Old Wooden backed Wylex CU's - The position???

[jj4091]

Why does everyone seem to have a go at Wylex, they weren't the only manufacturer who made consumer units with a wooden frame & some of them for longer than they did.

 

[davelx]

The old school wylex and rewireable fuses where built to a british standard which is still recognised in the regulations.

At least according to http://www.tlc-direct.co.uk/Book/4.3.8.htm they are recongnised but with a special requirement to derate cables fed from them which means circuits connected to them generally won't comply.

That derating factor has nothing to do with the fact that the rear body of the CU is wood. Even allowing for the derating, the standard circuits can usually comply in an older property that has solid walls

 

[Lectrician]

3036 fuses have long been recognised, and continue to be recognised in the regulations.

The fact that there is a derating factor for the 3036 proves it is still current and recognised

 

[flameport]

The 3036 fuses are probably acceptable (subject to the cables being the correct type and installed correctly)

The wooden frame / open back is not compliant with the current edition of BS7671 (or several previous versions either).
526.5 (iii) An enclosure partially formed or completed with building material which is non combustible...

As most of these old fuseboxes were mounted on plywood boards or other timber, this is clearly NOT a 'material which is non combustible'.
Mounting it direct onto brick, or fitting the paxolin back panel fixes that problem, but there is still the issue of the wooden frame forming part of the enclosure.

There is also 421.3, regarding arcs, sparks or particles at high temperature being emitted, and enclosures being made from arc-resistant material.

As for PIRs, these would be a code 2. No immediate danger, but clearly in need of improvement. Due to the age of these fuseboxes, it is very unlikely they would be large enough for a property today anyway - and any circuit over 30A cannot be connected to them either.

 

[Lectrician]

The only real issue with a 3036 comes when you have an old install with 2.5/1.0 T+E.

 

[kai]

...or a lighting circuit wired in 3/029 with the earthing missing, but class one fittings found in the house.

 

[RF Lighting]

But the fuse type doesn't make any difference to that installation.

It does on a 2.5/1.0 circuit

 

[Spark123]

One that puzzled me a bit, reg no 433.1.5 allows a ring final circuit to supply accessories to BS1363 as long as the current carrying capacity of the cable (Iz) is not less than 20A.
The current carrying capacity for a 2.5 flat twin and earth clipped direct from table 4D5 is 27A before any correction, where a BS3036 is used the Iz for it will be 27x0.725 = 19.58A without applying any other correction factors therefore does not comply with 433.1.5

 

[securespark]

But the fuse type doesn't make any difference to that installation.

It does on a 2.5/1.0 circuit

More than a tad late on this one, but you're quite right.

The issue concerns the csa of the cpc not allowing adequate disconnection times on a RF circuit.

It is addressed by swapping the 3036 for a breaker suited to the maximum Zs of the circuit.

 

[Spark123]

A 1mm CPC is too small to comply with the adiabatic equation when a 3036 is used, especially a problem on any spurs.

 

[FingRinal]

As most of these old fuseboxes were mounted on plywood boards or other timber, this is clearly NOT a 'material which is non combustible'.

Yet most kit is installed on the (fireproof) backing board installed by the REC.

The requirement is for the backing material to be non-combustible when tested to BS476 Part 4 or fixed directly to building fabric having the ignitability characteristic P of BS476 Part 5.

So is it right that such components are damned without checking whether or not they would pass the above tests? If you can do so, fair enough - but if you can't, how does that square off with your professional indemnity insurance and liability?

 

[holmslaw]

..

 

[ban-all-sheds]

The current carrying capacity for a 2.5 flat twin and earth clipped direct from table 4D5 is 27A before any correction, where a BS3036 is used the Iz for it will be 27x0.725 = 19.58A without applying any other correction factors therefore does not comply with 433.1.5

It does if you round to the nearest integer...

Prior to 16th Amendment 1 2002, the requirement was for the cable capacity to be 0.67 x In. Has there always been a correction factor for rewirable fuses? When they were all that were ever used (in homes) it seems a bit AAF for you to have needed a correction factor all the time - why not just adjust the size of the fuse wire, so that a "30A" fuse actually had what today would be classed as an In of 22A?

But it is interesting to read the text of Amd 1 - there the concern was not BS3036s, but 32A MCBs, meaning Iz had to be 21.44A, and for Ref Method 4 2.5mm² was rated at 18.5A. They tried ignoring this on the grounds that it had been done for years and was OK in practice but, and this I love, "the issue would not go away".

So the IEE asked the ERA to test flat T/E cable, and as if by magic the current ratings went up.

 

[FingRinal]

So is it right that such components are damned without checking whether or not they would pass the above tests? If you can do so, fair enough - but if you can't, how does that square off with your professional indemnity insurance and liability?

Because the regs are not rectroactive.

I'm not sure to what part of which question you are answering there

But the retroactive argument is always interesting, in that it is usually rolled out by those who prefer not to think. They take that position with every Reg and every Edition and follow it blindly - even when carrying out a Report in accordance with the current edition.

There is no Reg that says that. There is no explicit reference in any other relating document that says that -yet it is perpetuated like the best of trade counter knowlege. It might be hinted at in 'roundabout' terms such as 'likely to', but never explicitly.

People get bogged down in the detail. They memorize the Regs but not Chapter 1. They obsess about PIR codes without reading the info in GN3 about the purpose and reason for a PIR. The ESC makes things worse by dumbing down I&T to the lowest level possible. All we get is churned out rhetoric without care or consideration of the type of installation and it's use (and users).

It's hard to think, so most don't.

 

[FingRinal]

So the IEE asked the ERA to test flat T/E cable, and as if by magic the current ratings went up.

Magic...??? No. They just read the book 'Harmonization - My Part In It's Downfall'. An unpublished work, distributed in secret by the IEE and other 'interested' parties.