Zones for Concealed Cables in Walls, BS7671 Wiring Regulations
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- čas přidán 30. 07. 2024
- Zones for concealed cables in walls as defined in BS7671. Safe zones in the 17th edition and earlier, prescribed zones in the 18th edition.
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This is so helpful and clear. The diagrams towards the end really made the concepts clear for me. Thanks hugely.
Keep em coming, John. Many thanks.
.After having drilled through a cold water pipe that shouldn't have been where it was,and the mess it was considerable, drilling into a live cable would have been no joke either. So I went out and bought a stud/metal/cable detector . You can't rely on pipe's and cable's being where you think they are, get a detector and check before you drill or nail into any type of wall .There not 100%foolproof, but most time's they've saved me a lot of grief . Nice video John, best wishe's for Xmas ,and the new year.
This and the pages related to it in the On-site Guide come up in the Design Modules of tests in years 2 and 3 of Electrical Installation City & Guilds. Worth taking note if you're on those courses.
Quality explanation great stuff John well explained
John, you are absolutely fantastic at explaining things. Reassuring that I can use your videos for reference.
Well done sir
Really helpful to see the diagrams, thanks JW
Well presented, easy to see with those diagrams.
John good point about running cables horizontally in kitchens due to cupboards,I also think it would be good practice to do the same in living room's for sockets as there's less chance of people hanging mirrors or pictures low level as opposed to running cables vertically...
Incredibly helpful - thank you.
First things first. A few years ago I needed to extend a lighting circuit to another room and fit a switch. There was no one on You Tube who could explain it in simple enough terms for me to get my head round it. Now I have a few City and Guilds and belong to an electrical body so thumbs up. Now to the point. Cables, zones and RUNNING CABLES THROUGH INSULATION over 0.5m, derating factors etc.
Part 2 Video please.
insulation. GAH.
Why do building control ignore electrical regulations and insist on insulation in ceilings even if there are downlights that cannot have insulation round them?
@@TheChipmunk2008 Why do specification writers, architects, householders install the wrong sort of downlighter?
Thanks JW great stuff as always 👍
Lovely clear explanation. Many thanks.
The room with the "blood red walls" is where they execute the cable penetrators 😂 another great video JW thanks..
Great video well explained thanks
Very informative. Thanks John.
Can you do a video showing a typical kitchen and where the cables would be run bearing in mind the kitchen does have wall cabinets and cupboards etc.
Also, some newer kitchens are extentions with a concrete floor. Can you show the cable zones in such a location.
It would really be cool if anywhere such regulations exists you can count on them. But you almost never can. Especially near windows and in the ceiling drilling holes can be a nightmare as installers seem to implement this with meters of tolerance.
Great video.
Thank you sir.
Quality video, thank you
Great vid
Great intelligent presentation John.
Old rude saying for how not to connect!!! "Red to Black - Blue to Fu**"
Worth noting that an external corner that will be plastered after first fix, will have a skim bead attached, often with staples or nails...
This should be attached to the stud and the nails or staples used should be fairly shallow... not that much strength needed... but it is not that hard to skip the foot needed for the safe zone... I usually used 1 inch screws for my beads into studs... 1-1/2 through 5/8 plasterboard..lol...
I see you are half way there JW ....just another little tug on that fabric and its curtains for the Globe 😃
Great video thanks John. What about kitchen and behind appliances ex washing machine and dishwasher
Same zones apply in all rooms.
Not normally much point in having recessed cables behind kitchen cabinets and appliances, surface mounted would be more usual. Most kitchen cabinets have a gap behind them for that purpose.
As usual another quality and really well explained video.
There was a guy asking about heights of outlet and switch plates, in accordance with part M you gave the answer.
If you have just had a big extension on your lounge with socket O/T's at, say, 450mm centre height from ffl in the old part does a new extension have to have its socket O/T's at part M height of 1000mm (I think that's what the Part M height was). It's going to look pretty naff.
I have never like the sockets halfway up the walls.
It' is interesting to see the differences between UK and North American wiring standards. In NA most houses are wood frame, with wiring running through holes in the wooden studs. I don't believe we are allowed to embed unprotected wiring at a depth of less than 2" anywhere.
I am presuming 'embed' doesn't include the Romexes in the stud walls you mention? Here, the regs don't really differentiate between solid reinforced concrete, and drywall on studs... and everything inbetween
You just need a nailer plate over where it goes through the joist but the zones shown are basically the same in the USA except... instead of being only the height of the outlet it is considered six inches above the outlet as well... so if you use 24 inches as your height for outlets you use 30 inches as your maximum height for the holes through the joists and 18 inches as your lowest height through the joists scuse me..studs...
