Why is an exported earth bad?

[Mr Sworld]

Steps, anyone that anal about their hi-fi systems deserves what thet get.

Some of them seem to believe that buying a

 

[steptoe]

Yes there's an RCD.I can't see why each house can't just have it's own rod. It would surly be simpler...........

they do mate, thats why its a major problem, fault comes back in through your rod,

protective multiple earth, spiked at multiple points along its length, obviously if you neighbour is on the same T as you then you share everything, phase, neutral, earth and FAULTS.

the problem with PME is that its so simple its DANGEROUS,!

Mr Sworld

Re: Why is an exported earth bad?

Steps, anyone that anal about their hi-fi systems deserves what thet get.

Some of them seem to believe that buying a

 

[kme]

Steps, anyone that anal about their hi-fi systems deserves what thet get.Some of them seem to believe that buying a

 

[binky]

they do mate, thats why its a major problem, fault comes back in through your rod, protective multiple earth, spiked at multiple points along its length, obviously if you neighbour is on the same T as you then you share everything, phase, neutral, earth and FAULTS.

the problem with PME is that its so simple its DANGEROUS,!

.

So if you separate the garage from the house to avoid exported earth, and use an earth rod, then there's no advantage, cos the fault comes back up the rod ?:| ? :| ?:|

Or have I misunderstood something.

Also begs the question about bonding in premises split into flats where each flat is fed via switch-fuse and from there in 16mm FTE - do you bond in flat to CU or return all bonds to MET adjacent consumer head?

Having asked the question I'm off to read books :z :z, cos I now doubt what I thought I knew about this scenario.

 

[Apache]

No Binky

That's refering to PME where many earth rods are joined.

If you TT a shed or garage the rod isn't conected to anything else

 

[steptoe]

So if you separate the garage from the house to avoid exported earth, and use an earth rod, then there's no advantage, cos the fault comes back up the rod ?:| ? :| ?:| Or have I misunderstood something.

Also begs the question about bonding in premises split into flats where each flat is fed via switch-fuse and from there in 16mm FTE - do you bond in flat to CU or return all bonds to MET adjacent consumer head?

Having asked the question I'm off to read books :z :z, cos I now doubt what I thought I knew about this scenario.

NO, cos if you have done it properly then the fault cannot come up the rod cos it has no where to flow to, you have disconnected the return to earth via the house PME.

your earth rod is at the same potential as the earth where the fault is coming from, thus nulling its potential to cause a fault in your installation,

whereas a PME earth path would be at a much lower resistance and would allow the fault current to have an easier path to earth so the fault current would travel up your rod, along your CPC to your Earth conductor via your METand exit via your N,

this current could in theory be in excess of 10kA, and NO fuses in your earth or neutral ! :O:O

DO NOT EXPORT TN-C-S / PME EARTH

this is why you can only have one earthing system in any one dwelling.

 

[cheggers]

would he not be exporting TNS

it is tncs where it comes into the property then it is seperated , so in fact he will be exporting tns

 

[cheggers]

try this link apache they dont say that exported pme is wrong to a shed

http://www2.theiet.org/publish/wireregs/wiringmatters/documents/Issue16/2005_16_autumn_wiring_matters_electrical_installations_outdoors.pdf

also I would not disconnect the earth wire from your support wire

 

[steptoe]

would he not be exporting TNS it is tncs where it comes into the property then it is seperated , so in fact he will be exporting tns

I see where you are coming from,

TERRA

NEUTRAL

now

SEPERATE

but its no longer a supply once it has entered your property and become your responsibility, its then a final circuit, eg, ring final.

there is much more to it than simply splitting the neutral from the earth.!

its a nice theory, but not that simple unfortunately.

thats why its refered to a 'sub main' and not as a 'mains supply, you are NOT providing the star point for the earthing reference.

 

[steptoe]

try this link apache they dont say that exported pme is wrong to a shed http://www2.theiet.org/publish/wireregs/wiringmatters/documents/Issue16/2005_16_autumn_wiring_matters_electrical_installations_outdoors.pdf

also I would not disconnect the earth wire from your support wire

do you reckon the IEE will cover your ass for you in court?

you can bet they will say,

are you COMPETENT ?

says it all really for anyone considering using a PME supply to a shed and still thinks it safe.

remember the IEE are NOT law, nor is BS7671, EAWR is, and clearly states that you must be COMPETENT so as NOT to endanger life.

exporting PME/TNCS is IMHO extremely dangerous and I would mark this down as a CODE1 and disconnect every time on a PIR.

