Isn't there something in the regs about having a convenient (in terms of distance and not switching anything else vital off) isolation switch for servicing purposes, or is that just good practice? Or am I thinking of WRAS?
I think that relates to hard wired appliances which might need to be be serviced in situ, like ovens, boilers and extractor fans. There's hardly any servicing you could do to the transformers other than replacing them so from that point of view they're no different from a plug socket. If you felt the need to be able to isolate them then use a switched FCU instead of a plain one.
They don't always put the sockets/fuses in a convenient place, like my cooker hood (13A plug and socket inside the chimney) which blew a fuse when a lamp failed and the built-in oven (13A plug and socket behind the oven) in which the switch (which is never used) failed. I suppose it's neater to hide everything away.
The non isolating type usually have an internal fuse. The isolation transformer type don't usually.
There is not usually a manufacturers requirement for additional fusing on the isolating type.
Most will do 2 x 2.5 or 1 x 4.0. Some will do more. The BG one i rated for 3 x 2.5 and 2 x 4.0 IIRC.
What happens to the transformer in case of overload/short?
Many transformers have an integral thermal fuse. I would be surprised if a shaver transformer doesn't.
Many transformers have a fuseable link internal to the windings. I'd expect a shaver socket would.
Would an internal fuse successfully break a 50A fault current?
If its on the secondary, then it will either sit there an buzz at you (getting hot but not much bad should happen since they are normally only
30W or similar). Or it will include a thermal fuse that will open (possibly auto resetting if you are lucky).If its on the primary, there is no likely overload scenario, so you only need worry about a hard short. They are presumably designed to be robust enough to rely on the fault protection of the circuit in those cases.
Yup. The non transformer type tend to have a replaceable cartridge fuse though. The types in the transformers are often an integral part and not a user serviceable thing.
They're also called thermal fuses - so I'd guess would rupture before the windings went up in smoke.
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