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Switchgear / Panel Board Rating
2

Switchgear / Panel Board Rating

Switchgear / Panel Board Rating

(OP)
If the panel board is rated at 50kA @ 1s, what does it refers to?
The short circuit withstand rating which the assembly/structure can withstand for a short time.
(or)
The short time rating of the Main breaker (Icw in IEC).
(or)
The bus bar short time rating.

Is the SCCR rating in NEMA relates to the panel board assembly/structure rating?

RE: Switchgear / Panel Board Rating

TH SC rating in the panelboard primarily refers to the bus bar capability to withstand the dynamic forces (peak <1 sec) and thermal heat generated for 1 second.

Panelboards are designed to accommodate a wide variate of rating circuit breakers. However, The rating of the assembly (panelboard & circuit breaker) is driven by the lowest rating of the individual component.

See if the UL article below could help.

https://www.ul.com/wp-content/uploads/2014/04/ul_P...

RE: Switchgear / Panel Board Rating

Dear Mr NickParker
Introduction: If the panel board is rated at 50kA @ 1s, what does it refers to?
Q1. The short circuit withstand rating which the assembly/structure can withstand for a short time?, or
A1. It is dependent on what is included in the test. If the test [excludes] the main breaker, than the test is only the busbar assembly and the structure.

Q2. The short time rating of the Main breaker (Icw in IEC)?, or
A2. Usually the test includes a main breaker. In this case, the test includes the main breaker, busbar assembly and the structure for XkA Ys.
Note: The main breaker remain closed (i.e. with instantaneous trip defeated) for the complete short-time duration.

Q3. The bus bar short time rating.
A3. It is also possible to test the busbar assemble with busbar holders (in the open air) [without any structure]. In this case, the test covers only the short-time withstand rating of the busbar assembly and the busbar holders [excluding the structure].
FYI: Reference IEC 61439-x for detail in the IEC world.

Che Kuan Yau (Singapore)

RE: Switchgear / Panel Board Rating

The SCCR in a NEMA/UL panel will be (in practice) the short circuit rating of the lowest rated device in the equipment (when it was built). In olden days, this equipment had a published bus bracing rating. This is no longer shown on equipment nameplates, IIRC.

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