Islanding mode earthing requirements with PME supply to inverter in garage

It’s going to be incredibly difficult to wire in a new cable to the MET. The house has been extended so the meter cupboard is right in the middle, can’t easily get a cable out.

I don't see any great technical problem with connecting the electrode to the MET via the 10mm² c.p.c. in the submain - it's quite common to bond extraneous-conductive-parts to the earth bars in sub-boards,

If running new cables to the intake position is a non-starter, I do wonder how you're going to make the connection between the inverter control system and the disconnect-from-the-grid contactor though. I suppose a wireless link plus a UPS and the intake might be an option, but I've never heard of it being done that way.

    - Andy.

This is a good point. I can get a cat 6 cable in which connects to the energy meter (alternative to CT coil) and that would leave me with 6 twisted signal pairs remaining. The inverter has the ability to send an ELV signal for coordinating islanding mode. I haven’t really thought about how this would be setup. Perhaps a contactor exists which opens when power is lost but to close it again, requires the ELV signal.

This is a good point. I can get a cat 6 cable in which connects to the energy meter (alternative to CT coil) and that would leave me with 6 twisted signal pairs remaining. The inverter has the ability to send an ELV signal for coordinating islanding mode. I haven’t really thought about how this would be setup. Perhaps a contactor exists which opens when power is lost but to close it again, requires the ELV signal.

Akbar Ramzan said:

The inverter has the ability to send an ELV signal for coordinating islanding mode.

The control system needs to do more than "send a signal" - what about failure modes (island mode isolator fails to open or close, same with N-E bond relay)?

This is why a G99 notification is usually required from the DNO for this type of functionality.

It's not trivial to do, and consequences of something going wrong are either breach of legislation, or a whole host of electrical safety issues which can be lethal.

The inverter has G98 and G99 approval, it's a sunsynk 3.6kW. I know after the grid comes back online it waits a while and does it's checks + gets the timing and order of actions correct so it can't be in a dangerous situation. I will definitely review all of the manual beforehand.

To be honest, I will probably end up not going with the earth rod idea and just having a single RCD protected socket at the EPS output as it's a lot easier.

Akbar Ramzan said:

To be honest, I will probably end up not going with the earth rod idea and just having a single RCD protected socket at the EPS output as it's a lot easier.

How is the socket-outlet earth maintained if the DNO are working on the system and cut the supply cable? The guidance is not to have a "floating" socket-outlet in island mode - the reasons are stated in the Code of Practice for Electrical Energy Storage Systems.

Manufacturer's instructions allow 1 socket for a class ii item only

Akbar Ramzan said:

Manufacturer's instructions allow 1 socket for a class ii item only

Whilst that would be OK, the issues (as stated in the IET Code of Practice) include:

1. The use of a standard socket-outlet permits the connection by general users of multi-way adaptors, thus enabling more equipment to be connected.
2. in the UK we don't have 'Class II socket-outlets' to prevent users connecting Class I ... and generally users are unlikely to be aware of the safety issues.

In reality, though, aren't most people wanting backup going to want to power lighting (OK could be Class II, but more than one device), internet and TV ? The router may have a "safety voltage" power supply, but there are design features of Ethernet that require a controlled discharge to earth to prevent static charging ... and this also causes "fortuitous earthing". Similarly TV etc. - quickly, you get to the point that, sadly, it's no longer a "floating" power supply for a single device.