Oil Pipe Bonding.

You asked the same question 6 years ago. 

https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=61381

alanblaby: 
 

You asked the same question 6 years ago. 

https://www2.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=61381

Perhaps so, I had forgotten. Anyway, perhaps there are new perspectives on this subject. I am always keen to hear the latest opinions.

Z.

So, we have a P.M.E. installation with a TT earthed metal oil pipe running to a garden oil tank. Does that contravene 411.3.1.1?

z.

Zoomup: 
 

So, we have a P.M.E. installation with a TT earthed metal oil pipe running to a garden oil tank. Does that contravene 411.3.1.1?

z.

Nah, a simple pipe and rod doesn't an earthing system make, not even a TT one. 411.3.1.1 only worries about exposed-conductive-parts (not extraneous-conductive-parts) anyway.

I reckon you have a PME system and an extraneous-conductive-part - that'll likely need bonding to meet 411.3.1.2.

  - Andy.

AJJewsbury: 
 

Zoomup: 
 

So, we have a P.M.E. installation with a TT earthed metal oil pipe running to a garden oil tank. Does that contravene 411.3.1.1?

z.

Nah, a simple pipe and rod doesn't an earthing system make, not even a TT one. 411.3.1.1 only worries about exposed-conductive-parts (not extraneous-conductive-parts) anyway.

I reckon you have a PME system and an extraneous-conductive-part - that'll likely need bonding to meet 411.3.1.2.

  - Andy.

Is it a good idea to P.M.E. bond the metal oil pipe that runs out into the garden, thus exporting the P.M.E. system to outside?

Z.

depends - is it accessible to touch indoors ?

Or outdoors  ?

The advice from suppliers of fuel tanks generally says earth it, but from a static electricity perspective, so it does not need to be a low impedance.

Mike.

mapj1: 
 

depends - is it accessible to touch indoors ?

Or outdoors  ?

The advice from suppliers of fuel tanks generally says earth it, but from a static electricity perspective, so it does not need to be a low impedance.

Mike.

The oil pipe that runs from the oil boiler in the house is covered in plastic for mechanical/chemical protection I believe. The outside plastic oil tank has metal showing at its outlet position. There is a valve and filter all touchable and bare metal. I was considering the metal pipe supplied outside main bonded P.M.E. water tap situation..

The boiler in the house will have a C.P.C. connected to it as it will have a  240 Volt control/pump supply. The metal oil supply pipe will be electrically connected to the oil boiler.

So, we could have diverted neutral currents running down the oil pipe to the tank and its earth rod. And/or a metal valve at the tank that is above Earth potential and touchable.

I'd be happier removing the earth rod at the tank, but then what have I missed?

Z.

Short of replacing the oil pipe (outside the building) with plastic (e.g. https://www.bes.co.uk/qual-oil-underground-oil-pipe-10mm-x-50m-13105 ) then you've got the exported PME potential issue whatever. Bonding the oil pipe will make sure the boiler's c.p.c. doesn't have to carry all the diverted N current all by itself (although it's not likely to carry much unless the electrode at the tank as a quite low resistance).  Leaving the electrode in place might even mitigate the PME problem slightly by bringing the voltage of the soil next to the tank up towards PME voltage (a buried grid would be better though).

As I understand it, earthing LPG tanks is a must for anti-static reasons … the hazards for oil will be much less, but some may regard it as good practice all the same. I gather than oil tank installation is notifiable under building regs, so unless you're registered competent person under part J (rather than P) or want to involve the local BC, I'd suggest it's not something to be messed with without understanding.

   - Andy.

If we are seriously worrying about PME, surely we'd certainly want to avoid diverted Neutral currents … meaning because there's an earth electrode at the tank, it would be preferable for the entire installation to be TT …

It's what's done at filling stations - and don't forget, this pipe's not buried!

Also worth remembering that in trying to “pull the ground up to PME", the EPR drops off over a distance of as little as 3.5 m depending on the electrode configuration, so it really depends how far the electrode is from any other buried metalwork connected to PME.

gkenyon: 
 

If we are seriously worrying about PME, surely we'd certainly want to avoid diverted Neutral currents … meaning because there's an earth electrode at the tank, it would be preferable for the entire installation to be TT …

It's what's done at filling stations - and don't forget, this pipe's not buried!

 

I did not mention that for most of its run the pipe is clipped to a wall at low level, but for the last 3  or 4 metres runs under a concrete path then upwards to the oil tank. I like the idea of TTing the whole installation though. So obvious and simple a solution I had overlooked it.

Z.