EICR - Structural Steel Main Protective Bonding

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Timotei

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EICR on commercial premises approx 8 yrs old. Structural steel is confirmed by test as extraneous conductive part. No EIC / paperwork available.

MPB to gas / water services confirmed visually and by measurement - 1 continuous conductor serves both. Unable to visually locate MPB to structural steel, but MPB conductor for water / gas is not accessible throughout its run, so may be connected to structural steel at some hidden point. Only MEC and 1 x MPBC enter the DB.

Continuity test from exposed structural steel (by wander lead of approx 15 metres) to MET gives 0.2Ω.

Would you consider this to be satisfactory evidence of an unlocated MPB to structural steel? As this is potentially the resistivity of the MPBC and a significant amount of structural steel, my thoughts are "yes", with a C3 coding as there is no MPB connection available for inspection in accordance with 543.3.2

I have, however, been told by "someone" (who will remain nameless) that if my continuity reading is greater than 0.05Ω I must code as unsatisfactory with a C1 or C2. I have argued that the 0.05Ω figure is an exemplar reading for an end to end test on an MPBC, not applicable when measured as I have had to do (see above).

Would appreciate thoughts on how best to /how you would proceed.

Thanks,

Timotei
 

Fleeting

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There is no quoted resistance in BS7671 for a main protective bonding conductor.
 

Fleeting

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Verifying the metalwork as being extraneous on an existing installation would be impossible. Removing all parallel paths so it is essentially isolated and 'floating' from the electrical installation is not realistic.
 

Timotei

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I thought it was 0.05 ohm or greater than 22k? It’s been a while since I’ve had a look.
There is no quoted resistance in BS7671 for a main protective bonding conductor.

I believe the 0.05Ω figure comes from GN8.

Verifying the metalwork as being extraneous on an existing installation would be impossible. Removing all parallel paths so it is essentially isolated and 'floating' from the electrical installation is not realistic.

I take your point regarding the isolation / parallel paths.

Question remains whether my continuity measurement of 0.22Ω is sufficiently low to consider it "evidence" of a hidden MPB to the structural steel, or whether I should indeed be recommending a new MPB is installed with clear refrence to its location for future EICR etc?

Thoughts / advice welcomed.
 

Fleeting

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I doubt it is hidden. If you can ditch the existing bond at both ends and test from it to the steelwork.
 

Timotei

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I doubt it is hidden. If you can ditch the existing bond at both ends and test from it to the steelwork.
Thanks Fleeting.....and that's why I come on the site....sometimes the answer is staring you right in the face but you're so close you can't see it without someone else pointing it out!
 

Sidewinder

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The 0.05Ω is not the max value for an/a main earth or bonding conductor.
It's merely indicative of the expected max resistance across a bonding connection such as between the terminal and the pipework with a BS951 clamp fitted.
 
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