Some utilities give you a number that they agree never to exceed. That is the number you should use. It is not based on the equipment supplied at present. Over time the network might get stiffer, they might change out your transformer. But if you use their number it won't be more than their number, even if at present the number they give out far exceeds what the real value of available SCC is. In fact, my understanding is this is built into many of the tariffs these days.
Please explain. I'm not sure what that means that the SCC is built into the tariff. The tariff should be the result of a cost allocation. The same tariff will apply across different locations with different SCC.
Tariffs usually address different service types like single vs three-phase, different voltages, different service sizes, different metering, different load characteristics, etc. but I don't recall available SCC being a billing parameter in a standard tariff.
Primary available SCC can be an indicator of the maximum load that can be served with acceptable voltage drop, flicker, and/or motor start but that is usually transparent to the end tariff unless the customer requests excess facilities or has unusual supply needs. These excess facilities are usually cost-allocated as one-off direct cost assignments.
