12 Vdc Distribution and Branch Circuit Schematic Review

[Dave0963]

I've just bought a1974 22' Tanzer with a poor electrical system (no fusing, lots of tape, wire nuts and abandoned wires). I've used the ABYC Tables for ampacity and done the calculations for Voltage Drop and Derating for bundled wires, given conductor length and temperature ratings of the insulation.

The kicker motor is a pull start, so there is no electrical for an engine and also there is no provision for shore power. I will add a solar charger at a later date tied directly to the Pos and Neg Buses.

A question I have not been able to resolve is regarding fusing. I believe the fuse size is a function of the conductor size, ie the fuse is intended to protect the conductor. Many sites suggest selecting the size of the fuse to protect devices. From an electrical perspective, I don't see a safety issue with using an "undersized" fuse. Can anyone provide insight on the matter or a snippet of the ABYC Electrical Code that addresses use of fuses.

I have attached a copy of my Schematic and Panel Directory, is it appropriate to ask for input on my design?

I've tried to keep my Branch circuit ampacities low (below 2 amps) where possible to decrease voltage drop. I believe 14 awg is required for the Anchor light and also for the VHF (transmit ampacity is large).

Thank you for any and all feedback.

 

[kappykaplan]

I believe the fuse size is a function of the conductor size, ie the fuse is intended to protect the conductor.

Yes. Welcome to the forum!

 

[dlochner]

The Tanzer 22 is a great little boat. I owned 2245 for a long time and sailed it on Lake Ontario. There are days I wish I had her again.

The wiring looks good. The one change I would consider is using a larger gauge wire from the batteries to fuses. While 10ga can easily handle the amps, the distance may cause some unwanted line loss.

Fusing is always done to protect the wire, which means the fuse should be smaller than the rated amp carrying ability of the wire. Many electronics come with an inline fuse and recommend a small 2 or 3 amp fuse. This fuse is to protect the device from any power surges on the line, which is a separate issue. The main battery fuse should be within 7" of the positive battery terminal unless it is covered in a flame retardant sheath, then you get 60" (IIRC).

Are the lengths you show one way lengths or round trip?

ABYC has a "recreational boater" membership that is free. It is time limited to about a week and gives you access to all the Standards. These are read only, however, with a little tech savvy they can be downloaded.

 

[jssailem]

Welcome to the forum.
Nice schematic and fuse plan. Yes as @kappykaplan indicated, the fuse is for the wiring.
Only thought I had was, where do you need to have the information on your batteries. I have mine right next to the switch I use to turn the batteries on. I check it before or when I power up the system. You indicated you are going “solar” makes sense now a days. You may want to look in to a Charge Controller. It helps maintain the best voltage for your batteries. Straight solar can swing from more than is recommended to nearly nothing.

 

[pgandw]

IF your circuit goes to a SINGLE device (load), you could get away with using a smaller fuse at the panel to protect both device and wire. I really dislike device in-line fuses "somewhere near" the device, especially on smaller boats where even boat yoga won't get you the access you need.

But the moment a given circuit has more than one device, you have to fuse the wire at the panel, not the device. Then separately fuse each device in the circuit.

The other problem with a single fuse at the panel is will you (or subsequent owner) remember that there is no device fuse when you go to add a 2nd device on the circuit, see the wire is adequate for a bigger fuse, and put the bigger fuse in?

Fred W
Stuart (ODay) Mariner 19 Sweet P

 

[dlochner]

But the moment a given circuit has more than one device, you have to fuse the wire at the panel, not the device. Then separately fuse each device in the circuit.

Circuit Interruption devices (fuses, breakers etc) always go near the source of power, which can be the battery, the panel, or bus. The only case where this is not true is a wire from a regulated power source and the wire can carry the maximum amount of current the source can produce. This is usually a solar panel, battery charger, or alternator. In these cases the fuse needs to be at the connection to the unregulated power source (battery).

On branch circuits where the wire size gets smaller, a CI needs to be installed at the point where the branch starts.

 

[Stu Jackson]

BlueSea is a very helpful company and has a great website.

https://d2pyqm2yd3fw2i.cloudfront.net/files/resources/reference/20010.pdf

More here: https://www.bluesea.com/support/reference

 

[Foswick]

Circuit Interruption devices (fuses, breakers etc) always go near the source of power, which can be the battery, the panel, or bus. The only case where this is not true is a wire from a regulated power source and the wire can carry the maximum amount of current the source can produce. This is usually a solar panel, battery charger, or alternator. In these cases the fuse needs to be at the connection to the unregulated power source (battery).

This is correct - no disagreement whatsoever, but I think a point of clarification might be important for people that might not quite understand circuit design, just yet. To be clear: the critical design consideration is that circuit protection goes just upstream of the conductor it is trying to protect and not putting it close to the source.

What Dave wrote about putting circuit protection near the power source is exactly how most marine wiring ends up laid out, since we’re usually protecting an entire branch circuit from the panel outward.

Strictly speaking, though, the fuse or breaker should go just upstream of whatever conductor it is trying to protect. If that is the entire branch circuit, then the protection goes close to the source because everything else is downwind - not because the guiding principle is to put protection near the source. (I'm hoping that distinction makes sense and doesn't just muddy the waters.)

When we are talking about entire branch circuits, the end result is the same - the protection goes near the source. But, for example, if you peel off a short lead to a single device on smaller wire, that little run becomes its own protected circuit and the inline fuse belongs right where that smaller conductor starts. In effect, that point becomes the source for that little circuit - making Dave's statement still technically correct but maybe misleading if a person only thinks of the "source" as the main source as in the battery or panel.

Just adding this in case it helps anyone picture why an inline device fuse (for example) may not sit at the "main" source but is still correctly placed. Dave covered this in another post.