@Ash Redman There is no single electrical code in NA. Canada and the United States (and Mexico as well) each have their own national codes. Then each province or state layers on additional requirements. Residential wiring is about the same in the US and Canada, although there are differences such as whether using backstabbing on outlets is allowed or not. . I can't speak to industrial and commercial wiring, as that is something I am not familiar with. In Ontario homeowners are allowed to do their own electrical work, and residential wiring guidelines are published. (Although homeowner wiring is supposed to be require permits and inspection I suspect this is often not adhered to.) www.electriciantalk.com/f31/difference-between-nec-cec-31162/
@John Ward Hi. Thanks for the video. If wiring a socket, am I allowed to go straight up (yes) but then do a 90° turn within the zone under the ceiling in order to get around a door, before going down to next socket?
So combining the zones as to not have to go into the ceiling. I assume yes. Hah.
Wish the people that made my living room stuck to these standards properly. There's one vertical cable that comes down to the left of a socket in the middle of the living room, was going to cut out a channel nearby and put another box with network ports next to that electrical socket but found that the cable powering that socket actually came down like 4 inches to the right of the socket so bang in the middle of where I wanted to put my network socket. (thankfully I was careful when cutting so didn't damage any cable)
Its just a shame that 95% of home owners are oblivious to such things as safe zones - hence the continuous need for cable repairs where nails, screws and drill bits have done a bit of damage. Years ago a friends mother was complaining about a tingling feeling she kept getting every time she went to clean a brass framed mirror she had hanging on a wall, i checked it out for her and found out that whoever had hung the frame had screwed into a cable - just touching the line conductor, cable was in plastic unearthed conduit, so it went unnoticed for years - with the exception of the tingle of course!
Have you checked that the screw was in such a zone? I see it far too often that theoretically it should have been safe to drill here....
@RaxxHubNut I agree, that is why i am surprised that its required to have the cabling inside some kind of earthed capping/conduit outside of a zone, but just fine to only use a plastic capping/conduit inside a prescribed zone. I would have thought it would make more sense to presume that your average homeowner/tenant would be ignorant of such prescribed zones and insist that all buried cables should have some type of earthed covering. Then at least if someone does catch a line conductor with a drill - nail or whatever, it would trip the circuit straight away. like you say, we cannot blame 95% of homeowners for being oblivious, so i would say it would be fair to say that all cabling hidden within a wall is fair game for Mr or Mrs bloggs armed with either a hammer and nail or a cordless drill. :-) But, that said, modern systems with RCD's should at least reduce the chances of being electrocuted by objects - like the mirror in my previous post, that had accidentally been connected directly to the line conductor.
@@PlasmaHH Yes, first thing i checked, and sure enough it was directly above and in line with a twin socket further down the wall. I looked for that before anything else.
Don't worry, cupboard installers will find any cable buried in the wall, even those nowhere near where the cupboard is being installed, and even if you do mark the wall with big bright signs where the cables are buried. Then again, builders never seem to be able to get the walls straight or to install conduit in the wall straight where it has been poured into concrete. Favourite is to run the cables straight line, saves the time of putting in bends in the floor pour.
@@SeanBZA yep... and anyone doing plasterboarding on a stud wall will ignore the cables they could previously see clearly, 50mm deep in the stud, and use at least one random 75mm drywall screw for no good reason. Right into the cable.
Hi John, amazing videos, taught me so much. Is there a set height that sockets and switches have to be??
BS7671 does not have anything on switch or socket heights. However other things may apply depending on where the installation is, such as Part M of the building regulations. One common situation being that new build homes have sockets and switches between 450mm and 1200mm from finished floor level.
The switch in my bedroom looks like it’s half way up the wall
@@samuelhulme8347 1200mm is indeed about half up up a typical domestic wall, so that'll be installed to comply with partM.
Interesting to compare British and US standards. I'm a bit puzzled by the "zone extending to the other side of the wall". US walls are usually hollow frame construction, with vertical bays running floor to ceiling, and cables installed either vertically by stapling to the sides of the wood frame, or horizontally by drilling through the center of the frame members and threading the cable through. The wall internally does have any sides. Cables are running through the center.
Are British walls constructed with solid cores? How are the cables embedded in the walls?
Some walls are hollow, made from timber or metal framing.
Plenty are solid brick or block, and installing wires there involves cutting a channel into the brick for the wiring.
When i moved into a bungalow, i was planning to carry out a complete rewire and a new consumer unit.
The existing consumer unit was located in the attached garage, however all the existing cables were concealing via back entry and installed within the plaster of the adajcent kitchen wall.
When I removed the top coat plaster of the kitchen to reveal the existing wiring wow no less than 4 holes passing straight though the middle of power and lighting flat twin and earth damaging the bare earth cable. I guess that the previous owners had some kitchen fitters drilling the wall to secure kitchen units.
Needless to say the cables were distributed vertically in the garage and then passing though the ceiling and loft spece void. Why the cables were installed hidden in the kitchen is beyond me.
