Lollipop

[DetlefSchmitz]

John, I think you are ignoring the specific exemption in:

433.3.1 General
A device for protection against overload need not be provided:
(i) for a conductor situated on the load side of the point where a reduction occurs in the value of current carrying
capacity, where the conductor is effectively protected against overload by a protective device
installed on the supply side of that point

which is explicitly referred to in 433.2.1

(I could be wrong though, as so I so often am, and you may be talking about something completely different)

 

[JohnW2]

John, I think you are ignoring the specific exemption in: ...
433.3.1 General .... A device for protection against overload need not be provided: (i) ....

You're right. I missed that - but the reason I missed it was ...

... which is explicitly referred to in 433.2.1

... which is not strictly true. 433.2.1 "explicitly refers" to 433.3 - so I literally looked just at that, not at sub-clauses thereof. I suppose that makes it my fault, but I'm nevertheless pleased to see that, contrary to what we thought, it does take into account "the obvious".

Kind Regards, John

 

[EFLImpudence]

It does seem to solve the problem in question, but -

If you are arguing about the wording of various regulations, I think that 433.3.1(i) is even dafter.

It effectively says:

433.3 Omission of devices for protection against overload

433.3.1 General
A device for protection of overload need not be provided:

(i) for a reduced CCC cable, where one is already provided.

I did say it was obvious.

 

[JohnW2]

It does seem to solve the problem in question, but - If you are arguing about the wording of various regulations, I think that 433.3.1(i) is even dafter.

I agree - but, as I said before, if something like that was not stated somewhere (and linked to 432.2.1), THEN 432.2.1, as CURRENTLY worded, would mean to Mr Jobsworth that an additional OPD had to be provided, even when it was 'obviously unnecessary'.

Kind Regards, John

 

[SUNRAY]

I've never really thought about it before but, yes, those who wrote 433.2.1 clearly didn't think it through properly.

The requirement for an OPD at the point of reduction in CCC should obviously only apply if there is not already an upstream OPD which is adequate to protect the cable downstream of the reduction in CCC.

Kind Regards, John

I've just come back to this thread and found loads of unread posts. I've struggled to highlight the ideal point to quote and reply so apologies if I seem to be in the wrong place.
I can see the sense of the OCD at the point of reduction having worked on a 'submain' which re-used a 6mm² circuit then extended with 2.5mm² to a garage.
The typed MCB list attached to the main CU showed the circuit as Cooker B32 6mm² crossed through and changed to Garage B20 2.5mm² which was amended again to B40 6mm² The 2.5mm² section had been running hot enough to soften and shorted at a very sharp bend.

I don't know the full history but the Garage had been extended with an extra room and there were 2x 32A rings. The owner was running lots of heating in the room for his home made wine and was also a keen car diy'er so heating and welding etc. and a 3KW instant water heater.
We replaced the 2.5mm² feed with 6mm².

If there had been a 20A OCD at the junction...

 

[EFLImpudence]

Not sure what your point is -

If there had been a 20A OCD at the junction...

Or any other appropriate position.

 

[JohnW2]

I can see the sense of the OCD at the point of reduction having worked on a 'submain' which re-used a 6mm² circuit then extended with 2.5mm² to a garage.

Yes, of course, the 2.5mm² cable needs to have adequate protection.

However, IF the 2.5mm² cable were adequate for what it's supplying (seemingly not in the case you describe) , and IF the 6mm² cable does nothing more than feed the smaller cable, then it simpler just to reduce the rating of the OPD at the start of the 6mm² cable, rather than having to have a second OPD at the point of CSA reduction.

Kind Regards, John

 

[SUNRAY]

Yes, of course, the 2.5mm² cable needs to have adequate protection.

However, IF the 2.5mm² cable were adequate for what it's supplying (seemingly not in the case you describe) , and IF the 6mm² cable does nothing more than feed the smaller cable, then it simpler just to reduce the rating of the OPD at the start of the 6mm² cable, rather than having to have a second OPD at the point of CSA reduction.

