It will be a very brave genset maker that gives you any sort of single figure for the PSSC !! The output impedance of a genset and its ability to supply current is very load dependent - if is running at say less than 1/4 capacity and you apply full load - not a short, just full load mind, as a shock, you will at best collapse the output until the regulator recovers, or at worst stall it. (*)  What happens in short is similar, but you will not get out much more  than about twice full load current even as a short transient, without the output collapsing, and nothing like the ten times FLC or so required when trying to blow fuses in a sensible time.

Readings made with a loop tester/PSSC meter will be about as much use as a fruit machine - all it tells you is what happens if you scale up the voltage drop from a small test current, what would the current need to be as if it was 100% voltage drop. But that assumes of course the relation between current and volt drop is linear and unless the currents in consideration are small compared to the genset full load then it simply isn't true.

So if the genset has a full load of 500KVA, call it 800A per phase, the largest fuse or MCB you should expect to be able to always fast blow, in all load conditions, is in the range 80-150A . The absolute upper limit for setting  earth leakage trips would be similar, but less 10A and some delay is more credible.

Mike

(That is not quite worst case, I have not so fond memories of squeezing in to an enclosure never intended for it, alongside an engine that would not have looked out of place in a really large bus or some piece of farm machinery, to replace a shear-pin between the motor shaft and the alternator. That unit was probably 1/4 MW or so.)

It will be a very brave genset maker that gives you any sort of single figure for the PSSC !! The output impedance of a genset and its ability to supply current is very load dependent - if is running at say less than 1/4 capacity and you apply full load - not a short, just full load mind, as a shock, you will at best collapse the output until the regulator recovers, or at worst stall it. (*)  What happens in short is similar, but you will not get out much more  than about twice full load current even as a short transient, without the output collapsing, and nothing like the ten times FLC or so required when trying to blow fuses in a sensible time.

Readings made with a loop tester/PSSC meter will be about as much use as a fruit machine - all it tells you is what happens if you scale up the voltage drop from a small test current, what would the current need to be as if it was 100% voltage drop. But that assumes of course the relation between current and volt drop is linear and unless the currents in consideration are small compared to the genset full load then it simply isn't true.

So if the genset has a full load of 500KVA, call it 800A per phase, the largest fuse or MCB you should expect to be able to always fast blow, in all load conditions, is in the range 80-150A . The absolute upper limit for setting  earth leakage trips would be similar, but less 10A and some delay is more credible.

Mike

(That is not quite worst case, I have not so fond memories of squeezing in to an enclosure never intended for it, alongside an engine that would not have looked out of place in a really large bus or some piece of farm machinery, to replace a shear-pin between the motor shaft and the alternator. That unit was probably 1/4 MW or so.)