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Topic Title: Oil Bond
Topic Summary: Don't think it's required- advice appreciated
Created On: 09 September 2013 10:45 PM
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 09 September 2013 10:45 PM
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delta1

Posts: 130
Joined: 04 March 2009

Hello All,

Apologies if I'm raking over old ground.
So, looked at a board change today. Water bond all present and correct. Outside is plastic oil tank on blocks. Oil pipe runs along the outside wall for about 10m before entering the property.
Now, to my mind, the oil pipe doesn't require bonding, as I don't see how the pipe could be introducing a potential into the property. I can't really see the value in testing continuity from the oil pipe to the MET, as there is likely a connection to the water bond through the aga, along with the aga CPC.
Guess I'm looking for someone to say I'm on the right track and not missing anything. I'd be grateful of any (helpful) advice.

Kind regards

Edited: 09 September 2013 at 11:00 PM by delta1
 09 September 2013 10:54 PM
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daveparry1

Posts: 6323
Joined: 04 July 2007

I agree, no bonding to the oil pipe necessary,

Dave.
 10 September 2013 09:30 AM
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AJJewsbury

Posts: 11679
Joined: 13 August 2003

What's the oil pipe made of? If it's plain copper, fixed direct to a damp masonry wall for many metres, I'd bet it's picking up a significant earthy potential, especially after wet weather.

If the gas & water are both plastic coming out of the ground, and there are no other potential extraneous-conductive-parts connected to the MET, then you might be able to do a meaningful test by isolating the installation, disconnect the MET from the means of earthing (so the installation's earthing system should now be isolated from true earth, with the possible exception of the oil line) then test between the oil line and the means of earthing.

- Andy.
 10 September 2013 05:51 PM
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delta1

Posts: 130
Joined: 04 March 2009

Thanks for the replies.
Yes the pipe is copper along its whole length, clipped. Water comes out of the ground in metal. No gas present.
I'm now wondering if, given that the pipe could introduce a potential from the damp wall, whether to just bond anyway. I wouldn't be introducing a potential that wasn't already presentd by bonding, so I don't see the harm. It's probably an hour's work to bond it plus cable so I'll factor it in.
If anyone has any additional input, I'd be grateful.


Kind regards
 10 September 2013 08:03 PM
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iomtt

Posts: 20
Joined: 30 April 2008

Isolate supply and megger test between main earth incoming terminal ( disconnected ) and oil pipe if greater than
2.5 Mohm no requirement to bond

Also would point out a double glazed patio door or for that matter anything would require bonding if we required bonded a to described above

LOL
 10 September 2013 08:07 PM
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delta1

Posts: 130
Joined: 04 March 2009

Hi iomtt, where does the 2.5M figure come from please?

Kind regards
 10 September 2013 08:18 PM
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iomtt

Posts: 20
Joined: 30 April 2008

Andy touched on the subject above
I will find out for you tomorrow my source
This applies to stainless steel tables in kitchens etc etc and is a useful test to establish requirement of bonding
I will confirm the M ohm reading as well as its 9 months since I last applied this rule of thumb
 10 September 2013 08:21 PM
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delta1

Posts: 130
Joined: 04 March 2009

Are you referring to the 22kOhm figure (from memory) from GN8?

Kind regards
 10 September 2013 08:54 PM
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UKPN

Posts: 533
Joined: 17 January 2012

where an oil pipe, (or any pipe) in contact with the general mass of earth
enters the building in such a way that it can be touched at the same time as other metalwork connected to the PME terminal an equipotential bond should be applied to the pipe as close as practicable to the point of entry into the building.

where the integrity of the connection between the pipework and the
general mass of earth external to the building cannot be guaranteed to be at or about earth potential consideration should be given to the effect
of internally bonded metalwork exporting a potential outside the equipotential zone under certain fault conditions.

in this case precautions should be taken prevent a potential difference by the use of earth electrodes.

Regards

Edited: 10 September 2013 at 09:17 PM by UKPN
 10 September 2013 09:29 PM
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slittle

Posts: 3580
Joined: 22 November 2007

Bond it and stake it :-)

Or just TT the damn installation and stop worrying about this pme nonsense


Stu
 10 September 2013 09:50 PM
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John Peckham

Posts: 7572
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I investigated a case of what turned out to be a lost neutral on an overhead PME supply that caused a fire. The diverted neutral current went down the oil pipe and melted the braid on the flexible coupling to a filter just outside the timber boarded house setting fire to the oil.

