Yes I see what your saying if the pipe goes between two buildings then regardless the pme system will entering the outbuilding so not a lot of point bonding to an earth rod
Pme or earth rod
- Thread starter Rangers1882
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Ok but my original point was if you did do this earth rod that pipe work as well on the loss of the neutral conductor and loss of the one would this Tt system not act like a secondary earth and prevent this pipe work from becoming live ?? Thanks
It would take a bloody good earth electrode to stop significant voltages appearing on the earthing system in the event of losing a combined neutral and earth connection. Normal rods are likely to be too high resistance to help in that scenario.
I suspect the pipe itself would actually be a better earth electrode than most rods.
I suspect the pipe itself would actually be a better earth electrode than most rods.
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Yes I agree that's why I said you would need an adequate earth rod that could take the fault current and as you said low enough resistance which is hard thanks
If the pipe to substation path has a very low ( less than one ohm ) impedance then it will take over the task of the broken neutral. It will put a strain on bonding cables and those that cannot carry the neutral current will fail.
http://www.westyorksfire.gov.uk/news/blast-footage-prompts-warning
But in most cases the impedances of the pipe and rod will be high enough to limit current to an amp or two so bonding cables should be able to cope.
In both cases this current into ground is from the incoming PME "earth" and does not pass through the RCD ( if fitted ) so the RCD will not trip on this earth leakage currrent.
What does happen is the local ground potential is pulled up by the current flowing from the rod into the ground so the potential difference between local ground and the PME "earth" is not as great as the voltage drop along the neutral from the substation. Ground the substation is not at the same potential as the ground around the rod.
http://www.westyorksfire.gov.uk/news/blast-footage-prompts-warning
But in most cases the impedances of the pipe and rod will be high enough to limit current to an amp or two so bonding cables should be able to cope.
In both cases this current into ground is from the incoming PME "earth" and does not pass through the RCD ( if fitted ) so the RCD will not trip on this earth leakage currrent.
What does happen is the local ground potential is pulled up by the current flowing from the rod into the ground so the potential difference between local ground and the PME "earth" is not as great as the voltage drop along the neutral from the substation. Ground the substation is not at the same potential as the ground around the rod.
As I said in previous messages, adding a local earth electrode to a PME system "would achieve very little" and "would not serve much of a purpose", even in the event of the infamous 'lost neutral' event. I assumed that you understood that the reason for this is not that there is anything wrong with the concept but, rather, because almost any ordinary domestic earth rod is going to have far too high a resistance to have any appreciable impact on the situation.
Kind Regards, John
Yes thanks for your replies
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