Main equipotential bonding

21 Feb 2007
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United Kingdom
Just read the Wiki that says the max resistance of main equipotential bonding should be 0.05 ohms. I've used 10 mm squared for this. What length will give 0.05 ohms. Sorry but don't have the table to work it out. Steve.
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I think you may have mis-understood, it means that when you measure between the bonding & the main earth terminal you should have less than 0.5 ohmns, unless I have mis-understood your question.
Quote from the Wiki

"Main equipotential bonding conductors should be as short as possible and their resistance from bonded part to the MET should not exceed 0.05 ohms

My MEB conductor is as short as possible but is about 20 - 25 metres long. Worried that the resistance is too high. Just found a figure of 2.2 mohms / metre for 10mm squared (can anyone confirm that figure is correct). This gives a max length of 22.7 metres. So I must be at the limit.
My understanding on this is that there isnt a minimum or maximum value to be measured, all that needs to be confirmed is you do have good sound continuity between the MET and your pipe work.
In some cases a visual inspection is all that is needed to confirm continuity (as long as you can see the connection at the MET and follow the bonding cable in question along its entire length to the clamp where it terminates).
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Sounds like a loose connection somewhere.
Double check your tester to be on the safe side though.
My calculations say for a length of 10mm copper is....
At 20 meters 0.04 ohms
At 25 meters 0.05 ohms.
Sorry Festa but I did not measure the cable resistance. I have BCO 1st fix inspection on Friday morning. I installed a 10mm squared MEB cable. Worryingly I find that the length is very close to the limit. My guestimate from trying to measure the cable route is 24 metres. Maybe I shouldn't worry too much. I suppose 0.06 ohm MEB resistance is better than infinity (none at all !) Actually I just remembered that the MEB is not notifiable work anyway so should not worry about the BCO inspection of that part of the job. Steve.

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