Backyard Aquaponics
A place to discuss aquaponics

If I have some decent thick wires running to a load, but they go into a watt metre with thinner wires for a few inches, what happens?

Is it a case of the thinnest bit of wire sets the amount of loss for the total length of wire? Or does going immediately back to thicker wire mean my losses are minimal? The load (trolling motor) came with thick wires, so I'm guessing they are required.

amp meters aka watt meters all use a shunt to drop the current through the meter anyway. The issue is in the way an ampmeter is wired to your system, series means all the current goes through the meter, parallel means some of the current goes through the meter. On my DIY wind turbine panel the batteries, all 12 of them run through the amp meter, so the shunt allows a small fraction of the current through the meter. This is one reason why it is doubtful your new multimeter gives and accurate amp reading. the difference between a watt meter and an amp meter is according to the power formula watts are derived from volts and amps, whereas amps is the movement of current through resistance only. This is why wire size is needed for either measurement. It is also why battery cables are large diameter and house wire size is so much thinner. Voltage goes up, amperage goes down, for the same load. this is why we measure watts