On Tuesday, 18 August 2020 15:15:34 UTC+1, John Rumm wrote:
On 18/08/2020 11:28, tabbypurr wrote:
On Tuesday, 18 August 2020 00:09:20 UTC+1, John Rumm wrote:
On 17/08/2020 22:09, tabbypurr wrote:
On Monday, 17 August 2020 21:57:17 UTC+1, John Rumm wrote:
On 17/08/2020 16:59, Scott wrote:

Why do you think the system was introduced with 1, 2, 3, 5, 7, 10
and 13 amp fuses unless a lower rated fuse had safety benefits?

For the limited cases where overload protection is useful. They
will all handle fault currents.

When the BS1362 plug system was introduced in '47 the plug fuse was
normally the appliance overload fuse, appliances mostly had little or
more often no other overload failure protection.

Agreed - hence why I mentioned it.

However a good deal of appliances (even then) don't actually need any
overload protection... So there is a danger that you could cause more
problems in the quest for "safety". (i.e. nuisance fuse blows, plugs
running warmer etc).

those aren't dangers.

A fuse blow might be a danger - depends on what its in, in what
circumstance, and who will try to fix it.

It isn't. If you want to propose compulsory self resetting MCBs or polyfuses etc you can, but that's a separate issue with its own tradeoffs each way.


And putting a 3A fuse on a 2A load does not cause nuisance trips.

That depends on what that "2A" load is - what its surge characteristics
are, what inrush current it draws.

A CRT TV for example may only draw 150W when running normally, but may
take quite a bit more at switch on, and when degaussing.

We know people can fit the wrong fuse. So what?


More to the point, is the person choosing the fuse sufficiently aware of
the nature of the appliance to make a good assessment?

Not inherently. Fuses used to come with lists of appliance types for each fuse value. Fitting a 13A in lieu of a 3 is not a problem, fitting a 3 when suitable is a small gain in fire satfey.


(I remember (a long while back) standing in the Waters & Stanton shop,
when someone walks in off the street, and asks if they have 2.5A 20mm
glass fuse. The young chap behind the counter says "yes, do you want
quick blow or anti surge?". The customer says, "oh, I don't know, its
for a portable TV, what do you think?". Sales droid thinks for a bit and
says "probably quick blow". I politely butt in, and ask the customer if
by any chance they have the original fuse with them? She does, so I get
her to read the rating off the fuse - and as you might expect it has a T
in it. So even the somewhat clued up person working in a shop stuffed
full of high tech electronics and comms gear can make the wrong call)

IME one is lucky if the person behind the counter is clued up. Glass fuses are a separate issue to what we're discussing of course.


That has changed of
course, but there are still millions of appliances that have no
built-in overload protection and could benefit from it safety-wise.

I don't have a source of figures for how many are still out there. Do
you? Some, sure; millions perhaps?


ok I will bite...

I don't have a record of where they figures came from. But it's easy to come up with a very rough idea of the size of the issue.
1. How many substandard appliances have major retail sites sold?

What do you mean by substandard?

not meeting the legal requirements


2. How many PAT fail appliances are there per site?

What site are we talking about? Home or work?

all of them!


What proportion need & lack overload protection.

Few. (i.e. few will need it, and even fewer will lack it)

Bzzt. Lots lack it.


3. How many historic appliances are still in use? If you find just one per 63 people that's a million.

If you include all those babies using great grandpa's wireless huh?

are there any of those? I doubt it. But there are plenty of old heaters still in use, old lamps with undersize flex etc etc.


Now before getting further into this, remember I have already said that
there are times when using a selected and appropriate fuse *is*
important, and we both understand that for the vast majority of
appliances people are using today, the fuse rating will have little if
any effect on safety so long as it provides adequate fault current
(official meaning!) protection.

no, a lower fuse equals less energy delivered to the smouldering insulator before trip. Result: lower fire risk.


I am not suggesting that fitting a more closely tolerances fuse is
necessarily wrong, only that it may introduce unintended circumstances,
and it many cases will achieve no improvement in safety.

It always reduces fire risk. And fire is the number 1 means by which electrical failure results in injury, loss of property and death.


NT