Hi All
Planning an off-grid solar system and I’m pretty confident about most of it except for one thing - earthing. I believe the inverter I will use, a Victron Phoenix 12/350, has a floating earth - so there will be 230V L-’N’, 115V L-E and 115V ’N’-E. The system will power an existing (old) installation. I can see danger arising in two ways here:
1. Single pole switching will not make equipment dead - so for example when changing a light bulb, there will still be 115V between the ’Neutral’ and Earth, even with the light switch off.
2. A ’N’ - E fault could result in an overload and hence fire, with no protective device to isolate the supply in the ’N’. (I have read that floating earth’s can pose a fire risk; presumably this is why?)
So, my proposed solutions:
1. Fit an RCD between the inverter and the existing installation: this would prevent danger no. 2 and provide a level of protection against danger no. 1
2. Connect the earth from the installation to the neutral of the inverter and an earth spike for reference earth, leaving the floating earth from the inverter not connected to anything. To my mind this would constitute a TN-S system with reference earth.
So my questions:
1. Will my proposed solution work and be safe? (Assuming I get everything else right as well.)
2. Have I missed any other safety issues/pitfalls.
Please bear in mind when answering:
- The existing installation will, in practice, have its earth connected to the mass of earth via the bonding to the water supply, though I am aware that this cannot be relied upon for earthing.
- I am aware that the 350W inverter will be very limiting in terms of what loads can be supplied.
Finally, I’m unsure whether to reference earth the DC system negative (PV, batteries, etc. and associated wiring). I don’t plan to earth the array frame as lighting strikes are very unlikely. Any suggestions?
Thanks for reading to the end!
Planning an off-grid solar system and I’m pretty confident about most of it except for one thing - earthing. I believe the inverter I will use, a Victron Phoenix 12/350, has a floating earth - so there will be 230V L-’N’, 115V L-E and 115V ’N’-E. The system will power an existing (old) installation. I can see danger arising in two ways here:
1. Single pole switching will not make equipment dead - so for example when changing a light bulb, there will still be 115V between the ’Neutral’ and Earth, even with the light switch off.
2. A ’N’ - E fault could result in an overload and hence fire, with no protective device to isolate the supply in the ’N’. (I have read that floating earth’s can pose a fire risk; presumably this is why?)
So, my proposed solutions:
1. Fit an RCD between the inverter and the existing installation: this would prevent danger no. 2 and provide a level of protection against danger no. 1
2. Connect the earth from the installation to the neutral of the inverter and an earth spike for reference earth, leaving the floating earth from the inverter not connected to anything. To my mind this would constitute a TN-S system with reference earth.
So my questions:
1. Will my proposed solution work and be safe? (Assuming I get everything else right as well.)
2. Have I missed any other safety issues/pitfalls.
Please bear in mind when answering:
- The existing installation will, in practice, have its earth connected to the mass of earth via the bonding to the water supply, though I am aware that this cannot be relied upon for earthing.
- I am aware that the 350W inverter will be very limiting in terms of what loads can be supplied.
Finally, I’m unsure whether to reference earth the DC system negative (PV, batteries, etc. and associated wiring). I don’t plan to earth the array frame as lighting strikes are very unlikely. Any suggestions?
Thanks for reading to the end!