 

[cheggers]

The only problem with pme is if you loose the neutral but if the shed has a rcd fitted it would detect the imbalance in the live and neutral so would disconnect.

I do understand what you are saying step but in my 20 years experience I have never came across a lost neutral on the supply but i have come across loads of high reading (ra) rods and malfunctioning rcds.also if you did loose the neutral on the supply it is staked down to earth in multiple places along its length the only problem would be if you lost it from your installation to the joint in the road or over head.what are the chances of that (slim).as for Code1 I think your are being a bit over the top

 

[Flying Scotsman]

The only problem with pme is if you loose the neutral but if the shed has a rcd fitted it would detect the imbalance in the live and neutral so would disconnect.I do understand what you are saying step but in my 20 years experience I have never came across a lost neutral on the supply but i have come across loads of high reading (ra) rods and malfunctioning rcds.also if you did loose the neutral on the supply it is staked down to earth in multiple places along its length the only problem would be if you lost it from your installation to the joint in the road or over head.what are the chances of that (slim).as for Code1 I think your are being a bit over the top

qfa qfa qfa

Applaud Smiley well said that member have afew of these Guiness Drink Guiness Drink

 

[extension15]

Of all the questions asked and the many subjects covered, this is one of great interest on the forums..

I wonder how many Sparky's are guilty of 'exporting' inadvertanly (I have)..

But more importantly how many people have been killed or hurt as a result of?

; \

 

[Apache]

I would seriously like to know ext! There are many things in all professions that we worry about but would be interesting to know if it's really a problem out there in real life.

I've got an unvented hot water cylinder..........

 

[steptoe]

The only problem with pme is if you loose the neutral but if the shed has a rcd fitted it would detect the imbalance in the live and neutral so would disconnect.I do understand what you are saying step but in my 20 years experience I have never came across a lost neutral on the supply but i have come across loads of high reading (ra) rods and malfunctioning rcds.also if you did loose the neutral on the supply it is staked down to earth in multiple places along its length the only problem would be if you lost it from your installation to the joint in the road or over head.what are the chances of that (slim).as for Code1 I think your are being a bit over the top

I think thats a BIGGIE, not really like dropping a switch wire from your 2way lights is it?

it only needs to happen once to kill. I have saw it a few times, and reverse polarity many more times.

< 200ohms is not high

immediate danger to life, without external influence on your installation,

a fault on your neighbours installation on PME is also a fault on yours, thsat is why PME earth bonds and N cross sections are so large, to carry everybody else's faults, not just yours.

sorry if this seems very opinionated, but I can honestly see NO reason why anyone should put life at risk by exporting an already questionable earthing system beyond the original equipotential zone.

perhaps when the regs finally become settles it will be more visible as to the reasoning behind why RCDs are becoming more prevalent and bonding to within a E Z less obvious and hopefully we will also see less use of unreliable earthing systems where we depend on other consumers for our safety measures.

 

[Apache]

Suddenly I see why bonding is in 10mm

 

[The Godfather]

Guys, sometimes problems don't exist, until an accident occurs.

Don & His Boys.

 

[steptoe]

Guys, sometimes funerals don't exist, until an accident occurs.Don & His Boys.

in the words of a better man than me.

 

[Apache]

Equally I'd never leave the house if I constantly worried what could happen. I might get run over. I might have a heart attack. I might get squashed by a mad cow.

It's a calculated risk. It's unlikely but anything is possible. There has to be a reasonable degree of probability of something happening to spend time and money preventing it.

Or else we wouldn't do anything. Life's a risk. None of us are getting out of it alive

 

[cheggers]

I agree with everyone here but we do need to be a bit realistic

does anyone here every came across a lost neutral on the supply

how many people have come across a rcd not tripping

should we be putting in 2 rcds in line just in case of one fails

may be admin could make a poll for this I for one would be interested by the results