Junction Box for Extending Old Wired Fuse Board

[Vitesse]

I went to look at a job the other day for a customer to install a Hot Tub supply in the garden. Whilst there I found that an 'electrician' in the past had extended all the cables down from where an old wired fuse board used to be located to an RCD protected CU.

It was basically a bodge where they had crimped and terminal blocked all the existing T&E, to new and tried to ram it all inside a JB to make it look pretty but over time the JB had split in two and when I took the cover off I found an unsafe mess with obvious signs of damage between conductors that looked like someone had decided that a bit of insulating tape would resolve the problem!

I said to the customer the first priority before I do anything is to sort out that mess, which he has no problem with. I also pointed out that I would need to test each circuit to make sure they were all ok.

You can see the brickwork where the old fuse board used to be. Above the white is plasterboard that goes up about a foot before it disappears into the floor void above and all the T&E is run in galvanised steel attached to the brickwork. I can remove that plasterboard and free up some slack to allow me to terminate it okay.

My question is I am looking at terminating in a JB using din rail mounted Legrand Viking 3 terminal blocks, I can't remember the exact number of circuits it's written down in my note book in the van but I think it was 3 x 2.5, 2 x 1.5 and 1 x 6. If I go down this route does the JB need to be metal to conform with AMD3? It's probably in the grey area!!!!

Or does anyone have any better suggestions to extend the circuits down safely?

 

[Pete999]

I asked Elecsa technical way back when if I could use the New DRE-5 v2 DIN Rail Enclosure - https://www.connexbox.com/dre-5-din-rail-enclosure.html for a CU move, and was told 'no, it has to be A3 non combustible', only to watch an NICEIC/Elecsa 'Web in Air', where Darren Staniforth said such plastic enclosure could be used. I sent another email to Elecsa Tech Support, to ask if they could clarify such a discrepancy in their advice they are giving. Tumble weed, no reply.
Think the issue is, 421.1.201 is so vague, and the 'grown ups' haven't really got their collective heads around this. I spoke to a Connexbox rep, who was not a happy bunny. He said he was going to raise the subject with IET etc. I notice their gallery on the enclosure with a CU change is no longer on their site?

Well there's a surprise, the left hand doesn't know what the right is doing

 

[Risteard]

I do remember some edict from somewhere on a clarification of 'similar switch gear assemblies', as BS7671 only defines 'Switchgear'.

I'm afraid I don't have a link to that. However I have suggested that an upfront RCCB in a TT installation could be in an insulating enclosure as it is entirely possible to argue that this isn't a "similar switchgear assembly" to a distribution board (and that the IET Wiring Matters article suggested this was to cover the likes of three-phase distribution boards in large domestic dwellings). However this opinion of mine is not held universally and therefore you would need to come to your own conclusions about that in the absence of clarification from JPEL/64.

However it is difficult to see how anyone could classify a junction box as a switchgear assembly of any sort, least of all one similar to a distribution board.

Again, this is all my opinion and others must draw their own conclusions!

 

[Risteard]

AMD 3 is always a popular subject for IET-bashing, but it might have been one of the few options that stood a chance of controlling the spate of CU fires that was actually within their scope. They aren't reponsible for policing ports for defective imported goods made of too-flammable plastic, so they can't directly control what tat gets installed. They can't throw people in jail for installing it wrongly. But they still have to somehow reduce the incidence of fires. Bad connections have been overheating since the beginning of electrical wiring, often due to poor work. But they can't ban connections, nor realistically insist that every connection is enclosed in a non-combustible casing (all-metal PIR casing?). What they have to do is pinpoint the hotspots (literally) and do something to contain them.

In a CU there are many connections and potential heat sources, contacts that can arc and indeed probably will at some point, all lumped together in one place. In a domestic situation, other than the shower or cooker circuit by far the largest currents flow there, plus the highest PFCs are found there. The connections in the CU are the ones most likely to be disturbed again and again during EICRs. Compared to many other accessories, the CU is likely to be hidden from view. With all these fire risk factors located in one place, a logical man might say, if there was one electrical assembly in a house, other than current-using equipment, that was most likely to benefit from a non-combustible enclosure, on balance of probabilities it would be the CU.

