- Reaction score
- 199
The situation is:
Power is needed inside a greenhouse to power a specialized greenhouse heater, a timed motorized window opener and a light. The lights can be double insulated but the heater and windows device are both class 1.
The greenhouse has a metal frame that is in good contact with soil and the floor inside the greenhouse is a mix of soil and paving slabs
The house is TN-C-S
I originally thought making the greenhouse TT would be the best option but there is an issue with that because the house supply cable and a metal water pipe run close to one side of the greenhouse (about 1.5m away) so there is no available location to put in an earth rod with enough separation distance from the water pipe which is at PME earth potential
If the TN-C-S earth was used in the greenhouse then the metal frame of the greenhouse would have to be bonded with 10mm although this makes the risk of the greenhouse metalwork and the heater being at a dangerously high voltage in a PEN fault with anyone inside or just outside of the greenhouse in good contact with true earth (and the metal frame is likely to be touched (each time door is opened))
So In this case I am not sure using the TN-C-S earth and bonding the frame is a good option either, I was thinking also perhaps a matt:e or viridian pen fault devices could work but the problem would be that this box would only isolate the L,N & CPC but not the 10mm bonding conductor so renders it pointless as the greenhouse frame would remain connected to PME, these are also deigned for EV charging and there is no way the greenhouse sockets could reasonably be expected to be used to charge a vehicle as stated in 722.411.4.1
I imagine an isolation transformer would cost mega money (demand is around 2kw)
Thanks
Power is needed inside a greenhouse to power a specialized greenhouse heater, a timed motorized window opener and a light. The lights can be double insulated but the heater and windows device are both class 1.
The greenhouse has a metal frame that is in good contact with soil and the floor inside the greenhouse is a mix of soil and paving slabs
The house is TN-C-S
I originally thought making the greenhouse TT would be the best option but there is an issue with that because the house supply cable and a metal water pipe run close to one side of the greenhouse (about 1.5m away) so there is no available location to put in an earth rod with enough separation distance from the water pipe which is at PME earth potential
If the TN-C-S earth was used in the greenhouse then the metal frame of the greenhouse would have to be bonded with 10mm although this makes the risk of the greenhouse metalwork and the heater being at a dangerously high voltage in a PEN fault with anyone inside or just outside of the greenhouse in good contact with true earth (and the metal frame is likely to be touched (each time door is opened))
So In this case I am not sure using the TN-C-S earth and bonding the frame is a good option either, I was thinking also perhaps a matt:e or viridian pen fault devices could work but the problem would be that this box would only isolate the L,N & CPC but not the 10mm bonding conductor so renders it pointless as the greenhouse frame would remain connected to PME, these are also deigned for EV charging and there is no way the greenhouse sockets could reasonably be expected to be used to charge a vehicle as stated in 722.411.4.1
I imagine an isolation transformer would cost mega money (demand is around 2kw)
Thanks
