I have a cabinet with semiconductor fuses protecting a VFD inside, fuse has a 100ka IR and all component inside has a 10ka IR. UL508A SB4 talks about analyzing peak let thru values to determine SCCR, I understand the rationale that components IR after the current limiting device must be rated higher than the peak let thru but UL508A only talk about Class CC, K, G, L, J, and R and using the tables to determine the peak let thru, it doesn't mention semiconductor fuse which has a lower I2t values and is current limiting. Can I use the semiconductor fuse peak thru current to determine my cabinet rating even though its not mentioned in the SB4.2 table.
UL508A SB4
- Thread starter CCOOK
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Is the VFD the only thing in the power circuit in the box? If so, have you checked with the VFD mfr to see if their drive has been series listed with those fuses? The point being, it might be easier than you imagine.
UL 508A
UL 508A
Yes, the drive is developed in house and the rating is 5kA or 10kA based on horsepower rating and a contactor which is 10kA. The point of the analysis and using UL508A is to not test and raise the SCCR higher than the standard 5 or 10kA rating.
UL 508A
Yes, the drive is developed in house and the rating is 5kA or 10kA based on horsepower rating and a contactor which is 10kA. The point of the analysis and using UL508A is to not test and raise the SCCR higher than the standard 5 or 10kA rating.
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- Wisconsin
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- PE (Retired) - Power Systems
I doubt that you would be able to use semi-conductor fuses to protect general circuit components, although I think it would be worth discussing with your UL508A rep.
General purpose protection devices have most likely been tested under guidelines, but I believe semi-conductor fuse have no such standards.
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