So I am installing two hds 12's and a point 1 antenna full neama network with dedicated power.

I'm running power from batter to switch on dash then to a power block under console, it's a blue sea 6 fuse block with 6 gang ground. Each unit and neama will be powered from the block.

My first question is do I need to fuse between battery and switch and also fuse between switch to power block or will fusing one of those work?

Second question is do I need to fuse each power cable to each unit, or will the fuse in the block work?

If it's a true fuse box then it should be fine going to the graphs, but make sure you put the right size fuses in each spot. The 12's use a 5amp, I have no clue what the nmea network needs for a fuse size.


Yes put a fuse by the battery between the battery & fuse block, it's there in case the wire decides to melt.

I like and use the 6 gang Blue Sea fuse block you describe. Excellent choice for getting quiet isolated power to the electronics. Each of the fuse connections you use in the fuse block replaces the need for the inline fuse holder that comes with an HDS unit. the 5A fuse is correct for the HDS 12s. NMEA can use a 3A fuse. Put 5A and 3A fuses in unused fuse block locations as readily available spares, not that you should ever blow one.

Our electronics power is considered a critical application. For that category, #12 wire can support 20A with no more than 3% voltage drop at 10 feet. #10 wire can support 30A under the same circumstances. I always use #10 wire so that I have the option of 12V receptacles for floodlight, etc. on the fuse block as well.

You need only one fuse for the wire providing power to the fuse block. That fuse goes close to the rear end of the wire in the battery compartment. That fuse should be no larger than the 20 or 30 amp stated above depending on wire used. I never go above 25A even with the #10 wire. That fuse will protect the entire run to the fuse block.

I do not like your idea of a switch at the dash. You were off to a good start until you added this idea. WHY do you have that in the first place? It will add multiple contacts, which have resistance and therefore affect voltage delivered to the fuse block. You should have a switch that supports at least 20A if you want to be safe and allow for expansion on the fuse block. You won't find a dash mount switch rated for that load, trust me. Firmware based electronics should never be turned off by killing power just as a computer should never be turned off that way. (Call Lowrance if you don't believe me.) All this says no fuse block master switch at the dash so you don't accidentally crash the HDS units.

What you may need (at most) is a power switch for the NMEA network power. Do you have a master battery switch in the battery compartment? If so, you get your power from the on/off side of that switch (not the battery) so that when you shut down the boat by turning off the battery switch, you also kill the NMEA power at the fuse block, which is a very small drain typically. If you have such a battery switch you will not need ANY switch at the console at all for any reason.

If you do not have a battery switch in the rear compartment, the + lead from the 3A fuse for the NMEA power should connect to a simple two contact on/off switch at the dash. The NMEA + power lead also connects to this switch. You would use this to turn off the NMEA power. NMEA GND goes direct to the fuse block GND. HDS units are always shut down using the Power-Down button on the unit. That covers turning off power for everything, but WITHOUT the power feed going through a switch that doesn't exist.

The advice provided herein is not an internet/forum rumor, hearsay, or an old wives' tale. You're getting it from a bonafide electrical engineer, free of charge.....

It makes me shiver to think how many people have their boats wired without the advice of an electrical engineer.

grout, while it's not necessary, doing the wrong thing or heeding wrong/kooky advice can certainly lower reliability substantially and invite downright failure. In decades of tinkering with boats and even consulting with dealers on electrical rigging I've seen some very bizarre things and lots of stuff that was there because someone DIDN'T know what they were doing....

Thanks a ton. I will rewire without using a switch. I appreciate it.

I was close to having it spot on! Not bad for an insurance guy!

Yes, you did good. Just be sure that you get the NMEA where it can be turned off - either by a dedicated switch, or by having all the power for the fuse-block come from a battery switch under the rear deck. I do not want to be the cause of your battery getting killed.