Earthing

[paul b b]

Hello all,

an couple of earthing question for you.

1) if a house, say on a tt system had no earth spike, would the home owner get a shock of the taps if there was no earth fault? or only when there was a fault with an appliance?

2) on a tt system what size earth conductor should be run from the spike to the MET?

many thanks

paul

 

[Doc Hudson]

Hello Paul b b, Out of curiosity, is this a purely hypothetical question ? or does it relate to an actual real installation / fault you have been involved with ? Also I am not sure if I have said welcome to you, so welcome to the forum as well!

Doc H.

 

[Andy™]

if the house doesnt have a rod, or TNS or TNCS, then it could be classed as IT without the rod - needless to say this is dangerous. without an earth, you can get some very dodgy faults

for size of cable, that depends on many factors. can be anything from 2.5 to 16

 

[paul b b]

Hello Paul b b, Out of curiosity, is this a purely hypothetical question ? or does it relate to an actual real installation / fault you have been involved with ? Also I am not sure if I have said welcome to you, so welcome to the forum as well!Doc H.

Hi doc, and thanks for the welcome.

its more of a thought, i have been told a few stories about people getting shocks from taps, toasters etc... and was wondering about the cause ie.. would a faulty washing mac cause a shock when it was turned on, but have no sign that ther was a problem when it was not in use.

 

[Andy™]

Hi doc, and thanks for the welcome.its more of a thought, i have been told a few stories about people getting shocks from taps, toasters etc... and was wondering about the cause ie.. would a faulty washing mac cause a shock when it was turned on, but have no sign that ther was a problem when it was not in use.

if there is a fault, the earth should take current to trip breaker. but if its not earthed, then it is possible for the machine to fully function, but have a live cover. depending on where the earth fault is, this could be isolated to just the machine, or the entire house (i.e every appliance and metallic pipe)

 

[paul b b]

understood

thanks andy

 

[Evans Electric]

Paul b b I have never found a really good trade publication on earth rods . A TT installation without the rod could be dangerous although often the fault will go down the water or gas pipes and cause the RCD to trip .

That situation should be corrected at the earlyist opp, TBH.

Deke

 

[Andy™]

If gas & water is metallic, they will normally give a much lower reading than a rod. especially if your neighbour has PME (fault current will flow through underground pipework, into their house, through their bonding, to neutral)

but if they are plastic, then you will have an almost non-existant reading

 

[SPECIAL LOCATION]

Hi Paul.

As the guys said.. under "no-fault" conditions the metal work should NOT be live.

But under fault conditions metal cover made live,

assuming supplementary bonding is in place other metal work would be at live potential.

If someone touched it they would complete a path to earth, assuming their body was touching some other earthy part.

 

[Andy™]

also, if the next house is the same, under fault conditions in their house could make another house live

 

[binky]

for size of cable, that depends on many factors. can be anything from 2.5 to 16

Minimum 6mm - calculate using adiabatic equation using 30mA (or 100mA on older system) as I as per RCD protecting system

 

[batty]

Edf insist on 16mm even on TT and will not connect unless you use that size on new installs.

Batty

 

[sarni31]

Where is Steptoe when you need him ; \