IET logo
 
IET
Decrease font size
Increase font size
Topic Title: 'old style' twisted cpc's satisfactory/not unsafe
Topic Summary: in engineering and/or regulatory assessment
Created On: 17 March 2017 09:11 PM
Status: Read Only
Linear : Threading : Single : Branch
1 2 Next Last unread
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 17 March 2017 09:11 PM
User is offline View Users Profile Print this message



psychicwarrior

Posts: 555
Joined: 18 October 2010

How do folks...

I've seen plenty of old joint boxes with cpc's all twisted together over the lid. Plenty of comments given in discussion, 'ah the old ways, but sound none the less even if frustrating...' etc. Indeed there are similar questions asked over time with varying views.

Attended a centre the other day (installation ~10yrs old) and noticed in passing, that a lot of the mains voltage lighting across the flat roofs of the rooms (at least not readily accessible) was connected using unenclosed terminal blocks laid in and amongst insulation, dust and other debris. Most of the connections on the radial also had unsheathed twisted together cpc's. To be fair a lot looked very tightly twisted together some not so. All generally tatty standard of work in my opinion.

So to my question just concerning the twisted together cpc's ... what in forum regulars' experience is considered/or constitutes a reliable connection...in engineering terms, concerning Regs and just general acceptance/opinion ?

Is an unenclosed, unsheathed cpc twisted together and not 'locked down' (screwit, screw terminal etc) along a circuit acceptable; acceptable as in just an 'improvement required' assessment ?

It's fine having standards and Regs to aim at safety and consistency and measure etc, but is the above a sound and durable connection as some will maintain...... and if it is, how can that be established as such ?
 17 March 2017 11:07 PM
User is offline View Users Profile Print this message



broadgage

Posts: 2455
Joined: 07 August 2007

Not acceptable in my view and requires improvement, though not immediately dangerous. Twisted connections not IMO reliable as they may in time work loose. Should be made by terminal blocks, wagos, or POSSIBLY by soldering, or other suitable means.

Likewise terminal blocks loose above a false ceiling also require improvement, but are unlikely to be immediately dangerous.
 17 March 2017 11:16 PM
User is offline View Users Profile Print this message



mapj1

Posts: 9717
Joined: 22 July 2004

Actually I dont think a twisted join without solder or screwit or similar was ever permitted, even going back to some of the older pre-war regs I have sight of.

There was a period, when CPCs on lights were new and strange, and sideburns were fashionable, and Mungo Jerry was in the charts for the first time, that there was a lot of the new T and E being wired into circuits with accessories that had been originally made for the old T without E, so generally fittings were a terminal short, in ceiling roses junction boxes etc.
Cutting it long and putting the CPC join in a single slice of choc block outside the enclosure might just about be OK, but twisting hopefully and letting it take its chance is really not on.

IT may work, and undisturbed is no worse than bare overhead live wires but especially in a loft with boxes of Christmas decs and old suitcases, it is quite likely to be pulled, and would from me at least, attract the same opprobrium as ceramic screwits, which lose the appeal once you have trodden on one and broken the ceramic against the joist, leaving an upturned top-knot of live stuff to penetrate the sole of the sandals. at the very least one of the wago type things should be put in its place.
open choc bloc is a regs fail, but in my eyes slightly less dangerous, so long as its not obviously wired with wire that has been cut 'hairy'

-------------------------
regards Mike
 17 March 2017 11:37 PM
User is offline View Users Profile Print this message



sparkingchip

Posts: 10196
Joined: 18 January 2003

A couple of weeks ago I took out a old yellow MEM rewirable fuse board with a steel enclosure installed around 1967.

The only conductor connected to the the earth bar inside the fuse board was to earth the board itself. The lighting did not have a CPC and the four CPC's of the cooker, socket ring and immersion heater circuits were twisted into a three foot long tail coming down and out of the fuse board to the supplier earth terminal.

Andy B
 18 March 2017 09:26 AM
User is offline View Users Profile Print this message



dustydazzler

Posts: 1513
Joined: 19 January 2016

Back to the OP
If the install is 10 years old ish , seeing twisted bare earths outside the junction boxes or pulled long and in connector strip is a bit naff Imo

If the install was 50 years old I would expect to see some bare twisted earths , especially on the lighting
 18 March 2017 10:51 AM
User is offline View Users Profile Print this message



Zoomup

Posts: 3450
Joined: 20 February 2014

I have come across many of these types of arrangements when an old brown circular junction box had its C.P.C.s pulled out and then they were twisted together outside the junction box. I had assumed that that arrangement left more room inside the junction box for the propper important wires. In some cases the old tinned copper C.P.C.s were just twisted together. In others that may have had a screw connector attached. I never thought for one moment that there was a risk of danger or that they would untwist themselves or come loose-how could they? Many were under floors or out of the way in lofts. But it is not good practice in my opinion. Good workmanship and all that......

