On Mon, 29 Jan 2018 14:45:25 +0000, Andy Burns wrote:

jim wrote:

Elderly (tight) rellies can't fit occasional fusewires into old
carriers.

Maybe provide them with some replacement fuse carriers, ready to swap?

But really, what is the underlying reason for fuses blowing sufficently
often to be a problem?

The more likely cause for 'nuisance events' on ring main circuits is
overloading, typically too many heaters plugged in and switched on at
full power whilst switching on an electric kettle and/or toaster or else
a really sucky vacuum cleaner plugged into the same ring main being
switched on.

Nuisance events on the ring main circuit cabling itself are likely to be
improperly fixed sockets or crushed cabling effected by the occupants
walking about on suspended flooring which could transmit forces into
damaged cabling or badly terminated joint boxes otherwise most such
permanent wiring problems result in a permanent fault condition which
will immediately blow any replacement fuses every time.

Lighting circuits can also produce 'nuisance events' from damaged
cabling or fittings as well as from overloading (too many 100W quartz
halogen lamps for example - an extremely unlikely scenario these days).

The good old fashioned fuse has proven to offer quite sufficient
protection against the fire hazard of overloaded power and lighting
circuit cabling over the past 80 odd years or so. Indeed, replacing a
fuse with an MCB in an older CU fusebox has nothing to recommend it other
than the convenience of making potentially hazardous circuits live at the
flick of a switch.

The only "Upgrade" to the humble fuse that is worth having is the type
of circuit breaker than provides earth leakage detection which can
minimise the risk of electrocution as well as provide earth protection
where the earthing point impedance can't be made low enough to guarantee
protection by a humble fuse.

Other than for the questionable convenience of being able to swiftly
restore a potentially unsafe circuit at the flick of a switch, the MCB
introduces an additional level of complexity to the protective function
it is intended to mimic of the humble fuse, thereby compromising said
function.

The humble fuse offers the most reliability simply on account of its
reliance on the *unreliability* of a short piece of fusewire to carry an
overload current for any significant length of time. The classic fuse is
the most extreme demonstration of the KISS principle in operation.

The only way that a correctly wired fuse can fail to protect a circuit
from overload that I can imagine is if your basement located Wylex CU
happens to become immersed in liquid Nitrogen due to a spill from a
Liquid Nitrogen Tanker that has crashed into your front garden. An
extremely unlikely event, I think most of us would agree, where an
electrical fire might be considered a mitigation against the extreme cold
such an event would introduce into the house. :-)

--
Johnny B Good