OK you can contrive a situation where there is as much risk of terminal burnout in a multi-circuit junction box (although there still won't be any terminals carrying the total installation load like in the CU) but that is the exception rather than the rule. And if the terminals are say Wagos or other semi-foolproof types or well-engineered DIN rail terminals, actually they are less likely to make bad connections than the CU busbar.
So while AMD3 metal CUs are a workaround that fail to solve the the core problem, I personally don't think they are as bad an idea as some people make out, nor that it is illogical to require a metal CU, but allow a nearby multi-circuit JB to be plastic.

Well put.

 

[Pete999]

I'm afraid I don't have a link to that. However I have suggested that an upfront RCCB in a TT installation could be in an insulating enclosure as it is entirely possible to argue that this isn't a "similar switchgear assembly" to a distribution board (and that the IET Wiring Matters article suggested this was to cover the likes of three-phase distribution boards in large domestic dwellings). However this opinion of mine is not held universally and therefore you would need to come to your own conclusions about that in the absence of clarification from JPEL/64.

However it is difficult to see how anyone could classify a junction box as a switchgear assembly of any sort, least of all one similar to a distribution board.

Again, this is all my opinion and others must draw their own conclusions!

A junction box used in this scenario IS a distribution board, is it not? it's distributing circuits to the CU.

 

[westward10]

It is clear from BS7671 that the junction box need not be fire resistant. Just seems an oddity that if I relocate and replace a CU in a dwelling the CU would have to metal but the joint box I use to extend the circuits would not. I agree with Luciens' excellently scripted post entirely but it just seems wrong, though it is clearly not the case.

 

[Vitesse]

In my experience I have been to people's houses and I don't know if I have particularly good hearing but you can quite often hear the arcing in the CU. The reason I say that is I went to a house recently and another spark had been there before me and couldn't fix the problem. As soon as I took the cover off I could hear the buzzing straightaway, how the last guy had missed it I don't know?

It turns out someone hadn't terminated at least 2 of the MCB's cage clamps on the busbar properly and it had virtually eaten away the cooper prongs on the busbar.

 

[Risteard]

A junction box used in this scenario IS a distribution board, is it not? it's distributing circuits to the CU.

That isn't the definition of a distribution board given in Part 2 of BS7671 though, or indeed a consumer unit which is described as a type-tested distribution board etc.

Unfortunately I don't have my copy of BS7671 on me at the minute to list the precise Definitions.

 

[Pete999]

That isn't the definition of a distribution board given in Part 2 of BS7671 though, or indeed a consumer unit which is described as a type-tested distribution board etc.

Unfortunately I don't have my copy of BS7671 on me at the minute to list the precise Definitions.

It's an anomaly that the mandarins at the IET seemed to have missed imo, it's clear to me that bad connections, which after all is what we are concerned with can happen in theses JB just as easily as in a CU

 

[Risteard]

it's clear to me that bad connections ... can happen in theses JB just as easily as in a CU

Of course that is true. Indeed how often do we come across burnt-out neutral connections in a shower pullcord?

 

[Richard Burns]

Since I am a definite nay sayer about the non combustible enclosure issue and do not have the confidence that it is at all a good idea my views are somewhat skewed.
One can see what the IET have attempted (and in my opinion failed) to address and it is possible that in maybe one or two cases it may help.

However bringing in the argument that any junction in a cable is liable to overheat starts you on the path to eliminating plastic entirely as an enclosure material in any installation and this I believe would raise much greater risks of shock than the fairly low risk of fire (not overheating).

It is clear that the congregation of connections in close proximity can increase the risk, as evidenced by the OP's picture of the short in the JB, but without the designed heating of parts in MCBs and the switching arcs of tripping the risks are reduced. And in my opinion the risks were not high enough to address in the first place.

 

[Midwest]

If I was an apprentice coming into the industry in a few years time, I would come across reg 421.1.201 and would probably be told of some of the background of its instigation or conception, but I would naturally just accept it as it is, just as I would with the many other regulations.

