Using rods for bonding

[Rockingit]

Have a situation where a 6mm bonding cable put in place at first fix to bond gas bottles (to the kitchen gas/electric range cooker) isn't now going to work as the position of the bottles has moved significantly.

Putting a new run in isn't an option so rather than than hashing something together to extend that cable (with attendant ducting, burying etc), I'm wondering about fixing it instead to a rod or two (would be good to get the Zs down anyway) and then putting the gas bottles onto another set of rods. My logic is that £20-30 of rods could save me half a day of pratting about with the alternative.

Anyone got a view on this as I can't immediately think whether this would be acceptable or not! The installation is a PME to TN-S values (don't ask, it's what the DNO are happy with - they call it a SNE), this bonding is coming from a sub-board. All very 17th and shiny.

 

[Thomas123]

I would say its not acceptable, it should be bonded to the same earthing system as the electrical installation, with a reading of less than 0.05 ohms..

 

[Thomas123]

Just re read your post, Are these bottles away from the house?

 

[Rockingit]

Are these bottles away from the house?

Yes, they are externally fixed in a bottle cage/store/cupboard/whatever the builders do.

 

[sjm]

Sorry but the whole point of bonding is to BOND all exposed conductive parts and extraneous conductive parts to the same earth potential/v alue, so without bonding all the rods together the potentials will be different. So the anwer to your question would be NO!

Also 6mm bonding on a PME system?

However if the gas bottles are attached, using rubber hoses (as is usual), to a change over valve, then into the property in copper pipe, are you sure that the pipe is an extraneous conductive part? Does it enter the ground? Have you tested it?

 

[Rockingit]

Sorry but the whole point of bonding is to BOND all exposed conductive parts and extraneous conductive parts to the same earth potential/v alue, so without bonding all the rods together the potentials will be different. So the anwer to your question would be NO! So what do you think happens on a multi-rod TT? There are already several points of earthing buried deep into the ground for various reasons, and a PME system is only a multitude of grounded points anyway.

Also 6mm bonding on a PME system? Not PME (per-se) - Ze is around .7

However if the gas bottles are attached, using rubber hoses (as is usual), to a change over valve, then into the property in copper pipe, are you sure that the pipe is an extraneous conductive part? Does it enter the ground? Have you tested it? I was actually thinking that very same thing! Especially as the final connection is a rubber hose bayonet fitting.

I think I may have re-thought this whole thing through now!

 

[sjm]

Maybe I misunderstood you Rockingit but you were talking about 2 seperate rods not connected together.
A multi rod system is a system because all the rods are connected together electrically, not just by being in the ground (deep or not).
In a PME system all the earthing points are connected together by the neutral conductor!

 

[Deleted member 9648]

By bonding something with a separate rod you are in effect introducing another earth potential....the whole point is to remove that possibility....if it's PME why was a 6.omm put in on the first fix...should be 10mm......(cant see why gas bottles would need bonding anyway,unless there is a buried copper pipe involved somewhere)

 

[DurhamSparky]

sound like a hash to me...!

 

[Rockingit]

Yes, yes, yes..... I've turned my brain on now. The nature of how the actual pipes will work means it doesn't need bonding anyway.

OSG Table 4.3 refers as far as cable dia is concerned.

 

[IQ Electrical]

I would say its not acceptable, it should be bonded to the same earthing system as the electrical installation, with a reading of less than 0.05 ohms..

There is no limit in BS7671 for the resistance of a main protective bonding conductor.

 

[Thomas123]

There is no limit in BS7671 for the resistance of a main protective bonding conductor.

What would be the point in bonding then? It's to keep the potential the same. So it has to be under a certain value, that valid being 0.05 ohms

 

[IQ Electrical]

What would be the point in bonding then? It's to keep the potential the same. So it has to be under a certain value, that valid being 0.05 ohms

I agree but there's still no upper limit!
The 0.05 Ohm reference in guidance note 3 applies to supplementary bonding-it was the subject of an extended thread here and eventual clarification from the IET.

 

[Thomas123]

I agree but there's still no upper limit!
The 0.05 Ohm reference in guidance note 3 applies to supplementary bonding-it was the subject of an extended thread here and eventual clarification from the IET.

Bloody regs haha!