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Topic Title: Socket box earthing
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Created On: 26 September 2017 11:12 AM
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 Socket box earthing   - Baldyhugh - 26 September 2017 11:12 AM  
 Socket box earthing   - KFH - 26 September 2017 11:44 AM  
 Socket box earthing   - jonny705 - 26 September 2017 12:29 PM  
 Socket box earthing   - AJJewsbury - 26 September 2017 03:19 PM  
 Socket box earthing   - geoffsd - 26 September 2017 05:04 PM  
 Socket box earthing   - ArduinoXR - 26 September 2017 05:26 PM  
 Socket box earthing   - aligarjon - 26 September 2017 08:22 PM  
 Socket box earthing   - AJJewsbury - 26 September 2017 07:18 PM  
 Socket box earthing   - KFH - 26 September 2017 07:32 PM  
 Socket box earthing   - geoffsd - 26 September 2017 07:47 PM  
 Socket box earthing   - dustydazzler - 26 September 2017 07:40 PM  
 Socket box earthing   - AJJewsbury - 26 September 2017 08:15 PM  
 Socket box earthing   - geoffsd - 26 September 2017 08:24 PM  
 Socket box earthing   - leckie - 26 September 2017 10:03 PM  
 Socket box earthing   - ebee - 26 September 2017 10:09 PM  
 Socket box earthing   - geoffsd - 26 September 2017 10:16 PM  
 Socket box earthing   - ebee - 26 September 2017 11:04 PM  
 Socket box earthing   - aligarjon - 27 September 2017 07:48 AM  
 Socket box earthing   - mapj1 - 27 September 2017 12:09 AM  
 Socket box earthing   - leckie - 27 September 2017 05:04 AM  
 Socket box earthing   - ebee - 27 September 2017 05:37 AM  
 Socket box earthing   - leckie - 27 September 2017 06:18 AM  
 Socket box earthing   - davezawadi - 27 September 2017 07:50 AM  
 Socket box earthing   - AJJewsbury - 27 September 2017 10:52 AM  
 Socket box earthing   - AJJewsbury - 27 September 2017 10:58 AM  
 Socket box earthing   - davezawadi - 27 September 2017 12:08 PM  
 Socket box earthing   - ectophile - 27 September 2017 01:15 PM  
 Socket box earthing   - KFH - 27 September 2017 03:14 PM  
 Socket box earthing   - Alcomax - 27 September 2017 03:32 PM  
 Socket box earthing   - AJJewsbury - 27 September 2017 04:15 PM  
 Socket box earthing   - Alcomax - 27 September 2017 05:01 PM  
 Socket box earthing   - ectophile - 28 September 2017 08:38 AM  
 Socket box earthing   - MHRestorations - 25 October 2017 09:16 PM  
 Socket box earthing   - leckie - 25 October 2017 09:46 PM  
 Socket box earthing   - MHRestorations - 26 October 2017 10:59 PM  
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 26 September 2017 11:12 AM
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Baldyhugh

Posts: 366
Joined: 01 June 2007

Morning all.

This old chestnut again. Guidance note 1 states that if a flush metal box has at least one fixed lug then a lead from the socket to the back box is not required as it is adequately earthed by the fixing screws. I have gone by this in the past but have decided for my own peace of mind to now fit an earth lead to the back box regardless.
I personally don't like putting more than two cables in a termination as I find that they aren't caught equally by the screw. As most modern socket outlets have two earth terminals, I plan to put the two earths of the ring into one terminal and the earth lead to the back box in the other. I know that this might seem quite an obvious question to some but have seen others where the three earths were in the one terminal. Is there a requirement that they must be in the one terminal or is my plan of the ring earths in one and the fly lead In the other acceptable?

Peter
 26 September 2017 11:44 AM
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KFH

Posts: 567
Joined: 06 November 2010

If the earth terminal can take 3 wires I am happy putting them in one. However I am also happy putting the fly lead into the second earth connector. It could be argued that it is safer to put the ring connections into the separate connectors so that if one comes loose the other should still provide a connection. I have also seen one of the ring cpcs to the backbox with a flyllead to the accessory completing the ring, so only two wires in each connector, I am not so happy about this as the backbox connectors are often, to put it politely, poor and usually difficult enough to get one wire into never mind 2.