But without the specialist knowledge and expertise that others have, I would be surprised that I could replace an A3 consumer unit with a plastic enclosure with din rail terminal connections to extend the final circuits, so that I could lower or relocate another replacement A3 (or A4 or whatever) consumer unit. The logic of that would be beyond me. But then I would be just a lowly apprentice, and would tip my hat to their astuteness.

 

[crossplot]

View attachment 33359 I went to look at a job the other day for a customer to install a Hot Tub supply in the garden. Whilst there I found that an 'electrician' in the past had extended all the cables down from where an old wired fuse board used to be located to an RCD protected CU.

It was basically a bodge where they had crimped and terminal blocked all the existing T&E, to new and tried to ram it all inside a JB to make it look pretty but over time the JB had split in two and when I took the cover off I found an unsafe mess with obvious signs of damage between conductors that looked like someone had decided that a bit of insulating tape would resolve the problem!

I said to the customer the first priority before I do anything is to sort out that mess, which he has no problem with. I also pointed out that I would need to test each circuit to make sure they were all ok.

You can see the brickwork where the old fuse board used to be. Above the white is plasterboard that goes up about a foot before it disappears into the floor void above and all the T&E is run in galvanised steel attached to the brickwork. I can remove that plasterboard and free up some slack to allow me to terminate it okay.

My question is I am looking at terminating in a JB using din rail mounted Legrand Viking 3 terminal blocks, I can't remember the exact number of circuits it's written down in my note book in the van but I think it was 3 x 2.5, 2 x 1.5 and 1 x 6. If I go down this route does the JB need to be metal to conform with AMD3? It's probably in the grey area!!!!

Or does anyone have any better suggestions to extend the circuits down safely?

Well, sorry bud, but had I seen something in such poor condition, the least I would be advising is a rewire(If there is not sufficient slack to terminate into a new fuseboard) of the first and last legs of the ring main and lighting/ or affected circuits.
Im not doubting you will leave it in safe condition, but you are last man in.

Are you really going to be happy leaving a termination box metal or other in situ after you have seen it? I wouldn't!

Just my 2p's

 

[Andy78]

Well, sorry bud, but had I seen something in such poor condition, the least I would be advising is a rewire(If there is not sufficient slack to terminate into a new fuseboard) of the first and last legs of the ring main and lighting/ or affected circuits.
Im not doubting you will leave it in safe condition, but you are last man in.

Are you really going to be happy leaving a termination box metal or other in situ after you have seen it? I wouldn't!

Just my 2p's

What aspects of and issues with a connection box to extend cables would you not be happy with to necessitate hundreds of pounds worth of disruptive work ?

 

[westward10]

Well, sorry bud, but had I seen something in such poor condition, the least I would be advising is a rewire(If there is not sufficient slack to terminate into a new fuseboard) of the first and last legs of the ring main and lighting/ or affected circuits.
Im not doubting you will leave it in safe condition, but you are last man in.

Are you really going to be happy leaving a termination box metal or other in situ after you have seen it? I wouldn't!

Just my 2p's

Can't see how you can justify a rewire from viewing a single picture?

 

[Vitesse]

Well, sorry bud, but had I seen something in such poor condition, the least I would be advising is a rewire(If there is not sufficient slack to terminate into a new fuseboard) of the first and last legs of the ring main and lighting/ or affected circuits.
Im not doubting you will leave it in safe condition, but you are last man in.

Are you really going to be happy leaving a termination box metal or other in situ after you have seen it? I wouldn't!

Just my 2p's

Well as I said in the original post. I can free up slack by removing some plasterboard. The house was probably built in the 1980's and the internal wiring is in very good condition. The only problem with it is where some cowboy has come along and put that JB in and crammed everything inside it.

If it is terminated correctly in a suitable enclosure that contains correctly rated terminals then I am more than happy to do so. Why do manufacturers make such enclosures and terminals if you deem them unsafe? I am sure they do plenty of R&D to ensure what they sell is safe. If you took your train of thought then nobody would use Wago's or similar.