Conductor Short-Circuit Thermal Withstand (Onderdonk / ICEA)
Whether a conductor survives the fault current for the device's clearing time.
Example
You enter
- Conductor area (circular mils) 26240
- Available fault current (A, symmetrical) 10000
- Clearing time (s) 0.1
- Material copper
- Initial temperature (°C) 75
- Insulation short-circuit limit (°C) 250
You get
- Withstand of this size 6313 A
- Minimum size for the fault 41562
Details, formula, and sources
Whether a conductor survives the available fault current for the protective device's clearing time without exceeding its insulation short-circuit temperature, by the public-domain ICEA / Onderdonk adiabatic equation, plus the minimum size for the actual fault. A thermal-withstand screen, not a substitute for an engineered study.
(I/A)^2 x t = K x log10((T2 + B)/(T1 + B)); withstand = area x sqrt(C / t), min size = fault x sqrt(t / C), where C = K log10((T2+B)/(T1+B)). Copper K=0.0297 B=234; aluminum K=0.0125 B=228.
ICEA P-32-382 / Onderdonk adiabatic short-circuit heating equation (public-domain form), by name.
Public-domain engineering relation; the ICEA P-32-382 standard itself is licensed.
Estimate. AHJ and licensed professional govern.
Field names used by the API: area_cmil, fault_current_a, clearing_time_s, material, t_initial_c, t_final_c, withstand_a, min_cmil
- Adiabatic the equation assumes all fault energy heats the conductor with no heat loss, valid for short clearing timesOnderdonk / ICEA P-32-382
- Scope the protective-device clearing curve and an engineered study govern the final determination; this is a screenengineered short-circuit study