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SCCR Ratings

SCCR Ratings

SCCR Ratings

Where I work we manufacture a machine delivered as a stand-alone enclosure comprising inside a small control panel which holds some relays, the PLC, the HMI, and terminals for controls. The rest of the power components are laid out inside the main stand-alone enclosure (MCCB, VFD, Input reactor, sine filter, transformer, etc.). The customer needs to bring 480V to the machine with the option to bring the cables in through the top, directly to the MCCB, or through the bottom to a set of terminal blocks factory connected to the MCCB. My question is regarding the UL508A requirement for the SCCR. In my mind, coming through the top, we achieve 65kA due to our MCCB. Other components downstream are sized to handle it too, in the way they are protected. No problem.

My concern is when power is fed from the bottom and brought to the terminals first. They are Weidmuller WFF300, and their SCCR is that of untested power distribution blocks, which is 10 kA according to table SB4.1 of UL508A. This is clearly a bottleneck for me, unless we can disregard these, as they are themselves enclosed in a sub compartment of the main stand-alone enclosure. I read again and again on the matter and could not find a satisfactory answer to this specific case. Obviously, in some installations, it will make a huge difference if the customer specs out a SCCR the unit should be capable of handling.

Anybody knowledgeable with UL 508A SCCR?

RE: SCCR Ratings

You would need to get terminal blocks with a higher rating. It would not matter where the terminal blocks are located, any device in the power circuit is part of the SCCR listing, and the lowest level device sets the maximum rating, unless specifically tested and listed as a combination, which you will not find with terminal blocks.

There are many brands and models of power terminal blocks that are listed with a high SCCR, you just can't use that particular one.

"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

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