Bonding industrial buildings

I really don't see why this was coded C2. The water pipe can't possibly sustain several thousand amps without instant melting, and a 50mm cable that long will drop a good deal of the voltage anyway. The Gas pipe, although 5" is almost certainly connected to plastic distribution pipes within a moderate distance, and again there cannot be a significant external voltage difference without a very large current flow. I presume you have a local transformer, meaning your your supply is TNS, so the possibilities for significant Earth current to incoming pipework is very remote. I would be quite happy with these main bonding cables. Was a reason given for the C2, or a regulation reference?  Be aware that this kind of inspection of a large factory needs a very experienced inspector, otherwise this kind of report tends to be made!

The metal cross section of a pipe in mm2 is a lot more than its diameter - even a  15mm water pipe is equivalent to about 30mm2, larger pipes of course  have more metal. What is the earthing arrangement of your supply ? - I'm imagining private TX TNC-S but just to confirm.

The concern may be the current handling of the 50mm2 (good for 150A or so continuous and a few kA in short bursts) may be a bit thin for the potential fault currents that a 2000A supply can provide.? Is there an explanation for the previous C2 ?

Mike

TNC-S is very unlikely for such a large supply Mike, it is about 1.5MW!

It would be interesting to know what the C2 detected - on the face of it 50mm² copper main bond would be fine BS 7671's requirements for any earthing system (meeting both 544.1.1's 25mm² cap for non-PME systems and table 54.8's 50mm² for PME).

There was some confusion a few years ago with a belief that bonding conductors should be under a certain overall resistance (0.1Ω or 0.05Ω) - but that was never a BS 7671 requirement - simply a rule of thumb whereby test results could be deemed acceptable without needing further calculation. Higher readings shouldn't be treated as a fail, just involve some calculation to verify that it's reasonable for the length and c.s.a. of the conductor involved.

Or the C2 might refer inappropriate connections (typical BS 951 clamps might struggle with a 5" pipe).

   - Andy.

So, (in the style of Ghostbusters) What you gonna use?

Z.

100% David! I just wonder how much these erroneous codes, or at the very least, subjective codes, cost British industry. As you say, if the inspector was required to clearly set out their reasoning, it might just highlight deficiencies in understanding. Of course, that would also bring with it associated issues of spelling and grammar! 

in 2016 it had a code C2 put on it during a eicr

Was whatever the problems was 6 years ago not fixed?

    - Andy.

For that size of supply it is going to be a TN-S supply with a separate earth from the Tx. Or may be a TN-C-S (PNB) supply so PME conditions do not apply. So the bonds do not need to exceed 25mm, see Regulation 544.1.1. 

These protective conductors are all about equipotential bonding although they will carry some earth  fault current most of it hopefully will flow in the CPCs and back to the transformer star point via the earthing conductor.

Out of interest what was the observation that attracted the C2 code? 

If you want to go there Zoomup, what is the current rating of a BS951 clamp? For big pipes you can always put several in series quite easily, but will it withstand say 2000A for 5 seconds? Realistically this is as imaginary as Ghostbusters!

Proper pipe clamps exist, based on the exhaust clamp/ U bolt design.,.

That is a Furse3909TB_clamp for example
On steel pipes and building steels,  you may consider  a welded boss onto a suitable pipe flange or bracket.

and or straps sometimes flat band is used, much like a lighting conductor,  as it can be formed into shapes that a round cable cannot.

On smaller sizes though something like the BS951 on steroids do exist (larger pipe clamps)  OK for PSSC of a few KA.
Mike.