How do you earth mechanical protection?


Postby john1967 » Sun Apr 06, 2008 10:26 pm

Hope someone can help cos i have searched everywhere!
I am adding a spur, in the middle of the wall, horizontally from an existing ring main.
From what i have read this cable would need to be buried at least 50mm from the surface but this is not practical in this case.
I believe the other way to do this is to protect the cable .
What type of mechanical protection do i need to ask for at my local electrical factors (is "top hat" sheilding enough)
Also i believe the protection will need to be earthed - can anyone explain to me how this is done?
Thx in advance for you time and help

John1967
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Postby ericmark » Sun Apr 06, 2008 11:27 pm

At the moment you don't need extra protection.
On July 1st the rules ask for extra protections normally this will be an RCD which because near impossible to buried at 50mm will be the norm. The protective shield has to be to British standard so capping will not do and earthed conduit would be only way to protect existing cable. But if you use something like flexishield instead of twin and earth that would do but for sockets no point as from July 1st all sockets under 20 amp have to have RCD anyway so it will be just a case of using an RCD.
Only exception would be where special marked outlets are used for fridges etc.
It is normal to use oval conduit on additions as you don't need to remove as much plaster and capping on walls that don't yet have plaster on them and is really to stop damaging cable while plastering. Using metal capping plastering is easier but it does nothing to protect cable as a hilti gun can fire a nail through a girder so nothing less than a RSJ could mechanically protect.
ericmark

Postby john1967 » Mon Apr 07, 2008 1:13 am

that is some great information but i am still a little confused-----
so i dont need to use conduit even though it will be horizontal to the spur?
I am still not sure if i did go down the conduit route what i need to ask for or how to earth it
also what is the exception about fridges you talked about?
i believe the ring main is protected by an rcd by the way
sorry to be so thick - but i just wanted to do it right
thx for your response ericmark

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Postby ericmark » Mon Apr 07, 2008 2:09 pm

Pictures are better than words I recommend you follow links in projects section and down load Part P. I am not trying to promote Part P but it has some usefully drawing as to where you can put cables.
You can go vertical or horizontal but not both. It is so people who follow will realize where the cables run. And yes I agree one forgets about horizontal being permitted and I have myself hit horizontal cables but regs wise they are in permitted zone.

The 16th Edition is in force now on 1th July we move to 17th Edition so I have to be careful as people may still be doing job after change over date and comments on fridge supplies refer to after change over date so nothing for you to worry about.

For interest only and will not affect your job some appliances either could cause danger if they fail like smoke alarms, fridges, freezers, where if they fail food could go off without you realizing and also items of high earth leakage like cookers and ovens either way there are some items where Earth leakage trips may not be considered as appropriate although everything in my house has earth leakage and has done for last 20 years but anyway with notices you can still get away not fitting RCD's on some circuits.
ericmark

Postby john1967 » Tue Apr 08, 2008 11:42 am

you have been really helpful - the job is now underway :D
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