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Prescribed Zones + Multiple Circuits
Ste
4 Posts
Question
If two circuits are being run where the outlets are in line with each other horizontally, and where the cables are run adjacent to each other horizontally in the prescribed zone between the outlets (1 radial for 13A sockets and another for 5A lighting sockets in my case) is there a preferred method of routing the cables through or around the back box for the other circuit?

I know the cable for the 5A lighting outlets could be fed through the back box for the 13A sockets (and vice versa), but can they be also run around the top or bottom of the other circuits back box and then into their own back box and will the point where the cable goes around the corner of the back box still be within the prescribed zones? Crude drawing attached, A is through, B is around.



Full disclosure - this is DIY job that I'm planning ahead of notifying building control. I could go vertically up and down and around the ceiling for each outlet, but will start to run into current rating issues due to the cable lengths involved.

Thanks

 
15 Replies
geoffsd
158 Posts
Zones are created horizontally and vertically from accessories only for cables connected to those accessories so, strictly speaking, diagonally from the corner of another accessory is not a safe zone.
AJJewsbury
1757 Posts
I don't think there's a standard solution. Where possible the problem is avoided (e.g. by dropping down from the ceiling or (for internal walls) running one circuit on one side of the wall and the other on the other side, going right through the wall were needed to reach the appropriate box). Where it's not easily avoidable, I've either run the 'other' cable either behind the box or just over the top of it - the latter justified by the observation that frontplate accessories are significantly taller/wider than flush boxes so there's a (slim) area of wall that's within zones but outside of the back boxes. Obviously going behind the box is easier in a stud partition wall.

Or if any doubt, just use a cable that doesn't have to be in zones - such as a BS 8436 type.

   - Andy.
Chris Pearson
1651 Posts
Some people frown on the practice, but I would just go straight through the back boxes - with grommets to protect the cables in the holes of course. You could even use the same mini-conduit for both circuits.

If these are extensions to existing circuits and not in a bathroom, etc. you don't have to notify.
-2400-
85 Posts
Just out of interest, what is the current rating issue that you see as a problem? 
(*If* you did want to go up/down, particularly with the 5A lighting circuit, the forum could probably help with a suitable solution)
Alcomax
212 Posts
For "safe zone" , I read " a place where you may expect a cable to be, buried less than 50mm from the surface".
So in the absence of diagrams or documentation  or warnings of such a cable, at such a depth, being in what would normally be "an unexpected place", that cable would need protection against impact, in so much it is not going to be damaged and you are going to have to rip it out and replace it.

In the first instance 522.6.1 needs to be complied with first. It cannot be wished away.

Regs 522.6.202 and 522.6.204 are expanding on the theme of impact in selection and erection. They are not a "get out" for use of BS8436 cable in an "unexpected place" at a depth of less than 50mm, unless it is made very clear where that cable is buried by obvious information being present. Of course then it would no longer be in an unexpected place.

I get that reading 522.6.202, in isolation, can  give the impression of a  green light to using BS8436 in an "unexpected place", but if the cable is impacted and it is damaged you need to replace it, falling foul of 522.6.1 as it is very clear from the outcome, that the wiring system was not selected and erected to minimise damage arising from it being impacted. The "fail safe earth fault protection" bit is all well and good, nobody died, but the cable did.

The vertical/horizontal / top of the wall 150mm "zones" are articulating a common sense positioning of cables " where you expect a cable could be buried at <50mm".
Once there is a cable in that particular straight run to an accessory, it is, by dint, "a safe zone", a place where " a cable may be buried". There is nothing precluding a cable unrelated to that accessory sharing the same route for compliance with 522.6.1.

So negotiating past an accessory with an unrelated cable, I would install it where it does not interfere with use of the back box , say you need to alter it for something deeper later on. So going through it is not such a good idea. Your "expected place for a possible cable" is north/south/east and west of this point. I would go round it, but I expect a pedantic building inspector would try to find fault with that. So one up for being able to self certify😁. In any event, it complies with 522.6.1
 
OlympusMons
138 Posts
I'm with Chris here, go through the back boxes, use deeper ones if necessary. Even though the faceplates are slightly bigger than the back boxes, the cable routes above or below would need the cables edge-wise to front, flat would be outside the curtilage of the faceplate. It just makes sense to be able to see the route of the other circuit in the backbox once a faceplate is removed.
Ste
4 Posts
-2400-:
Just out of interest, what is the current rating issue that you see as a problem? 
(*If* you did want to go up/down, particularly with the 5A lighting circuit, the forum could probably help with a suitable solution)

The lighting is fine - the radial for the sockets is the issue. The cables are clipped to block, the wall is lined with a metal stud wall which will have 25 or 50mm of APR insulation behind the plasterboard (depending which wall) and on top of the wiring. Using Method 102 and calculating for cable length would give 2.5mm a current rating of < 20A by running it up and down to the outlets vertically. An option that would avoid that is branching the radial at the point it comes in the room but not sure if that's a 'dirtier' solution than running through the backboxes? Or I could just go with a 16A MCB I guess

Ste
4 Posts
Chris Pearson:
Some people frown on the practice, but I would just go straight through the back boxes - with grommets to protect the cables in the holes of course. You could even use the same mini-conduit for both circuits.

