Hi.
With a fixed installation, i.e. one where the grid ground connection is never interrupted (unlike on a van or boat), is the use of the ground relay of a multiplus necessary?
Or should it be disabled in that case?
Thanks
asked
use of ground relay with a fixed installation
It detects and switches automatically. No action needed.
Yes, when it's enabled, it bonds AC-OUT neutral and ground when there's no grid and it releases them when grid's back.
But it can be disabled all together, so that there is no automatic bonding/unbonding between AC_OUT neutral when grid's out/in.
I was asking if it should be disabled all together when, in a fixed installation, the ground connection is never broken (unlike a van or boat).
@jterrag
It depends on the grid code being used.
For some it is enabled and cannot be changed.
For the most part it is best to have it enabled, it is safety related and with most safety devices/mechanisms you don't need it until you need it.
My setting for the grid code is "off-grid" so there is no back-feeding and I can deactivate the ground relay.
It's just that I'm not clear on its usefulness when the ground connection is never broken. Could you please explain why it is useful, not in general, but in that particular setting?
You absolutely need the ground relay for a functioning Residual Current Device breaker !
If there is no connection between N and PE, it also does not detect a differential current !
The purpose of the neutral to safety ground connection is to provide a path for fault currents so that the circuit breaker (or fuse) will trip on a fault. Without that connection the chassis of the device with the fault could reach lethal voltages.
It is essential that ONE and ONLY ONE connection between safety ground and neutral is made in any electrical system. This is generally at the service entrance. However if an isolation transformer creates a new neutral that is isolated from the up-stream power source, it is necessary to create a connection between the new neutral and safety ground. When the Multi/Quattro disconnects from the grid and switches to inverting mode, the connection to the up-stream neutral no longer exists. The internal ground relay then creates a new neutral-safety ground connection.
The only time the internal ground relay should be disabled is when some external device creates the connection between neutral and safety ground. For example, if a 240 volt inverter is connected to an autotransformer to create 120/240 volt split phase power. It has it's own ground relay that is controlled by the Multi.
