- Reaction score
- 10,210
@essex
If the fault is after the last earthing point on a PEN conductor then it is useless - hence we do not take this into account.
Faults take the path of least resistance, PME is strapped down at very regular intervals to ensure a lost concentric connection will track back to the nearest point which is either the next rod or the substation itself, if you are on about the customers end then a break just before the customer will also raise the potential of any earthed metalwork in the building regardless, the risk is deemed so low that this is not a concern, you will often find the first earth strapping is within a few meters of the property to lower any such risk.
You said you would not TT a metallic building outside when a PME earthing arrangement is supplied. This is the exact opposite of the Reg.
I was reflecting on the context this whole thread is in IE domestic and outbuildings, guidance notes clearly state you can earth rod the out building if it does have structural metalwork, or metallic incoming services, it also says this is one of a few options, I choose the other option of bringing in a suitably sized earth to bond such metal work.
In what you describe I would say you have extended the earthing. Not the zone. (1)The very fact that there is (and likely always will be) a PD between what you have bonded and true earth means that when outside it is virtually impossible to extend the EBZ. The only way to achieve this would be to ensure your earth bonded to the shipping containers is the same potential as true earth. Using anything other than an earth electrode then this is just not possible. In my opinion,(2) which I believe is clearly backed up by 7671 you should have never connected those containers to a PME supply. It is specifically stated this should not be done.
(3)Any issue with the supply neutral will give results precisely what you have described. If it would have been a complete breakage in the PEN then it would have been more than just a tingle. As for the other services I would have just supplementary bonded them so that everything was the same potential.
(1)-I agree but we are not talking any voltage of concern here, normally hard to measure though it is that low and well within SELV limits to be considered a concern.
(2)Where does it state this, I agree the regulations are specific for many installations about earthing to PME say to caravans, funfairs, temp' stands etc etc but these containers and the prefab offices are classed as permanent, they been there 20+yrs now also my comment was more in line to the domestic arena to which this thread is based, guidance notes that are linked to in a previous thread express earth rodding an out building is one of a few options available on a PME supplied property, with regards to the OP's query then I stand my position on this and say there is no reason to rod if you have PME supply, even if you have incoming metallic services, all you need to do is bring out a bonding cable to meet the requirements of the installation and its supply. Like I said before, why create a less reliable earth connection when you have a reliable one provided.
(3) The choice to do this was based on knowing the network layout, this was not a network fault and has been confirmed, we suspect it was from an adjacent site who had recently has a generator fitted and incorrectly installed, upon questioning the owner he said he would contact the company, the fault mysteriously disappeared after this but I cannot say it was definitely the cause. I understand your concern because regulations are strict on PME earthing to caravans, funfairs temp' stalls etc but this was weighed up on this particular site, again my original comment was in the context of this thread and domestic outbuildings (with incite I should have been clearer)
RCDs will not even work as the link from the neutral is before the RCD so the RCD is not detecting an imbalance. The current goes back down the neutral, through the RCD before it goes back down the earth connected to the main head and to anything earthed or bonded.
I agree - no disagreement there.
Most spas are fully plastic including all pipework and all electrical pumps etc should be Class 2. If they are getting a tingle something is seriously wrong.
I disagree, I have seen spa's, hot tubs etc which require earth connection to the pump supply, class 2 is great when everything is in good condition but seals failing, motor running hot etc all can lead to water ingress, then you still have the same risk on a class 2 install.
If the fault is after the last earthing point on a PEN conductor then it is useless - hence we do not take this into account.
Faults take the path of least resistance, PME is strapped down at very regular intervals to ensure a lost concentric connection will track back to the nearest point which is either the next rod or the substation itself, if you are on about the customers end then a break just before the customer will also raise the potential of any earthed metalwork in the building regardless, the risk is deemed so low that this is not a concern, you will often find the first earth strapping is within a few meters of the property to lower any such risk.
You said you would not TT a metallic building outside when a PME earthing arrangement is supplied. This is the exact opposite of the Reg.
I was reflecting on the context this whole thread is in IE domestic and outbuildings, guidance notes clearly state you can earth rod the out building if it does have structural metalwork, or metallic incoming services, it also says this is one of a few options, I choose the other option of bringing in a suitably sized earth to bond such metal work.
In what you describe I would say you have extended the earthing. Not the zone. (1)The very fact that there is (and likely always will be) a PD between what you have bonded and true earth means that when outside it is virtually impossible to extend the EBZ. The only way to achieve this would be to ensure your earth bonded to the shipping containers is the same potential as true earth. Using anything other than an earth electrode then this is just not possible. In my opinion,(2) which I believe is clearly backed up by 7671 you should have never connected those containers to a PME supply. It is specifically stated this should not be done.
(3)Any issue with the supply neutral will give results precisely what you have described. If it would have been a complete breakage in the PEN then it would have been more than just a tingle. As for the other services I would have just supplementary bonded them so that everything was the same potential.
(1)-I agree but we are not talking any voltage of concern here, normally hard to measure though it is that low and well within SELV limits to be considered a concern.
(2)Where does it state this, I agree the regulations are specific for many installations about earthing to PME say to caravans, funfairs, temp' stands etc etc but these containers and the prefab offices are classed as permanent, they been there 20+yrs now also my comment was more in line to the domestic arena to which this thread is based, guidance notes that are linked to in a previous thread express earth rodding an out building is one of a few options available on a PME supplied property, with regards to the OP's query then I stand my position on this and say there is no reason to rod if you have PME supply, even if you have incoming metallic services, all you need to do is bring out a bonding cable to meet the requirements of the installation and its supply. Like I said before, why create a less reliable earth connection when you have a reliable one provided.
(3) The choice to do this was based on knowing the network layout, this was not a network fault and has been confirmed, we suspect it was from an adjacent site who had recently has a generator fitted and incorrectly installed, upon questioning the owner he said he would contact the company, the fault mysteriously disappeared after this but I cannot say it was definitely the cause. I understand your concern because regulations are strict on PME earthing to caravans, funfairs temp' stalls etc but this was weighed up on this particular site, again my original comment was in the context of this thread and domestic outbuildings (with incite I should have been clearer)
RCDs will not even work as the link from the neutral is before the RCD so the RCD is not detecting an imbalance. The current goes back down the neutral, through the RCD before it goes back down the earth connected to the main head and to anything earthed or bonded.
I agree - no disagreement there.
Most spas are fully plastic including all pipework and all electrical pumps etc should be Class 2. If they are getting a tingle something is seriously wrong.
I disagree, I have seen spa's, hot tubs etc which require earth connection to the pump supply, class 2 is great when everything is in good condition but seals failing, motor running hot etc all can lead to water ingress, then you still have the same risk on a class 2 install.