Despite GN1 I also prefer to earth/bond the backboxes.
 26 September 2017 12:29 PM
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jonny705

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I know when I did a re-wire the assessment guy said don't bother with the back-box fly lead no more as rcd protected.

I have also seen a lot, the ring cpc terminated into the box, and a single flying lead to the actual fitting, normally when someone has broke the cpc (probably by stripping it) and its now too short , so a way round it i guess.

I had this on a lot of sockets only the other day, so I extended the cpc with through crimps and stuck them in the actual socket.

If the socket has two eath points, the cheaper ones tend not too, I always think its bettter to use indvidual ones as if one breaks ,you at least have the other one on -well thats my theory .
 26 September 2017 03:19 PM
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AJJewsbury

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If it's a circuit with high protective conductor currents (i.e. the situation where dual earth terminal accessories were designed for) then you have to have the to ring c.p.c.s in separate terminals - so your back box flylead doubles up with one of them. Probably not a bad approach in general either.

In the distant past I've looped one c.p.c. unbroken into the back box terminal and then that and the other ring c.p.c. into the socket's PE terminal - the idea being earthing remains intact (if via the fixing screws) if one earth terminal screw comes loose (a kind of poor man's high integrity before the advent of dual terminals).

- Andy..
 26 September 2017 05:04 PM
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geoffsd

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Typical guidance - whatever it says,

is the back box an exposed-conductive-part?
 26 September 2017 05:26 PM
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ArduinoXR

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Originally posted by: geoffsd

Typical guidance - whatever it says,



is the back box an exposed-conductive-part?


No, it is not readily accessible.
 26 September 2017 08:22 PM
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aligarjon

Posts: 3875
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Originally posted by: geoffsd

Typical guidance - whatever it says,



is the back box an exposed-conductive-part?


no, but the screw heads are.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 26 September 2017 07:18 PM
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AJJewsbury

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is the back box an exposed-conductive-part?

I'm starting to feel very uncomfortable about that definition ... to my mind unless the plasterwork/wallpaper/paint around it reliably provides the equivalent of one of the layers of double insulation, I don't think the need to earth it really goes away.
- Andy.
 26 September 2017 07:32 PM
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KFH

Posts: 567
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As an old electrician said to me "if there is no bonding lead and there is a fault that makes the back box live when you pull the accessory off who is going to be the one that finds the fault?"
 26 September 2017 07:47 PM
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geoffsd

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Originally posted by: KFH

As an old electrician said to me "if there is no bonding lead and there is a fault that makes the back box live when you pull the accessory off who is going to be the one that finds the fault?"

It would be an earth (CPC); not a bond, but -

wouldn't that be working on a live circuit?
Is that the real problem?


IF the box is not an exposed-conductive-part, then why does it need earthing?
 26 September 2017 07:40 PM
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dustydazzler

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It's metal. It's near a live wire. Earth it.
Many old sparks that I have worked with strip one normal length earth and strip one extra long earth and put a kink in the long one and and tuck the kink into the box lug before placing the cpc s together in the socket as you do
No need for a separate earth tail
 26 September 2017 08:15 PM
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AJJewsbury

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IF the box is not an exposed-conductive-part, then why does it need earthing?

As a thought experiment, let's say a flush box isn't exposed, so therefore not an exposed-conductive-part. But it is screwed (sideways) into a steel C-stud in a partition wall for support. The C-studs themselves aren't in the proximity of live conductors so aren't exposed-conductive-parts, so they don't need earthing either, according to the definitions. Likewise the steel shelf brackets screwed into the same C-stud system further along the wall. A simple single fault within the box would make the whole lot live, with no earthing to initiate ADS.

(If you don't like the C-stud scenario, try foil backed plasterboard, stainless steel splashbacks or those aluminium partition framing systems that seem so popular in offices)

- Andy.
 26 September 2017 08:24 PM
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geoffsd

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Then they will be earthed by their contact with the socket.
 26 September 2017 10:03 PM
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leckie

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Blimey, look if you want to attach a fly lead then crack on, but if the box has a fixed lug you do not have to. Do not judge people that comply with the regulations, if you want to add additional back up protection and comply with the the requirements for 40 years + ago that is also fine.

And if you are going to connect to two different earth terminals, put the CPC's into separate terminals, not the same one, this will be in line with the requirements for high protective conductors currents, and that might actually be beneficial.
 26 September 2017 10:09 PM
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ebee

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Originally posted by: geoffsd
.

