Question for the electricians

[RMS]

We have a house with a detached out building that has a water supply pipe emerging from the concrete floor. The pipe comes out the ground in copper and has a stop tap then it changes to plastic. (approx 0.5m copper). There is no bonding attached to this pipe.

Electrics supplied from the house are present within the out building. The feed to the outbuilding is a 4mm ² PVC 2core SWA cable. (armouring used a cpc).

The earthing arrangement for the property is tns.

When carrying out an EICR, what code, if any would you assign to this? Also if this fails to comply with BS7671, what methods could be used to achieve compliance?

I have my own thoughts on this. Interested to here others.

 

[ricicle]

For non-PME systems there is a minimum size requirement of 6mm² for main protective bonds. (depending on the earthing conductor size)
In this case the supply to the building uses the armouring which is steel. The MPBs need equivalent conductance and as copper is about 8x more conductive than steel you will need around 48mm² of steel to comply.
I'm not sure that 4mm 2 core has that csa of armouring.
TT'ing the system would be an option. In my opinion 0.5m of extraneous copper is just on the limit of what I would consider an issue. Any shorter and I would be considering whether or not it was worth bonding or not. (particularly if the pipe was hidden away in a cupboard)

 

[RMS]

http://www.earthingnuts.co.uk/pdf/pvc_xlpe.pdf

 

[dingodeano]

How are the banjo's terminated? What size is the cpc is connected both ends to Main earth terminal / CU ? If that table is correct it's no good to use armour as combined bonding & CPC if the conductor between banjo and main earth terminal /cu is 4mm also. So if this is case and the banjo>Met>cu conductor can be substituted for a conductor that will handle the same resistance reading of the max fault current for curcuit and 10mm equipotential bond then it would be ok to use armour.
Or does that table mean the copper equivalent of 4mm steel armour is only 9mm in copper?

 

[RMS]

If a 10 mm ² bonding conductor is required for the pipe and the armouring is to be used as a bonding conductor as well as a cpc then looking at the table the copper equivalent for the armouring would equate to 8.86mm ² and therefore would be unacceptable.


ricicle
I was hoping someone would pick up on the fact that the earthing arrangement is TNS and therefore subject to calculations a smaller sized main protective bond would be acceptable. In this case the metallic pipe could be locally bonded back to the DB in the out house.

In the end I decided to have the pipe changed to plastic as it entered the out house and the remaining copper was boxed in.

 

[RF Lighting]

Stricly speaking to the letter of the regs then you would have needed to either TT the shed and bond the pipe from the MET of the TT installation, or, increase the size of earth conductor from the house to the shed.

In reality I think you'd have been fine with a slightly undersized earth especially as it's a TN-S.

Changing it to plastic has of course saved you all that messing around, and keeps your install compliant.

 

[Starspark1]

RMS,

You have given the copper equivalent of the armoured which is 8.86mm if you measure the resistance of the copper pipe in the outhouse back to the MET use this resistance and convert this into its copper equivalent. If this value plus the 8.86mm exceeds the 10mm which i trust it would then this would comply with BS7671??

 

[vibrobullit407]

RMS,

You have given the copper equivalent of the armoured which is 8.86mm if you measure the resistance of the copper pipe in the outhouse back to the MET use this resistance and convert this into its copper equivalent. If this value plus the 8.86mm exceeds the 10mm which i trust it would then this would comply with BS7671??

Are you saying that BS7671 states that the use of a metallic water pipe can be used as a main bonding conductor? If so can you please refer me to this regulation. Could you also show me how you would carry this out "if you measure the resistance of the copper pipe in the outhouse back to the MET use this resistance and convert this into its copper equivalent". How do you know what condition this copper pipe is in or what materials its made of (might not be copper through its entirety) as it is ran underground? What if some body replaced a part of the pipe for something like a burst with plastic? Also is it a good idea to run the main bonding in a combination of materials and components (10mm copper single core - 15mm copper pipe + steal armourings) in parallel with each other?

In the past when I have come across this I have either ran a 10mm back to the MET or changed the pipe to plastic dependent on cost. Another idea would obviously to TT the out building and bond the pipe to this.

 

[Starspark1]

Are you saying that BS7671 states that the use of a metallic water pipe can be used as a main bonding conductor? If so can you please refer me to this regulation.

Are you saying you cant?

Could you also show me how you would carry this out "if you measure the resistance of the copper pipe in the outhouse back to the MET use this resistance and convert this into its copper equivalent".

http://en.wikipedia.org/wiki/Electrical_resistance_and_conductance.
Click the search, click top suggestion. About 1/3 way down.