If these are extensions to existing circuits and not in a bathroom, etc. you don't have to notify.

Sadly it's in an extension that had a flat roof - the cables in the ceiling were covered in tar where it had been poured through various holes in the roof in some dodgy patching jobs and several of the cables in the wall were run at 45 degrees across entire walls from the back box to the ceiling when we chipped the plaster off that had got damp. All things considered just decided to rip it all out and start again.

AJJewsbury
1757 Posts
Using Method 102 and calculating for cable length would give 2.5mm a current rating of < 20A
How is the length affecting your current rating calculation?
    - Andy.
AJJewsbury
1757 Posts
Alcomax:
For "safe zone" , I read " a place where you may expect a cable to be, buried less than 50mm from the surface".
So in the absence of diagrams or documentation  or warnings of such a cable, at such a depth, being in what would normally be "an unexpected place", that cable would need protection against impact, in so much it is not going to be damaged and you are going to have to rip it out and replace it.

In the first instance 522.6.1 needs to be complied with first. It cannot be wished away.

Regs 522.6.202 and 522.6.204 are expanding on the theme of impact in selection and erection. They are not a "get out" for use of BS8436 cable in an "unexpected place" at a depth of less than 50mm, unless it is made very clear where that cable is buried by obvious information being present. Of course then it would no longer be in an unexpected place.

I get that reading 522.6.202, in isolation, can  give the impression of a  green light to using BS8436 in an "unexpected place", but if the cable is impacted and it is damaged you need to replace it, falling foul of 522.6.1 as it is very clear from the outcome, that the wiring system was not selected and erected to minimise damage arising from it being impacted. The "fail safe earth fault protection" bit is all well and good, nobody died, but the cable did.

The vertical/horizontal / top of the wall 150mm "zones" are articulating a common sense positioning of cables " where you expect a cable could be buried at <50mm".
Once there is a cable in that particular straight run to an accessory, it is, by dint, "a safe zone", a place where " a cable may be buried". There is nothing precluding a cable unrelated to that accessory sharing the same route for compliance with 522.6.1.

So negotiating past an accessory with an unrelated cable, I would install it where it does not interfere with use of the back box , say you need to alter it for something deeper later on. So going through it is not such a good idea. Your "expected place for a possible cable" is north/south/east and west of this point. I would go round it, but I expect a pedantic building inspector would try to find fault with that. So one up for being able to self certify😁. In any event, it complies with 522.6.1
 

Don't confuse "zones" with 522.6.1 - they're specified only within the context of 522.6.202/203/204 etc. Using BS 8436 cables (or MICC or SWA or steel conduit etc) is clearly offered as an alternative to routing cables within "zones".

522.6.1 only calls for the minimisation of damage should mechanical stress occur. It's not asking for damage to be completely prevented, not (arguably) for the risk of the particular mechanical stress of the cable occurring to be minimised (just the resulting damage).

   - Andy.

Alcomax
212 Posts
AJJewsbury:
Alcomax:
For "safe zone" , I read " a place where you may expect a cable to be, buried less than 50mm from the surface".
So in the absence of diagrams or documentation  or warnings of such a cable, at such a depth, being in what would normally be "an unexpected place", that cable would need protection against impact, in so much it is not going to be damaged and you are going to have to rip it out and replace it.

In the first instance 522.6.1 needs to be complied with first. It cannot be wished away.

Regs 522.6.202 and 522.6.204 are expanding on the theme of impact in selection and erection. They are not a "get out" for use of BS8436 cable in an "unexpected place" at a depth of less than 50mm, unless it is made very clear where that cable is buried by obvious information being present. Of course then it would no longer be in an unexpected place.

I get that reading 522.6.202, in isolation, can  give the impression of a  green light to using BS8436 in an "unexpected place", but if the cable is impacted and it is damaged you need to replace it, falling foul of 522.6.1 as it is very clear from the outcome, that the wiring system was not selected and erected to minimise damage arising from it being impacted. The "fail safe earth fault protection" bit is all well and good, nobody died, but the cable did.

