Main bonding..... yet again!

[Bobster]

Hi Rob, thanks for this, I'm having a thick moment, and no access to GN3 where or what is the "m" in your formulae?
Rob sussed it after numerous mugs of tea, and waking up, thanks again, please ignore my request, you have my permission to put a dumb if you feel like it I won't be offended.

No need for that Pete, I should've probably added to that post.

It was just extrapolated from an article the IET published.

 

[Pete999]

No need for that Pete, I should've probably added to that post.

It was just extrapolated from an article the IET published.

Cheers Rob, strange how the older you get, the longer it takes to get started in the mornings, bit like an old car I guess. after a few coughs and splutter you get into gear eventually.

 

[Pete999]

Well I don't know it seems that the 0.05 ohms relates to the resistance of the banding conductor and the connection vis the Earth clamp on the pipework, it does seem quite clear from GN3 and the numerous you tube videos from respected engineers that the case involves the bonding conductor AND the earth clamp's connection to the pipework. As can be seen from the statement that the length of the Main bonding conductor has some bearing on the problem. One statement suggests that anything over 25mtrs the conductor csa should be increased, which in my eyes confirms that the resistance reading does include the bonding conductor, and not just the resistance of the pipe and the earth clamp. I do agree with some that the reading should be taken from the disconnected bonding conductor and the PIPE as described in the video that was posted earlier. Just saying.

Bad spelling? Risteard, if it's PIPE you are referring to I was merely emphasising PIPE. Sorry Mate don't know who posted "Bad spelling" just an assumption, apologies.

 

[Dangerous Brian]

1. We might consider the use of the maximum prospective earth fault current (PEFC) as a possible means of determining the length of main protective bonding conductors but this method gives an impractically low value – at least if the PEFC is taken to be 16,000A. If the conventional maximum figure for touch voltage of 50V is divided by 16,000 amps in order to obtain the maximum resistance of the bonding conductor – in order to then obtain a maximum length – we arrive at a figure of 0.003Ω.

Comparing this with the values in Table 1 shows this value to be unrealistic.

Rob, isn't the fault current limited by the supply fuse to a lower level than the measured PSCC? Would this give a better determination of the size of the main bonding conductors?

 

[Bobster]

Rob, isn't the fault current limited by the supply fuse to a lower level than the measured PSCC? Would this give a better determination of the size of the main bonding conductors?

It would limit it yes, an you could calculate it. It wouldn't be lowered by much an the difference in conductor size would be negligible.