One possibility would to install an MCCB with earth fault protection, but not too sensitive, to avoid tripping from leakage currents.

Earth fault protection on small circuits is often at about 30ma as this gives protection against dangerous electric shock. For large circuits such as 160 amps, much less sensitive earth protection can often be used, set at several amps.

You will need  either an MCCB with an earth fault sensing that can be set to 300mA or higher, or the equivalent of a separate programmable RCD - the so called 'earth fault relay'

Take a seat before looking at the prices though.

Mike.

What about fitting Earthing Discs in Conducrete (its like cat litter)?

Sergio Fernandez said:

What about fitting Earthing Discs in Conducrete (its like cat litter)?

That won't reduce Z_e, which for a TN-C-S or TN-S supply has to be measured to the distributor's earthing terminal, with the consumer's earthing disconnected.

Could they convert it to a TT system possibly?

That will not really make much difference - after all, you can have an RCD without having to convert to TT.

Mike.

Sergio Fernandez said:

Could they convert it to a TT system possibly?

It would be possible, (depending on whether suitable isolation is in place, taking into account that in TT systems you need to be able to isolate the Neutral for safe working).

But it won't resolve the need for residual current fault protection, and may well cause EMC issues for VSDs.

Yes that's the route I was thinking I was going to have to go with the inverter. Shame it's going to bump the cost up but not really any other way round it I don't think. I'll have to have a play with the setup once installed to see what the leakage looks like so we can find a reasonable setting that doesn't trip all the time 

I wonder if the existing supply beefy enough to cope with the extra 160A?

As it's TN-C-S the 0.23Ω will be for the L-N loop as well, drawing 160A on one phase would likely reduce the supply voltage by 160*0.23 = 36.8V - which would be right on the edge of ESQCR even if the supply at the transformer was at the maximum 253V - so would fall below if it happened to be lower. Granted if things are reasonably balanced over 3 phases the N current should be reduced and so v.d. reduced a bit - but if there are any other loads on site it could count the other way.

   - Andy.

It had a 3ph transformer upgrade from 100A to 200A last year. The load balancing on site should be pretty good as the only thing other than a few lights it runs is a 3ph dust extractor and a small 3ph drier unit