Hi folks.


From Lurch:

I have fitted many HRC fuses and have only had them blowing
under fault conditions, very rarely because 1 bulb has blown.

Exactly how they should behave. MCBS OTOH misbehave routinely.

Rewirable are next to useless in any situation,

That isnt credible. They do exactly whats needed, and meet all the
latest requirements.


damn near blinded me
because of rewirable fuses, but thats another story!

I have a feeling you have a story to tell us

There are /un/enclosed wire fuses that I've seen in extremely old
installs that are a risk, but where theyre covered up by the ceramic
holder, as in any modern or even semi modern CU, fuse wire explosion
is not a problem. I await your story, but meanwhile dont forget that
one case of almost injury proves nothing, since MCBs are also known to
cause injury through stair falls.


From: Owain )
"N. Thornton" wrote

| Indeed, wire fuses are safer than MCBs on light circuits (only).
| There are safety pros and cons for each option, but repeated
| loss of lights is the biggest risk, and wire fuses avoid that.

Because they provide a lower standard of electrical protection.

Their trip characteristics are very different, but under fault
conditions they do their job. They dont cause a problem there.

A trip device that does not cause numerous unwanted and sometimes
dangerous trips is a better standard of protection.


Loss of lights is a risk which can be avoided by proper circuit
arrangements
(more than one lighting circuit per storey, if not per room) and the
provision of ELUs at hazard spots (stairs and kitchen) together with
proper
selection of luminaires. Tripping MCBs on bulb failure is an
excellent
additional reason for avoiding mains voltage incandescent lighting.

It could, but this is all very unrealistic. You can specify that for
some commercial installs or a few rich householders, but in the real
world you just wont find that in most houses. Few will meet all that.


| They are also more convenient, as wire fuses rarely blow. When
| they do, downtime is longer,

As long as it takes to find some 4mm cable to rewire the fuse with.

Thats their one downside, and is easily resolved by putting a fuse
wire card on the CU. That is a far more workable and easier solution
than your suggestion above.


From: )

but there's certainly
a very legitimate place for cartridge fuses, which have usefully
different
time characteristics and current-breaking capacities to circuit
breakers.
For domestic lighting circuits as found in established UK wiring
practice,
I'd agree with Nick that there's a pragmatic safety gain to replace
an
MCB (esp. a 'B'-characteristic quick-trip one) with a physically
compatible
DIN-rail fuseholder fitted with an appropriate cartridge fuse. MEM,
for one,
sell these as a standard CU accessory.

Indeed, it removes 99% of a very well known risk, one that injures and
kills people.

Rewirable fuses remove that risk too, though they also have the
potential for miswiring. Even there, one has to look at the relative
risks. I dont know what the stats are, ie:
in how many places rewirables are miswired,
how many of those lead to fire or shock,
and how many injuries and deaths result from those.
I also dont know the stats for MCB-caused accidents and deaths, due to
loss of lighting and subsequent falls down stairs, failures to get out
of fires alive, welding of the MCB contacts, trip mechanism failure,
deliberate miswiring as a result of nuisance trips, etc.

I would not rush to assume that MCBs are safer on lighting circuits
until I actually knew the figures. From what little I know, I am
fairly convinced that cart fuses are safer than MCBs on lighting, and
I expect rewirable fuses may well be too.

Until we get the figures, it is impossible to actually know. Assuming
that quicker fault disconnects and less overcurrent tolerance leads to
greater safety is in truth an assumption rather than a fact.


Regards, NT