Short version of question:
Multi RS Solar, off grid, ground relay closed. What should the earth loop impedence be?
Long version:
I've got a Multi RS Solar fed from Grid when I need to charge the batteries if there is insufficient solar but otherwise the input relays are disconnected. The Grid Earth is still connected to the input though, there is also an earth rod in the garden in parallel in case of the DNO supply is cut and I end up islanded with no Earth.
The output of the RS feeds my main house distribution board. However the earth for this is taken directly from the main DNO earth point.
The RS is also taken to the DNO earth point.
I also have a bypass switch so I can essentially take the RS off line and feed the distribution board directly from the DNO supply.
I recently bought a TIS 1005 socket tester that can do a loop check and test the RCD as well.
I've noticed that when the input relays are CLOSED on the RS, the loop tester says the loop impedence is ok (I e. Green or below 1.9 ohms) but with the input relays OPEN on the RS and therefore "off grid" the loop tester says the impedence needs checking (I.e. yellow or above 1.9 ohms and less then 93ohms).
The option to enable the ground relay when the input relay is open is enabled on the RS and there is no AC between N and PE. The RCD test button the TIS tester works fine as well and trips the RCD as expected.
The electrics in the house have all previously been signed off by a qualified electrician but I avoided doing an earth loop test on the inverter in case it damaged it (i.e. I used the bypass switch), I'm starting to regret this now!
Is this normal behaviour?
What sort of values should I expect?
Is this just a limitation of the grounding relays in the RS? or the fact that the tester is looking at a simulated sine wave instead of proper mains?
When the house was tested previously the main earth was asking 0.5ohms.
Would doing a live earth loop test be ok or is it likely to damage the inverter? Sorry, showing some ignorance on this one :)
