Concerned.

[la poste]

Greetings.

I was at a friends house today who has a TT system earth rod.

All bonding is in place he has a 17th edition dual RCD board.

I was wiring in a standalone RCD unit for his garden shed and got a shock off of the earth bar.

I am concerned because he wants to put all brass switches on his lights.

I don't know why I got this shock but if his earth bar is live then anything conneted to it will be live also.

None of the RCD's have tripped and I cannot understand why I got this small finger tingling shock.

I understand that appliances can have earth leakage that can accumulate at the earth bar in the board but I consider this a potentially dangerous situation.

If there is earth leakage then why no RCD tripping?

Any comments would be appreciated.

Thanks.

 

[Andy™]

what was the voltages to live & earth?

 

[initforthemoney]

Sounds to me like the voltage is being brought in on the spike.

Time to get digging.

 

[la poste]

[quote name='Andy

 

[Theorysparky]

i think Infor.. was suggesting the spike has gone through a cable

hence the need for a spade....

 

[la poste]

i think Infor.. was suggesting the spike has gone through a cable hence the need for a spade....

Right OK. Thanks.

It's a little worrying though.

Definately an earth fault and with a new board.

IR results on the circuits tested are absolutely fine although not all circuits are tested. Still got some lights to do but no circuit is tripping an RCD.

Must be coming from somewhere.

 

[initforthemoney]

Its also possible a next door property maybe faulting to earth and being brought in on the rod.

 

[PC Electrics]

What's Ra?

 

[Apache]

What's Ra?

It's like Ze, but taken from the rod

:coat

(sorry)

 

[steptoe]

try disconnecting the MEBs also before testing,

it is possible you are pulling in a PME fault on your MEB.

when you say substantial, in what way,? V or A

remember,

VOLTs JOLTs

CURRENT KILLS

is it a voltage issue or a current issue we are looking at.?

normally if you spike the incomer with your rod it will blow the supply, but not always.

if you can let us know some more specifics we can help you a lot more.

 

[steptoe]

EDIT

have you checked polarity?

can sometimes be a common fault esp if they are changing over and downgrading to PME,

and are you sure that even though you have a spike you are NOT connected to what you are meant to getting as a Neutral as well.

 

[la poste]

Thanks for your answers I have an update.

I went to the property again and did more tests.

I disconnected the rod and tested for voltage, nothing. I tested the earth bar to the rod, nothing, I tested earth bar to neutral all nothing. I touched the earth bar and nothing. Neutral and earth are completely separate.

I switched on every appliance in the house and nothing, no voltage on the earth bar.

But I got thinking, earlier in the day I was testing the cable that runs down to the bottom of the garden, This cable is to be put into a standalone RCD, I insulation tested this cable to 1000V and when satisfied finished tests.

I then went up to the house to terminate the cable in the RCD enclosure and that is when I got my shock, I am thinking the shock may be due to charging the cable up and because I was attaching the cable to the main earth terminal via a fly lead at the time of the shock this could be it. The cable is a 2 core SWA earthed through the outer sheath.

What do you think?

Also I spoke to the supplier today and they said that the area is suitable for PME so I may be getting rid of the spike altogether, I am just waiting for confirmation in writing that the supply can be PME'd.

I think PME is better than an earth spike, does anyone disagree with anything I have said?

One more thing, I was thinking I could put some sort of voltage monitor on the rod to buzz if the polarity becomes reversed IE current starts flowing into the house although I am not sure where to get one and if I PME then this will become unnecessary.

 

[sparkytim]

+1

When doing Insulation Resistence tests do you allow discharge of test voltage before you disconnect test leads? i.e. release test button and wait for a secound or two before you touch anything.

If not then YOU are acting as discharge route and hence getting shocks.

 

[PC Electrics]

I think PME is better than an earth spike, does anyone disagree with anything I have said?

Yes, Steptoe.

I feel another long thread coming on.........more Guinness required.

 

[Evans Electric]

What's Ra?

The ancient Egyptian Sun God

 

[Evans Electric]

I'd rather have anything other than an earth spike

 

[la poste]

I think PME is better than an earth spike, does anyone disagree with anything I have said?

Yes, Steptoe.I feel another long thread coming on.........more Guinness required.

Great stuff I am all ears.

I have a choice between investing in a good quality earth rod or connecting the earth to the neutral.

 

[Andy™]

with TNCS, in normal use, there can be a voltage difference between installation earth, and the earth you stand on.

worst case, if there is a lost neutral before the service head, the installation can be over 230v to ground, and your RCD is guaranteed not to trip if you get a shock

with TT ( & true TNS. not this TNS with PME all over), installation earth will always be at or around ground voltage

the only reason TNCS is used is because its cheaper than TNS, both in materials & installation time

 

[la poste]

But one disadvantage of TT is that if for some reason an RCD fails you will have no earth protection.

With an earth resistance of 100 ohms an earth fault current would be just over 2 Amps, this would not trip any MCB and any metal would be at 230 volts until someone touched it.

RCD's are meant as a backup to MCB's or fuses and not as a primary and only source of earth fault protection.

That's the way I was taught anyway.

 

[steptoe]

I think PME is better than an earth spike, does anyone disagree with anything I have said

why would you think that.?

why is it a better idea to give someone else the control over whether you have an effective earth or not.?

personally I would like to be in control of the earthing arrangements in my house and actually know I have an earth.

TNCS/PME opens up a whole can of worms to which you have no control over,

almost all of which is covered in numerous war and peace threads already.

in short,

I would never have TNCS/PME in my house,

and IMO TT is preferable.

only an opinion mind, and lots of others disagree.

(remember as well, you will probably still have to TT your outbuilding)

[quote name='Andy