The most basic problem with DIY work

[JohnW2]

And 13A fuses in a standard plugtop feeding a 0.75mm cable-lamp, or similar, isn't too clever either.

You may or may not think it's "too clever" but IIRC BS1363 allows use of a 13A fuse with 0.75mm flex.

Are you sure? Quite apart from the fact that it doesn't sound 'too clever' (per BS7671), it would seem rather odd that BS1363 would be saying anything about cable size/fuse rating.

stillp?

Kind Regards, John

 

[JohnW2]

...That evening was teacher parent night and on seeing the science teacher it came up and the teacher was unaware about field effect transistors and said how they must be new. At which I explained they were invented first but perfected second and since patented in 1926. ... The problem was my son had already passed his amateur radio exam at 14 years old so was quite into electronics this was some 16 years ago now he also has level 5 in electronics but still laughs at the teacher when reminded.

There is always going to be an issue of some pupils knowing a lot more than teachers about some aspects of some subjects. By the age at which people take GCSEs (and, even more so, A-Levels), a good few students will have developed particular intererests and ('privately') advanced their knowledge about them to way above the level required for the exams and, in some cases, beyond the level to which the teacher has been educated. It takes fairly mature attitudes on behalf of both teacher and pupil to manage that situation without embarassment or offence.

'Excessive knowledge' can also make it difficult to answer exam questions to the satisfaction of the examiners. I was in a similar situation to your son, in that I took the RAE aged 13 (so that I could get my licence on my 14th birthday) and I remember that my level of knowledge about things electyrical/electronic made it quite difficult for me to know 'what they wanted me to say' when subsequently answering GCE and A-Level questions on these topics.

Kind Regards, John

 

[ban-all-sheds]

On the face of it it makes no sense to specify fuse ratings for mechanical tests, but elsewhere it requires non-rewirable plugs to be marked with the maximum fuse rating according to the cord size, as per that table.

 

[JohnW2]

On the face of it it makes no sense to specify fuse ratings for mechanical tests, ...

Interesting. I think I can perhaps understand the reasoning. The flexing and cord-grip tests might be slightly influenced by thermal effects. Presumably for this reason, the tests are all specified to be undertaken at slightly (~10%) over the CCC of the cable, and the required fuse rating (for the tests) then follows from that (I suppose they could have specified a 10A, rather than 13A, fuse for 0.75mm²/7A).

However, this is obviously only about the performance of those particular tests. Despite what plugwash suggested, that table does not in any way suggest that a 13A fuse with 0.75mm² cable in an acceptable situation 'in service'.

Kind Regards, John

 

[ban-all-sheds]

elsewhere it requires non-rewirable plugs to be marked with the maximum fuse rating according to the cord size, as per that table.

 

[JohnW2]

elsewhere it requires non-rewirable plugs to be marked with the maximum fuse rating according to the cord size, as per that table.

Ah, I read that but the significance didn't sink in! Are you saying that it actually refers to that Table (Table 2) indicating the the 'fuse rating for tests' figure in that Table has to be marked on a non-rewirable plug as the 'maximum fuse rating'? If so, that clearly makes little sense, particularly given that the very same table indicates the CCCs of the cables concerned - which, for 0.75mm² and 1.0mm² is lower than that of the tabulated fuse rating. Surely even the BSI are familiar with the concept that the rating of the fuse should not exceed the CCC of the cable it is protecting?!

Would it be possible for you to post a copy of the offending bit of BS1363?

Kind Regards, John

 

[ban-all-sheds]

Disclaimer - that is from BS 1363:1984 - it may have changed but I'm guessing from what plugwash says he doesn't think it has.

 

[JohnW2]

Disclaimer - that is from BS 1363:1984 - it may have changed but I'm guessing from what plugwash says he doesn't think it has.

Thanks.

Ah - that's a little different from what I thought you were saying. It does not say that the plug must be marked with the fuse rating from Table 2 as being the 'maximum fuse rating'. What it says is that it must be marked with the rating of the fuse which has been fitted, adding that this figure must not exceed the Table 2 value for the cable concerned. However, if the person who fitted that fuse was being compliant with BS7671 CCCs (as the BSI would presumably expect them to be), they would have to fit a fuse (and mark the plug accordingly) whose rating was appropriate to the cable (per BS7671 CCCs) - which obviously would also be less than the Table 2 rating, thus satisfying BS1363.

