Continuous-Load OCPD and Conductor at 125% (NEC 210.20 / 215.3)
The single most reused NEC sizing step, standalone.
Example
You enter
- Continuous load (A, on 3 hours or more) 40
- Noncontinuous load (A) 20
- Device and assembly rating false
You get
- Minimum OCPD and conductor ampacity 70
- Overcurrent device (240.6(A)) 70
Checked against published worked examples from: EC&M.
Details, formula, and sources
ScopeThe breaker and minimum conductor for a mixed load are 125% of the continuous part (on 3 hours or more) plus 100% of the rest, rounded up to a 240.6(A) standard rating. 40 A continuous + 20 A noncontinuous -> 70 A minimum -> a 70 A device; a listed 100%-rated assembly drops the factor and one device size. Before ampacity adjustment; the motor, HVAC, and welder articles carry their own percentages. A design aid; the AHJ governs.
Formula or tablemult = rated_100 ? 1.00 : 1.25; A_min = mult x l_cont_A + l_noncont_A; ocpd_A = smallest NEC 240.6(A) standard rating >= A_min.
Source and editionThe continuous-load overcurrent and conductor rule of NEC 2023 210.20(A) (branch) / 215.3 (feeder) and 210.19(A) / 215.2(A) -- 125% of the continuous plus 100% of the noncontinuous load, device from the 240.6(A) standard ratings, with the 100%-rated-assembly exception -- by name. A computational aid; the AHJ-adopted NEC edition governs.
Free accessNEC is free to read at nfpa.org/freeaccess. The ampacity-adjustment, termination-limit, 240.4(B), and equipment-specific (430/440/630) rules are stated as out of scope, not modeled.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesl_cont_A, l_noncont_A, rated_100, A_min, ocpd_A
- Continuous load a load at its maximum current for 3 hours or more takes the 125% factor; a listed 100%-rated device-and-assembly drops it to 100%NEC 210.20(A) / 215.3
- Device selection the smallest 240.6(A) standard ampere rating at or above the computed minimumNEC 240.6(A)
- Conductor the conductor's pre-adjustment ampacity must also meet the same 125% + 100% sumNEC 210.19(A) / 215.2(A)