Kind Regards, John

Like you, I'd not think of inserting an MCB half way along a circuit, I'd rate the OCD at source to cover the whole circuit. My own shed is a 20A fuse feeding the old 4mm² shower circuit cable which is extended with 2.5mm² using a JB.
I was working on the assumption that whoever uprated the B20 to B40 thought the 6mm² went all the way to the Garage and saw no reason to not uprate it, however if there was a B20 at the point the cable reduced in size (as has been mentioned in this thread) the overheating situation would not have been happened.
I'm not defending the mistake but I can see how it could have happened.

 

[ericmark]

When I worked in manufacturing we had detailed plans of all cable runs and sizes, if one did an alteration you had to also modify the plans, so it could start as 6mm² drop to 2.5mm² and back up to 6mm² and you would see when you looked a plans what had been done.

OK there were errors, I saw an office block with a 4mm² radial where some one had broke the radial and fitted 2.5mm² cable in the middle of it with extra sockets, clearly he thought it was a ring.

But when my dads house was rewired they left minimum paper work, installation certificate, and compliance, but it does not say which socket is fed from which MCB. I have found dead sockets, clearly they had not found them, so not removed in rewire, however since there was nothing to show location of each socket, who knows.

 

[JohnW2]

Like you, I'd not think of inserting an MCB half way along a circuit, I'd rate the OCD at source to cover the whole circuit. My own shed is a 20A fuse feeding the old 4mm² shower circuit cable which is extended with 2.5mm² using a JB.

Indeed so.

I was working on the assumption that whoever uprated the B20 to B40 thought the 6mm² went all the way to the Garage and saw no reason to not uprate it, ...

Yes, either they didn't realise (in which has they didn't really look carefully enough), or else they were plain stupid.

.....however if there was a B20 at the point the cable reduced in size (as has been mentioned in this thread) the overheating situation would not have been happened.

Yes, in theory not. Although a B20 shoudl allow about 29A to flow for around and hour, that is deemed to be 'safe'.

Kind Regards, John

 

[securespark]

when I returned every one was watching their back.

Partly because the 15th went super ubercrazy with bonding, connecting nearly everything made of metal.
I think I've bored you before with an elderly relative's house which had the Crittall windows bonded and even links put between the frames and the opening lights....

It is always explained that regs are a minimum standard. Many people working to the 15th got worried and interpreted the need to do more bonding than was necessary.

 

[ericmark]

Yes agreed. However one reads court cases and often one thinks there by grace of god goes I.

I read the report on Emma Shaws death and have to admit I would have sent an electricians mate to plug in a loop impedance tester and note reading.

OK I would not have raised paperwork with the electricians mates name on it, but he should have been skilled enough to plug it in push a button and write down the readings, if it says OL then write down OL, and if I had seen a reading of OL I would have gone to site and retested.

How it is seen as OK to go into a site hut and fudge up some results I don't know? It is not what the electricians mate did which is a problem, it is what the courts did, so now you can't use electricians mates without an electrician being with them at all times.

 

[SUNRAY]

I think I've bored you before with an elderly relative's house which had the Crittall windows bonded and even links put between the frames and the opening lights....

I did a fair bit of work in the late 70's - early 80's for a developer and had to bond ALL EXPOSED METALWORK. The inspectors would test every window handle and hinge on wooden windows etc.

They got the plumbers to 'ream out' copper T pieces and slip them over the pipe then run a piece of pipe to the adjacent pipe, ie this linked 2 pipes together without a water connexion and still the inspectors of the time wanted to see earth clips doing the same job.

 

[EFLImpudence]

Did they test to see if it was bonded by holding a live wire in one hand and touching the part in question with t'other?

 

[John D v2.0]

that was when someone at the IEE bought shares in the clamp makers!