The tenant was in at the time smelled burning and threw a bucket of water on the fire putting it out (yes I know water on an oil fire). The FB attended having been called and they turned off the electrical supply inside the house. Whilst all and sundry were looking at the fire damage one of them touched the remains of the oil flexible and there was a spark which scared all those present as they could not understand how this could be with the electricity to the property turned off. It was not until the power was turned off to the 2 adjacent properties that the problem went away. No power in the 3 properties for a couple of days whilst an electrician investigated but could not identify the cause.

I was called in to investigate and I could not get to the bottom of the cause as when I arrived everything appeared normal. It was not until I closely questioned a builder on site, who I suspected as he had been doing some plumbing on site, that he mentioned the sparking and almost in passing said the DNO had attended and gone up in a bucket and fixed something that everything fell in to place. He had a picture on his phone of the DNO up in the bucket.

I would recommend TTing such installations as Stu says or inserting an insulated joint outside the premises to ensure there is no path to earth through the oil pipe or gas pipe if it comes from a bottled supply.

I am sure some readers won't believe me but I have the photos of the seat of the fire.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 10 September 2013 10:02 PM
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stateit

Posts: 2217
Joined: 15 April 2005

I believe you JP...

I just don't believe the problems in finding clamps to fit 10mm oil pipe...

-------------------------
S George
http://www.sg-electrical.com
 10 September 2013 11:06 PM
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John Peckham

Posts: 7572
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BS951 are not designed for small OD pipes. Not BS951 compliant but a copper Pyro P clip does the job with a nut and bolt and a crimp lug on the end of the bond.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 11 September 2013 09:24 PM
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delta1

Posts: 130
Joined: 04 March 2009

So basically, test the pipe to the earthing conductor, and pray it's separate!? It's a shame that I can't isolate the water pipe from the other pipework, or indeed the oil pipe. As I see it, I'll only be testing for a definite separate rather than a definite extraneous (if that makes sense).

As the tank is plastic and up on blocks, I would think that any currents from a lost neutral would take the route of the metal water pipe. TT isn't an option at the property. My gut is still saying not extraneous, but my conscience is niggling now. It is PME, by the way.


Kind regards.
 12 September 2013 09:26 AM
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AJJewsbury

Posts: 11679
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So basically, test the pipe to the earthing conductor, and pray it's separate!?

Other thought was to test the wall itself to earth with an insulation tester as distance away from the pipe - say a croc clip onto a wad of wire wool or scruntched up aluminium foil held in place with something insulating (i.e. not your fingers!) - I've got readings of well below 5k Ohms trying something similar in the past. If a small section of wall has a measurably low resistance to earth, then a copper pipe clipped direct to it over several metres almost certainly will.

- Andy.
 12 September 2013 03:40 PM
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geoffsd

Posts: 375
Joined: 15 June 2010

If you cannot definitely determine that the pipe is NOT extraneous then it should be bonded.

As you cannot determine this because it is connected to extraneous-c-ps and cpcs then the bonding will not be introducing a hazard unnecessarily.
 12 September 2013 05:40 PM
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ebee

Posts: 5773
Joined: 02 December 2004

I got a mate of mine to drill out some 13 to 31 mm dia copper bar with a 10mm drill thru the centre then sawcut into two equal "C" sections.

Split bobbin kind of idea to place two halves on 10mm copper then BS 951 earthclamp on the diameter.

OK not to BS 951 either but it made it easy and (I think) effective

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 12 September 2013 05:48 PM
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delta1

Posts: 130
Joined: 04 March 2009

Andy, yes, that's a thought thanks. Geoffsd, yes, that's was my thinking was also.
Thanks for all the advice given folks, much appreciated. I'll update on the outcome.

Kind regards
 13 September 2013 07:02 PM
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kj scott

Posts: 2144
Joined: 02 April 2006

If you must bond it; then also install an earth electrode as Stuart has recommended; it will solve a number of potential problems.

-------------------------
http://www.niceic.biz
 13 September 2013 07:53 PM
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geoffsd

Posts: 375
Joined: 15 June 2010

Would that not just be an unnecessary additional bonded extraneous-c-p?
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