Additional protection when running from 'Load' into existing cu
I have a query from my electrician which I would appreciate a response to.
To provide a little bit of context - I have a SunSynk 8KW inverter wired up and operating normally with the feed from the grid going into the inverter grid connection, and a battery and PV wired in appropriately.
We are attempting to make use of the UPS feature to power the whole house in the event of the grid failing (understanding that we can't exceed 8KW etc - which is well within the maximum normal limits)
To do this, we are going to wire the 'Grid' and 'Load' from the inverter into a automatic transfer switch, under normal operation the Grid will be present, when the grid goes down the Grid connection will disappear, causing the inverter to liven up the 'load' connection and the ATS to switch over
The question is - because we are going to share a common wire from the consumer unit into ATS, do we need to put any additional protection in line when operating from the load port, otherwise the power is going to be fed into the consumer unit from the other end, bypassing the RCD. (Note, I already know about the earth neutral bond we have to make)
On your original picture show the ATS it does not make sense to me. If I understand it correctly this would allow the Grid to either connect to the L or the G port. This is not permitted as the Grid should never be allowed to connect to the L port.
You can use an ATS rather than a manual switch. It is just a more expensive solution just to cover the event that you loose the inverter.
In your original description you indicated that if the grid disappears it will 'liven' up the Load. This is not correct. The load port is always active unless you are using the inverter as a UPS. While it will function as a UPS, this is not the preferred way this type of hybrid inverter is used. The inverter is designed to be able to power the load from the battery and PV and only use the grid if required. If the Grid fails the inverter automatically disconnects from the Grid and continues to supply the load from the Load port. This is why you do not really need an ATS because the inverter does this all for you. The only reason why you may use the switch as I have shown is to connect the load to the Grid in the event that the inverter fails.
The reason the inverter disconnect from the grid when the grid fails is to prevent the inverter from trying to push power into the grid.