In other words, I see nothing in those BS1363 words which suggest that one can ignore the BS7671 requirements for the size of the 'fitted fuse' (for a given cable size).

Kind Regards, John

 

[ban-all-sheds]

OK - apologies, I misquoted, but that was irrelevant.

I have no intention of allowing this to go the way that so many other discussions have, so I'll say this, and not respond any more:

I can see quite clearly in those BS 1363 words that this:

You may or may not think it's "too clever" but IIRC BS1363 allows use of a 13A fuse with 0.75mm flex.

is correct.

The highlighted paragraph clearly says

All non-rewireable plugs shall be marked on the
engagement surface with the rated current of the
fuse-link fitted, which shall not exceed the value
given in Table 2 for the appropriate size of
flexible cord.

And Table 2 clearly says

 

[JohnW2]

The highlighted paragraph clearly says:
All non-rewireable plugs shall be marked on the
engagement surface with the rated current of the
fuse-link fitted, which shall not exceed the value
given in Table 2 for the appropriate size of
flexible cord.

It does, indeed, but it doesn't actually say that the 'fuse-link fitted' may have a higher rating than that permitted by other Standards, (merely that it must not exceed the Table 2 rating).

As you say, there's nothing more to discuss.

Kind Regards, John

 

[securespark]

John, if this helps, the ESC now say that up to 700W, you use a 3A fuse and over that, a 13A fuse.

There is no inbetween (5A) anymore.

Manufacturers are now fitting appliances having 0.75mm² flexes with 13A fuses.

I found out the hard way because to me, the regs say that 0.5 flex is 3A and 0.75 is 6A, so when I came across a fridge on a PAT test with a 13A fuse on 0.75 I failed it. And got into hot water.

Doesn't make sense...

 

[Jackrae]

It seems quite clear - to me at least - that table 2 fuse ratings are a complete balls up using the 3A and 13A fuse preferences as a baseline to work from. It appears to totally ignore the capability of heating effect of the load that COULD be carried by either a defective appliance or the cable being used for a purpose not originally intended by the manufacturer.
If using a cable for a purpose for which it wasn't intended is a problem then the manufacturer should either fit a fuse sensible for the intended purpose or fix the cable to the appliance so that it does not have an alternative use.
However, nuff said on the subject.

 

[EFLImpudence]

The ESC do not make the regulations.

 

[JohnW2]

John, if this helps, the ESC now say that up to 700W, you use a 3A fuse and over that, a 13A fuse.

As has been pointed out, the ESC don't make regulations, and nor can they over-ride existing regulations. Having said that, I would have thought that the ESC were the last body one would expect to be advocating inadequately protected cables. Do they not say anything about cable size as well as fuse rating? What they are suggesting is equivalent to giving their blessing for a 2.5mm² radial circuit to be protected by a 32A OPD!

Manufacturers are now fitting appliances having 0.75mm² flexes with 13A fuses.

Well, again, manufacturers certainly don't make regulations. The CCC figures we are used to, and the concept that a cable should be protected by a fuse rated no greater than the CCC of the cable are not unique to BS7671, so I find it hard to see how a 13A fuse protecting a 0.75mm² cable can be considered acceptable. ... unless, of course, one wheels out the argument that whatever is on the end of the cable 'cannot create an overload' - but I've personally never been very comfortable with that concept. Also, as I've said, I personally don't think I agree that BS1363 is saying that one can 'fit' a fuse which is higher in rating than the the CCC of the cable, if that is the justification they're trying to use.

I found out the hard way because to me, the regs say that 0.5 flex is 3A and 0.75 is 6A, so when I came across a fridge on a PAT test with a 13A fuse on 0.75 I failed it. And got into hot water.

Into hot water with whom? Did you argue your case?

Doesn't make sense...

It sure doesn't.

Kind Regards, John

 

[ban-all-sheds]

I personally don't think I agree that BS1363 is saying that one can 'fit' a fuse which is higher in rating than the the CCC of the cable, if that is the justification they're trying to use.