My systems monitor (Blue Sea M2 VSM 1850) came with one current transformer. A CT is a round ring with 2 wires that you put one leg (wire) of the power supply through. It gives me the amperage draw on one leg of the 220v shore power. I wanted to see the total current draw so I added a 2nd CT on the other leg. My boat uses 50 amp single shore power. This also worked with a split cable to (2) 30 amp breakers. The problem was that the CT wires are not labeled, so I tried every combination until I found the only one that worked. *See attached diagram. Rich & Sandi Vaughn M/V Ocean Lady 1990 Ocean Yachts MY48 Quincy, MA
BTW, with only one CT on one leg, the polarity of the CT did matter. Although it read a current, it wasn't correct when compared to the reading on my DC current clamp meter, but the proper polarity read correctly. Someone else suggested this on Amazon for $18 ($36 for 2) for shore power amp monitoring. https://www.amazon.com/CrocSee-CRS-022B-Frequency-Multimeter-Transformer/dp/B07K3S4K9L?th=1
