winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
However as winnie pointed out, is is also possible that the ground fault returns on an intended path, but this is true for all GF common circuits.
When you have a grounded secondary, there are a huge number of paths available for current that do not involve the residual current detector (zero sequence current transformer), and thus a GFCI is very likely to trip on a fault.
When you have an ungrounded secondary, then you significantly reduce the number of available paths, which reduces the chance that a residual current detector will trip on a fault.
In the limiting case of an RCD on the output of an ungrounded transformer, most if not all of the fault current paths will return via the RCD and thus it is unlikely to detect the faults. For the OP, if the decision is made to put ground fault detection on the 24V lighting circuits, I'd suggest that the residual current detection hardware hit individual lighting circuits, not a single (essentially useless) RCD on the output of the 50A 24V transformer
-Jon