The nameplate on a low-voltage switchboard looks like a list of acronyms, but three of them decide whether the equipment survives a short circuit: Icw, Ipk and Icc. If those values sit below the fault current of your installation, the switchboard can deform or catch fire exactly when it is needed most. Here is what each one means under IEC 61439 and how to check it against your project in five minutes.
IEC 61439-1 (edition 3.0, May 2020) sets the general rules for low-voltage switchgear and controlgear assemblies, and part 2 covers power switchgear assemblies. Among other data, the manufacturer declares short-circuit capability through three ratings: rated short-time withstand current (Icw), rated peak withstand current (Ipk) and rated conditional short-circuit current (Icc). These are values declared by the manufacturer and backed by its design verification.
Think of them as three different questions. Icw asks how much heat the switchboard can take. Ipk asks how much force it can take. Icc asks what happens if an upstream breaker clears the fault before the full energy arrives.
Icw is the r.m.s. current the switchboard can carry for a defined time without unacceptable damage. The usual time is 1 second, although 3 seconds is also declared. That is why a datasheet reads, for example, "Icw = 50 kA / 1 s". This value protects busbars, connections and supports from heating. It applies mainly to main circuits and busbars, which must hold while the upstream breaker decides whether to trip.
In the first instant of a fault the current is not a perfect sine wave: it carries a DC component that raises the first peak. That peak creates huge electrodynamic forces between busbars that can bend them or tear supports loose. Ipk is the maximum peak value the switchboard withstands, and the standard links it to the r.m.s. current through the factor n: Ipk = n × r.m.s. current.
Factor n according to table 7 of IEC 61439-1
A real industry example: the Siemens SIVACON S8plus switchboard declares, on its horizontal main busbars, an Icw of up to 150 kA (1 s) and an Ipk of up to 330 kA. The ratio is exactly 2.2, the table value for faults above 50 kA.
Icc, the conditional short-circuit current, applies when the switchboard is protected by a current-limiting device (a limiting breaker or fuses) that clears the fault before it reaches its peak. With that protection, a switchboard can be installed where the prospective current exceeds its Icw, as long as the nameplate declares the Icc and the specified device is the one that was tested. The condition is strict: if the brand or rating of the device changes, the declared Icc no longer applies.
Specification lesson. Asking for "a 65 kA switchboard" is not enough. Require the nameplate to state Icw with its time (1 s or 3 s), Ipk and, if it depends on upstream protection, the Icc with the exact device that backs it up.
Follow three steps. First, calculate the prospective short-circuit current at the switchboard busbars, starting from the transformer that feeds it. Second, compare: Icw must be greater than or equal to that current, and Ipk greater than or equal to n times it. Third, confirm that the declared time (1 s or 3 s) covers the real clearing time of your protections.
Illustrative example: a 1,000 kVA transformer at 480 V with 5% impedance delivers a rated current of about 1,200 A and, on an infinite bus, a fault of about 24 kA. Since that falls between 20 and 50 kA, n = 2.1 and the expected peak is about 50 kA. A switchboard with a 25 kA Icw covers the calculation, but with little margin if you add load tomorrow or the grid gets stronger. This is a simplified calculation; your project's short-circuit study prevails.
The standard allows three routes to design verification: testing, calculation and design rules. For short-circuit withstand, a high-current laboratory test is the strongest evidence. In May 2019, Industrias Ectricol S.A.S. published the result of a test on a motor control center column at 480 V with 65 kA and an Ipk of 144 kA, run at the LAPEM laboratory in Mexico, with no deformation of the enclosure and a satisfactory dielectric test afterwards.
In Colombia, the RETIE technical regulation was updated by Resolution 40284 of June 23, 2026, published in the Official Gazette on July 1. Before buying or accepting a switchboard, ask your supplier and your certification body to confirm the requirements in force and the product conformity certificate.
At Ectricol we manufacture in Funza, Cundinamarca, low-voltage distribution switchboards, motor control centers and transfer switchboards for oil & gas, mining and industry.
Icw is the r.m.s. current it withstands for a defined time (normally 1 s), Ipk is the maximum peak it withstands mechanically, and Icc is the current it withstands when an upstream limiting device clears the fault. The manufacturer declares all three under IEC 61439.
Icw measures thermal withstand to a fault sustained for seconds. Ipk measures mechanical withstand to the first peak, which occurs within milliseconds. A switchboard must meet both.
Multiply the r.m.s. current by the factor n from table 7 of IEC 61439-1, which runs from 1.5 (up to 5 kA) to 2.2 (above 50 kA). For example, 65 kA times 2.2 gives about 143 kA.
Yes, provided the nameplate declares the Icc and the same limiting device it was tested with is used. If the breaker or its rating changes, that Icc is no longer valid and must be reviewed with the manufacturer.
Ask for the design verification report (testing, calculation or design rules) and the product conformity certificate required by RETIE. A high-current laboratory test is the strongest evidence.
Can your switchboard withstand your plant's fault current?
The engineering team at Industrias Ectricol S.A.S. reviews the prospective short circuit with you and specifies a low-voltage switchboard with the right Icw, Ipk and Icc, made in Colombia.
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