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Topic Title: How would you extend 6 cables to a shifted CU
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Created On: 29 April 2014 09:59 PM
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 29 April 2014 09:59 PM
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bowmandj

Posts: 139
Joined: 04 October 2011

As part of my retraining to come back into the electric install field I am working with an electrician friend and using Gedankenexperiment methods to think of scenarios of change and how we would go about implementing that change.

One we cannot agree on is the scenario where we are changing a CU in a cupboard under the stairs. An old style fuse unit is coming out and being replaced by a split RCD 17th edition version.

The old unit is high up in the cupboard near the apex of the right angled triangle formed by the pitch of the stairs and the end wall of the cupboard. The new CU is much wider then the old fuse unit so has to go several inches lower where the triangle widens.

But this means that all of the fixed wiring (coming in through the apex where it runs into the ceiling/floorboard void of the upstairs floor) is too short to reach the new CU. No slack is available even if the floor boards are lifted.

So how does one extend the cables to reach the new CU. Let's say two rings, two light radials, a cooker feed and an immersion feed.

Do we crimp extend, use maintenance free connectors (Hager/Line), use old fashioned junction boxes (as access to check is easy) or insist on a total rewire to the first connection (light rose, socket etc.).

Continuous wire runs are best but expensive; and a joint is no more a disruption then an added socket, spur take off or added light rose.

How would you tackle this scenario balancing cost saving, safety, regulations and idealism (e.g. NICEIC inspection :-)
 29 April 2014 10:06 PM
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aligarjon

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If the cables had to be joined where they are i would use a large adaptable box and maintenance free connectors. i wouldn't attempt to crimp in such a tight space. label the connections as clearly as possible. lots of JB'S would be messy and difficult to fix them all if the cables are short

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 29 April 2014 10:19 PM
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Zs

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bowmandj,

what is gedankenexperiment? has that got something to do with thinking or maybe having thanked?

Anyway, if it is thought, then your are in the very honoured position of gedanking before being faced with it and I envy you that. I'd like to suggest that you have a look at a smallish enclosure with a din rail and some din rail mounted connectors. I think they are lovely to work with and they make maintenance very easy because they are leicht zu lesen if you get my drift. ( Ich gedank that might mean that they are easy to read). French is much more my thing you understand.

I also envy you the planning before embarking and wish you luck.

Zs
 29 April 2014 10:23 PM
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mantutu

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As above, I have used adaptable boxes and used a mixture of din rail mounted connectors and maintenance free types. The current maintenance free types I have found lacking, in that they do not have the capacity to accept cables larger than 4mm.
Panel builders often use the din rail type connectors, and they offer a reasonable solution to extending cables.
 30 April 2014 06:50 AM
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MrP

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Plastic enclosure top hat din rail with SAK terminals 50X50mm trunking down to your new board http://catalog.weidmueller.com...D=group38792268639556
Job done looks like it grew there
Good luck buddy
MrP Day 14
 30 April 2014 07:42 AM
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dickllewellyn

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Plus one for the din rail connectors.

It may not be the cheapest way of doing the job, but certainly the most satisfying, and it looks the business. I quite often do lighting joints this way now too as I can bring all the wires in the top side, and link between connectors on the bottom side with gay abandon.

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 30 April 2014 08:50 AM
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mapj1

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Of course in a real situation you may need to mix and match depending on the shape of the space available and how easy the working is. For example you might want a couple of simple rectangular JBs, for the heavier cables like shower or cooker, and then do to the DIN rail approach for all the rest.
For what its worth WAGO make some dinrail connectors under the name 'TOP-JOB' that are bothe DIN rail and screwless, I have used these to great effect inside genset powered equipment where we had a similar short wires problem plus a lot of vibration. There are terminal and 2 terminal variants in a variety of current ratings. Worth having a few sizes in the tool box. They can also be used in many designs of modern DIN rail CUs as a far better way of anchoring odd joints that sometimes arise as a lack of forethought by the previous occupant, and look much more business compared to those embarrassing bits of flying choc bloc, that always make it look a bit like a telephone cabinet.
regards Mike.
PS If the customer will stomach it, then while your there put in a cheap bulkhead light and a socket in the cupboard - it makes it so much easier to read the meter and if they ever want to put IT equipment in there or plug in a clip lamp or drill, you will be in someone's good books.

