To further the question, can the 12V supply be from two points?  The main supply (everything on) supplied via the navigation switch at the power panel, and the mini-part being powered by an always on supply near the devices.  The difference in the two being caused by wire length voltage drops, all sourced from the same house batteries.

You can isolate power on different segments of a N2K network.  As in, just one data network, but different sections with their own power.  There are power taps that'll do this.  Even ones that are one physical connection to the network but with two separate 12vdc connections. Along with being able to block power being sent out one side.  

But you'd really want to have a clear grasp of how your network is wired and that it's operating smoothly.  That and being careful about any displays or devices that might be dynamically configuring themselves based on other devices always being present.

@mresman sure, you can provide heavier gauge wire to bring proper voltage to other points on the network and use a power tap to 'inject' it there.  They could be powered through the same breaker if that was desired.  

I have my N2K network on a breaker called "instruments" and that's separate from two other upper and lower helm breakers.  This way I can power my depth sensor and lower helm station displays from the 'instruments' breaker and have that data visible when we're anchored out, without having the much more power-hungry chartplotters also running.  It does power all my n2k devices, so I'm not being as 'power stingy' as I could be.  But that was a trade-off against running more 12vdc wire and adding more taps.

Bill hit the nail on the head with his mention of power isolators. You have options like Ancor's power isolator ( https://www.ancorproducts.com/en/270113) or Maretron's power tap, which is self isolaing with two power feeds, one going in each direction ( https://www.maretron.com/products/pdf/Micro%20Cords%20Tee%20Pwr%20Datasheets.pdf ). 

Bill's caution about devices that reconfigure themselves based on other devices is a good one. But, if you're just going to power a very small number of devices all the time you can just verify these devices work well together and then power up the remainder when needed.

-Ben S.

Nice!  This looks like what I am looking for.  I understand the concern about instruments identifying sensors, but my MHU side will be pretty simple (MHU + Triton) and it will always be engaged when the rest of the system is operational.  There is no second MHU.

Thanks!