Rcd when there isn't an earth

Postby colemanc78 » Sat Nov 10, 2007 3:56 pm

[color=red][/color] i'm supplying my garage with electricity but there isn't an rcd on my house cu so i was going to take a feed off my spare 16 amp mcb to a 16 amp RCD directly under my house cu then 4mm2 swa to the garage. the only thing is there is no evidence of any form of earth at the incoming tails tnc-s, tns or tt systems, will a rcd still work?? what test can i do to see if there is an earth?? b4 i get in touch with the yeb
any help is greatly appreciated
Last edited by colemanc78 on Sun Nov 11, 2007 11:26 am, edited 1 time in total.
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Postby Kristof » Sat Nov 10, 2007 11:51 pm

hi , i think it is fair to say that you have no idea about electrics whatsoever LOL and i don't mean it in a disrespectful way. I suggest getting an electrician as that's under part P. Plus you new circuit will have to be tested and a safty certificate issued. I do realise that you ask the question because you want diy job but that job is too big for diy i'm afraid
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Postby colemanc78 » Sun Nov 11, 2007 10:58 am

thanks for ur help lol!
can you tell me whats wrong with my idea?
is there anyone else willing to help?
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Postby kbrownie » Sun Nov 11, 2007 1:41 pm

Hi colemanc78,
Firstly i'd be concerned about your earthing system, i'm guessing that you have TT earthing arrangement so you should have an earth cable connected to your main earthing terminal. This will be connected to an earth electrode outside your property, should be evidence of this and from your main earth terminal to CU via 16mm earth cable.
Therefore no earth at incoming supply. But supprissed no RCDs. How old is your property? Check at your supply for earth being supplied prior to your intake box where you main fuse is before the meter. Then it would be a TN-S arrangement. If there is no earth you need that sorted out quickly. May be easier working back from CU earth bar to find incoming earth supply!
Kristof was a bit harsh, but right on the button this a part p project and has legal requirements that should be upheld.
You could give notice to the council and DIY. but it will be inspected and you will have to prove the installation is designed, installed and tested correctly and they will charge for there services.
I don't know how much electrical knowledge you have but I too love to do DIY jobs around the house. If you know of any part p sparky's get them in for the job and ask if you can give them a hand, it's not complicate installment.
Regards, be safe and best of luck
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Postby jenny49 » Sun Nov 11, 2007 5:12 pm

i have a problem when i put a new ceiling rose on the light in the next room stays on the colours inthe ceiling are two red and two black
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Postby kuzz » Sun Nov 11, 2007 5:14 pm

A typical rcd used domestically would be rated to carry 60-80A of load & trips when even very slight currents "leak" down the earth path. 30mA. So yes you need an earth.
To my surprise it seems you can get consumer units with 16A rcd's, but the only ones I've seen are rated at 10mA. To low for what you want.
I assume you have got earth on the property, but don't no what your looking for. You would be very lucky not to of burnt down now if you hadn't.
Where the cable from the street comes in to the house there will be a cut out with a fuse. You should find the earth soldered to the sheath of the incoming cable tn-s, on the cut out tn-c-s. or if you live in a more rural area you may have overhead mains with no earth provided by your electricity company. In this case you should have an earth rod in the ground & an rcd already protecting all circuits. tt
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