Circuit breakers and fuses

[catsketcher]

Thanks everyone for your considered replies. As I built the boat I am the only one to blame for the current state of the wiring, which all works okay. I will keep on working through my new panel ideas but still come back to a question based on my original query. If I need a fuse (rated carefully to protect the appliance) and I want all fuses to be easy to find (like a few of the nice boards shown above) in one easy place (right next to the switches) why do I need a breaker too (apart from the windlass and other high current loads which have their own breakers near the battery)? Or are the breakers now used as switches?

[Lake-Effect]

Originally Posted by catsketcher

If I need a fuse (rated carefully to protect the appliance) and I want all fuses to be easy to find (like a few of the nice boards shown above) in one easy place (right next to the switches) why do I need a breaker too?

As long as the chosen fuse value protects both the device and the wiring, then the short answer is: you don't need a breaker too.

The main reason someone might not want to do this is because of the number of things you need to supply DC power to, because you'd be pulling wire from every device to the panel. So lots of wire, lots of fuses, and probably lots of switches at the panel.

The more usual way boats are wired is by sections. Eg for nav gear, one breaker (labeled NAV EQPT), properly sized power wires going to the helm pod and the nav station, then a fuse panel (or inline fuses) at the pod and at the nav station to feed gear, NMEA backbone, etc.

[Time2Go]

Originally Posted by Scorpius

My goodness: Circuit breakers and fuses in series on every circuit. That certainly sounds like overkill to me. Do you have provision for circuits like the bilge pump, VHF radio, and fan in the head that should NEVER lose power even with the master switch off or a dead battery?

Scorplus,
Definitely a belt and suspenders approach
Yes, There is another fuse block coming off the unswitched distribution
bus bars Before the house switch for Bilge, VHF and so on.
Don't know how to keep things on if all batteries are dead??

Noelex,
This is a refit of an almost 40 year old boat.
The PO made a total and complete mess
The existing panel had a combination of 5, 10, 15, 20 amp breakers
in addition and Im not kidding, connected to load side
of the breakers are red, black, white, green, beige wires
and the main positive feed is Black.
We wanted to be able to mimic what's there until
we get it all sorted, without having to swap breakers in and out/
We were always going to bring out all connections to more
accessible location via an umbilical harness.
Minimal cost difference to use fused terminal blocks
compared to regular terminal strips.
Basically we are using the panel as a collection of on/off switches
with backlighted indentifiers and on/off indicating LED's
The whole project came in at about 1K
Cheers
Neil
PS: What a great forum we have
I'm always learning here

[Boatwright]

3 AG or ATC fuses have several advantages: Simplicity; Cost; Available everywhere

Please keep simplicity as your #1 goal, it makes completion of your project so much easier. I have completely re-wired two of our boats over the years. It's a killer job.

If you are building your own panel on an under 40' boat with simple systems 3AG fuses have a number of advantages:

The widely available fuse holders mount in a drilled hole.

They are compact. Our current panel with 18 individually switched circuits is only 16" x 8".attachment.php

They conveniently allow fuses sized for the equipment, without extra fuse holders. IMO a bunch of in-line fuse holders downstream of a circuit breaker violates the simplicity rule.

[billgewater]

I have changed from circuit breakers to switches and fuses. Each switch has its own light - very handy at night. The LED lights have a variety of colours. It has proved to be cheaper and easier to manage. The switches, fuses and mini led lights and labels are all mounted on a swing out board. The switches are standard low profile rocker switches that are mounted through round holes rather than the rectangular press - in type.

All connections are via bus strips and /or push on terminals. Soldering may sound good but it is harder to do and certainly harder to do at sea.

The important thing is to not tie yourself to any propriety systems. You need to have access to gear that allows modification under your requirements.

The use of clear labels that you can design yourself is also very important. I use one of those home label printers. It is also used to label wires that appear at other places around the boat, plus for other things such as notices around the loo so that landlubbers don't do anything naughty.

A problem with swing out boards is that many wires from the back of the board to the bulkhead or whatever, can make the board harder to keep open, but I have manged this by making a suitable longer loop for the wires.

