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Hi cliffed,This may help determining an extraneous conductive part
These posts are definitely extraneous as they measure 101Ω to the MET. However, they are pretty much the same as the rod in the ground (66ohms). If anyone touched them under fault conditions the RCD would trip as they are below 1667ohms.
I've heard conflicting arguments about this.
Its clear to me why an Extraneous Conductive Part (ExtCP) needs bonding IF it measures between 1667Ω and 22KΩ to the MET, as between this range the current into the human (poorly worded) between a fault and the ExtCP will be >10mA.
The bit that is not clear to me is why do we still need to bond IF the ExtCP has a sufficiently low resistance to MET, meaning that the RCD will trip if we come into contact with it under fault conditions.
I have used 1667Ω as this is the known figure to trip a 30mA RCD in order to limit voltage to 50V. However, we use a figure of 200Ω for stability reasons AND we would have to be certain that the ExtCP is not going to be altered in any way (thus perhaps increasing its resistance to between 1667Ω and 22KΩ).
In my scenario, the posts are <200Ω to earth AND are not going to be altered, so why do they need bonding? What risk do they pose?
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