Can overlapping zones be used to run cables between a socket and a spur socket. For example cable comes into socket from floor. The spur is say 2m higher and 2m to the left of the socket. My hypothesis is that the cable can be run through a wall chase going vertically from the socket and then horizontally to the right of the spur as the zones for each socket overlap.
I have quite often seen the cabling from light switches, go horizontally to a door frame, then vertically upwards behind the frame, then buried under the plaster above the frame to the ceiling. If the switch is >150mm from the door frame (which quite often are), then I assume that these installations are against regulations!
Not permitted and never was. As architraves around door frames are secured with nails there is a very high chance of the wiring being damaged.
Does the 150mm from the ceiling also apply to diagonals? For example what would be the correct way to run the wiring in prescribed zones for for a two-way for a stairway light?
yes, if running up a stairwell it would include the 150mm from the ceiling, thus making a diagonal prescribed "safe zone" :-)
The way I was taught was up to the ceiling zone from the switch, along the ceiling zone to above the light if a wall light, and then down to the light... always up and down from the ceiling for lights...
Only if the diagonal slope of the wall is adjoining to the ceiling (top of the wall).
If your consumer unit is in a cupboard and your putting cables in to go down the wall vertically into it. As the consumer unit is consealed would you still class the wall above it a prescribed zone?
Yes
How does it apply to window reveals? I have reveals that are at 45 degrees (not the normal 90) and wanted to add a switch for an outside light. Can the wall be chased horizontally from another powered switch?
Nothing defined at 45 degrees.
You can go horizontally from a switch, however that's only of use if there is a neutral at the switch - many circuits do not have that.
Maybe "safe" zones could be confused by non-electricians to mean free of cables, i.e. safe to drill etc. in. So "safe" would be totally misleading in that context. In that respect, the question really is why they were called "safe" in the first place.
I don't get it: where do the vertical zones beneath the socket/switches lead to? Can they connect to the zone in the flat below? But that might not necessarily have the same wall arrangement or it may not even exist. So why are they allowed?
Also, what happens in the case of a reinforced concrete frame building? These usually have concrete pillars where the walls join at a corner. That means you cannot have a zone in that corner. They also have horizontal concrete beams, usually forming the top part of a wall (for aesthetic reasons) or going through the top part of a wall (if the beam is vertically oriented to the wall). In both cases, you cannot then have the 150mm zone at the top of the wall. Are there separate guidelines for these kinds of buildings?
The vertical zones are for when cables are under the floor or above the ceiling, cables can then be installed vertically to the socket or switch. Zones do not extend below the floor level or above the ceiling.
Finished walls not generally bare concrete, so wires would be installed behind plaster / drywall or similar in the case of concrete framed buildings.
What code for cables buried in a wall less than 50mm in a prescribed zone with no RCD protection C2 or C3?
I'd say C3 if buried in a wall less than 50mm in a prescribed zone and C2 if buried in a wall less than 50mm outside a prescribed zone.
Hi . How does this work with a 'cathedral ceiling' with gable ends ? Many thanks
I've read of people installing a back box with a blank plate on it to create a prescribed zone so a cable can be run vertically up or down a wall to the blank box then along horizontally to an accessory. This doesn't sound like it's allowed?
Not allowed - the cable must be connected to something such as a socket or switch at that point, just having a blank plate is not sufficient.
So just to confirm: This means I can chase an internal or external corner out and place cable around the corner? My electrician said I cant go anywhere within 150mm from a corner?!
That corner he/she potentially crosses may already have existing cable drops within the permitted zone. So sometimes it's better to try and avoid the internal external corners horizontally. unless your certain there aren't cables within.
What happens when things get moved? My kitchen has a 6mm T&E for what presumably used to be the cooker circuit coming down behind a cupboard in the middle of the wall. No doubt there was a cooker switch+socket at the end of it when it was installed in 1962. That is long gone and the cable magically becomes 2.5mm2 T&E and goes to a socket round a corner on the adjacent wall now. That's kitchen fitters for you, and it would be sort-of OK if they'd changed the MCB to 20A, but they didn't. More to the point there must be a buried junction (also not allowed) although it may be behind a cupboard (maybe OK?) and there is nothing to indicate where the buried cable might be. Some of this may have been permitted when it was done, I guess - how long ago did these rules on safe/prescribed zone appear? and when was the prohibition on buried junctions put in?
I suppose the compliant way to do it would be to have the junction box under a blanking plate in line with the wire (and change the MCB to match the thinner wire or use fatter wire to match)?
I'm not about to get rid of it all and do it properly anyway, but it's been somewhat unsafe for a couple of decades at least. And this question of later alterations is a significant one - they happen a lot, especially in kitchens.
If an accessory is moved, the cables should be moved with it - it's not permitted to leave cables in a wall unless they are still within the zones.
