Earthed metal protection

I

ianphilip007

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hi there

may need to bury some meter tails in wall (25mm 16mm earth), not my usual practice, now they will not be below 50mm so they will need earthed mechanical protection. can any one advise as whats best to use for mechanical protection and the size of the earth cable required for earthing it ?

many thanks
 
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i would be inclined to use the collected flakes of arnies skin fashioned into an impenetrable capping shield, with one of chuck norris's pubes as an earth...but if you havnt got such things readily available, i would have thought galvanised capping would suffice also...
 
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Reg 522.6.6 requires an earth conduit to BSEN 61386 or earth trunking to BSEN 50085 or be mechanically protected against nails, screws and the like or be in the safe zones or under certain circumstances have additional protection to 415.1.1. I don't think galv capping is sufficent unless very thick. The requirement of 415.1.1 is 30mA RCD with 40mS trip at 5 Idelta n, which for tails means a 30mA RCD front end which would be unacceptable due to nuisance tripping and not segrating circuits.

So my interpretation of the regs is galv steel conduit or trunking to the standard above or a sheet of thick galv plate over the tails. I would have thought the earth strap would need to be able to carry the max PFC until the suppliers fuse trips in case someone does decide to drill through despite the protection, it would make a nice bang.
 
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ianphilip007 said:
hi there

may need to bury some meter tails in wall (25mm 16mm earth), not my usual practice, now they will not be below 50mm so they will need earthed mechanical protection. can any one advise as whats best to use for mechanical protection and the size of the earth cable required for earthing it ?

many thanks
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There's no requirement in BS7671 for earthed mechanical protection.
Earthed metalic cable sheath, earthed conduit or trunking, but no mention about earthed mechanical protection.
 
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hi spin, what the fela is trying to say, is that his cables wont be RCDprotected, s theyre meter tails, and they ar to be buried, and dont have the "buried more than 50mm" exemption.

In my opinion, capping is not to be use in this instance. it offers little or no protection, and is only used to potect the cables from the plasterers float.

best to use either trunking, steel plate, or conduit. If using steel conduit, it will have to be either 40mm or 50mm, as you cannot put the cables through different conduits due to eddy currents.
 
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johnboy6083 said:
hi spin, what the fela is trying to say, is that his cables wont be RCDprotected, s theyre meter tails, and they ar to be buried, and dont have the "buried more than 50mm" exemption.

In my opinion, capping is not to be use in this instance. it offers little or no protection, and is only used to potect the cables from the plasterers float.

best to use either trunking, steel plate, or conduit. If using steel conduit, it will have to be either 40mm or 50mm, as you cannot put the cables through different conduits due to eddy currents.
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Cables concealled in walls require additional protection against penetraion by nails and screws.
This can be provided by burying the cables at a depth greater than 50mm (it's not an exception, it's one of the methods that can be used),
Using a cable that incorporates an earthed metallic sheath (one that complies with any of the British Standards listed in 522.6.6(i) or 522.6.101(i)),
Installing the cables in earthed conduit or trunking,
Providing mechanical protection sufficient to prevent the cables being penetrated by screws or nails (no mention in BS7671, about the mechanical protection being earthed, then again why would it need to be earthed, if the mechanical protection protects against penetration by nails and screws?),
or by installing the cables in a safe zone and providing 30mA RCD protection.
 
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fair point. i meant an exemption, as in it allows the exemption of an RCD. I would always earth it down, in order to allow ADS. some DIYers would keep drilling, until the steel protection was peirced.
 
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What do you think 'Read chapter 41 'means. On the other hand ignore my advice, the uk will be a safer place when you're inside for manslaughter.

Are you an electrician?
 
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The last one I had said 'electrical technician', and I see you've swerved away from your lack of knowledge problem.

I'm not really interested in continuing a conversation with someone so ignorant of the basics of safe electrical work. God help people using your installations.
 
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oxocube said:
The last one I had said 'electrical technician', and I see you've swerved away from your lack of knowledge problem.

I'm not really interested in continuing a conversation with someone so ignorant of the basics of safe electrical work. God help people using your installations.
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Not aware we were having a conversation.
As far as I'm concerned all you've done is spouted some inane opinions, and made some derogatory comments.
Now if you could actually back your opinions/comments up with some coherent argument, then I might consider engaging in conversation with you.
Unfortunately suggesting somene reads the chapter that relates to providing protection against electric shock, when the thread is about providing additional protection to cables concealled in walls, just doesn't cut it as a coherent argument.
 
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I agree that spinlondon is right. The regs do not state that the protection against screws and nails needs to be earthed. Whether one would earth it as a matter of principal is a different discussion.
 
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KFH said:
I agree that spinlondon is right. The regs do not state that the protection against screws and nails needs to be earthed. Whether one would earth it as a matter of principal is a different discussion.
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Agreed! Although as someone said you might find one idiot would drill straight through it. Was working on a flat in london where it was supplied via T+E that wasnt RCD protected. Ended up buying a couple of sheets of 600X400mm 3mm thick sheets to protect upto the CU, which was then just plasterboarded over. Meant it was protected both sides and I think it cost less than 20 quid. Could have drilled it and put a crimp on some 10mm cable but didnt at the time.
 
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I find all this very hard to believe, the cables are buried less than 50mm deep. Therefore there are only two alternatives;

1, They should have 30mA rcd protection, but that would not comply with various regs in sect 132 regarding separation of circuits and convenience, so is unacceptable.

2. They must be enclosed in earthed metal as specified by regs 522.6.7, 7 and 8 and various regs in sect 41.

And with that I'm out.
 
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Oxo, I believe Spinlondon is refering to the same reg you are. If you read 522.6.6 (iv) be mechanically protected against damage suffiecient to prevent penetration of the cable by nails. screws and the like. Doesnt mention it has to be earthed. Unless theres a reg that over rides that, that ive missed? Im only a newbie so correct me if im wrong.
 
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all can be resolved with a fight to the death armed with nothing more then a 1m piece 1.5 T+E and whatever you can find in your lunchboxes.... ding ding seconds out. my money is on spin, he rides a big bike...must be tough and bearded? probably has a brick in his lunchbox
 
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rob121 said:
Oxo, I believe Spinlondon is refering to the same reg you are. If you read 522.6.6 (iv) be mechanically protected against damage suffiecient to prevent penetration of the cable by nails. screws and the like. Doesnt mention it has to be earthed. Unless theres a reg that over rides that, that ive missed? Im only a newbie so correct me if im wrong.
Click to expand...

I have some self drilling screws that will drill into RSJ's, and will go through 3/4mm steel in seconds. Thats another reason why it should be earthed.
 
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wade88 said:
all can be resolved with a fight to the death armed with nothing more then a 1m piece 1.5 T+E and whatever you can find in your lunchboxes.... ding ding seconds out. my money is on spin, he rides a big bike...must be tough and bearded? probably has a brick in his lunchbox
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I've only got a handbag and a moped.
 
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What I can't picture is what if, like any meter tails anywhere they are not goint to run in a straight line, So yes stick them in scaffold tube and earth it but it's going to be one hellava fabrication job getting the tube to bend even a little to get past the obstructions we meet every time you run 25mm cable, what about the pre armoured stuff, not swa, I cant remember who makes it, does that go up to 25mm??
Pict
 
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Earthed metal protection
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