UL 508A Technical Standard
The reference standard for the Industrial Control Panels in the USA
UL 508A is the reference standard for the Industrial Control Panels in the USA. The basis are the safety rules prescribed by the National Electrical Code (NEC). The NEC has ARTICLE 409 dedicated to the Industrial Control Panels, but it contains few details. That is why in 2001 UL508A was issued. Latest update of the standard is Augusto 2016.
UL 508A is applicable to Machinery Electrical Panels only. In case a Machinery has a distribution panel inside (mainly circuit breakers and bus bars, the standard to comply with is UL 891. EN 60204-1 and EN 61439-1 and -2 are the equivalent European Standard, respectively for Control panels and for Power Distribution panels called Switchboards in North America.
It is a widespread opinion that in order to design an Electrical Panel in compliance with the North American standards, it is enough that all componentes be Listed or Recognised. In reality that is only one condition. However be aware that, even if a component is Listed it could be used in a wrong way: as an example, the use of UL 508 (Branch Circuit Protection or BCP) as Feeder protection, or circuit breakers UL 1077 (supplementary protectors) used as BCP.
Another important difference with the European standards for control panels is the sizing of Cables, Thermal and Magnetic protections. The American way is prescriptive while the European standards have much less rules.