Originally Posted by
Isetech
How you read this part of the regulations pasted below, could be where all the confusion originates.
This example in P1 would represent a larger generator or alternate supply from a large device, not a little 5 kva unit installed in your garage.
For example if you had a 15 KVA generator or 16 kva inverter or bigger (depending on the supply) connected at the meter (point of supply), P1 would apply.
Installing a 5/8/12 KVA standby system doesnt apply if the supply is 60 amps or above, why, because you can only connect the neutral and earth together at the point of supply. The inverter is not the point of supply while the unit is connected to the grid, it only becomes the point of supply once it switches to islanding mode.
How can you resolve this challenge for smaller standby units with built in changeover/islanding relays, simple the unit should be supplied with a built in relay with suitable devices to isolate the unit if the relay fails and or the voltage exceeds the touch voltage as per the regs.
7.12.3.1.2 In an installation that is supplied from a combination of
transformers and alternative supplies located near to each other, the neutral
points of each of these items shall be connected to a single earthed neutral
bar (see P.1 and figure P.1). This earthed neutral bar shall be the only point
at which the neutral of the installation is earthed. Any earth leakage device
shall be positioned in such a way as to avoid incorrect operation due to the
existence of any parallel neutral/earth path.
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