Next door had the same problem. He used just steel capping and RCD so that it's all covered by just the plaster. As in my house, some runs are not in Safe Zones - but do go to sockets or switches and are all vertical or horizontal. Should be easy to detect - a decent magnet would do it!
Just an update. The RCBO plan has been shelved having missed the offer so it is back to RCDs and MCBs. The garage CU will now be a RCD protected unit with MCBs the supply cable will come from an non RCD protected MCB in the main CU this arrangement should mean faults in the garage circuits should not affect the house circuits which was my main concern when considering RCBOs. The garage supply cable will either run down 50mm below the surface for 2m or run on the surface behind a kitchen unit. I got an MK CU with RCD and fully populated for £73, a couple of MCBs need swapping but I can do that when the main CU is replaced as the existing one is an MK.
Thanks for all the help and advice particularly Adam.
Richard
If you have the RCD, then no additional protection is required - although for cables that are being installed before plastering, capping is normally a good idea to protect them from damage during plastering.
Cables tend to not be magnetic unless armoured.
The requirements these days specify RCD protection for all sockets - regardless of how the cables are run.
Pretty much.
Depending on the installation method, that's borderline for a 45A MCB.
Have a look at the table:
Your described installation method more closely matches number 47 (BS7671 18th ed, blue book) for the section through the ceiling. That is described as "Single-core or Multicore cable - in a ceiling void, or in a suspended floor.", and the reference method listed is B. So that reduces the capacity of the 6mm^2 to 38A.
While that *might* still be acceptable - depending on what load is going in the final CU[1]. However in applications like this, it would be much much better to have overload protection for the submain as well, since its impossible to predict what might change in the future and you don't really want to rely on a future installer understanding the restrictions imposed by a sub optimal submain.
So smaller head end MCB, or bigger cable...
[1] (if the load is less that that so overload of the submain is not possible, then you can argue that the head end MCB only needs to provide fault protection for the submain)
They are in safe zones then as they extended from switches and sockets in the vertical and horizontal directions.
Good, thank you.
Agreed - but the steel capping might be :-)
At least tht's OK then.
In which case you can use a non RCD protected MCB to power your secondary CU.
Yup, like in the pictures:
But some aren't within 150mm of edges.
While the picture is clear, I find the regulation anything but when it comes to zones defined by sockets, switches etc. 522.6.202 has - so far as relevant -
"Where the cable is connected to a point, accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to the point, accessory or switchgear. Where the location of the accessory, point or switchgear can be determined from the reverse side, a zone formed on one side of a wall of 100 mm thickness or less or partition of 100 mm thickness or less extends to the reverse side"
On a plain reading that seems to mean one can't use the zone defined by a socket, switch etc to run a cable that's /not/ connected to a socket etc in the zone but is just "passing through" on the way to another room, a garage or wherever.
But you said they were vertical and horizontal not bent.
Surely not. The whole point of the safe zones is to indicate where it is safe to run the "just passing through" cable because these zones coul;d equally be designated danger zomnes when it comes to drilling holes, etc.
Iy you took a different route for the cable avoiding these zones there is nothing to indicate where the cable runs, making it particularly vulnerable.
They are straight but not within 150mm of an edge.
The wiki article gives the definition of the 3 safe zones. The cables only need to be in one of them. They may if needed use 2 or all 3 of them.
They don't need to be...
A safe (or in this context a better word might be "expected") zone is one of three separate and distinct areas:
1) Horizontally or vertically intersecting with the location of a visible electrical accessory. Hence the position of the zone is not a fixed place, but is defined by where the accessory actually is. So if you see a socket you know not to drill directly above, below, or to either side of it. That socket might be 2m from the nearest corner - but it still defines a zone around it.2) At the intersection of two vertical walls - this applies even if there is no visible accessory. So don't go drilling in the corner beside a chimney breast even if you can't see a switch or socket.
3) At the intersection between wall and ceiling.Basically, if installing cables, they need to be in a least one of these zones. They can be in more than one, but there is no benefit or requirement for this. Hence avoid running cables at odd angles, or changing direction of them mid run.
My point was that IMO the regulation doesn't actually say what it is generally taken to.
I'm happy to be guided to how to be read it so the zones created by an accessory etc on the wall apply to a cable that is not connected to it. The only way I can see is to read "the" as "any" so it becomes:
"Where /any/ cable is connected to a point, accessory or switchgear on any surface of the wall or partition, /any/ cable may be installed in a zone either horizontally or vertically, to the point, accessory or switchgear."
But if so, WTF don't they say that in the first place? Reading "the" to include "any" is not normal. (And still means fitting an accessory with nothing connected to it does not create safe zones.) .
I am a very strong advocate of DIY by competent DIYers but sometimes we all need to recognise when it is best to "get someone in", perhaps this is a case when that would be wise. Please don't flame me for making the suggestion.
Yes. But that only happens on occasion
I'm firing up the barbie. Seriously, installing cable in walls is not difficult.
NT
One of the worst areas I see in the home where cables are not in the sage zones is on the kitchen and more specifically for the cooker.
Typically the cable going to the cooker isolation switch is in safe zones.
There is typically a cooker cable junction box in the wall behind the cooker.
Then there is a short run of cable from the cooker isolation switch to the cooker cable junction box and it's always diagonal! I have never seen a vertical and horizontal cable run between the isolation switch and junction box.....
If you have various accessories (switch, outlet plate etc) positioned diagonally to each other - there is always a rectilinear path between them that does not stray from their respective zones.
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