Adrian C wrote:

There I was tonight in this super newly installed electric shower (oh,
and gas - but that's for another tale) and using it for the first time.
10.5kW, 44Amps or thereabouts. Wired via an RCD and spliced into the
existing meter tails to the existing consumer unit. My thoughts are on
how great this mains pressure shower actually is.

Then the lights went out. Silence.

Great

Call for SWMBO. Nothing. She'd left the house to potter in the garden
shed. I'm wet, covered in soap suds, can't see a thing, where is the
blinkin torch...

Ah, the meter ain't displaying. We've blown the supplier main fuse. All
other fuses, trips and RCDs fine.

The guy from the emergency electrical service sorts it out, and we are
back on again. However, our supplier fuses are old - probably 50 or 60
years - and from his comments look to be wired with 30 amp fuse wire.
That said, the shower overload has taken out both the live and neutral
fuse wires. He whistles though his teeth, sez "neutral, that is weird"
and trundles off with a promise to be back tomorrow to uprate the fuses
to a more consumer friendly 100 amps.

I can't see anything strange in the neutral fuse expiring, it has been
on duty for ages - and the overload of our new shower has shown it the
cards. So why is this guy whistling through his teeth?

Is tomorrow going to be a likely sales opportunity for his company?


There shouldn't be a neutral fuse by the standards of the past mumble
decades, which is why he was surprised.

If it that ancient, they might well replace the cutout completely now or
real soon. At the very least, it's almost certain he'll replace the neutral
fuse with a solid link at least for now and replace the live fuse.

Another issue is what the cutout is actually rated at - you can't bung a
100A fuse in any ancient old crap. But a 60A supply fuse should cope OK with
a shower plus reasonable other loads unless you spend an hour in the shower
while running the leccy cooker and fan heaters flat out. As a very general
rule of thumb, a typical fuse in this class (and there are a few classes of
cutout fuse) will take around 30 mins to blow at double it's rated load, ie
120A for a 60A fuse so you can get away with a bit.


--
Tim Watts