Guess who makes this product; my least favorite boating electronics manufacturer, Xantrax! No wonder this product earned a C. I didn't even know that when I put the grade on the item. It may work. Can't swear it. But I do have two installed. One on each alternator.
I was in the engine room one day and like most people when ever I'm anywhere on the boat I'm looking for potential problems. I look at the back of the alternator and the Zap Stop is in two pieces. The fuse is still good but the wire literally came off the fuse connector. No load was on the line, not tight, simply hanging there, and the wire parted. Lot of good that would have done us.
I still have one Zap Stop on each alternator. I never expect to nor ever hope to have a real need of them. I don't play with battery switches when we're under power, period. But one never knows what someone else might do.
Further to complicate matters this is sold as a marine product and you can see in the picture that only one wire is in fact a tinned marine grade but the one wire exiting the fuse is only copper and I'm guessing the other one is too. Zap Stop Grade C