IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Earth bond to oil supply in house
Topic Summary:
Created On: 04 September 2013 04:28 PM
Status: Post and Reply
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 04 September 2013 04:28 PM
User is online View Users Profile Print this message


Avatar for mossep.
mossep

Posts: 333
Joined: 05 December 2010

Gone to a job at an old cottage. TT supply, metal oil tank in external shed with boiler in the same shed. This is around 3m from the main building with flow and return heating pipes running underground into the cottage.

Client wants a new consumer unit installed but at present there is no main protective bonding. Can a bond be run to where the flow and return enter the house through the floor, or does it have to run to the oil supply in the outbuilding? It will be a real headache to take up the paving and ornamental roses to bury a new earth cable.

Any suggestions?

Martin

-------------------------
www.mossep.com
 04 September 2013 04:40 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11251
Joined: 13 August 2003

Are the buried pipes copper?

It sounds like you've got two separate buildings (presumably there's electric in the shed, if only for the boiler controls) - so according to the last but one paragraph of 411.3.1.2, you've got two lots of bonding to do.

How does the boiler wiring get out to the shed?

- Andy.
 04 September 2013 04:56 PM
User is online View Users Profile Print this message


Avatar for mossep.
mossep

Posts: 333
Joined: 05 December 2010

The shed has a 2.5mm SWA feeding it from the cottage, its run underground and looks like its been there for 20 odd years.

-------------------------
www.mossep.com
 04 September 2013 07:43 PM
User is offline View Users Profile Print this message


Avatar for OldSparky.
OldSparky

Posts: 592
Joined: 28 June 2011

i would just bond where the pipes enter the building,
 04 September 2013 09:47 PM
User is offline View Users Profile Print this message


Avatar for UKPN.
UKPN

Posts: 462
Joined: 17 January 2012

Its a TT supply, the bonding does not come under the PME constraints.

Regards
 05 September 2013 01:06 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11251
Joined: 13 August 2003

Its a TT supply, the bonding does not come under the PME constraints.

True, but you'll still need extraneous-conductive-parts bonded to a MET (or BEMT) in each of the two buildings. The only difference from PME is that the conductor size might sometimes be slightly smaller (e.g. 6mm2 instead of 10mm2).
- Andy.
 05 September 2013 01:12 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11251
Joined: 13 August 2003

It will be a real headache to take up the paving and ornamental roses to bury a new earth cable.

You might want to think about what reg 543.2.6 says about using extraneous-conductive-parts as protective conductors - i.e. using the CH flow/return pipes as the bonding conductor between the house and shed. So you'd have the F/R pipes bonded to the MET in the house and then in the outbuilding the F/R pipes, oil line and boiler controls (and any other circuits) c.p.c. bonded together.
- Andy.
 05 September 2013 03:05 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 960
Joined: 04 November 2004

Originally posted by: AJJewsbury

It will be a real headache to take up the paving and ornamental roses to bury a new earth cable.


You might want to think about what reg 543.2.6 says about using extraneous-conductive-parts as protective conductors - i.e. using the CH flow/return pipes as the bonding conductor between the house and shed. So you'd have the F/R pipes bonded to the MET in the house and then in the outbuilding the F/R pipes, oil line and boiler controls (and any other circuits) c.p.c. bonded together.

- Andy.


Could be a good solution if electrical continuity shall be assured, either by construction or by suitable connection, in such a way as to be protected against mechanical, chemical or electrochemical deterioration"

But can you with buried pipes?

Regards
 05 September 2013 03:33 PM
User is offline View Users Profile Print this message



WiredScience

Posts: 92
Joined: 25 January 2012

Originally posted by: Parsley

Could be a good solution if electrical continuity shall be assured, either by construction or by suitable connection, in such a way as to be protected against mechanical, chemical or electrochemical deterioration"



But can you with buried pipes?



Regards


Can you with a buried copper conductor? I would hope that the 30mm csa pipe's resistance will remain sufficiently low, until such times as it is damaged or corroded to the extent where it leaks. In which case remedial action will be taken (usually sooner than if there is an electrical problem). Of course, the pipe may be disconnected at some point in the future, but that doesn't happen with bonding conductors, does it?
 05 September 2013 03:38 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11251
Joined: 13 August 2003

But can you with buried pipes?

I might argue that if a copper pipe corroded suffered corrosion, it would start leaking long before its copper c.s.a. got below 10mm2 - which would be noticed as a failure of the heating system. So the pipework is 'continually monitored' in that respect - and would either be repaired or taken out of service. If it was taken out of service, then the need to run a bonding conductor out the outhouse is probably also removed.

The main danger that I can see is of the flow/return (but not oil) pipes being replaced by plastic - perhaps a suitable notice as both ends would mitigate that risk. (At that point, burying some G/Y alongside the new pipes wouldn't be too difficult.).

Certainly not ideal, but I think the risks are small and could be managed.

- Andy.

Edited: 05 September 2013 at 03:51 PM by AJJewsbury
 05 September 2013 03:39 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11251
Joined: 13 August 2003

Ah, great minds think alike - although WiredScience types faster than me!
- Andy.
 05 September 2013 05:16 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 960
Joined: 04 November 2004

Fair point, this is where your engineering judgement comes in.

If you're a scheme member you may also want to get their approval before using the existing uninspected buried pipework.

Regards
 05 September 2013 05:50 PM
User is offline View Users Profile Print this message



WiredScience

Posts: 92
Joined: 25 January 2012

Originally posted by: Parsley

Fair point, this is where your engineering judgement comes in.



If you're a scheme member you may also want to get their approval before using the existing uninspected buried pipework.



Regards


And being a deviation from "normal accepted practice", they will no doubt consult their rule book and advise that G/Y must be installed whatever the cost or inconvenience.
 05 September 2013 07:00 PM
User is online View Users Profile Print this message


Avatar for mossep.
mossep

Posts: 333
Joined: 05 December 2010

Thanks for all the comments, I would have used the pipes as a continuation of the main protective bonding conductors so its nice to see others suggesting it. At the end of the day the oil line is not bonded at all at the moment, so doing it this way is a vast improvement. Wether or not the copper flow and return pipes corrode in the future is an issue for some one else to deal with.

Thanks

Martin

-------------------------
www.mossep.com
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.