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

[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.