Quote:
Originally Posted by CharlieJ
In my explanation at #12, a better word than “alternate” would be "redundant". That is the intent of the Standard and what is shown in A31 Figure 3.
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That is profound. I don't know how I missed it in prior looks at Figure 3, but I've missed the forest for the trees. The key point is NOT the case ground -- it's the negative! If, as I would have often done, the case ground goes to the main DC negative bus (it does) and the
Inverter negative goes to the main DC negative bus (normal practice for virtually ALL negative leads), it's not really redundant (in what I assumed to be a "normal"
installation, the case ground and the DC negative would share a common wire from the DC bus to the shunt (with two terminal ends in common), the shunt itself, and the cable from the shunt to the
battery negative, again with two terminal ends in common. That's the same amount of "common" that I proposed by treating the
inverter negative as a "bus" -- they would share the connection to the bus, the cable from the bus to the shunt, and the cable from the shunt to the
battery negative.
However, a close look at the diagram shows it IS redundant, with the only commonality the battery negative terminal. They show the negative going DIRECTLY to the battery negative. No bus, no shunt, nothing. Inverter ->Battery. I hate doubling up on the battery post (two 4/0), but there it is.
I'll have to carefully re-read A31, but I don't think they address this in the document body. The picture is worth 1,000 words!