Given the voltage drop at the pump, yesterday evening’s project was to wire the pump with 8 AWG (10mm sq) for the positive feed, and a bit of 2 AWG (35mm sq) for the negative feed.
Unsurprisingly, the pump worked very happily, and the clamp ammeter gave me glimpse of ~10 – 11 amps of max draw; looked like inrush current.
I’m not sure I’d recommend my cabling technique, however.
That little UNI-T meter is very nice; the clamp feature is useful for things like this, and the auto-ranging voltmeter and ohmmeter capabilities are neat. It’s a UT210E.
Dad looked up the values in a boat electrics book (I have one too, but it’s packed away in a box somewhere), and we concluded that for the 6 metres of cabling (two 3 metre legs) over 10 AWG / 5mm sq should be fine (if not overkill).
We also checked the max draw over the feed to the wiring locker, and concluded that the 20+ amps that get pulled over the 7 metres of cable are too high for the cable size, so it’ll need replacing. I can replace this cable first, with 6 AWG, and see if the pump gets happier. If it doesn’t get happy enough, I’ll do the dedicated run via the battery compartment instead of via the wiring locker.