Then they will be earthed by their contact with the socket.


Geoff No No No and No.

I would never rely on the socket screws being of sufficient tightness to form an effective electrical connection between accessory and back box.

Decorators etc leaving slack not to mention damp corrosion.

This at least "one fixed lug" concept is baldylollocks.

On a ring one cpc to earth terminal then tother cpc doubled then connected to back box then on to earth terminal whether dual or single earth terminal.

I have (as previously mentioned) seen nylon screws replacing socket screws (mind boggles)

I`m with AJJ and Dusty on this one

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 26 September 2017 10:16 PM
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geoffsd

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Originally posted by: ebee

I would never rely on the socket screws being of sufficient tightness to form an effective electrical connection between accessory and back box.

No, not saying that, Aligarjon said the scews were exposed-c-ps - so they will be earthed by contact with the socket (screw holes).

I`m with AJJ and Dusty on this one

That's fair enough - and I do the same.

However, I am trying to determine IF (people think) the back box IS an exposed-c-p.
 26 September 2017 11:04 PM
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ebee

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no it`s not exposed.

but bearing in mind it may well be surrounded by damp plaster then it would be prudent to treat it as such

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 27 September 2017 07:48 AM
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aligarjon

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Originally posted by: geoffsd

Then they will be earthed by their contact with the socket.


Agreed, it was just an observation. I have never used fly leads on sockets.

Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 27 September 2017 12:09 AM
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mapj1

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The real unknown is to ask "is there a credible failure that livens the backbox ? "
I guess it depends who does it, if the T and E comes in through a non grommet hole, already stripped as singles, and the socket is a deep one squashed tight into a box that is too shallow, then yes.
If it comes in via a grommet, and there is plenty of room, and the length that is stripped to singles is kept suitably short, then probably pretty incredible, or at least no more risky than other things we accept, thinking of T and E in unearthed metal capping, or meter tails on TT into a metal CU.
The problem is that the one without the grommet is also probably also going to be the one with the missing link and loose screws as well
To be fair, you do have to pretty much lose the screw completely to get a non-contact with the eyelets in most sockets, a bit loose to stuff the new wall paper behind is not enough to break the connection.
I'm happy without the link wire in most cases.

-------------------------
regards Mike
 27 September 2017 05:04 AM
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leckie

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Apart from people taking off faceplates while the power is still on, I don't think there is a credible risk of anyone getting a shock if a socket is screwed back onto a fixed lug. I have never heard or experienced that and so I don't bother fixing a fly lead. BS7671 has to my mind agreed with that for many, many years. I'm not going to account for what if scenarios regarding people loosening sockets to wall paper etc., if you start taking account of every possibility you can go on forever. If some think that this does represent a risk and then they should of course fit a fly lead. I suspect we all have habits that we think are an improvement on complying with the minimum standard for our own reasons. I like to install supplementary bonding in bathrooms regardless of RCD protection being installed to all the circuit on the basis of touch voltages being reduced in the event of a fault, but you don't see that being done very often now. I have been clamping meter tails entering consumer unit for at least twenty five years before anyone had ever mentioned a need for it to me and insisted that my employees did the same as well as rechecking the connection of tails and any larger conductors with their torque calibrated screwdriver hand before fitting the lid on. That always was a risk of a loose connection from the moment manufacturers started using cage clamps. I have always glued in grommet strip because of the amount of times I have seen it not fitted correctl, or coming off at the slightest touch. These are all little things that in my opinion make sense based on witnessed evidence and thing that I think reduce the risk to extremely low of a tangible hazard occurring. I am not of the opinion that fitting an earth lead does that. Dog rough Leckie.

Edited: 27 September 2017 at 05:11 AM by leckie
 27 September 2017 05:37 AM
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ebee

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Leckie.

Ditto Supp bond bathrooms.

Ditto Tails secured.

Map & Leckie,

Reliance on what often becomes a slack connection does not sit well with me. 2 seconds extra work and tuppence extra materials to ensure continuity seems worthwhile

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 27 September 2017 06:18 AM
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leckie

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That's fair enough Ebee, as I said its up to how you interpret the risk of possible danger, and we all have out own bugbears.