The vertical/horizontal / top of the wall 150mm "zones" are articulating a common sense positioning of cables " where you expect a cable could be buried at <50mm".
Once there is a cable in that particular straight run to an accessory, it is, by dint, "a safe zone", a place where " a cable may be buried". There is nothing precluding a cable unrelated to that accessory sharing the same route for compliance with 522.6.1.

So negotiating past an accessory with an unrelated cable, I would install it where it does not interfere with use of the back box , say you need to alter it for something deeper later on. So going through it is not such a good idea. Your "expected place for a possible cable" is north/south/east and west of this point. I would go round it, but I expect a pedantic building inspector would try to find fault with that. So one up for being able to self certify😁. In any event, it complies with 522.6.1
 

Don't confuse "zones" with 522.6.1 - they're specified only within the context of 522.6.202/203/204 etc. Using BS 8436 cables (or MICC or SWA or steel conduit etc) is clearly offered as an alternative to routing cables within "zones".

522.6.1 only calls for the minimisation of damage should mechanical stress occur. It's not asking for damage to be completely prevented, not (arguably) for the risk of the particular mechanical stress of the cable occurring to be minimised (just the resulting damage).

   - Andy.


There is no confusion. I said I like to think of these "Zones", or whatever, as being a place where you expect cables to be. So forget about any notional zone. The risk of damage is less, because they are not likely to be impacted and so, damaged. On the other hand, if you are to place them in a position, say a diagonal, where they are more likely to be impacted, that is clearly increasing the risk of damage.

In order for your diagonally run  BS 8436 cable to fire the B type breaker, the cable is damaged and will need to be replaced. I can see no reasonable argument that this is minimising the damage arising from impact or penetration. The cable is either damaged or it is not damaged. There is no half way.

522.6.1  clearly sets out what is expected from the installation of a cable. Minimise damage. So put it in a place where it is expected to be and it will not get hit by someone drilling a wall.
522.6.204 offers an alternative, if it is not reasonably possible to install as with 522.6.202 [i] .  The choices offered by 522.6.204 are many. You may chose BS 8436  [522.6.204 [i], but someone could say, why not select mechanical protection sufficient to prevent penetration of the cable? [iv].

Look at it another way. If you are to take 522.6.202 literally, in isolation as a "rule", over arching all before and after, then if you selected a wiring system from the list in 522.6.204 and installed in the areas stipulated by 522.6.202 [I], then it seems this literal reading compels you to install a 30mA RCD....

What was a reason for using BS8436 cable? An alternative for switchdrops on lighting circuits without RCD protection when the 17th came in 2008.
Applying 522.6.202 incorrectly as a primary rule, you would need to install 30mA RCD regardless, making the use of BS8436 in switch drop positions redundant.
At the end of the day it is your choice. If a cable is not where it would normally be expected to be and it is more likely to be damaged as a result, was your decision to not use positioning as described in 522.6.202[i] a reasonable one?

Ste
4 Posts
AJJewsbury:
Using Method 102 and calculating for cable length would give 2.5mm a current rating of < 20A
How is the length affecting your current rating calculation?
    - Andy.

Assuming full load on a 20A MCB at the end of the circuit the voltage drop is > 5% for 2.5mm T&E.

 

ebee
775 Posts
The purpose of the "safe zones" is to reduce the risk of accidental damage. If we put cables in such places we can reasonably expect them to be "safer" than other places . Actually in real life not many ordinary people know about safe zones or even give a thought. How often do we see a picture haning right above a run from a switch or socket? Very often!. In my opinion using either of your methods would probably comply. But you must at least consider any likelyhood that cables/points for a circuit might be changed later (perhaps many years later) and therefore lose that zone not only for that particular circuit but also for the other circuit sharing that zone.

Around the outsides will be difficult but possible. Behind is better, BUT if someone needs to drill thru the backbox in future to get a better fixing (that does happen) then the cable could be compromised.

In essence keeping zones created by a circuit related only to that circuit should be the aim really.

Having said that I suspect that many of us might have done some such where needs must.
AJJewsbury
1757 Posts
522.6.1 clearly sets out what is expected from the installation of a cable. Minimise damage. So put it in a place where it is expected to be and it will not get hit by someone drilling a wall.
But if we continue to follow that logic, a cable concealed within zones isn't totally immune to being accidentally hit by nails or drilling (as not everyone out there even knows of the zones, as ebee says) - but a cable on the surface would be clearly visible and so at a much lower risk of such accidental damage by drilling or nails etc.. So should we read 522.6.1's requirement to minimise damage as prohibiting concealed cables altogether? Or rather should we think of it less of an absolute, but to be read within the context of whatever's reasonably practical in the circumstances? If aesthetic considerations preclude surface cables then concealed ones can be considered. If cables can't readily be kept in zones (because the layout doesn't allow it, or the path blocked by structural steels or concrete floors & ceilings or because the the zone is already occupied by incompatible cables) then the option of concealing cables outside of zones (along with the additional precautions in 522.6.204) could be permitted?
 
why not select mechanical protection sufficient to prevent penetration of the cable?
Mainly because in these days of nail guns and multipurpose drill bits, there's doesn't seem to be a practical way of reliably achieving that. Even several mm of steel doesn't seem to provide reliable protection.
 
