Last edit: 31/03/2025
APPENDIX D
Annex D was introduced in the april 2020 version of UL 508A. It clarifies what was previously common but not formally correct practice.
A manufacturer of electrical automation panels is not required to use a certified busbar system or to subject it to short-circuit tests, provided that it complies with Table G3.1 of UL 891 (called Table D3.1 in UL 508A).
This table is now included in the new annex, which formally makes this practice possible.
“FACE TO FACE” OR “EDGE TO EDGE” ARRANGEMENT
The table, in addition to giving specifications regarding the maximum thickness of the busbar, the maximum current and the maximum nominal voltage, distinguishes between busbars mounted in a “Face to Face” or “Edge to Edge” arrangement.
For example, in the case of busbars arranged “Edge to Edge”, if the distance between the insulators is not greater than 533 mm, provided that the size of the busbar complies with table D3.1, and the rest of the architecture complies with SUPPLEMENT SB (with all devices having SCCR equal to 50 kA), the switchgear can be declared with SCCR = 50 kA.
