I am getting a lot of installations where UPS's are the supply points. All of the UPS's so far do not have any fault levels recorded on their rating plate and I would imagine that this is because the fault level would be determined by the amount of batteries installed in any particular UPS which would vary.

My questions are:
1. How is the fault level determined. (assuming the manufacturer cannot answer that question).
2. The internal configurations are not known so can an ELI test be done on the load side of the UPS and from there work out the fault level through I=V/R.

One further question not related to UPS's.

If a fault level for a particular circuit is close or equal to the circuit breaker's KA rating how does installing fuses upstream instead of circuit breakers help reduce the fault level (as explained to me once by an engineer). Perhaps someone with a lot of theory knowledge could explain this as the fault level can be calculated using transformer and cable impedance etc which has no bearing on reducing fault levels with fuses.