A good friend of mine doesn't get many consumer unit change jobs because he is too expensive - he will only fit double pole RCBO boards and that is expensive. He refuses to use anything other than twin brown or a combination of brown single/sheathed cables for switch wires drops or strappers as he doesn't think it is acceptable to over sleeve a blue core. He believes the core colour should be continuous throughout its length. Forty years ago when most fitted 16mm tails and 6mm main bonding conductors and earth lead, he used 25mm tails and 16mm for all bonding. He had worked out the problems of diverted neutral currents,etc, many years ago and always said 16mm was not rated up to 100A, so ahead of his time. He is a brilliant engineer and does what he thinks is correct. Not that he does much domestic as he has mostly done heavy industrial, agricultural and hazardous areas of filling stations, still works every day at about 75!
 27 September 2017 07:50 AM
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davezawadi

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This is a very unsatisfactory position that many of you are taking.
We have many people claiming that they know better than the regulations, and that makes me wonder in what other areas you think you know better? What other non-compliances am I going to find in your work?
OK you are claiming increased safety, but is there any evidence that the regulation position is in any way unsafe? Everything now seems to claim "increased safety", but this is often because no one seems to be willing to challenge this dubious claim.
In the 15th edition we had the "earth every exposed metal item", which was definitely less safe than doing nothing, because it turned many areas (commercial kitchens in particular) into fully conductive environments which increases the severity of any shock. If you want a safer installation you can use steel conduit or MICC and metal clad accessories everywhere. How much increased safety will there be, well in my view such a small amount that it is not worthwhile, unless there is an environmental reason for such protection. Increased safety might come from RCD protecting all the circuits, and this is the current regulation position. It does not require RCBOs on every circuit, although some may want the increased convenience this may produce.

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 27 September 2017 10:52 AM
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AJJewsbury

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The real unknown is to ask "is there a credible failure that livens the backbox ? "
I guess it depends who does it, if the T and E comes in through a non grommet hole, already stripped as singles, and the socket is a deep one squashed tight into a box that is too shallow, then yes.
If it comes in via a grommet, and there is plenty of room, and the length that is stripped to singles is kept suitably short, then probably pretty incredible

The most common failure mode I've come across is one of the fixing screws stabbing a wire as the faceplate is screwed home - typically after the householder as removed/loosened the faceplace for redecoration. (Always seemed a bit of a design flaw in BS 4662 to have the screws penetrating blind into the wiring space...)
- Andy.
 27 September 2017 10:58 AM
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AJJewsbury

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We have many people claiming that they know better than the regulations

Indeed - and a good thing too I say! if no-one ever challenged anything, we'd still be on the 1st Ed...
- Andy.
 27 September 2017 12:08 PM
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davezawadi

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It may be a good thing Andy, but that is not exactly my take on this because it will become a workmanship quality thing next, and before you know it a trail of code C1s on EICRs! If you don't believe me, you need to look at some of the rubbish being issued by inspectors because they don't have a clue of the actual regulations. Typically this starts with referring to sheathed cables as "double insulated", and not understanding what "mechanical protection" means. It then becomes worse, and I assure you that the worst statement is "I don't like the look of....".
The use of plastic screws in accessories (which I see quite often) defeats the entire design principle of earthing, but is even recommended by some!

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 27 September 2017 01:15 PM
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ectophile

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Originally posted by: davezawadi
The use of plastic screws in accessories (which I see quite often) defeats the entire design principle of earthing, but is even recommended by some!


Surely, the point of using plastic (nylon) screws is to replace earthing with double insulation. If you have a plastic light switch secured with nylon screws, then there's nothing that the end-user can touch that could become live.

-------------------------
S P Barker BSc PhD IEng MIET
 27 September 2017 03:14 PM
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KFH

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Originally posted by: davezawadi


The use of plastic screws in accessories (which I see quite often) defeats the entire design principle of earthing, but is even recommended by some!


I have frequently used plastic screws on lighting switches with a metal backbox and metal screws but no cpc, or perhaps even worse a cpc connected to the backbox which is not connected to earth as it is a later addition to a non earthed lighting system, usually replacing the old wooden back boxes, major fire hazard, hard hat on but I have forgotten which colour I should be wearing.

The fact that the guidance note is saying that adequate earthing is provided by the screws into a fixed lug indicates that earthing of the backbox is required. I just like to do it properly as much from over 50 years of habit as much as anything else. I would not code the lack of flyleads on an EICR.