The cable is either damaged or it is not damaged. There is no half way.
Maybe it's not just damage to the cable to be considered - but also consequential damage (or other dangers) - a nicked conductor (if the damage doesn't trigger ADS) could overheat or arc so damage the surrounding structure or start a fire, likewise the risk of shock. MICC, SWA, BS 8436 or in steel conduit would fare much better on those scores than T&E even though the cable would still have to be completely replaced.

  - Andy.
Alcomax
212 Posts

Call me old fashioned, but application of a standard should be in context.  I am baffled as to why so much effort is being expelled in the pursuit of extolling some supposed virtue of installing BS8436, buried less than 50mm in an unexpected place and, additionally, the subsequent lack of concern that it may be damaged after?

I would like to keep the thread in context please, with no selective quoting, otherwise it makes as much sense as the Coronavirus Daily Update.

 

AJJewsbury:
Alcomax:
For "safe zone" , I read " a place where you may expect a cable to be, buried less than 50mm from the surface".
So in the absence of diagrams or documentation  or warnings of such a cable, at such a depth, being in what would normally be "an unexpected place", that cable would need protection against impact, in so much it is not going to be damaged and you are going to have to rip it out and replace it.

In the first instance 522.6.1 needs to be complied with first. It cannot be wished away.

Regs 522.6.202 and 522.6.204 are expanding on the theme of impact in selection and erection. They are not a "get out" for use of BS8436 cable in an "unexpected place" at a depth of less than 50mm, unless it is made very clear where that cable is buried by obvious information being present. Of course then it would no longer be in an unexpected place.

I get that reading 522.6.202, in isolation, can  give the impression of a  green light to using BS8436 in an "unexpected place", but if the cable is impacted and it is damaged you need to replace it, falling foul of 522.6.1 as it is very clear from the outcome, that the wiring system was not selected and erected to minimise damage arising from it being impacted. The "fail safe earth fault protection" bit is all well and good, nobody died, but the cable did.

The vertical/horizontal / top of the wall 150mm "zones" are articulating a common sense positioning of cables " where you expect a cable could be buried at <50mm".
Once there is a cable in that particular straight run to an accessory, it is, by dint, "a safe zone", a place where " a cable may be buried". There is nothing precluding a cable unrelated to that accessory sharing the same route for compliance with 522.6.1.

So negotiating past an accessory with an unrelated cable, I would install it where it does not interfere with use of the back box , say you need to alter it for something deeper later on. So going through it is not such a good idea. Your "expected place for a possible cable" is north/south/east and west of this point. I would go round it, but I expect a pedantic building inspector would try to find fault with that. So one up for being able to self certify😁. In any event, it complies with 522.6.1
 

Don't confuse "zones" with 522.6.1 - they're specified only within the context of 522.6.202/203/204 etc. Using BS 8436 cables (or MICC or SWA or steel conduit etc) is clearly offered as an alternative to routing cables within "zones".

522.6.1 only calls for the minimisation of damage should mechanical stress occur. It's not asking for damage to be completely prevented, not (arguably) for the risk of the particular mechanical stress of the cable occurring to be minimised (just the resulting damage).

   - Andy.


There is no confusion. I said I like to think of these "Zones", or whatever, as being a place where you expect cables to be. So forget about any notional zone. The risk of damage is less, because they are not likely to be impacted and so, damaged. On the other hand, if you are to place them in a position, say a diagonal, where they are more likely to be impacted, that is clearly increasing the risk of damage.

In order for your diagonally run  BS 8436 cable to fire the B type breaker, the cable is damaged and will need to be replaced. I can see no reasonable argument that this is minimising the damage arising from impact or penetration. The cable is either damaged or it is not damaged. There is no half way.

522.6.1  clearly sets out what is expected from the installation of a cable. Minimise damage. So put it in a place where it is expected to be and it will not get hit by someone drilling a wall.
522.6.204 offers an alternative, if it is not reasonably possible to install as with 522.6.202 [i] .  The choices offered by 522.6.204 are many. You may chose BS 8436  [522.6.204 [i], but someone could say, why not select mechanical protection sufficient to prevent penetration of the cable? [iv].

