30 metre run of Main Protective Bonding Conductor to Gas Main and Water Main

[Les Macaulay]

Hi Fellow Sparks. I have to install a 30 metre run of Main Protective Bonding Conductor to Gas Main and Water Main in a commercial building. Is it permissible under the IEE Regs to clip a single 10 sq.mm PVC cable directly to the building surface for this, or should it be enclosed? Also, is it permitted to use one conductor for both Gas and Water as long as the first termination is unbroken at the earth clip? Cheers - Les

 

[Andyfm]

yes and yes

 

[Les Macaulay]

Thanks for a quick answer, Andyfm.

 

[Andyfm]

As long as no protection is needed against vandals, or vermin or cars etc I can`t see a problem ( though it does`nt always look very pretty)

 

[JamesBrownLive]

As long as no protection is needed against vandals, or vermin or cars etc I can`t see a problem ( though it does`nt always look very pretty)

What about protection against Pikies nicking it :shocked3:

 

[cagedanimal2010]

obviously without a break in the cable and it getting the correct readings no prob!!


Danny

 

[Knobhead]

What about protection against Pikies nicking it :shocked3:

James always the optimist.
You do what’s right for the situation, but who knows what will happen in the future.
We plan for today and with a bit of thought for the future.
Pikies aren’t on my spreadsheet!

 

[MarkieSparkie]

Hi Les, I'm surprised that nobody else has spotted a major flaw in your plan, namely that the maximum length of 10mm[SUP]2[/SUP] cable you can run and still achieve a maximum bonding conductor resistance of 0.05 Ohms is 27m, therefore you will need to run 16mm[SUP]2[/SUP] (43m Max) to achieve compliance with BS7671.

 

[Knobhead]

Pikies aren’t on my spreadsheet!

They nicked it!

 

[johnboy6083]

Where in the regs does it mention unbroken conductor. Would ging crimps satisfy this or not? I've heard that itsto stop plumbers ect removing bonds when making alterations ect.

 

[ezzzekiel]

27m is the max recomended for 10mm but your not far out s woldnt worry about it too much

 

[malcolmsanford]

I like to also know the reg that says a bonding conductor as to be ≤ 0.05 ohms ..................... I always felt that this was a guide, and though a good one not set in stone.

If the building is metal framed then could you not utilize the framework as your bonding conductor.

 

[jamie-spark]

No such thing as 0.05

We were working on a large installation a while back and there was no bonding in place. After calculating the csa of the armourings ect found the tn-s install would require bonding conductors 120mm ect as they were so far from the origin and the resistance loss in the swa. We were concerned about this and phoned the IET technical helpline. The gentleman on the phone infomed us that they do not know where this <0.05 ohm came from . He informed us that as it states in the regs the maximum size of a bonding conductor for tn-s is as stated 25mm2

 

[telectrix]

is not the 0.05ohms the figure we should get between bonded extraneous pars, e.g. gas and water pipes?

 

[Jimmyb]

It's only supplementary bonding that has to be <0.05 ohms

 

[malcolmsanford]

And yet again please tell me a reg that states supplementary bonding value should be <0.05 ohms.

Reg 415.2.2 gives us the only desired value in the regs concerning supplementary bonding and that is R ≤ 50V/Ia and the ohmeric value will always be dependent on the protection device.

 

[andyb]

It's a strange one Malcolm, GN3 page 74 mentions main & supplementary bonding should be of the order of 0.05 Ω or less.

But gives no reg number to back it up.

I think that this is picked up when people do their 2391 and they quote it there after, I know I did.

 

[ezzzekiel]

same principal under single fault conditions keeping the resistance of the bonding conductor low ensures a voltage drop of less than 50v on the conductor making the potential difference between parts at a safe touch voltage of 50v

 

[malcolmsanford]

Thanks Andy but the GN 3 is Guidance notes the same as OSG are guidance notes, though I will agree that the GN 3 is actually referenced in chapter 6 it is still just a guide.

I was not having a go mate, but I think we need to distinguish the regulations from guidance notes, the notes are tools just as any tools and are great reference materials, especially the ones that are produced by the IET, but the BS 7671-2008 is not produced by the IET and therefore what we try to adhere to.

I just think it's wrong that posts are submitted saying that "it's in the regs" when it isn't. The <0.05 value is a guide, but it is not in the regs, and so if you have a value over this and feel as the designer that it is safe then the value can be anything, as I stated in my post the only reference to an ohmeric value is in reg 415.2.2 ans that is not a constant when referring to supplementary bonding.

 

[andyb]

Totally agree Malcolm,
I was just trying to understand where the >.05 came from if it isn't in the reg's

And your last paragraph is spot on, you could start a whole new thread entitled ''it's in the reg's''

 

[malcolmsanford]

To me Andy it is just the same as the diversity guide in the OSG and the set of tables 7 where maximum lengths are given circuits, neither of these are in the regulations.

 

[andyb]

The diversity guide in the OSG is pointless, how many threads run along the lines of '' 3 bed house, apply diversity, 135 amps, help''
Never use it.

 

[malcolmsanford]

I have to agree totally Andy. But in fairness to the OSG on the 1st page of appendix 1 says about 3 or 4 times that there are other ways of applying/getting diversity.

I do use the one in the OSG for cookers as I think it is a good one. The others really are just rough and IMO not good guides.

View attachment Guidelines_network_design.pdf

An engineer I know gave me a copy of this a few years back and for me it is a great guide on how to apply diversity and I've these same values throughout my career and for me they are as good 40 yrs ago as they are today. And to be honest if the DNO use this, and really they should know, then it's good enough for me.