Well, talking about prescribed zones is all well and good John, informative even, but what we really want to know is who lets you wear minion pajamas ?
Let's say you were putting in sockets along the wall horizontally in the kitchen, if the cooker switch is in between the sockets, could you run the cooker cable through the socket back boxes, to the cooker switch?
Yes, although the zones only extend from sockets/accessories if the cable is actually connected to them, so the zones for the socket would not cover those for the cooker cable. Doesn't matter if they are all in line, as the zones all overlap, but it would matter in some other situations, such as cables for a lighting circuit concealed in the wall above a socket outlet - the socket zone would not cover the lighting cable.
@@jwflame Hi John, thank you so much for the reply. My main inquiry is for cables from more than one different circuit being allowed to pass through other back boxes. It sounds like it's ok if the cables still fall in the prescribed zone if you were to remove the back boxes that it has passed through.
I come across a lot of 1950/1960 properties where I find cables behind skirting boards. Was this previously an acceptable cable zone?
There were no specified zones before 1987, so cables were installed wherever the electrician considered it appropriate.
@@jwflame ok thanks JW 👍
can you help with a video on on cable/pipe finders gadgets. I have used two over the years but they seem very unreliable. the current one I have seems to think the entire hallway in our house is live, even if not on the wall
The trick to a lot of them is ensuring that your other hand is also touching the wall. Also turn it on whilst it's against a known clear bit of wall.
I've not found any that I'd consider particularly good though. So called stud finders are also not particularly useful for wooden studs and a very strong magnet works better to find the lines of nails/screws.
I am still looking for one that works on concrete or could walls..lol..
All cable / pipe finders are unreliable junk. They only work properly in carefully arranged sales demonstrations, where the fake walls don't have foil backed plasterboard, shielded or armoured cables, conduit, cable capping, plastic pipes and all the other things that are found in real buildings.
HI JOHN
WOULD IT BE LEGAL TO HAVE EACH DOUBLE SOCKET OUTLET ON ITS OWN TRIP FED BY 4MM +EARTH CABLE ?
Yes, provided all of the other usual requirements are met (correct rating of circuit breaker, cable installation methods, impedance, RCD, etc.)
Why on earth would you want to do that.
@@supersparks9466 pun ‘earth’
This might be a controversial question, but can you "cheat" by using fused spur accessories if for some reason you wanted to create a zone? Obviously the fused spur could reduce the CCC of the circuit. Or is this just really poor design?
I can't think of a specific example in my head, but perhaps for whatever reason, it's easier to add a socket this way without demolishing certain decorations, for example
The upper ceiling zone is so stupid as that's where all heavy duty wall-rails go for hanging shelving.
I wonder if that is on purpose? Normally the upper 50mm is a wood beam in a proper house though. No cables in that.
Only watching this because a carpenter put a nail through my cable
Not a fan of those internal and external corners zones, that just where the chippys fix the skirting boards
I'd be willing to bet they renamed the safe spaces to prescribed spaces because an idiot googled "where are power cables in walls" and saw the safe spaces.. "oh, they are the safe bits.. I'll drill there.. *BANG*'
That's not as funny as imagining some poor sod drilling through a power line
Yes, seems pretty clear why they changed it. "Safe space" might suggest that when wires are put there it makes it safe to drill without thinking. "Prescribed space" is what it should have always been.
A) Don't run diagonally. B) If direction changes install a box with a cover or accessory or switch. C) Imagine it's your house. What's so difficult? BobUK.
More rhetorical chages!
So just found this video to see if my electrician running the ring main around behind the skirting board was right ....what do you know it isn’t 🤦♂️😬
Thanks for the precious content! I am a subscriber, watched a bunch of your videos... was surprised here by the speed of your pronouncing some sentences. The British English compounded by the fast enunciation made some parts difficult to understand. May I kindly beg for a bit slower speaking pace please - for your international audience? Thank you for the understanding!
Who ever come up with this rubbish. We was always taught the cables must only be installed vertically. The only exception is a cooker or socket outlet after a isolator. That’s the only way we run cables. Most other trades do not expect a cable to run any other way . I have known a few times câbles being drilled or cut through as the last thing the carpenter or builder expected was a cable going horizontal or in a corner ..
These zones were introduced around 1987 in an amendment to the 15th edition.
It would be inconvenient and wasteful having two double sockets 2 meters apart and requiring a length of cable several meters in length to meet a restrictive regulation only allowing for vertical cable entry.
The house will look pretty hideous with all those painted pink stripes.
BigClive would probably like it though!
@@chrisg6597
Damn, you beat me to it. Clive would love that colour scheme. In fact, he's probably painted his house like that.
@@bdf2718 Yes, it would match his passion pink Poundland Powerbank.
Great explanation, thank you!