I have a situation with an electrical installation supplying an electrical accessory in another installation.
There is an orchard with its own supply to a shed.
A house has been built on the orchard land and has its own seperate supply.
There is a pump in the orchard shed to supply water to the house. This pump is being supplied from a socket installed in the orchard shed and fed from the house.
There are other pumps and equipment nearby on the orchard supply.
My concern is that there is now possibly a chance for touch voltages between the electrical equipment or the iron cladding of the shed.
Is this situation compliant and is any bonding required to prevent the different potentials?
Any help is appreciated, thanks.
Bonding
Re: Bonding
Correct that there is a risk of touch voltages.
Most obviously an earth fault in the pump motor will result in high current flowing in the PEC of the pump circuit.
The pump motor will therefore have a voltage higher than the MEN point of the house, due to impedance in the PEC.
The value could be significant (and can be calculated) - but since it's a socket outlet the fault protection must operate within 0.4 sec.
In fact even quicker; because this socket is part of a domestic installation so must have RCD protection.
So unlikely to be a problem.
however just the fact that this pump is connected to one installations earthing system, and other conductive materials within arm's reach are connected to a different earthing system, creates a risk if these 2 systems are at different potential.
Such difference is unlikely to be significant under normal conditions; but some kinds of faults (eg a faulty mains N on either installation) could result in enough difference to be a problem.
Clause 5.6.1 requires us to minimise such risks, so doing nothing isn't an option.
The rest of 5.6 has specific bonding requirements for specific situations, but none for this type of situation.
Installing a bonding conductor (preferably a dedicated one) from the pump to the shed's earthing system will take care of any differences of potential between the two earthing systems.
I would also want to see warning labels installed; both at pump and at shed MSB.
That's because anyone turning off the shed's main switch will expect it to de-energise everything within the shed.
Most obviously an earth fault in the pump motor will result in high current flowing in the PEC of the pump circuit.
The pump motor will therefore have a voltage higher than the MEN point of the house, due to impedance in the PEC.
The value could be significant (and can be calculated) - but since it's a socket outlet the fault protection must operate within 0.4 sec.
In fact even quicker; because this socket is part of a domestic installation so must have RCD protection.
So unlikely to be a problem.
however just the fact that this pump is connected to one installations earthing system, and other conductive materials within arm's reach are connected to a different earthing system, creates a risk if these 2 systems are at different potential.
Such difference is unlikely to be significant under normal conditions; but some kinds of faults (eg a faulty mains N on either installation) could result in enough difference to be a problem.
Clause 5.6.1 requires us to minimise such risks, so doing nothing isn't an option.
The rest of 5.6 has specific bonding requirements for specific situations, but none for this type of situation.
Installing a bonding conductor (preferably a dedicated one) from the pump to the shed's earthing system will take care of any differences of potential between the two earthing systems.
I would also want to see warning labels installed; both at pump and at shed MSB.
That's because anyone turning off the shed's main switch will expect it to de-energise everything within the shed.
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Re: Bonding
Thanks for response. Yes definitely putting warning labels.AlecK wrote: ↑Tue Nov 01, 2022 12:33 pmInstalling a bonding conductor (preferably a dedicated one) from the pump to the shed's earthing system will take care of any differences of potential between the two earthing systems.
I would also want to see warning labels installed; both at pump and at shed MSB.
That's because anyone turning off the shed's main switch will expect it to de-energise everything within the shed.
As the pump is connected via a plug and socket outlet, can the bonding conductor go directly to the socket in case someone plugs something else in?
Re: Bonding
Good thought, and I probably should have thought more about the fact that you're planning to use a socket.
If someone does plug another Class I appliance into this socket, there will be greater risk of different earth potentials.
Not just earthed items within arm's reach of the pump, but earthed items within reach of wherever the appliance's lead reaches to.
One answer is to not use a socket, and connect the EBC to the pump / motor body in the normal way.
Another would be to run the EBC directly between the two MSBs.
Connecting the EBC to the socket will perform the required bonding function; although it depends on the integrity of the earth connection between plug & socket.
That might seem to be contrary to 5.5.2.1 & Fig 5.3; which require protective earthing to be connected to the supply for the item;
but as it's not a PEC, but instead an EBC, I don't think it breaks that rule.
We normally connect EBCs directly to the metalwork that's required to be bonded (in this case the pump motor body).
That's specifically required in several subclauses of 5.6; eg for bonding water pipes 5.6.2.2 specifies connection to pipe, as close as practicable to where it emerges from ground.
However I can see nothing in 5.6 to prohibit a detachable connection (plug and socket) in this case; and - as you've realised - bonding the pimp directly leaves the possibility of other items being plugged in.
Even if the socket is labelled (eg "house water pump only; do not use for other equipment"); some fool will use it anyway.
Regardless of how you do it; probably worth removing any doubt about what this unusual extra conductor is, by labelling it at both ends.
If someone does plug another Class I appliance into this socket, there will be greater risk of different earth potentials.
Not just earthed items within arm's reach of the pump, but earthed items within reach of wherever the appliance's lead reaches to.
One answer is to not use a socket, and connect the EBC to the pump / motor body in the normal way.
Another would be to run the EBC directly between the two MSBs.
Connecting the EBC to the socket will perform the required bonding function; although it depends on the integrity of the earth connection between plug & socket.
That might seem to be contrary to 5.5.2.1 & Fig 5.3; which require protective earthing to be connected to the supply for the item;
but as it's not a PEC, but instead an EBC, I don't think it breaks that rule.
We normally connect EBCs directly to the metalwork that's required to be bonded (in this case the pump motor body).
That's specifically required in several subclauses of 5.6; eg for bonding water pipes 5.6.2.2 specifies connection to pipe, as close as practicable to where it emerges from ground.
However I can see nothing in 5.6 to prohibit a detachable connection (plug and socket) in this case; and - as you've realised - bonding the pimp directly leaves the possibility of other items being plugged in.
Even if the socket is labelled (eg "house water pump only; do not use for other equipment"); some fool will use it anyway.
Regardless of how you do it; probably worth removing any doubt about what this unusual extra conductor is, by labelling it at both ends.