We have a 4 bank breaker panel, with 10 positions per bank, for a total of 40 circuit breaker positions.  How on earth does a small 37' sailboat use up virtually all of them?  

As I found, it may have to do something with the echo chamber that is the internet.  So this post won't be about the gizmos and gadgets.  Or the minutia of DC components, 12V vs 24V systems, etc.  You can find that everywhere.  What this post is about is how we decided to do things a little different, and in deciding to, we've vastly simplified the electrical wiring on our boat while making her safer and easier to maintain.

The Same Information, A Million Different Ways

Example of The Type of Information You'd Find Everywhere. Most of it is just rehashing the same information.

When we were first surveying Petrichor, I was impressed by the documentation and labeling of all circuits.  Granted, I was a bit naive to marine electrical and ABYC standards in general.  But everything appeared to be in good shape.  Included with our boat were spreadsheets listing out every circuit, their ampacity, voltage, current rating, and what they were.

I didn't have much experience with the practical implications of how Petrichor was wired, but it seemed simple enough.

I had done a lot of reading from everywhere I could find in print and on the internet; consulting our boating friends and mentors, everything seemed to be in agreeance.

Though now that I think back to it, most of the stuff we read in print was outdated - books take time to write, print, publish, and distribute.  Most times, the best you would get is an updated edition from a year or two ago.

What I had found and read on the internet was an echo chamber of the same information dispensed in slightly different ways.  The ideals of the free exchange of information that is the internet also doesn't distinguish between plagerism and the rehashing of the same information for the purposes of things like SEO (aka gaming search engines to get more hits).

The best reference that I could find was ABYC E-11 from 2008.  It lays down 78 pages of best practices and standards - something an engineer can work with! Though on second thought, it's from 2008 - over a decade ago.  Surely, a lot has changed since the publication of that specification.

I had printed out as many articles from reputeable sites as I could find, like:


I didn't limit myself to just Marine electrical.  I also read on more sensitive applications, such as Aviation where a mistake or two would definitely put us in perile:

The list goes on and on, not to mention endless forum threads:

One Breaker Per Curcuit

So back to the original question: How on earth does a small 37' sailboat use up virtually all of them?  

It's because the simplest of implimentations is always done - you wire up one breaker to its own circuit.  Simple enough.  But what does that mean in a practical sense?

It means a lot of wires running throughout the boat.

For brevity, I'll stick with just the most common type of wiring: 12V DC.  The simplicity of 12V DC means that the battery banks supplies 12V (actually, it's anywhere between 10V and 16.4V, but we'll leave that for another article), and to power something, just connect the red wire to the positive side, and the black/yellow wire to the negative side.  

Yellow is ABYC standard for boats.  It's often called safety wire... since AC uses White (Neutral)/Black(Hot)/Green (fault ground).  If you mistook a black A/C wire for a black DC ground wire, you may be in for a bit of a shock.

Consider all the different gadgets and gizmos that make a boat both comfortable and afloat:

  • Mast lights (required)
  • Navigation lights (required)
  • Bilge pumps (safety)
  • Water pumps (comfort)
  • Cabin lights (safety)
  • Cabin fans (comfort)
  • Stereo (comfort)
  • Refrigeration (comfort)
  • Battery Chargers (potentially AC and DC)
  • Inverters (comfort/convenience)
  • Bilge Alarms (safety)
  • Propane Switches (safety)
  • Alarms (safety)
  • Chartplotter (required for majority of boaters)
  • etc...

There can be tens or hundreds of devices.  All of which have at least 2 wires (some have a chasis fault ground) to power them.  So for example, if you have lights in your main cabin above the settees, for reading, general lighting; that would mean something like 10 potential lights and 20 wires.  They would all have to be routed back to the breaker panel or an unprotected bus bar that combines all the components.

Now you want fans for the hot days when you're not on shore power.  I can imagine you'd need 2-4 fans.  That's another 8 wires.  We're up to 28 wires now.

Granted, they're low voltage wiring... so 18 gauge wires, tinned and stranded (ABYC) - but you can see how you can get to hundreds of wires for the main cabin alone.

All of them would be routed around to keep them neat.  And they would all be bundled together.  So yes, while it was nice that the ends of the wires were all labeled, hundreds of feet of wiring would be bundled together without knowing what is what.

If one device shorts, it can melt all the insulation on the wire powering the device; and it would also melt the insulation of all the wires bundled with it - effectively bonding them all together.  What a nightmare.  It violated Petrichor's principals of:

  1. Safety - Nothing takes priority over safety, especially asthetics
  2. Inspectability - Everything must be easily inspectable

Is there something that can be done?

Turns out, the answer is yes, something can be done about it - though it requires a lot of work.

Zoning Out, Sub Panels In

Taking a page out of home wiring, you can indeed help mititgate the problem.  You can do it by creating different zones in your boat.  For each zone, put in a sub-panel.

What that means is that now, instead of having a breaker position for main cabin fans and another for main cabin lights, you simple have one breaker called "Main Cabin Power."  And another for "V-Berth Power;" and another for "Head Power."  Just separate out the different cabins into a zone that needs power.  You've just gone from 20 breakers down to just 3.

From there, you now install a sub-panel in the most convenient location in the each cabin.  You can have a single run of 4-6 AWG wire (it's now very important to size the wire properly for the amount of power which may be needed) from the breaker to the each cabin's sub-panel.  Then, you wire your gadgets and devices to the sub-panel; individually fusing them all.

Now, you have a fuse at the main breaker in case the cabin draws too much power and a fuse for each component placed much closer to the component itself.

And that's exactly what we decided to do with Petrichor.  She came with a 40 position breaker panel.  When we started, every position was taken.  When we finished, we had an extra bank of breakers which turned into our always on breaker panel.

It takes a few more components and the wiring isn't quite as easy as 1 breaker per curcuit, but it really simplifies things.

Breakers will no longer be used as single pull single throw switches that get flipped on an off constantly - increasing their duty cycle and wearing them out sooner.

When someone's in the v-berth, just flip on the v-berth breaker to power that cabin.

If something isn't working in the head, check for a blown fuse in the head; or turn off power by flipping off the head breaker and trouble shoot at the head sub-panel.

The rest of the boat's components, be it for safety or comfort, can continue to be powered.

The number of wires running the length of and snaking about the boat is reduced from hundreds to just 10 or so.

With the always on bank of breakers, it's pretty dead simple... every breaker on the always on bank should always be on.  If something shorts out in that bank, anyone regardless of knowledge about electricity can be quickly trained to spot it and to sound the alarm.

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mostly #dc boat #rewire of breaker panel complete. i'll need a handful of blanks to cover the new open positions... but #before - we had 2 #shore powers and thus 2 #AC #buses. but with no charger/inverter; no microwave; and no water heater, our AC needs go way down to just 6 circuits. #after - i reordered the AC circuits to group up outlets according to its positiononthe boat bow to stern; removed a bunch of wiring for #shore 2 plug; and we freed up an entire bus for a separate "always on" DC bus so we dont confuse it with the circuits that are on the main dc breaker. i'll need to get a couple new labels, but i kept what we used to have for habits sake. only took about 4 hours, but it was in 95 degree heat with all power turned off. aaand now there's a rediculous amount of air gap separating the DC and AC buses. #sailboat #sailboatlife #electrical #sailingaroundtheworld #svpetrichor #fixerupper #refurb #beforeandafter

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