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daiplayer

Working in a house , have already rewired the kitchen , have been ok'd to rewire first floor lighting .( due to poor condition)

Am trying to keep costs down for customer when bringing house wiring up to standard.

Will be doing some more remedial works but am trying to suss out whether they need bonding upgrade.

Its a TT with a Ze of 207 , ( high i know ) what can i do about this ? inform dno :- convert to TNC-S?

Any way : PEFC : 1.11 a , ( LOW ) PSCC 1.2KA . HIGHEST Zs in house 3.43 , existing bonding 6mm .

As a rule of thumb ive heard of people using 0.5 of main supply tails : 16mm .

However if i inform the DNO of the high Ze and they convert to TNC-S , pefc will rise to eg: 230/0.35 : 657A min.

Any ideas ? or can show me how to do the adiabatic with this ?
 
You could enquire about converting to TNCS, however you could just put another rod in.
6mm bonding is adequate if you are doing an EICR, I would upgrade to 10mm2 if you are changing the fuseboard or adding points.
 
The DNO will not care about your Ze value. That's your problem! But 207ohms isn't a hanging offence.
What's the protection for the installation. 30mA rcds on all circuits, or what?

I agree best to ask for PME but you'll probably have to wait for some weeks.

re
ny ideas ? or can show me how to do the adiabatic with this ?

Don't understand, what are you tring to calculate, the size of the earthing conductor?
 
im not upgrading board. Its already has a 30ma rcd and apears to have been done by a cowboy. ( work needs doing on it ) .

Will a longer rod bring Ze down ?
 
What is the condition and the location of the existing rod? Test at the rod itself to find out.

May need replacing and relocating with a longer rod. Cheap fix for both of you.
 
The DNO will not care about your Ze value. That's your problem! But 207ohms isn't a hanging offence.


re
Don't understand, what are you tring to calculate, the size of the earthing conductor?

All really . earthing conductor is 6mm at the mo .
 
Going deeper will without doubt get you a better reading, more importantly it will be morelikely to be stable. TN levels are achievable but you need a bit more work to get them,
Go for the thickest couplable rods you can get your hands on mate
 
The 6mm earth and 6mm bonding will most likely be fine if the installation is left TT

Indeed, the most it is going to carry is 30mA! That allows your Ze to be as high as 1666ohms (not recommended).

Re adding a rod: If you go that route it will need to be at a distance away at least 3 times the length of the existing rod - there's some interesting papers on the 'net' if you can be bothered. Including here http://www.electriciansforums.net/e...electrical-forum/42851-earth-rod-spacing.html
As stated above, it's better to bang in two new chunky rods coupled together. Doesn't work if you are sitting on a lump of granite, however!
 
your main earthing conductor on a TT system is fine at 6mm as long as it's not buried unprotected. as previous posts, go for a longer rod, at least 1m from the biulding.
 
Best option is to see if you can get a free upgrade to TNC-S, then upgrade main earthing to 16mm and main bonding to 10mm.
 
if using 2 rods, they should be spaced 1.5 x the rod length.
 
For the cost of a couple of 5/8's rods and a connector and new piece of 10mm GY I'd be putting a new rod in, further from the house.
 
might take 6 weeks though. Might be easier ter get the cheque by banging in Rods.

Whats this about black art I thought that was the spreads domain
 
Its a TT with a Ze of 207 , ( high i know ) what can i do about this ? inform dno :- convert to TNC-S?

Any way : PEFC : 1.11 a , ( LOW ) PSCC 1.2KA . HIGHEST Zs in house 3.43 , existing bonding 6mm .

As a rule of thumb ive heard of people using 0.5 of main supply tails : 16mm .

However if i inform the DNO of the high Ze and they convert to TNC-S , pefc will rise to eg: 230/0.35 : 657A min.

Any ideas ? or can show me how to do the adiabatic with this ?

I think you need to sit down with your calculator and revisit some of these sums and your testing..... if you have a Zs of 3.35 when you have a Ze of 207, then that means you have an R1R2 value of -203.65. Now that's a cable I'd really love to know where to buy.

The low pfc values that you get on TT installs are part of the reason for the requirements for RCD protection; it is realised that you will never get anywhere near disconnection times with that little current.

To lower your Ra then as others have said, bang in some nice LONG 5/8 rods down to at least a couple of metres.
 
Parallel paths with that bonding and all the CPC I would guess be the reason he as got a low Zs there RT

That was my first thought as well, but in which case you'd surely then expect a Pefc of around 50-70A based on those figures?! Although..... 1.11A x 230V = R255 = 207 + 48 (roughly). But then again, you wouldn't be getting r1r2 value of 48ohms..... So, methinks some double checking in the testing department might still pay dividends.

Happy to be proved wrong, it's just the numbers leapt at me straight away!!
 

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