We are having a real issue with using the 408a method to determine our SCCRs. Our problem is that our panels operate heaters using SSRs and run at about 100A in the on state. If you are familiar with table SB4.2 you know that this table is nothing but a major hindrance if youre above 30A. Bottom line is...this table gives all of our panels a 5kA SCCR, when the fact is that high-speed J fuses adequately protect the SSRs based on the manufacturers data. I understand why UL is using blanket ratings, but IMHO it is too restrictive and NEC should exempt industrial heater controls from having to use table SB4.2. A more sensible approach would be to require on-panel LABELLING as to proper and specific fuse replacements and let us use fuse ratings based on reality, not blankets. What do we have to do to get this exception written into NEC 409?
UL408A table SB4.2 kills our SCCR!
- Thread starter rplecha
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
UL's method is not the only method you can use to determine the SCCR of a panel.
It is just the only one anyone uses
A manufacturer could certainly get UL to list its heater controls at a higher rating if they wanted to. But then they would have to pay to have them retested.
It is just the only one anyone uses
A manufacturer could certainly get UL to list its heater controls at a higher rating if they wanted to. But then they would have to pay to have them retested.
Wait a minute....if there are other approved methods I'd sure like to know about them. The wording of the NEC code is....."UL508A is an example of an approved method." and that's all it says. That wording should imply that there's other methods, but what are they? My sticking point is in that blanket fuse table sb4.2. If I could somehow lose that constraint I'd be very happy.
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