TN-C-S earth and Island mode inverter

[snarler45]

I am installing a Victron Quattro in an island mode configuration (in the UK, the DNO is the NG). I will be adding a stand-by generator. My property has a standard TN-C-S (PME) earth arrangement. I am an electrical engineer (testing) not an electrician. The regs state the DNO earth cannot be relied on (it should be disconnected when island mode kicks in). I assume a local earth (TT?) is required - the installers says not. As a professional member of the IET I am a little confused but do not plan to be for long!!!.
Any suggestions on how the system should be earthed?
I saw there was another thread that did not really answer the question.
When connected to the grid the standard PME will be in use - all good and understood.
When the grid fails or is isolated manually or I run my standby generator the islanding relays cut the grid (and the earth). What do we need to do to maintain safety and prevent any RCBs tripping?
Same question when I add the standby generator.

Most installations in this country are not set up for anti-islanding (even if you have batteries) which means that if the grid goes down only your ECS will stay up. I build and test things like data centers and we make sure the systems stay up by using a UPS and a generator. I am doing the same thing at my property.

I have a G99 for 6kW export.
The system will be commissioned this week.

Bren

 

[James]

My understanding is that the suppliers earth connection should never be disconnected.
because you cant rely on it being connected in a power failure, I.e. the water company just sent a jcb bucket through your supply cable, you should also have an alternate means of earthing.

this would normally be an earth rod or similar and your protective devices should be specified so that they will still work as intended when the grid supply is down and your backup supply is active.

in most cases, the suppliers earth and your own earth should be permanently connected to the main earth terminal.
Generators may need to have a N to E link added but this should only be done at the generator, it is not allowed to join them after the dno service head when connected to the grid.

p.s. I am about to do something similar at a commercial unit to provide backup power for an office suite using a victron unit of some sort with power passing through it most of the time but with battery backup when the grid fails.

however in this case, they have their own transformer and earthing grid with multiple connections, so i may be able to decide that there is a reliable source of earthing even if the grid fails. (more research to be done on that point)

 

[pc1966]

however in this case, they have their own transformer and earthing grid with multiple connections, so i may be able to decide that there is a reliable source of earthing even if the grid fails. (more research to be done on that point)

My understanding is you need to have a means of earthing if the supply fails, but if you can reasonably assume that is not down to a local JCB incident then relying on the local substation transformer's earth is fine if the fault scenario is a loss of HV power.

An added rod is always good! Except if you hit a buried service...

 

[snarler45]

My understanding is you need to have a means of earthing if the supply fails, but if you can reasonably assume that is not down to a local JCB incident then relying on the local substation transformer's earth is fine if the fault scenario is a loss of HV power.

An added rod is always good! Except if you hit a buried service...

Thanks James - The earth is TN-C-S. This means the earth is derived from the neutral at my inlet. The DNO live and neutral are disconnected by the inverter going into islanding mode. The cause of the disconnection may be a JCB back actor which means that even if the earth is left bonded to the company neutral it cannot be relied on => an earth rod is needed along with the relevant switch.

Has anybody done this in practice? The Victron kit is often used for off-grid installations not hybrids like mine.
It looks as if we will be doing a lot of testing.