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daiplayer

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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 ?
 
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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

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Arms
Esteemed
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?
 
D

daiplayer

  • Thread Starter Thread Starter
  • #4
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.
 
D

daiplayer

  • Thread Starter Thread Starter
  • #6
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
 

Taylortwocities

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Arms
Esteemed
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

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Mentor
Arms
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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.
 
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daiplayer

  • Thread Starter Thread Starter
  • #11
earth rod spacing : interesting . earth rod length = space distance . is that apllicable to terraced houses both TT ?
 
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.
 

Taylortwocities

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Arms
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O

Octopus

  • Thread Starter Thread Starter
  • #15
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.
 
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sedgy34

  • Thread Starter Thread Starter
  • #16
i would see if dno can make it a tncs and 10mm bonding to incoming services
 
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SPARTYKUS

  • Thread Starter Thread Starter
  • #17
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
 

Rockingit

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Mentor
Arms
Esteemed
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.
 

Rockingit

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Mentor
Arms
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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!!
 
May have had the earth conductor still removed for the Ze test and may not have reconnected it to do the PEFC .....................done that myself a couple of time..............................oopps
 

Rockingit

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Malcolm - let's face it; either which way, it's not going to be you or me out with the sledge hammer knocking rods in. Fancy a beer that day whilst we watch?
 
You know what mate I have yet to put a rod in with an SDS ...........................it's still hit and hope with me, luckily or hopefully more like, I want my days of fitting rods to be of a minimum now, but never say never ...............fancy some scratchings with that beer ???
 
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daiplayer

  • Thread Starter Thread Starter
  • #24
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.
Sorry my typo : r1+r2 of 3.35. lol

think im gunna just put longer rod in . yes they are covered by rcd od course ( dis times etc) just trying to keep costs down for customer ( single mum ). doing this will enable the continued use us existing bonding . therefore wont hav to ripp up her laminate flooring to run new 10mm.

Conversion to PME will mean upgrading , therefore cost and damaged flooring.
 

Rockingit

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Mentor
Arms
Esteemed
.it's still hit and hope with me, luckily or hopefully more like, I want my days of fitting rods to be of a minimum now, but never say never ...............fancy some scratchings with that beer ???
Not an earth rod, but a couple of summers ago I was on a festival site and there was a problem with one of the tent pins (metal stakes) on a massive tent/stage... the pin HAD to be where it was, but had hit rock - the problem being that if you dug the rock up there'd not be enough friction left afterwards for the pin. A JCB came along with one of those hydraulic thumper things on the arm, but after 10 mins the driver gave up and disappeared......so for 2 whole days a site team of fit strong lads (and a couple of lasses) took it in turns just to whack this thing with 18 pound sledges - and a fraction of a mil at a time, it eventually went in.
 
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Engineer54

  • Thread Starter Thread Starter
  • #26
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
Where on earth did you get that from?? You'll be seeing very little advantage, spacing more than 1.5 to 2 times max, the driven length of the first or existing rod....

By linking to a Yank web page perhaps more importantly to note the size/length of ''THERE'' standard earth rods, smallest being 8 foot, but generally 10 foot!!!! Bit different to the thin 3/8'' 1m twigs that i keep getting told are suitable for purpose!! Like hell they are!! ...lol!!
 
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Engineer54

  • Thread Starter Thread Starter
  • #27
Sorry my typo : r1+r2 of 3.35. lol

think im gunna just put longer rod in . yes they are covered by rcd od course ( dis times etc) just trying to keep costs down for customer ( single mum ). doing this will enable the continued use us existing bonding . therefore wont hav to ripp up her laminate flooring to run new 10mm.

Conversion to PME will mean upgrading , therefore cost and damaged flooring.
So the families safety and well being, is secondary to your customer, than the thought of disturbing a laminate floor?? And what's worse , you seem to agree with them!!!
 

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