UK Bonding water pipes

[Apex13]

Looking for a bit of advice on bonding on a new build shed.
The main water pipe enters the building in plastic/ alkathene so my understanding is that the main water does not need bonding.
But the pipework then feeds out to a heat pump which sits outside the building so I would say that the pipework that exits the building and is connected to the heat pump is now making contact with the ground through the heat pump that is bolted to a concrete pad so does this mean the pipework becomes an extraneous conductive part so does need to be bonded?
Part 2 of this question is that if the pipework does require bonding then what size of earth cable is required as looking at the regs book (table 54.8) my understanding is that is goes by the size of the main earthing conductor which is 240mm and anything over 150mm should be a 50mm earth but surely this doesn’t mean it requires a 50mm earth cable clamped to a 25mm copper pipe.
Thanks for any advice.

 

[westward10]

What is your earthing system?

 

[Apex13]

It’s a TN-C-S supply
I believe if it’s a TNS system then it wouldn’t need to be any larger than 25mm which still seems quite overkill to attach to a small water pipe but at least it’s a bit more manageable than a 50mm

 

[westward10]

TN-S can be reduced to 6.0mm² in a secondary building providing the cpc of the supply cable is not less than this size regardless the csa of the earthing conductor.
What size is your earthing conductor for the TN-C-S?

 

[Apex13]

There is no secondary building, it is a new build shed that has its own Scottish Power supply into a plant room. There is a main mccb panel board with a 400A incomer and 240mm tails including a 240mm earth for some reason which were installed by the contractor installing a solar/PV install. We have them come in and mounted beside the panel board 2 x 3ph DB’s with a 125A supply to each from the panel board in the same room.
Is it your opinion that the pipework does need bonding?

 

[westward10]

What size main protective bonds are currently installed?

 

[Apex13]

Currently the only other main bonding required is the structure steel of the shed which has a 50mm run just over 1m from the MET to a main beam of the shed.

 

[LastManOnline]

the pipework that exits the building and is connected to the heat pump is now making contact with the ground through the heat pump that is bolted to a concrete pad so does this mean the pipework becomes an extraneous conductive part so does need to be bonded?

There may be lots of metalwork located outside that is "in contact with the ground" but that would not necessarily mean it requires bonding to the MET.(electric gates ,oil burners ,lighting lanterns etc, etc). Generally speaking their connection to earth is of a very high resistance and there is no danger of them providing a path for fault currents occuring elsewhere.A simple Fli test will confirm what the measurement to earth is.

 

[DWCOCKBURN]

The shed should be considered a separate electrical system and the earthing system should reflect that fact.
The shed 'system' distribution board will be protected by a 80amp 30mA RCD (presumably), so a 6mm main earth conductor should be connected from the earth stake to the dist. board and the main supplementary bonding conductor from the dist. board to the incoming water supply need also only be 6mm and located as close to the point of entry to the shed of the water pipes as is possible.

 

[mainline]

Looking for a bit of advice on bonding on a new build shed.
The main water pipe enters the building in plastic/ alkathene so my understanding is that the main water does not need bonding.
But the pipework then feeds out to a heat pump which sits outside the building so I would say that the pipework that exits the building and is connected to the heat pump is now making contact with the ground through the heat pump that is bolted to a concrete pad so does this mean the pipework becomes an extraneous conductive part so does need to be bonded?
Part 2 of this question is that if the pipework does require bonding then what size of earth cable is required as looking at the regs book (table 54.8) my understanding is that is goes by the size of the main earthing conductor which is 240mm and anything over 150mm should be a 50mm earth but surely this doesn’t mean it requires a 50mm earth cable clamped to a 25mm copper pipe.
Thanks for any advice.

Have you measured it to see if it is infact extraneous.

 

[mainline]

The shed should be considered a separate electrical system and the earthing system should reflect that fact.
The shed 'system' distribution board will be protected by a 80amp 30mA RCD (presumably), so a 6mm main earth conductor should be connected from the earth stake to the dist. board and the main supplementary bonding conductor from the dist. board to the incoming water supply need also only be 6mm and located as close to the point of entry to the shed of the water pipes as is possible.

I think the ops installation is a bit more than the average garden shed.

 

[DWCOCKBURN]

It's just a separate TT system guys.

If you were to treat the shed as being inside the PME zone; you will need to use a 10mm main supplementary bonding conductor to the incoming water supply inside the shed, which in turn will need a 16mm supply cable CPC, which in turn will require a 25mm T&E supply cable.
A little excessive for a supply to a 2gang socket and a batten holder.

 

[westward10]

The supply cable would need a 10.0mm² cpc and T&E does not extend to 25.0mm².

 

[DWCOCKBURN]

The bonding conductor would need to be 10mm.
I have used 25mm T&E on a number of occasions.

 

[westward10]

The bonding conductor would need to be 10mm.
I have used 25mm T&E on a number of occasions.

No you haven't.

 

[DWCOCKBURN]

Haven't I?

 

[DPG]

Is this the 5 minute argument?

 

[DWCOCKBURN]

Oh dear!

 

[littlespark]

No supplier or manufacturer do a 25mm t&e in the bs6242Y or B standard. Only up to 16mm.

You can get 6491X in 25mm which is the standard grey sheathed tails, but they are single conductor, not twin.

Of course, you can get 25mm in armoured and other types of cable, but not “t&e” as we would understand it

 

[DWCOCKBURN]

I am quite old.
I have used 25mm T&E on a number of occasions.

 

[littlespark]

Age has nothing to do with it… there has never been a 25mm t&e.
Maybe something in the old imperial sizes, but I doubt it

Sorry to state the obvious, but we’re meaning 25mm squared as in Cross Sectional Area…. Not 25mm across the cable

 

[DWCOCKBURN]

I my youth I used it.
The drum was very heavy.

 

[mainline]

I my youth I used it.
The drum was

Maybe manufactures will reincarnate it.

 

[DPG]

I my youth I used it.
The drum was very heavy.

Bigger wire = more weight, assuming length of wire remains constant.

I'd be interested to see a link to any mentions of 25mm T&E (used in the UK that is, and not some far off land).

 

[7029 dave]

Funny how none of us have seen such a cable and between us must be hundreds of years experience.