How do you know what condition this copper pipe is in or what materials its made of (might not be copper through its entirety) as it is ran underground? What if some body replaced a part of the pipe for something like a burst with plastic.

Continuity Test?
Whats to stop someone cutting a bonding conductor?Whats to stop someone replacing a part of pipe a bond is on and not reattaching the bond??

 

[RF Lighting]

Are you saying that BS7671 states that the use of a metallic water pipe can be used as a main bonding conductor? If so can you please refer me to this regulation.

Are you saying you cant?

I am. You can't.

Could you also show me how you would carry this out "if you measure the resistance of the copper pipe in the outhouse back to the MET use this resistance and convert this into its copper equivalent".

http://en.wikipedia.org/wiki/Electrical_resistance_and_conductance.
Click the search, click top suggestion. About 1/3 way down.

Irrelevant.

How do you know what condition this copper pipe is in or what materials its made of (might not be copper through its entirety) as it is ran underground? What if some body replaced a part of the pipe for something like a burst with plastic.

Continuity Test?

That doesn't prove the condition. You would get contiuity through one strand off a 0.5mm² flex. Doesn't make it a reliable connection

Whats to stop someone cutting a bonding conductor?Whats to stop someone replacing a part of pipe a bond is on and not reattaching the bond??

Nothing, but I expect most people wouldn't as they realise it is forming part of a bonding arrangement. It's going to be entirely not obvious that a bit of pipe is.

 

[RMS]

RMS,

You have given the copper equivalent of the armoured which is 8.86mm if you measure the resistance of the copper pipe in the outhouse back to the MET use this resistance and convert this into its copper equivalent. If this value plus the 8.86mm exceeds the 10mm which i trust it would then this would comply with BS7671??

One word springs to mind?

Ridiculous!

 

[vibrobullit407]

Are you saying that BS7671 states that the use of a metallic water pipe can be used as a main bonding conductor? If so can you please refer me to this regulation.

Are you saying you cant?

yep

Could you also show me how you would carry this out "if you measure the resistance of the copper pipe in the outhouse back to the MET use this resistance and convert this into its copper equivalent".

http://en.wikipedia.org/wiki/Electrical_resistance_and_conductance.
Click the search, click top suggestion. About 1/3 way down.

As mentioned pointless. Not only do you not know the length (its underground)you also do not know all the material that the pipe can be made up of!

How do you know what condition this copper pipe is in or what materials its made of (might not be copper through its entirety) as it is ran underground? What if some body replaced a part of the pipe for something like a burst with plastic.

Continuity Test?

Would a continuity test show differing materials i.e lead pipe, steel pipe connected to the copper? Thus meaning the calculations you have performed for just the csa for the copper are a bit null and void! As mentioned this just confirms that the pipe goes from 1 place to another not the condition!

Whats to stop someone cutting a bonding conductor?Whats to stop someone replacing a part of pipe a bond is on and not reattaching the bond??

Well that would be silly as it should have a label stating that it should not be removed!

Are you seriously suggesting that this is compliant, viable and correct to use the water pipe for this? If so then perhaps you should leave the electrics to the professionals!

 

[RMS]

BS7671 does allow the use of an extraneous conductive part to be used as a bonding conductor. (543.2.6) providing certain conditions are met.

It strictly prohibits the use of gas and oil pipes but does not mention water pipes.

In this case it would be impossible to comply with 543.2.6 as you can't guarantee that the pipe will not be removed or modified. You can't assure continuity by construction or by suitable connection.

 

[Starspark1]

RF/Vibro could you point me to the exact reg that says you cant?
As Rms has just pointed us all to the reg that says you can provided certain conditions are met.

I feel your final part of the post was a bit harsh was it not? Considering we are not always right or know everything hence why RF is asking for help on another post and yourself with lack of knowledge here //www.diynot.com/forums/electrics/light-switch-in-bathroom.326860/#2423749 it wasnt so long ago that you wrongly assumed something and werent entirely correct!! we cant always be right and know everything all the time guys!! Nobodys perfect!

As for the labelling that means nothing to a lot of people if they want to cut/remove etc etc they will regardless!! example on a much more dangerous scale the copper thieves stealing from sub stations etc!
Also the label is only at the end whats to say they wont cut it somewhere through its run as last time i looked earth wire does not conform with bs951.

It is not my fault that there is a difference of opinion here bs7671 is open to interpretation.

We are all constantly learning we cant know everything and i enjoy the fact that i can be corrected there is no need for such harshness it will just deter people on this forum.

 

[RF Lighting]

Read his post again. The conditions of 543.2.6 can not be met with an old unknown water pipe.

The regulation is intended for the steel framework of a building etc.

If you're so sure it is acceptable, tell us the regulation that says it is.