-------------------------
regards Mike
 30 April 2014 09:15 AM
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MadCookie

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adaptable + maintenance free would be my solution too, if you had the space, but some times you have to go with the flow on these type of jobs and adapt you're prefered method with achievable methods.
 30 April 2014 09:16 AM
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bowmandj

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Good set of inputs so far, thanks all.

Nobody has gone for crimp or solder yet. My electrician friend was of the view that continuous metal conductor was best (crimp, rewire or solder) whereas I would be happy with a contact joint like MF connectors or even screw down (given that the CU with screw connections is only 6 inches further down).

I like the idea of a DIN rail collection of different gauge MF connector blocks. Very neat but more pricey then some solutions.

Incidentally the 'bloke down the pub' suggestion was to keep the old fuse box and gut it to make an enclosure in the right place and with the cables in place, then use strip connectors up to 60A rating to join old to new stibs http://www.screwfix.com/p/60a-...ack-of-10/27483


The 12 way strip would take the 6 cables L&N and a second lower rated strip on top would take the earths.

With the 60A strip you can pass through a 2.5 or 1.5 from each side to get double screw pressure on the conductors as well as having side by side lay contact.

Edited: 30 April 2014 at 09:38 AM by bowmandj
 30 April 2014 09:25 AM
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bowmandj

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To Zs.

The word gedankenexperiment essentially means a 'thought experiment' and is just a German phrase to mean perhaps 'brain storm' or 'think tank' in our parlance.

Much as we might say 'de ja vu', 'Dos vedanya' or 'status quo'
 30 April 2014 09:49 AM
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Crazycolours

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Originally posted by: bowmandj

Good set of inputs so far, thanks all.



Nobody has gone for crimp or solder yet. My electrician friend was of the view that continuous metal conductor was best (crimp, rewire or solder) whereas I would be happy with a contact joint like MF connectors or even screw down (given that the CU with screw connections is only 6 inches further down).



I like the idea of a DIN rail collection of different gauge MF connector blocks. Very neat but more pricey then some solutions.



Incidentally the 'bloke down the pub' suggestion was to keep the old fuse box and gut it to make an enclosure in the right place and with the cables in place, then use strip connectors up to 60A rating to join old to new stibs ">http://www.screwfix.co...0a-.....7483





The 12 way strip would take the 6 cables L&N and a second lower rated strip on top would take the earths.



With the 60A strip you can pass through a 2.5 or 1.5 from each side to get double screw pressure on the conductors as well as having side by side lay contact.


Hi bowmanji,

Don't use your 'bloke down the pub' idea - it will look a bodge! Use appropriate size adaptable box and din rail connectors with 50x50 trunking. Din rail connectors are available in all the ratings that you require and look professional (which you are of course).

Regards, C.
 30 April 2014 11:33 AM
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bowmandj

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Hi Crazycolours

don't worry this is not a real situation (yet). I and an electrician friend are 'brain storming' various solutions to scenarios we have seen and what we would do if we had to do the job. The example I gave is one I have seen could be done in the future. I was replacing a broken socket cover but I always look at every installation to see where it is at and what might be good to do in the future. The CU replacement is just such a change.

Had the customer wanted extra circuits then the old fuse box would have had to go and a new 17th split CU go in. So I am just looking at the various peoples ideas of how they would go about executing this work; a sort of 'work experience by committee' if you like.

It is interesting to see how some people feel a 'professional' look using modern technology is perhaps best even if the connection strip option is technically okay (and cheaper).

Finding the middle ground between 'replace with the best modern practice' and 'minimal pragmatic change' is the hardest thing to do.

If the house were small and compact and had an old dear living only on state pension should I install differently to a large detached house with a professional level of annual income household and expensive car on the drive.?
 30 April 2014 12:11 PM
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OMS

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If the house were small and compact and had an old dear living only on state pension should I install differently to a large detached house with a professional level of annual income household and expensive car on the drive.?


Go back a step - first decide why swapping out the consumer unit and leaving existing wiring and accessories in place is a worthwhile exercise.

