wiring question
- Thread starter samohtom
- Start date
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The purpose of the "50mm deep or protected" rule is to avoid the personal risk of someone knocking in a nail and hitting a cable - making the nail (or screw) live. If you do that with an RCD protected circuit, then the RCD should protect against lethal shocks - but you've still damaged the cable.
Mechanical protection would prevent you damaging the cable in the first place - unless you refuse to give up and put the nail through the protection
In your case, I'd consider steel conduit - not for regs compliance per se, but simply because a floor is a fairly hostile environment. Also, consider extending the ring across - the difference in work and disruption installing a conduit capable of cabling a spur and one capable of extending the ring isn't a great deal. This would most likely mean removing the socket and using it's back box as a terminal box - you'll need to make six connections. At the other side (the new sockets), you can spread out sideways - running the cable out to one end, across the sockets, and back.
Mechanical protection would prevent you damaging the cable in the first place - unless you refuse to give up and put the nail through the protection
In your case, I'd consider steel conduit - not for regs compliance per se, but simply because a floor is a fairly hostile environment. Also, consider extending the ring across - the difference in work and disruption installing a conduit capable of cabling a spur and one capable of extending the ring isn't a great deal. This would most likely mean removing the socket and using it's back box as a terminal box - you'll need to make six connections. At the other side (the new sockets), you can spread out sideways - running the cable out to one end, across the sockets, and back.
In answer to your earlier question, you would have to earth the metal conduit.
Assuming the existing socket you will get the supply from has a metal back box recessed into the wall, you connect your conduit from here, and likewise at the other end. At the metal back boxes, you should provide an earth link wire from the socket wiring to the back box.
By using the above method, you must ensure the conduit is connected to the back box by a bush. All joins in the conduit must be provided by couplers. More than likely, you will need to use single core cables, these must not be buried in the wall or floor without the use of conduit.
Do you have the tools to thread and bend metal conduit?
Are you competent to use metal conduit correctly?
If NOT, I recommend you use twin and earth cable in plastic round conduit, or special cable designed to go in concrete floors, but it would need to be reasonably deep to avoid damage.
Assuming the existing socket you will get the supply from has a metal back box recessed into the wall, you connect your conduit from here, and likewise at the other end. At the metal back boxes, you should provide an earth link wire from the socket wiring to the back box.
By using the above method, you must ensure the conduit is connected to the back box by a bush. All joins in the conduit must be provided by couplers. More than likely, you will need to use single core cables, these must not be buried in the wall or floor without the use of conduit.
Do you have the tools to thread and bend metal conduit?
Are you competent to use metal conduit correctly?
If NOT, I recommend you use twin and earth cable in plastic round conduit, or special cable designed to go in concrete floors, but it would need to be reasonably deep to avoid damage.
hi if your tiler wants you to put ply over the sub floor it will want screwing down, my tiler asked for 5 screws within a 5 inch box a lot of screws and a ball ache but i wouldn't of wanted a cable close under it unless mechanically protected.
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I don't think the OP is getting a complete grasp of the requirements of RCD protection or mechanical protection.
Simply
*Cables should be routed within permitted safe zones (will post this soon)
*If they are not within safe zones then they should be buried greater than 50mm or have mechanical protection (sometimes part A building regs, does not allow the chase to be at that depth)
*All buried cable that is not mechanically protected or less than 50mm within walls require 30mA RCD protection
*Cables within the permitted safe zone still require RCD protection unless they are mechanically protected or buried greater than 50mm (again look at part A)
//www.diynot.com/wiki/electrics:installation_techniques:walls
Metallic containment will require earthing, metallic capping is not considered mechanical protection.
You could use special cables that do not require the additional protection of metallic containment.
Simply
*Cables should be routed within permitted safe zones (will post this soon)
*If they are not within safe zones then they should be buried greater than 50mm or have mechanical protection (sometimes part A building regs, does not allow the chase to be at that depth)
*All buried cable that is not mechanically protected or less than 50mm within walls require 30mA RCD protection
*Cables within the permitted safe zone still require RCD protection unless they are mechanically protected or buried greater than 50mm (again look at part A)
//www.diynot.com/wiki/electrics:installation_techniques:walls
Metallic containment will require earthing, metallic capping is not considered mechanical protection.
You could use special cables that do not require the additional protection of metallic containment.
Casamena - sorry I don't give up that easy...renovated the whole flat myself so far apart from plastering. Not too shabby at diy - did this floor/doors/skirting/architrave/coving myself:-
According to the diagrams the areas from the outlets right down to the floor are safe zones, whether the floor is a safe zone I don't know. There's no way I'll be letting anyone nail or screw anything into it - if I decide to tile it I'll level it and tile direct onto that rather than plywood, same as I've done in the hall...it's just about doing it properly. Regulations annoy me, not because of what they're there for but because they tend to dress everything up in jargon instead of putting it in plain English. From what PrenticeBoyofDerry says, as long as it's RCD protected and mechanically protected it should be fine. Need to read up also on what the "bush" in a back box is - if it's another way of saying screw it to the back box, then why not just say that grrr. I need to read up on what the 30mA refers to though and whether my consumer unit RCDs are rated at that or not (I know they work, 'cos I had a guy check all the electrics a couple of years back) - my guess would be the 30mA refers to a change in current required for it to trip rather than the amount of current you can draw before it trips. Will have a read though, thanks for the help.
According to the diagrams the areas from the outlets right down to the floor are safe zones, whether the floor is a safe zone I don't know. There's no way I'll be letting anyone nail or screw anything into it - if I decide to tile it I'll level it and tile direct onto that rather than plywood, same as I've done in the hall...it's just about doing it properly. Regulations annoy me, not because of what they're there for but because they tend to dress everything up in jargon instead of putting it in plain English. From what PrenticeBoyofDerry says, as long as it's RCD protected and mechanically protected it should be fine. Need to read up also on what the "bush" in a back box is - if it's another way of saying screw it to the back box, then why not just say that grrr
. I need to read up on what the 30mA refers to though and whether my consumer unit RCDs are rated at that or not (I know they work, 'cos I had a guy check all the electrics a couple of years back) - my guess would be the 30mA refers to a change in current required for it to trip rather than the amount of current you can draw before it trips. Will have a read though, thanks for the help.
We are now talking about electrical safety, I have no doubt that you are capable of making things aesthetically pleasing, that does not particularly mean that they have been done safely.
.
According to your diagrams they are, with regard to the floor you have duty to take precautions against mechanical damage to the cable that could cause a potential danger, the requirements(regulations) are vague but this is something you must access and consider.
You may not but what when/if you sell on, what happens then?
often necessary to use some jargon as plain English does not always allow you to put the information over correctly, without some git pulling you up
By the diagram and if you follow informed advice given i have no doubt it will.
This a method of attaching the conduit tubes to the backboxes, the conduit requires threading and the bush is a nut that secures the conduit to the backboxNeed to read up also on what the "bush" in a back box is - if it's another way of saying screw it to the back box, then why not just say that grrr
RCD work differently to MCBs, as they detect earth leakage, this creates an imbalance between line(live) and neutral when that value is greater than that that the RCD is valued at the RCD will trip. So if you have a 30mA RCD and earth leakage of that value then the RCD will trip (they actually trip at a little less, somewhere near 26mA).
If you look at the RCD in your board it will likely to display two values, one will be the current that it can safely carry, often 63A or 80A on domestic boards, then there is the RCD earth leakage trip value, this is now required to be 30mA, but there are other less and more sensitive devices.
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