It has taken me ages to type the above Autocricket has even changed some of the words I have managed to type correctly. I hope I found them all.
 27 September 2017 03:32 PM
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Alcomax

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Originally posted by: KFH

Originally posted by: davezawadi





The use of plastic screws in accessories (which I see quite often) defeats the entire design principle of earthing, but is even recommended by some!




I have frequently used plastic screws on lighting switches with a metal backbox and metal screws but no cpc, or perhaps even worse a cpc connected to the backbox which is not connected to earth as it is a later addition to a non earthed lighting system, usually replacing the old wooden back boxes, major fire hazard, hard hat on but I have forgotten which colour I should be wearing.






my reply [ edited due to odd reply box syndrome ]

Ditto above, though to mention one of the previous posts saying that the insulating screw is providing double insulation...it is not really. It is just an insulator.

Another scenario for using nylon would be where there is an original switch drop installed without CPC/ earthing provided and the original metal back box with insulated plastic lugs has been removed and replaced with a modern metal back box with metal lugs.

Somewhere in the past, about pre 1970, it was understood that you could not have an exposed conductive part [ a metal fixing screw ] not earthed, hence insulated lug metal back boxes on lighting circuits with no CPC provision.

Edited: 27 September 2017 at 03:51 PM by Alcomax
 27 September 2017 04:15 PM
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AJJewsbury

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to mention one of the previous posts saying that the insulating screw is providing double insulation...it is not really. It is just an insulator.

I don't think ectophile was suggesting that the single nylon screw by itself provided double insulation, but by changing the screw to insulating you were changing the method of protection from electric shock from ADS/EEBADS to double/reinforced insulation. The nylon screw just provides the 2nd layer of insulation, the first being the basic insulation of the wiring inside the back box. (All that presumes that a live backbox doesn't pose a hazard however).

If you really want to get into the detail of the regs, you'll find that screws, bolts, rivets etc are currently exempt from the requirements for protection against electric shock under fault conditions anyway (410.3.9), but that double/reinforced insulation doesn't permit the reliance on insulating screws where their replacement with metallic ones might occur (412.2.2.2 (ii)). Go figure the consistency in that!

- Andy.
 27 September 2017 05:01 PM
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Alcomax

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If you really want to get into the detail of the regs, you'll find that screws, bolts, rivets etc are currently exempt from the requirements for protection against electric shock under fault conditions anyway (410.3.9), but that double/reinforced insulation doesn't permit the reliance on insulating screws where their replacement with metallic ones might occur (412.2.2.2 (ii)). Go figure the consistency in that!


Get your point however, it is an unusual situation, so the remedy [ in lieu of installing a CPC ], is likely to not be consistent. Not sure that process of an insulating screw into a metal lugged metal back box is anything else but the process of installing an insulator and nothing more. Not really a full blown re-inforced/ double insulation thing. The whole thing becomes non standard but workable. For sure someone can replace later with metal screw and you are back to square one. But we are getting into the realms of stupid proofing installations.
 28 September 2017 08:38 AM
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ectophile

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I was working on the assumption that the live and neutral already have basic insulation. The screw then provides the second level of insulation.

It's not ideal if there's a metal back box. But if the incoming cable is insulated & sheathed, then it shouldn't normally become live, and even if it does, the customer shouldn't be able to touch it.

-------------------------
S P Barker BSc PhD IEng MIET
 25 October 2017 09:16 PM
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MHRestorations

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Old post I know, but I'm definitely with ebee on this. The box IS potentially exposed conductive metalwork (never known a box come loose due to other work going on?). And the horrible 'we don't bother now because of RCDs... GAH, RCDs are *ADDITIONAL* protection. Never ASSume...

Sorry to rant as one of my earliest posts, but the 'everything's on an RCD' line drives me bananas as an excuse for shortcuts.
 25 October 2017 09:46 PM
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leckie

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Well there has not been a requiem t to earth a back box with a fixed lug since the fourteenth addition as I recal. Certainly a long while. If sparks want to provide a link to a back box to protect decorators removing sockets, etc., then that is fine. That is based on their own judgement. But it's not based on BS7671.
 26 October 2017 10:59 PM
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MHRestorations

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Absolutely Leckie, thanks for the reply btw. I tend to regard the IEE regs (yes, i went there <grin> as a guideline. Best practice unless you can do better, like a speed limit.

But, yes, I agree that BS7671 is fairly unequivocal that I'm going OTT And I will continue to do so
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