Re-reading the Victron document “Wiring unlimited” I stumbled over the following sentence in chapter 7.7 regarding grounding of ESS systems:
“The DC ground cabling should be able to carry a fault current at least equal to the DC fuse rating.”
I cannot quite understand where this requirement comes from, (and if the word “should” means “must” in this context).
Obviously it means, that there exist fault scenarios where all DC current will run through the grounding cable until the DC fuse blows. But I can’t think of any.
For the maximum DC current running through the grounding wire, one end of the wire has to be connected to the negative pole of the battery, and the other end must be connected to the positive pole (behind the DC fuse).
How could this possibly happen?
In a standard installation neither of the battery poles is connected to ground.
Even in a fault situation, where one pole is accidentally connected to ground (e.g. by short circuit), the other pole still needs to be connected to the other end of the grounding wire.
Or is this sentence just a “safeguard” for Victron to say “if anything, however improbable, happens, the grounding wire will never burn, since it can withstand the maximum current in the whole system”.
Any feedback on this (possibly from Victron themselves) would be very much appreciated!
You have to check local laws/regulations if grounding the battery is allowed/required.
Grounding the battery bypasses the galvanic isolation between DC and AC which is part of some certificates (German ESS certificates for example).
Not everything written in “Wiring unlimited” applies to every system everywhere in the world. The installer always have to check the local laws/regulations.
However, this does not answer my question, which was:
“What kind of fault could possibly happen, to require a grounding cable to carry the maximum DC current?” or rephrased: “Why should the DC grounding cable be so thick?”.
Of course, if DC grounding should be required, this could make any fault condition more likely.
But still, for the grounding cable to have to carry the maximum DC current, the other end of this cable has to be connected to the other pole of the battery.
I still cannot see how this can happen, since this very other end is (and must be) connected to the grounding busbar to accomplish grounding.