6mm main earth on tt system

[rich.250]

Thanks for your response man thats exactly what i done fitted rcd to that circuit only and bonded water and oil pipes which brought zs at d.b. Down to 60 ohms from 100 so worth doing.incidently i got a pfc of 4amps at d.b. Is this acceptable

I hope 4a is below your device sc ratings LOL

 

[tc50]

Measured between l -e and l-n both 4amps? Not ka

 

[gdr7671]

Measured between l -e and l-n both 4amps? Not ka

impossible!- recheck

 

[Pip]

..................

Hi People, So just to confirm, as I have a similer situation in respect of addition / extension of a ring main at a property with a TT system, which does not have any main earth electrode, (which I will be fitting this week) but has a VOELCB feeding the Consumer unit, which is very full as I wanted to install an RCBO on the circuit I've fitted, but can't get it in! So would changing the VOELCB for an RCD to cover the whole CU suffice, or have I opened a can of worms here and try and talk the customer to upgrade the whole board??

Thanks in advance

 

[Amp David]

It doesn't have an earth electrode and it TT, i'd get this sorted firstly TBH.

 

[rich.250]

Hi People, So just to confirm, as I have a similer situation in respect of addition / extension of a ring main at a property with a TT system, which does not have any main earth electrode, (which I will be fitting this week) but has a VOELCB feeding the Consumer unit, which is very full as I wanted to install an RCBO on the circuit I've fitted, but can't get it in! So would changing the VOELCB for an RCD to cover the whole CU suffice, or have I opened a can of worms here and try and talk the customer to upgrade the whole board??

Thanks in advance

Definitely sort the lack of earth first!!! It may come out of the voltage operated trip...... Incase your looking in the MET.
Also if your doing additions and installing a Rcd upfront it won't comply with 314.1.
Also you could be asking for trouble with combined leakage and existing faults on ccts.
New cu or seperate cu for new ccts?

 

[malcolmsanford]

Hi People, So just to confirm, as I have a similer situation in respect of addition / extension of a ring main at a property with a TT system, which does not have any main earth electrode, (which I will be fitting this week) but has a VOELCB feeding the Consumer unit, which is very full as I wanted to install an RCBO on the circuit I've fitted, but can't get it in! So would changing the VOELCB for an RCD to cover the whole CU suffice, or have I opened a can of worms here and try and talk the customer to upgrade the whole board??

Thanks in advance

As the lads have said I agree you need to sort this out. By all means rod it as soon as possible, but I would be advising the customer to check and see if the DNO can supply a TNC-S for them. Nothing wrong with a TT system, but your relying on the most part on the RCD for total fault protection, whereas with a TNC-S you will have also the back up of the MCB tripping on fault as well.

As for the VOELCB you need to change it, unless of course you can safely test it !!!. I doubt even if you found a meter to test it, it would be in any sort of calibration, so changing it is the best option.

This said
A) You need the customer to agree and pay for it, not always easy.

B) If they do agree, then there is nothing wrong in what you propose. Yes technically you can argue that your contravening section 314, but you can also argue that by replacing the VOELCB that you can not test, with a RCD that you can test and confirm, your leaving the installation safer.

It is really like everything you can argue to nth degree, a split board that has 1 RCD covering say 5 MCBs, could be construed as contravening division of installation, but it is recognized a split board conforms, until you get the borrowed neutral, and then put all the lights on a single RCD, and often a single MCB, purely because people are worried that if you put it on 2 MCBs the neutral will still be back feed from the other closed MCB when you isolate either device, so is that better division, especially if on the old BS 3036 CU you had 2 lighting circuits, now you have only one

So by all means change the VOELCB with an upfront RCD and don't worry about it. Advise the customer that it would be better to have a modern configuration, but the bottom line is we are not the electric police, and if you have made the installation safer you can sleep easy.

 

[Pip]

Thanks Rich, As I thought, Can of worms.
Defo no Earth from the VOELCB!
The VOELCB has the 4mm bonding linking the central connector of the unit, to the water pipes, and oil tank, and links to the CU earth bar, there is no MET, which again I will add when doing the earth rod and 16mm conductor. If the customer will go for it I'll leave the VOELCB in place, but remove the earth cables so at least I have a means of isolation when it comes to fitting the new CU.

I take your point re combined leakage on possible existing faults on the CCTs, so I may go back to plan 'A' and get an RCBO in on the circuit I've done, leave the VOELCB as is and advise Code 2 on it and the rest of the none RCD protected circuits, i.e. the shower.

A small new CU on certain circuits might sort the whole thing, I like the way your thinking, Thanks Pip

 

[rich.250]

How old is the property. Lots of older TTs used bonding as the earth. Tbh I don't know if in years gone by this was exceptable. But would explain it,
I'd be wary of saying things need to be on Rcd or it may sound as if your trying to get more work.
Just make sure the ccts you work on are up to current standards and your on a winner.

 

[Engineer54]

How old is the property. Lots of older TTs used bonding as the earth. Tbh I don't know if in years gone by this was exceptable. But would explain it,
I'd be wary of saying things need to be on Rcd or it may sound as if your trying to get more work.
Just make sure the ccts you work on are up to current standards and your on a winner.

It's never been acceptable since i've been in the industry, and i've never personally seen this on older properties either. But i'm not saying that there not out there!! By the way, If there is no made earth electrode of any kind, it's not a TT system!!!

 

[rich.250]

I didn't think it was. I've seen a couple like it,
And no I guess not a 'TT'!! Can't have a earthing system if there is none LOL

 

[Pip]

Thanks for all your input guys,
New Rod installed, with 16mm cable, RCBO on the circuit I have installed. Ze of 21.5, PFC of 2.4Ka
Have left the VOELCB as is but have informed customer of the issues, Code 2 and a Code 3 regarding no RCD's
She has been informed of before as the property is over 100 years old, but had an extension in 2005 where the CU was changed to a Volex board with MCB's and the sparky said then it was no good, why he did not intall a rod at the time I don't know.

Going forward customer may decide to upgrade, who knows.

thanks again