The Yandina Owner's Manual (
Owner's ManualPDF) describes one of my primary reasons for NOT installing an ACR: the need for additional fusing (see FUSES & CIRCUIT BREAKERS on pg 2). It says:
"Fuses in the battery leads to the combiner only provide protection from a short to ground on the battery cables themselves which must pierce the insulation. Conduit covering can reduce this risk.
If it is a metal vehicle and the unprotected cables are close to grounded metal the risk of a short is much higher and fuses may be a good protection. The size of the fuses has to be much higher than the charging current available because when the combiner first closes quite large currents can flow from one battery to another. These battery to battery currents are limited by the wire gauge and length of the red wires which must not be shortened. A slow blow fuse of approximately 30% to 50% of the total Cold Cranking Amp capacity of the batteries in the smaller bank is a guide to value. Although the risks are minimal without a fuse, the results of an accident can be catastrophic and even life threatening."
If my two battery banks were located in the same, or adjacent, compartments, I wouldn't worry about chafing/shorting of the ACR cables that connect the two banks. In reality, they are located about 8 feet apart and the wires have to transit several separate compartments (where chafing may not be visible). The largest of these compartments is the engine compartment and engine itself (and another houses the aluminum fuel tank). Since the engine IS the ground for the boat, to me, the "metal vehicle" warning applies here.
The CCA capacity of one of my batteries is 700A. Yandina recommends a 210-350A fuse in this case. But, In no way would I expect a 350A fuse to protect the positive wires Yandina uses on their ACR--the gauge looks way too small to handle 350A (or even 200). I think the wires would fry first if shorted.
In other words, to add an ACR without adding to the risk of shorting and electrical fires may take a bit of engineering and some additional hardware. For me (with batteries banks separated by several compartments), the OFF/1/2/ALL switch seems a safer & simpler bet.