wiring at 50mm below surface

[electricphil]

We are having a conservatory built and the electrics are part of the package. I was surprised to see the cables for the sockets being installed at floor level. The electrician explained that when the plaster board was fitted the wiring would be 50mm below the surface. Comments!

 

[Darkwood]

I will try be more clear, the outer sheath is designed for environmental protection of the inner insulation it can be ordered in many combinations and tolerences for the environment it is going to be subject to, i use specialised cables like Lapp and Igus in Energy Chain systems, any sheath has a tolerence to mechanical damage so it would be wrong of me to say it dosent provide any but regarding T&E pvc cables it is soft easily damaged thus provides minimal mechanical protection. In a sense it can be disregarded it is that low unless you consider attacking it with a feather duster which im sure it will resist, re' the regs any cables regarded as having mechanical protection would be your Micc's and swa's etc as im sure you know but even on these if they have an outer sheath it is there for environmental protection of the inner cable constructs.
This was also made clear when i did the stupid PAT test course where many made the error of thinking the outer sheath is there for mechanical protection, consider oil resistant flexes which again are made up of inner insulation and outer sheath... you can easily split the sheath open with finger pressure applied the correct way but used correctly they will not degrade while running your oil pump on a machine.

Yes you raise a good point regarding the meter box but each situation as it comes and in this case you will only be going through one building construct straight into the meter box, and lastly regarding the numerous older properties with no cavity, they are often loose rubble filled in the middle so require the protection to from the crushing weight that can occur and also alot of old properties were subject to polysterene insulation in the walls which eats pvc so another reason to protect the cables as you dont always realise its there.

 

[SJD]

Yes you raise a good point regarding the meter box but each situation as it comes and in this case you will only be going through one building construct straight into the meter box, and lastly regarding the numerous older properties with no cavity, they are often loose rubble filled in the middle so require the protection to from the crushing weight that can occur and also alot of old properties were subject to polysterene insulation in the walls which eats pvc so another reason to protect the cables as you dont always realise its there.

When fitting a new consumer unit, and the existing meter tails just pass through the cavity wall, and you planned to use those tails directly as they were - would you instead retrofit some mechanical protection where they pass through the wall?

 

[Darkwood]

Like anything else in the property if your doing the board change and re-use the existing tails as tagging in any other circuit that might not comply it will just be noted assuming its safe, if your changing them then u need to provide protection if they will be considered at risk from damage regardless of previous methods

 

[chrisreid186]

i always run cable in safe zones but had a conversation with a sparks and he said if the cables are grater then 50 mm from surface then you can run them wherever, is this right?
so it would be ok to drop a cable down from the ceiling into a stud wall,then drill through the floor plate and into the floor boards without a accessory on the wall in line with the cable, the stud timbers are 4x2 which is approx 90mm, plus standard plaster board which is 12.5 then 3mm of finish, so if you drilled the middle of the stud you should be ok? makes sense just need a second opinion

 

[telectrix]

i always run cable in safe zones but had a conversation with a sparks and he said if the cables are grater then 50 mm from surface then you can run them wherever, is this right?
so it would be ok to drop a cable down from the ceiling into a stud wall,then drill through the floor plate and into the floor boards without a accessory on the wall in line with the cable, the stud timbers are 4x2 which is approx 90mm, plus standard plaster board which is 12.5 then 3mm of finish, so if you drilled the middle of the stud you should be ok? makes sense just need a second opinion

common sense says yes, but bear in mind that builders and wood butchers have the use of nail guns with 4" nails. if it's possible to fire one through a cable buried 2" deep, you can guarantee that they will manage to do it.

 

[richy3333]

common sense says yes, but bear in mind that builders and wood butchers have the use of nail guns with 4" nails. if it's possible to fire one through a cable buried 2" deep, you can guarantee that they will manage to do it.

Isn't letting a joiner have a nail gun just evidence of natural selection in action?