Look at it another way. If you are to take 522.6.202 literally, in isolation as a "rule", over arching all before and after, then if you selected a wiring system from the list in 522.6.204 and installed in the areas stipulated by 522.6.202 [I], then it seems this literal reading compels you to install a 30mA RCD....

What was a reason for using BS8436 cable? An alternative for switchdrops on lighting circuits without RCD protection when the 17th came in 2008.
Applying 522.6.202 incorrectly as a primary rule, you would need to install 30mA RCD regardless, making the use of BS8436 in switch drop positions redundant.
At the end of the day it is your choice. If a cable is not where it would normally be expected to be and it is more likely to be damaged as a result, was your decision to not use positioning as described in 522.6.202[i] a reasonable one?

 
 
 
 
AJJewsbury:
522.6.1 clearly sets out what is expected from the installation of a cable. Minimise damage. So put it in a place where it is expected to be and it will not get hit by someone drilling a wall.
But if we continue to follow that logic, a cable concealed within zones isn't totally immune to being accidentally hit by nails or drilling (as not everyone out there even knows of the zones, as ebee says) - but a cable on the surface would be clearly visible and so at a much lower risk of such accidental damage by drilling or nails etc.. So should we read 522.6.1's requirement to minimise damage as prohibiting concealed cables altogether? Or rather should we think of it less of an absolute, but to be read within the context of whatever's reasonably practical in the circumstances? If aesthetic considerations preclude surface cables then concealed ones can be considered. If cables can't readily be kept in zones (because the layout doesn't allow it, or the path blocked by structural steels or concrete floors & ceilings or because the the zone is already occupied by incompatible cables) then the option of concealing cables outside of zones (along with the additional precautions in 522.6.204) could be permitted?

The logic is clear, it is where the cable is expected to be. If it is in an unexpected place it is at risk of the casual driller. You are permitted to qualify your installation method and rational for doing so.
I made it clear there is a choice. If you chose to install in areas which other trades or persons with some knowledge of these thing would regard as "unexpected", you need to mitigate the risk. How you do it is your call. For sake of argument, I would regard a whole house 1st fix done in BS8436 with cables buried at less than 50mm, diagonally, or in generally unexpected places, unusual to say the least. I think if this was transposed to a new build site as a means of cost saving, primarily in time, there would be a big problem as the charge would be you would be non compliant with 522.6.1.

 
why not select mechanical protection sufficient to prevent penetration of the cable?
Mainly because in these days of nail guns and multipurpose drill bits, there's doesn't seem to be a practical way of reliably achieving that. Even several mm of steel doesn't seem to provide reliable protection.

This is particularly selective quoting. It has flawed logic in any event, as, if the threat of Nail Gun is real, you should not be putting the cable there. Put it somewhere it is to be expected, or go leave clear on-site diagrams and documentation of where you have hidden all these cables, though that is not acceptable, to my mind, unless it is in a controlled environment, so that precludes the domestic sector.
In context, it is clear there is an alternative of various methods, if you have no choice but to install in "unexpected places".  But it is your choice to justify. Do not forget 522.6.2, if your justification is based on severity [ AG2...AG3], you best select your alternative method that has the highest protection against mechanical attack.

 
The cable is either damaged or it is not damaged. There is no half way.
Maybe it's not just damage to the cable to be considered - but also consequential damage (or other dangers) - a nicked conductor (if the damage doesn't trigger ADS) could overheat or arc so damage the surrounding structure or start a fire, likewise the risk of shock. MICC, SWA, BS 8436 or in steel conduit would fare much better on those scores than T&E even though the cable would still have to be completely replaced.

  - Andy.

Not sure how this selective quote helps support the supposed virtue of installing a cable where it is more likely to be damaged?

The whole point of selection and erection is achieving an acceptable balance between good installation practice, efficacy - what is "fit for purpose"- and safety. How you decide to apply all this is down to you. Can you demonstrate  that this choice was reasonable?

The "Impact" section of the regs is essentially the same back to 16th Edition. I have not checked 15th. But something in emphasis has changed since the 16th.
For 18th , I think 17th also, we read 522.6.202. In the 16th, the equivalent was 522.06.06. Following from this was reg 522-06-07 ..." where compliance with 522-06-06 is impracticable....."
In 2008 the 17th generally forces 30mA for twin and earth, unprotected, buried <50mm in expected positions. This 30mA requirement has been bunched into the impact section and, to my mind, it has unwieldy wording as a result. It would have been clearer if "impracticable" had been retained.

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