Earth Rod

T

timmyquick

My nan has had a problem with tripping of her TT supply whole cu protected by 30ma RCD. Found problem about 6 cables from outside all plugged into a home made box with a socket strip inside it. Got damp. Told my nan dodgy as hell but wont listen!. But i was curious about the earth rod which is located under the stairs which is about 6 metres away form the CU just wondered is that normal to have an earth rod placed inside the house. I know that all the electrics were done by a sparky 15 years ago by the local authority before my Nan purchased the house.
 
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The earth rod really has to go into damp earth to make a good contact - I'd suggest if its indoors this is hard to guarantee. Unless the earth resistance measures low enough (50V *30mA >>> 1500 ohms absolute mnax, and I'd prefer 100 ohms or less...) when the weather is at its driest, it may well not comply. In doubtful cases, a new rod outside, in paralell with the old one might be required.
If you can borrow a loop impedance tester you could measure the Zs of the earth rod. (You will need to disconnect the RCD for this test, so it should only be done with the house 'off', and the rod will become live during the simulated fault.)
Otherwise just add a new one outside.
 
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why does it become live, do you isolate it to do the loop test?
 
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passing a current down a high impedence earth connection will put a voltage on it

isnt that fairly obvious?
 
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timmyquick said:
My nan has had a problem with tripping of her TT supply whole cu protected by 30ma RCD.
Should be 100mA time-delayed.

Found problem about 6 cables from outside all plugged into a home made box with a socket strip inside it. Got damp. Told my nan dodgy as hell but wont listen!.
Don't upset her too much - she might cut you out of her will, and with her attitude to electrical safety that could pay out any day now.
 
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timmyquick

Been telling my nan for years about her dodgy electrics ( mainly all outside, she has never touched any electrics in the house ), but what can you say to persuade her to save a *hit load of money for professional when you are just on a state pension?.

Also thought that it is not prohibited to have an whole CU protected by a 30 ma RCD?, just not suitable for todays requirements? In fact just been to my dad's flat today and the council have fitted a new CU to accommodate the new kitchen they are installing. They have put a new ring in as the whole flat was on 1 ring. And surprise surprise, they replace the CU just so they can add 1 extras mcb and it is all protected by a 30 ma RCD. I have a book i recently purchased domestic electrics which is supposed to be a guide and follow the 16th edition and that says you should use a 100ma time delayed RCD for all circuits on CU for tt supply and have a 30 ma RCD for some circuits. So what is a D.I.Y.ER supposed to make of it when a qualified electrician does not seem to follow the latest recommendations on new or replacement installs?
 
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timmyquick said:
So what is a D.I.Y.ER supposed to make of it when a qualified electrician does not seem to follow the latest recommendations on new or replacement installs?
Nothing, except to reflect that it is quite common for DIYers to take more care, and work to a higher standard, than many professionals in all sorts of fields.
 

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