 

[brman]

Darkwood, your first sentance states that a sheath is not mechanical protection, then states that it provides 'limited' mechanical protection.
Which is it to be?
Yes it won't provide much protection against large or heavy particles of debris dropping the full height of a house within a cavity wall.
However many properties do not have cavity walls, some that do have meter cupboards inset into the cavity wall and often external meter cupboards are placed under windows.
In many instances debris dropping onto cables is not a consideration and in many other instances the drop is not the full height of a house.
As such sheathed conductors do not necessarily require further mechanical protection.

Plus, if it is a new house, there will be cavity insulation blocks which will prevent any larger bits of debris anyway.

I can see Darkwoods point and it certainly is worth considering but I'd rather not core a 2" hole for a pipe unless I really had to.

 

[Darkwood]

[MENTION=50795]brman[/MENTION] ... the point im trying to get across throughout this thread is the outer sheath shouldn't be looked at as mechanical protection but environmental protection with regards to standard household pvc/pvc cables, i also said each case should be assesed on its own merits and yes could agree if the double wall has solid block insulation in it then you could come to the conclusion that it wont be necessary to provide mechanical protection as with the flush meter cupboard senerio mentioned earlier where it actually sits within the cavity an the cables would not be at risk.

 

[brman]

@brman ... the point im trying to get across throughout this thread is the outer sheath shouldn't be looked at as mechanical protection but environmental protection with regards to standard household pvc/pvc cables, i also said each case should be assesed on its own merits and yes could agree if the double wall has solid block insulation in it then you could come to the conclusion that it wont be necessary to provide mechanical protection as with the flush meter cupboard senerio mentioned earlier where it actually sits within the cavity an the cables would not be at risk.

Point taken

 

[Deleted member 26818]

Darkwood, you seem to be under the impression that mechanical protection and environmental protection are separate and distinct entities.
They're not.
Environmental protection includes amongst other mechanical protection.
Appendix 5 lists impact as an environmental condition and assigns it the code AG.
Non-sheathed conductors (other than some earthing/bonding conductors) must be provided with mechanical protection.
They can be run in conduit or trunking. Trunking must have an IP rating of at least IP4X or IPXXD.
IP4X is protection against penetration by a wire greater than 1mm in diameter, IPXX4 is protection against a wire greater than 1mm in diameter with the added proviso that a 100mm length will not come into contact with live parts.

 

[Darkwood]

Think we are trying to argue the same point from different angles, all im trying to do is to explain exactly what you have just said, you shouldn't look at the sheath as mechanical protection but environmental protection and yes mechanical endurance is one of the properties, then i merely stated the very limited protection pvc/pvc gave and can be more or less disregarded for its mechanical strength.
Putting it a different way is like saying the outer sheath protects the inner cables from UV radiation which is not untrue but it will have a scaled ability to do so again standard pvc/pvc has a low tolerence to UV but in saying the outer sheath is there to give UV protection can be misleading, i am merely saying you should look at the sheath for providing Environmental Protection which then covers all its attributes and not say the outer sheath is there for mechanical protection as this give the impression it has no other function but mechanical protection and this would also be misleading as it may provide poor protection.

 

[Darkwood]

[MENTION=26818]spinlondon[/MENTION] ... Re-reading through its clear we are both whistling the same tune but just using different words i haven't disagreed with your advice given and actually re-enforced in my own wording, i think the confusion here is your under the impression im saying mechanical protection isnt part of environmental protection which i never have im just trying to say it would be better worded that the outer sheath is the environmental protection and in the case of PVC/PVC it has a poor mechanical tolerance thus as you correctly stated the OP would need to make a judgement on whether its good enough without extra protection provided, and i the case of tails running through walls i gave my experience and advice and others including yourself pointed out situes where it wouldn't be required to which i fully agreed.

 

[Grey Master]

Back to topic:
Regardless of how deep the cables are buried they will need to be RCD protected espescially for sockets that may be used outside (16th ed)