Watcher:
The chassis of the SMPS is connected to system earth anyway. So any leakage current higher than 100mA will trigger and trip the local RCD protection. If that fails then the central house 300mA RCD will trip.What I am worried about is the possibility of mains voltage somehow finding its way to the DC output of the power supply and eventually in the pool water giving people an electric shower!
The SMPS leakage currents I talk about aren't dangerous, but you really don't want them in a wet
environment, its diconcerting at best.
Unless everything is isolated from the environment the earthing system is the key safety feature, it
should be regularly tested (I'd recommend a local RCD on the pool with a test button). Then everything
can be bonded to this earth. So long as the earthing system is intact any fault will trip the RCD or
if a hard short probably blow the fuse/trip the breaker too.
[ RCDs normally sense the difference in current through live and neutral, thus see any leakage from
live to earth as a discrepancy - choose the most sensitive RCD for the load if you can ]