motor branch-circuit
protection, see 240.6(A), 430.52(C), and Table 430.150.
- Install an OCPD in series with each ungrounded
conductor [240.21]. Since the neutral is typically the grounded conductor (at higher voltages, it might not be), you don't install an OCPD there. And you don't install an OCPD in a grounding conductor because it's grounded.
- Location, location, location. Locate OCPDs (and other electrical equipment) to
prevent exposure to physical damage [110.27(B)]--but do so in a way
that leaves those OCPDs readily accessible [240.24].
- For fuse requirements, see 240.50 through
- For breaker requirements, see 240.80 through