Bye,

Z.
 18 March 2017 11:40 AM
User is offline View Users Profile Print this message



Angram

Posts: 652
Joined: 23 March 2009

This is not an answer: but, I remember when very young my early hero electrician explaining that "earth" wires inside a "fuse box" were all just twisted together in one large bunch. They were not important enough for a brass strip of their own!

The Wiring Regulations were much less expensive too.

Difficult to do fault testing.

Mike
Porcelaine screwits were widely used at one time, held in place by blackley tape causing low insulation readings.

Angram
 18 March 2017 11:46 AM
User is offline View Users Profile Print this message



dustydazzler

Posts: 1513
Joined: 19 January 2016

The very early small metal boards had no earth port terminal , the earths were wound around an external nut and bolt
 18 March 2017 11:57 AM
User is offline View Users Profile Print this message



psychicwarrior

Posts: 555
Joined: 18 October 2010

That's the rub isnt it. Its not the 'done thing these days' [twisted unsheathed cpc], but it's not immediately dangerous. It might be potentially dangerous though, although in reality it is unlikely to untwist unless disturbed, or does it just require improving (which never gets done perhaps) and its not dangerous at all..... exercise your judgement. Im sad P9 not joined on on the twisted CPC thing. ;-) I miss the posts.

As for the unenclosed/protected terminal blocks for live conductors...well I do consider it 'potentially dangerous' in anything other than a controlled environment with skilled people (what the hell does that mean)....otherwise you might as well not bother with enclosures and such like.

In the case I saw, I'm understanding that rock wool is not exactly easily combustible, but even so......any one else up there (decorator, roofer, handyman, unauthorised etc) with them laying around all over....what do you say "oh just mind the floating around terminal blocks when you are fishing around" :-) :-)

Afternoon of rugby coming up.... it will be electric !
 18 March 2017 12:01 PM
User is offline View Users Profile Print this message



dustydazzler

Posts: 1513
Joined: 19 January 2016

Speaking of P9 , I miss his posts
 18 March 2017 02:54 PM
User is offline View Users Profile Print this message



potential

Posts: 1642
Joined: 01 February 2007

In the mid 1960s when I first started, CPCs were just becoming a requirement for lighting.
From that time IME twisting together earth wires with no other form of clamp or twist connection has never been acceptable.
Many fuseboxes (as they were called then) only offered a single threaded post to secure all earth wires to.
One of the reasons Wylex boxes became popular was because they offered an earth bar, albeit with fewer ways than fuses in the box!
They also offered MCBs too.
Many manufacturers took a long time to catch up with the regulations with regard to CPCs.
It was still common to see a single threaded earth post in some switchgear in the early 1970s.

spelling correction

Edited: 18 March 2017 at 06:04 PM by potential
 18 March 2017 04:30 PM
User is offline View Users Profile Print this message



normcall

Posts: 8523
Joined: 15 January 2005

1966 brought the requirement and it still took until about 1970 for ceiling roses to actually come with earth terminals. Of course it was considered safer to terminate the bare earth wires (nor sleeving then) on the outside of the 20A joint boxes rather than have bare wires wandering around inside. The cheaper end of the market used to simply cut the earth wires off , whereas the 'better' contractors left them intact as you might be asked to install a fluorescent fitting in the kitchen and there it was, already to be used. Of course, you might be really lucky and have more than one sparks each doing it differently on an estate. .

-------------------------
Norman
 18 March 2017 06:02 PM
User is offline View Users Profile Print this message



jcm256

Posts: 2303
Joined: 01 April 2006

Many a T joint I made on bare earth wire stranded 7029, you unwound one strand and winded it in a coil tight around the other strands about leaving about 4 inches, separate the other 6 strands and wind three clockwise and three anticlockwise making a neat T joint, soldier the joint either with a gas lighter or a blowlamp. Yes many a time did this to take an earth from a cut-out which used to have a doubled up 7029 from the lead wipe to a screw on the metal cut out.
O the joy of rattling a bull wire fish wire under the floorboards to catch a cable or earth wire, those were the days.

