Not mentioned, but even better, are the split powertaps available from Maretron and elsewhere (Furuno and maybe Airmar, I think). Garmin goes on to show how the situation can be fixed by putting the powertap in the middle of the backbone and thus halving the effective wire runs. The diagram below, found in Garmin’s NMEA 2000 Fundamentals ( PDF here), usefully illustrates a fairly modest N2K network that will suffer too much voltage drop at one end. Which is why some manuals, like Garmin’s below, go to some trouble regarding powertap placement… Electrical resistance is dependent on wire size - DC especially so (hence the fascinating “ War of Currents“) - and the few DC wire tables that even include 22 guage don’t look good. Its well insulated power wires are apparently perfectly safe (despite some internecine standards organization hubbub on that score) but they simply can not carry much DC juice very far. As discussed on Monday, the popular ‘light’ (or Micro) size NMEA cables only contain 22 AWG power (and data) wires. I think I got this diagram right, and I think it’s important to understand if your boat might end up with more than a few NMEA 2000 powered devices on its network.
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