Bit of help with a TT installation please...

[timo1]

Hi, i'd appreciate a bit of help with this one if poss. Went to look at a job on a TT installation, property was a single story bungalow and has since been developed with another floor. As usual everything has been immaculately decorated, floors laid etc..and no thought given to the electrical services!! New owner is very realistic and happy to upgrade bonding, along with a decent bit of extra work.

I have checked and there is a 16mm earth from the earth stake/rod outside which goes directly into the C/U. there is no bonding present on either the water or gas. C/U is in the middle of the house, gas is positioned on the outside wall about 5 - 10 metres from the stake.

Ideally I would like to run bonding from the gas and water to the C/U but this is not an option, I'm all for a challenge but the route has me beat.

One solution I thought of would be to create a MET near the gas position and join the main earth and gas/water together, possibly in a weatherproof enclosure, obviously clearly labelled at source and at C/U. Property is RCD protected also.

Not ideal I know, looked at regs and can't see anything directly against it, any thoughts? Thanks in advance.

 

[J25GTi]

thats the debate

Seems pretty clear cut to me really?

 

[Spazz]

I had this the other week

TT system with no bonding and only 1.5, earth from the rod.
That got upgraded then ran a 10mm bonding cable to the gas around the outside of the building, then for the water (even though it was plastic all the way from the mains to the entrance of the building) I ran a cable down to a rad pipe and ran it along the whole run to the boiler where the main water came into the property and bonded it to the water pipe (metal pipe) where it came through the wall from the mains.
I know I didnt have to but the customer wanted it and I knew he had history of messing with his boiler as it stopped working on a regular basis so wanted that bonded as well just in case (you never know!!)

 

[spark 68]

Only regs I can see regarding MET is Bonding/Earthing conductors must only be removable by a tool, the Earthing conductor should be removable to facillitate testing, it must be accessable and protected from corrosion and mechanical damage where applicable.

Some of these regs 54-04-02 group are taken from GN8 and the matching 16th ed big brown book, which matches to 542.4 in the current regs.

As others have said the other thing is the cable to the CU must be able to handle the max fault current, which is not really a problem on TT (but could be on TNC-S).

So, different ?, yes, but can see no regs against at the moment.

 

[GLENNSPARK]

so lets say the MET is a henley block external to the C/U.....and the main bonding is goin into it.....together with the main earthing which then carries on into the C/Us MET/earth bar.....

 

[spark 68]

Better still, call it an Earth Marshalling Terminal :wink_smile:

 

[sedgy34]

so lets say the MET is a henley block external to the C/U.....and the main bonding is goin into it.....together with the main earthing which then carries on into the C/Us MET/earth bar.....

your talking hyperthetical, how about reality to the actual situation

 

[GLENNSPARK]

your talking hyperthetical, how about reality to the actual situation

its a similar scenario......

 

[sedgy34]

its a similar scenario......

ok im assuming you would pass it off if you carried out an EICR

 

[GLENNSPARK]

i would consider the connection/s whether they were both electrically and mechanically sound and also check to see if the earthing and bonding conductors were up the max. fault current....as long as i was satisfied that 542.1.3.1 had been met then i would ..yes...

 

[PC Electrics]

So, different ?, yes, but can see no regs against at the moment.

That's because there is no reg against it.

BS7671 has nothing to say about the position of the MET, only that there must be one. And that bonding must connect to the MET.

Now, with any regulations there is one rule above all others: unless it is forbidden by the regs, then it is allowed.

Therefore, I see no issue with the OPs proposal.

Those who think it doesn't comply should state which regulations are not being complied with.

As the arrangement would be unusual, then the CU and bonding points and MET should be appropriately labelled so anyone in the future can see what's been done.

 

[timo1]

Hi Sedgy, I understand your reservations but I dont/cant walk away from work, especially as the customer isnt refusing the extra work, its just that I cannot get the bonding back to the C/U, sounds weak I know but you have to take my word for it. In fact it could even be why there is no bonding perhaps. I cant think of a reason why it would be unsafe?

 

[PC Electrics]

Think of it this way:

even if your method is unusual / unorthodox, you will be making a currently unsafe installation (no bonding) safe. The installation will be safer than it was before. So all is good.

Fill yer boots.

 

[johnboy6083]

It's standard practice in larger installations to have EMT's away from the incomer. if you size the cable to the EMT the same as the main earth, the. There's no problem.

 

[sedgy34]

Hi Sedgy, I understand your reservations but I dont/cant walk away from work, especially as the customer isnt refusing the extra work, its just that I cannot get the bonding back to the C/U, sounds weak I know but you have to take my word for it. In fact it could even be why there is no bonding perhaps. I cant think of a reason why it would be unsafe?

if the customer dont mind paying go back to the CU

 

[GLENNSPARK]

Hi Sedgy, I understand your reservations but I dont/cant walk away from work, especially as the customer isnt refusing the extra work, its just that I cannot get the bonding back to the C/U, sounds weak I know but you have to take my word for it. In fact it could even be why there is no bonding perhaps. I cant think of a reason why it would be unsafe?

do what you need to do to make this installation safe Timo....as has been said already...theres no reg against your plan.....its just some cant think outside the box.....