The 5kA SCCR Component

[Dale Hayes]

The infamous 5kA SSR (aka “Switch”).

From UL508A Table SB4.2 the maximum amp for a 600V type CC fuse is 20Amps to
raise an untested SSR “aka switch” above the 5kA default value.

Same scenario for a 300V 30Amp Class T fuse that can also raise the untested SSR
“aka switch” above the 5kA default value.

What is a person to do with an untested 60Amp SSR (aka “switch”) that defaults
out at 5ka per UL508A Table SB4.1. Do they make a 60Amp fuse that will Ip out
at 5ka and increase the SCCR to 50kA, 100kA or 200kA?

Need Help!

[richwaskowitz]

Not sure what you mean by untested switch. If it is not UL listed, you cannot use the default table in UL508A (per our UL rep.). Are yo saying that this switch is listed but does not have an SCCR / interruping rating?

[petersonra]

I am not sure an SSR qualifies as a switch.

What does the UL listing for the SSR call it?

[Jraef]

SSRs can fall under "switches", "switch units" or "motor controllers" depending on their use in the circuit.

The reason for the low current limitation on "roll your own" series combinations is because they are essentially acknowledging that below those values, the potentially destructive energy is low anyway. That doesn't mean you can't get there with larger fuses and devices, it just means that UL will not allow it without testing.

I think that your only choice is to search out an SSR that has been tested and listed at a high SCCR in combination with a protective device (usually a fuse) by the manufacturer. People like Siemens, Schneider, those kinds of companies with the deeper pockets to pay for the testing. I have also seen an article stating that Crydom has done SCCR listing of their SSRs with fuses up to 100kA, but a search of their website gave no results. Might be worth a call to them though.

[petersonra]

Now that I think about it, i seem to recall that either Watlow or Chromolox has some higher SCCR SSRs.

[Contech]

I have called Croydom and was able to get the original data, not that it is applicable any longer. They basically told me that the decision to discontinue the listing was an economic one. Sounded like they considered the listing fees to be too high.

Bottom line is after lots of searching I was unable to find any SSR with a combination rating.