‘Grandfathered’ equipment falls under new UL 508 regulations


If you have been in the market for panel-related electrical equipment recently, you probably already know that a new UL standard for control panels went into effect on April 25, 2006. You should also know this standard applies equally to your existing installations, regardless of age or application.

UL 508A-2001 Supplement SB works hand-in-hand with the 2005 NEC Sec. 409 and requires that electrical panels have a short circuit current rating (SCCR) calculated and displayed on the equipment. While this has an obvious effect on design and construction of new panels, any installation that is subject to inspection will now be held to this standard and you should prepare for implementing the requirements. Enforcement may vary from place to place during this introductory phase, but don’t depend on a grace period.

Panels that are operating properly and subject only to routine maintenance aren’t an issue for now, but if you want to modify or upgrade, you can expect new questions from your inspector. “Many times when we get in the field, we ask,‘Am I replacing like for like?’ Inspection permits a lot of that,” said Alan Manche, director of industry standards for Square D/Schneider Electric. “If I start adding things and modifying things, it brings into question, what’s the impact of that? Folks will start asking, ‘What is the short circuit current rating of this panel?’ based on the 5k contactor or relay that I put in there. An old panel or an old piece of machinery may have to be modified to ensure compliance with 409 and make sure that the ratings are in place for a safe installation.”

Existing equipment built from leftover parts and mixed manufacturers will only make implementation more complicated. Aside from full current testing of the assembly, the only way to determine the SCCR for a panel will be analysis of each component subject to the standard. Tim Fitzjarrald, senior project engineer for UL, has this advice: “You have to look at either the marking on each of those devices and determine which is the lowest and assign that value to the line side of the branch circuit protective device. Or, you can go to the UL Website and we have a combination of devices that have the higher fault rating.”

Options to bring older equipment into compliance short of replacement will depend on your ability to follow the standard’s specifics and apply them in your installation. Many electrical OEMs have expanded the amount of SCCR data available on their Websites for their current and older products. UL also has more generic information that may apply where you can’t get specific figures. If all else fails, you can call on help from the outside.

“Hopefully, you can show the authorities having jurisdiction that you understand supplement SB and that you’ve come up with a short circuit rating that’s correct,” Fitzjarrald suggested. “Or, it’s always possible to get us out there and we can help you determine that.” Comments were made during a related Webcast; sign up to view at www.controleng.com/webcasts .

Peter Welander , process industries editor, Control Engineering

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