domestic earthing

[whittledr]

Currently in a TT earthed property. The supplier refused to connect to incoming as its too close to the ground to physically fit.
TT has always given good readings to not cause any issue.
It has been mentioned to me by a qualified HV spark that I could simply tag my main earth terminal to the neutral of the intake to create a PEN. While I understand that would 'work' is it a good idea?
I know he knows what he is talking about but I am often doubtful of his advise in general!

 

[Strima]

It has been mentioned to me by a qualified HV spark that I could simply tag my main earth terminal to the neutral of the intake to create a PEN

Only the DNO can do this as the have to be certain conditions met to ensure the neutral is suitable to be connected to earth.

 

[DPG]

You cant just create your own PME connection. The DNO need to make sure the supply network is suitable for it, and only then will they make the conversion.

When you say they refuse to connect, has this property not had a supply connected before?

 

[DPG]

Think we typed that at same time Strima!

 

[whittledr]

When you say they refuse to connect, has this property not had a supply connected before?

The supply was in the building in 1933, when I moved in I asked for an earth and told it wasn't possible to achieve.

 

[DPG]

The supply was in the building in 1933, when I moved in I asked for an earth and told it wasn't possible to achieve.

I see, thanks.

 

[Marvo]

Don't do it. Under certain supply fault conditions a home-made TNCS that's not PME'd at several points upstream as well could cause a very large current to flow through your earth spike and in turn cause high touch-voltages on the chassis of your appliances.

You say your existing TT has a good 'reading', what does your earth impedance measure in ohms?

 

[Strima]

Think we typed that at same time Strima!

Great minds and all that... ?

 

[MJPD29]

Absolutely not. Do not create your own pme.

 

[justeez81]

Hi.

It is possible for the DNO to connect a TN-C-S system however it would depend on how the main is connected and earthed along route back to the substation. Back in theb30s the DNO never provided an earth or guaranteed one. Now a days they do with minimum ELI requirements for each. If you ring your DNO they can assist you with some information on the type of main (pilc or XLPE) and give you a price for a cut-out change along with a PME connection. I5 is true in rRe circumstances that a loss of a neutral in mains or service cables can liven up metalwork in the property, but with modern concentric style neutral core cables this is virtually impossible unless connection at the secondary substation is loosened or corroded. Extremely uncommon. Biggest issue with TT is nuisance tripping RCDs on small load draws.

 

[driverman]

OP wrote PEN earthing. Is that not a different earthing system to PME?

 

[driverman]

OP... is your supply to the cottage overhead supply from poles?
If so, if you follow the poles down the line supplying your cottage and neighbours, at every other pole you may see green/yellow signs about 6 foot high on the poles indicating PME available.
Like been said, only the DNO can officially make your supply PME

 

[whittledr]

OP... is your supply to the cottage overhead supply from poles?

Hahaha cottage! Suburban 3 bed semi in Birmingham, ain’t no cottage!

 

[whittledr]

Thanks folks for the confirmation of my own thoughts, you added more knowledge to my instincts!

 

[pc1966]

Biggest issue with TT is nuisance tripping RCDs on small load draws.

The use of 100mA delay incomer avoids that in all but the most flaky of installations.

Nuisance trips of 30mA 'instant' RCD/RCBO is just a part of modern life, though at least with RCBO the impact is a bit less (and probability given less normal leakage per RCBO).

 

[pc1966]

The use of 100mA delay incomer avoids that in all but the most flaky of installations.

If you are going to have an up-front RCD for traditional TT use then don't make it a normal 30mA instant one as it will be prone to tripping with the whole house on it.

Using a 100mA delay RCD there will avoid that as you are very unlikely to have as much as 50mA of normal leakage, and the delay aspect avoids spurious trips on switching events.

 

[Julie.]

OP wrote PEN earthing. Is that not a different earthing system to PME?

PEN means Protective-Earth Neutral and refers to the same conductor being used for the Neutral and Protective earth, strictly the cable/technique is CNE (combined neutral + earth) as opposed to SNE (separate neutral + earth) but it's widely used it's probably more common than the proper term. (Like calling transmission towers "pylons").

If you combine the neutral and earth then it's generically known as TN-C-S of which there are several types PEB - the CNE conductor is earthed at one point only, PNB - the CNE conductor is connected to neutral at one point only and PME - the CNE conductors are earthed at multiple points through the lv network.

Although most people think TN-C-S is the same as PME this is not the case, although synonymous in built-up areas; in more remote areas where there is just one customer to one transformer if an earth is provided, it is likely to be PEB - formal earthing at the transformer only.