Unsafe, well maybe know of one case where houses caught fire due to a jointer sending 400 volts to a housing estate. It was noted that for some reason only the ones with separate earth wire caught fire, so it was a job for rewiring with twin and earth.

jcm
 18 March 2017 07:06 PM
User is offline View Users Profile Print this message



spinlondon

Posts: 5494
Joined: 10 December 2004

If the CPC is outside the JB, what about the T&E sheath?
Is it inside the JB, or are the Cores exposed?
 18 March 2017 09:26 PM
User is online View Users Profile Print this message



geoffsd

Posts: 1787
Joined: 15 June 2010

Originally posted by: mapj1

Actually I dont think a twisted join without solder ...


Interesting.

A solder joint must be mechanically and electrically sound before the solder is applied.
The solder prevents oxidation.

So, rather than untwisting, could oxidation be the real problem? - today, that is; it obviously didn't happen in the past.
 18 March 2017 09:28 PM
User is offline View Users Profile Print this message



psychicwarrior

Posts: 555
Joined: 18 October 2010

Originally posted by: spinlondon

If the CPC is outside the JB, what about the T&E sheath?

Is it inside the JB, or are the Cores exposed?




Well that's a good one to think about. :-) There's another one...visible cores outside an enclosure....potentially dangerous, or just improvement.
 18 March 2017 09:53 PM
User is offline View Users Profile Print this message



psychicwarrior

Posts: 555
Joined: 18 October 2010

Genuinely I enjoy reading the little musings and insights from the time served experience of 'what was, once' :-)

Back to the question of reliable connection by twisted cpc's - and the assessment (in respect of regs and or engineering quality) is it potentially dangerous or just improvement required....as that is the meaningful consideration isn't it (irrespective of periodics and eicr's) ?

I suppose if you saw a loose one with other markers of poor work/wear and tear, then you might put down potentially dangerous.....but on a decent install with no other probs, you might comment to yourself....could be improved...but its ok. When is a twist a good twist :-)
 18 March 2017 11:25 PM
User is offline View Users Profile Print this message



mapj1

Posts: 9717
Joined: 22 July 2004

A solder joint must be mechanically and electrically sound before the solder is applied. The solder prevents oxidation.


Only in part. The solder actually wets the copper, so the area of contact is no longer a few points of contact where the forces of the joint have squeezed the wire out of circular - much like all tyres are a little flat at the bottom, or there would be no great contact area with the road.

The solder flows, assuming everything was clean and well fluxed, and will cover the whole outer of each strand, wicking between them, giving an enormous contact area. A solder joint is much better in terms of current carrying and overheating than a simple twisting, to get the same contact area, as for example some crimps do, an enormous force is needed to almost cold weld the metal.

While I agree it feels rough, solder can be used as a mechanical fixing, and not just by plumbers, Modern electronic practice with surface mount components, is to rely totally on the solder to hold the components on the board, no further mechanical support is needed, except for larger components, or with electronics for aircraft and other high vibration settings, where parts may also be glued.

Certainly neither the 14th edn or the 15th actually said you must have a strong mechanical join before soldering. There are general words that imply when joined it needs to be adequate for the location, and no higher resistance than an un-jointed cable.

I presume we have all seen the trick of making a twisted join with an overwrap of solder wire, wrapping it in foil from the lunch box and heating it with a cigarette lighter wound up to max?

-------------------------
regards Mike
 19 March 2017 01:22 AM
User is online View Users Profile Print this message



geoffsd

Posts: 1787
Joined: 15 June 2010

The regs. may not say anything specific but the principles of soldering conductor joints do.

Are you saying you would be satisfied with a joint solely held together by the solder?


I also maintain that crimping is not a suitable method of jointing solid cores but it happens.

The regs. give no indication on crimping either.
 19 March 2017 10:55 AM
User is offline View Users Profile Print this message



mapj1

Posts: 9717
Joined: 22 July 2004





are fine, and especially under heatshrink, are less likely to fail than simple twist, and adequate in tension.
What is important is that it does not move while the solder is semi-liquid, and having a good mechanical joint prior to soldering makes that less likely.
http://www.symtechlabs.com/sup...media/misc:twist2.jpg

is more traditional. Under flexing all soldered joints tend to fail where the section stiffened with solder ends, and the strands snap one by one.

-------------------------
regards Mike
Statistics

New here?


See Also:



FuseTalk Standard Edition v3.2 - © 1999-2017 FuseTalk Inc. All rights reserved.

..