Another bloody TT question

[Millboy]

Hi chaps, This is part looking for advice, part moan. Bear with me..

Ive been asked to look at a rewire, no spec just what I think would be necessary (usually a mid range install, nothing fancy but no £1 sockets etc.) Now the install is 40-50 years old and is an overhead supply, as is common to the area the house is in. Looking at the earth coming in it is 2.5mm unsheathed, partially protected by rusty metal capping, and goes out the wall, disappearing under the concrete at the rear of the house, never to be seen again.

I included in my price a new rod, earth pit etc etc. Another electrician has been and told the client that the existing rod is fine and he's tested it blah blah blah (I tested it at 70 ohms). The point isn't that the reading is too high, IMO on a rewire everything needs to be put right ie. the rod needs to be accessible, connections protected etc. and that I'm not happy with the bare minimum size earthing conductor.

That's the moan over with now the question... The client says they want to go ahead with the rewire but keep the existing earth "if it satisfies the regs". Now I know there's a reg that says the connection should be accessible and protected from corrosion in the 17th, but if it was ok to bury them 40 years ago, then can it stay and not conform to the
current edition of regs?

 

[Moses]

my understanding is that the Gn/Y insulation on the eartrhing conductor is sheathed so 16mm if not mechanically protected.

comeon tel.

give the man good information

He needs a good strong earth, 25mm got to better than the 16mm to the Rod.

Go with 25mm OP.


It will give a good strong earth for best safety and all that!

 

[Amp David]

Sav, you write man,

Cable to the rod need to be 25mm all the way for proper good earth!

Anything less will give you not a strong earth.

Come again!?!?

 

[Moses]

Come again!?!?

As we all know any practising electrician worth his salt knows the CSA of the G/Y to an earth Rod.

 

[Guitarist]

I'm firmly in the camp of upgrading it lol. I'll have a good look through the book tomorrow and if I can find a few regs to quote I think I can convince them to have it done. To be honest I'm annoyed that they've taken "super duper spark"s opinion over mine anyway.

Don't you just love the game of "playing one tradesman off against another" ?

Tell her that you don't appreciate having your professionalism questioned, and if your word isn't good enough for her then it's best she gets someone who will tell her what she wants to hear!

 

[telectrix]

table 54.1. 16mm. could use 50mm if you wanted to really tempt the pikeys.

 

[sparkdog]

I always use 16mm for TT earths mainly because its less likely to get damaged or snipped.I wouldn't use some old 2.5 mm that can't be seen.How do you know what condition its in?It might be all corroded and about to fail.

 

[Swicade]

Agree with Sparkdog here.

Aswell as that i'd probably go along the line of telling the customer that as the connection to the rod is buried a safe connection cannot be gaurenteed (as it cant be seen) so to verify connection you'd have to dig the path up, as it's dug up already it's best to replace the lot as 40yr's+ of corrosion will have lessened the earth path and it's only a matter of time before the connection my just rot away leaving no 'safe' earthpath. The fact the other electrician hasn't dug up the concrete just means they cant verify a true earth connection.

Sometimes you have to be alittle creative to make sure the customer agree's to have the right and proper work done and isn't fooled into making a bad decision just to save afew pennies.

 

[Guitarist]

When I have to give a customer a large estimate and they visibly pale, I like to quote the old "Monsters inc" line.... "I scare because I care"

 

[Tonkatoy27]

New install to 17th edition = earthing to 17th edition. If it was ok to pick up any old existing earth then we wouldn't bother with a stake, the Ze would still be below 1666 ohms just using the water and gas bonding. (probably)(as long as everything was 30mA RCD'd etc.) Seems silly that the customer is scrimping over £50 for a stake and upgraded earth to make safe a £1-3k rewire although I know the type. Tell them that at the very least the other sparky would have to list it on deviations which would make a bit of a mockery of the paperwork.

 

[Guitarist]

New install to 17th edition = earthing to 17th edition. If it was ok to pick up any old existing earth then we wouldn't bother with a stake, the Ze would still be below 1666 ohms just using the water and gas bonding. (probably)(as long as everything was 30mA RCD'd etc.) Seems silly that the customer is scrimping over £50 for a stake and upgraded earth to make safe a £1-3k rewire although I know the type. Tell them that at the very least the other sparky would have to list it on deviations which would make a bit of a mockery of the paperwork.

You're assuming that the other sparky will even issue paperwork. Been to a few jobs recently where new CU fitted by "qualified electrician" has no cert with it at all, plus loads of deviations from the regs which are just unacceptable. These cowboys getting more prevalent in the current economic climate it seems....

 

[Engineer54]

If that hidden rod (or plate) was installed 50 or more years ago, then it's almost certain it's coming to the end of it's useful life span (very much depends on the acidity or alkalinity of the soil to be honest). When it was installed it was more likely to be nearer the 10 ohm mark, which is what the old electricians aimed for!! (how times change, ...What!!! lol!!)

As others have already stated, old Reg's are OK for PIR's (or whatever you call them now). But If you are installing a completely new installation, then like the installation, the latest BS 7671 must apply to the earthing conductor along with connection to rod being accessible for maintenance and testing... Personally, for a domestic installation i would'nt think going over a 10mm earth conductor is necessary if run in a plastic conduit...

What was you charging to provide and install a couple of 5/8'' coupled rods and earth pit to make them bulk?? lol!!

 

[Guitarist]

If it's a new rod, and cable not buried, then 4mm is adequate according to the osg.

 

[soulman]

I do believe that 6mm is the minimum for tt installation. I only ever install 10mm bonds as well as 10mm earthing conductor which is more than adaquate for tt system. (not buried)

Cheers

 

[Deleted member 26818]

The minimum CSA allowed is 2.5mm² if protected against mechanical damage, 4mm² if not (542.3.1, Table 54.1 & 543.1.1).

 

[Guest123]

As we all know any practising electrician worth his salt knows the CSA of the G/Y to an earth Rod.

Apart from you it would seem......

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