What alternatives exist ? - front end RCD perhaps, replace fuses with plug in MCB's

The "brain dump" needs to back up and look at the problem first and then the potential solutions

Regards

OMS

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Failure is always an option
 30 April 2014 12:20 PM
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mapj1

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To a degree, yes, not because the regs differ, because they don't, but because the likely load, roughness of use, condition and potential for further expansion of the installation is very different, as is customer expectation.

Your example of the old lass, will never want two showers and the cooker all on at once, and one meandering ring will probably do for all the sockets she ever needs, but I'd strongly urge an RCD somwhere in easy reach, but not just one that cuts all the lights off as well. A five bed house with 2 electric showers and big kitchen with every mod-con may require more circuits and a 'go in big and leave lots of slack' approach with lots of RCBOs.
Equally the sort of house intended for young children requires more imagination with impact protection and 'fiddle proofing' than one occupied by a single adult, but the latter may be more appreciative of new sockets or switches being moved to easy reach locations and more tolerant of cosmetic stuff like surface trunking and blanking plates achieve this in budget.

so yes, horses for courses
M.

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regards Mike
 30 April 2014 12:35 PM
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bowmandj

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To OMS

I agree.

We had discussed a lot more options for this scenario. The bit we could not agree on, and so the reason I put it out to the greater knowledge, was the jointing of the cables where we did choose the CU swap option. So my post restricted to that alone, and it was interesting to see the responses for cable jointing.

But yes we had gone through a lot of other options as well from modify the current fuse box to MCB's, add a small CU and extend only the RCD circuits and leave lights on the old box (with or without MCB change) to installing a supply line RCD (wary that this could kill lights, freezer and fridge for an RCD trip on steamy kitchen).

Jointing the cables was the one we were at opposite ends on.
 30 April 2014 04:57 PM
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Fm

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What about the industry standard of connector block lashed up with insulating tape, i always try to better the minimum standard so use duck tape
 30 April 2014 05:12 PM
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AJJewsbury

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Nobody has gone for crimp or solder yet. My electrician friend was of the view that continuous metal conductor was best (crimp, rewire or solder)

Certainly the traditional view - early versions of the regs insisted that all joints were 'united with solder'. Currents regs seem to take a dimmer view - 526.2 demands that for soldered joints we take account of 'creep, mechanical stress and temperature rise under fault conditions'. As some solders are fully molten at 180 degrees and maximum conductor fault temperatures starting at 160 degrees you can see the worry.

Crimping solid core cables is also controversial (just search this Forum) - the basic issue being that most small crimps are designed for stranded rather than solid conductors - the few types where the manufacturer accepts their use on solid cores it's conditional on using their special tooling - the cost of which makes using MF or DIN rail terminals look very attractive (unless you're doing hundreds).

- Andy.
 30 April 2014 06:21 PM
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rocknroll

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LOL I think there is a new breed wind up here, on my visits I never see these all singing dancing connection techniques, all I ever see is a RB4 with the appropriate strip connectors inside all very neatly done and cables neatly clipped to the new CU, if there is an excess of circuits which is not very often in domestic premises then two RB4,s together, some a work of art of what is a tried and tested method.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
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"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
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 30 April 2014 06:28 PM
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OMS

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Originally posted by: rocknroll

LOL [IMG][/IMG] I think there is a new breed wind up here, on my visits I never see these all singing dancing connection techniques, all I ever see is a RB4 with the appropriate strip connectors inside all very neatly done and cables neatly clipped to the new CU, if there is an excess of circuits which is not very often in domestic premises then two RB4,s together, some a work of art of what is a tried and tested method. [IMG][/IMG]

You're lucky to see the RB4 - I've seen plenty of choc blocks inside the stripped out old consumer unit - which usually has some quite innovative materials stuck to it to fill up the gaps. There is no enclosure problem that can't be fixed with a "bit of plastic sheet" and a mastic gun

4oz tobacco tin and screwits ?


regards


Regards

OMS

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Failure is always an option
 30 April 2014 07:43 PM
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bowmandj

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So we are back to the 'bloke down the pub' option again :-)
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