Ground relay test disable

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energy asked Feb 10, '20

Ground relay test disable

I have read quite a bit on Ground relay test failures and the bottom line seems to be: Earth Neutral properly before the inverter and keep neutral and earth separate after the Multis.

Why is that necessary?

I have an example of a property with 40 meter from the grid connection to the inverters. Ground resistance increases from 0.14 Ohm at the PoC to 0.34 at the inverter inputs. After the Multis, the cable runs 120 meter to the house and another 100 meter to some outside pumps.

I am concerned that the earth resistance gets too high if I do not add earth pegs at the house and pumps on the property. The property is on a hill with high lightning exposure.

If the requirement originates from the electronics in the inverter, then just say so and I have to accept it.

Grounding

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Answer 1 · 2020-02-10T14:41:25Z

Alexandra answered · Feb 10, 2020 at 02:41 PM

This is to do with Electrical standards safety, so that under fault conditions there is a low impedance pathway for the fault current to flow rather than through the things not supposed to be energised. So if you accidentally short a live on the neutral the breaker will trip. If you disconnect N/E then it wont trip and whoever is on the receiving end of the current becomes the ground path. Electricity always flow the path of least resistance, so hopefully out of the main service entrance,sometimes this does sacrifice equipment. But that is cheaper than a persons life.

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Answer 2 · 2020-02-10T16:27:56Z

energy answered · Feb 10, 2020 at 04:27 PM

The intention is to always have a RCD downstream from any neutral to earth connection. My problem is exactly the safety aspect. The earth impedance gets too high with the long cabling so at say 1kA fault current at 1 Ohm earth resistance you can have 1kV surges. I suppose one can clamp that with lightning protection, but it would be easier to add earth connections and more RCDs.

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