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EV Charging Calculations

Rach J

This is in relation to Annex A722.

The calculation for minimum resistance to earth for a three-phase charging installation in A722.3 Earth electrode resistance is:

Note that Im is the maximum neutral current as calculated in A722.1.

And if  or the calculated RAev is >200Ω then the above equation should be ignored and the max RAev is 200Ω.

Just from logic and by reading the second requirement, it seems to be that a normal situation would be for Im to be < 70(IL1 + IL2 + IL3)/U0Cmax. However, if that is the case, then in normal situations the required maximum resistance to earth comes out as a negative number.

Am I missing something here?

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    but that exception has been removed now

    Other here will know more of the intention of the committees, so wait to say what they have to say, but my guess (based on almost the same formula being present in the 2018 version) is that the intention was to keep it in, but the juggling of the words didn't quite come out as intended. There have been a few instances of that sort of thing over the years. What's the old saying about being originally written in good English but thereafter modified by committee...

       - Andy.

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  • 0

    but that exception has been removed now

    Other here will know more of the intention of the committees, so wait to say what they have to say, but my guess (based on almost the same formula being present in the 2018 version) is that the intention was to keep it in, but the juggling of the words didn't quite come out as intended. There have been a few instances of that sort of thing over the years. What's the old saying about being originally written in good English but thereafter modified by committee...

       - Andy.

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