pro's advice needed

[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 ?

 

[somersetsparks]

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.

 

[Taylortwocities]

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?

 

[daiplayer]

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 ?

 

[Paul.M]

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.

 

[daiplayer]

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 .

 

[trev]

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

 

[somersetsparks]

The 6mm earth and 6mm bonding will most likely be fine if the installation is left TT

 

[Taylortwocities]

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!

 

[telectrix]

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.

 

[daiplayer]

earth rod spacing : interesting . earth rod length = space distance . is that apllicable to terraced houses both TT ?

 

[Guitarist]

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.

 

[telectrix]

if using 2 rods, they should be spaced 1.5 x the rod length.

 

[Taylortwocities]

earth rod spacing : interesting . earth rod length = space distance . is that apllicable to terraced houses both TT ?

It's a black art, and not aprecise science. Have a look at this paper Bringing Grounding Down to Earth | content content from Electrical Construction and Maintenance (EC and M) Magazine

I am sorry that it is American but Figure 2a and text gives a decent overview of overlapping effective resistance areas. Enjoy!

 

[Octopus]

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.