National Electrical Code Articles and Information
National Electrical Code Top Ten Tips: Article 240 -- Overcurrent Protection
by Mark Lamendola
Based on the 2023 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. Note that with the 2023 revision, Article 245 was added. Basically, the parts of Article 240 that apply to systems rated over 1000VAC or 1500VDC were pulled out of Article 240 and put into Article 245. Why it isn't Article 241 is unclear, perhaps that will change with the 2026 NEC.
- 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 do that you use Overcurrent Protection
- General background: Article 240, consisting of
eight parts (nine parts up through the 2020 revision, see note above this list), 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
ground fault. Exactly how it defines either one is why we have different OCPDs for different applications.
- 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. Again, we have different OCPDs for different applications. And for motors, this condition (called "overload") is handled separately from equipment protection (from a short-circuit or ground fault) due to inrush current. More on that in a moment.
- 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 Part II. To size motor and branch-circuit overload protection, see Part III. To size motor branch-circuit
protection, see Part IV; pay attention to 240.6(A), 430.52(C), and Table 430.52(C)(1) .
- 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