The difference between house wiring and control systems is that boats are much more complicated. It is because of this complexity, that really good planning and the ability to repair or change circuits becomes more important. A house may have 4 or 5 circuits but a boat may have 20 or more. Labels and indicator lights are much more important. The ability to easily change protection levels (i.e. fuses) is also much more important.

[stormalong]

I have participated in many discussions on this topic. When I saw this latest thread I decided to take some pictures before responding.

My electrical has evolved over the thirty years that I have owned this boat. When I first bought this boat the individual wires from the house wiring came directly to the circuit breaker panel. I chose to add terminal strips and a ground buss very early. The red wire cable harness eliminates a whole bunch of duplex wires going to the panel. When I first bought the boat hinging down the panel caused power interruptions of the circuits. The entire boat was wired with un-tinned duplex wire without enough strands to prevent metal fatigue. Every DC wire in the house wiring has been replaced. Looking at the terminal strips the circuits of the left group are DC. The right side group Is the AC (picture 4). The AC wires are original - they were proper marine wire from the builder. The AC wiring could be neater.

The only fuses on the boat are in individual devices such as Radar, radios, etc.

Something else that has evolved over the years is the high current portion of the electrical system. Shown in the last picture. This is in the engine space. On the right hand side are circuit breakers for the windlass and the main panel. There is a row of circuit breakers across the top for the inverter, and Ham radio loads plus the battery charger, solar and wind power going into the batteries. The black and red above these circuit breakers is a copper buss bar wrapped in heat shrink tube. Partially obscured by the air filter is a pair of three post buss bars (positive and negative) that all power goes through. They are covered by a lexan sheild. Also in these pictures are on-off battery switches for the house and engine batteries, shunts for measuring solar and wind current and a battery combiner (ACR). The battery bank is below and behind the wiring you see in the engine space, under the quarter berth. It consists of six Trojan T-105s in series parallel and a single engine start battery.

Given the constraints of the placement of the batteries and the space available this is my ideal of how the electrical system should be. All of the circuits on the main panel are in use except for one AC breaker. each piece of electronics has it's own, appropriately sized breaker. Other than the sailing instruments and lighting circuits every device is individually protected. The lighting is divided into port and starboard circuits.

In addition I have added lights to the panel using the following scheme: Always on: not lit, OK to be on: Green, Usually off: Red. The usually off category includes bilge pumps, water pressure pump, emergency strobe and propane gas valve. I want these to stand out if they are on. The one exception to this if the panel main breaker - it came with a red light so at a glance I know the panel is powered.

[stormalong]

Somehow my pictures didn't make it into my post above. Here they are.

[KP44]

Originally Posted by catsketcher

Gday everyone

I get that circuit breakers are there to protect the wire and fuses to protect the appliance but why do I need breakers if the fuse is sized lower to protect the appliance?

What happens if a wire shorts to ground before the radio's little fuse? That is where the breaker comes into play. Even though "it can never happen", breakers prevent a catastrophic event when the impossible occurs.

And breakers allow you to quickly and completely shut down a circuit, which is very handy when installing a new radio or adding a GPS antenna.

Ninety percent of good seamanship is in preparation.

[KP44]

"...If I need a fuse (rated carefully to protect the appliance) and I want all fuses to be easy to find (like a few of the nice boards shown above) in one easy place (right next to the switches) why do I need a breaker too...?"

The fuse in the radio's red wire is likely to protect the 18 ga wire, and not there to protect the appliance. Your 15 amp breaker protects your 14 ga wires and the 5 amp fuse protects the radio's short feed lines.

[flightlead404]

Originally Posted by Frankly

[QUOTE Typically the circuit breakers are at the beginning of the circuit, and the fuses close to the appliance. You need the breakers in case the wire gets shorted before where the fuse sits in the circuit.QUOTE]


That observation has more to do with a surplus of lawyers than any electrical first principals.

A circuit can be protected at any point along the path for overcurrent, ground faults and short circuit are best protected at the power source. "Kill two birds ..." If you follow the latter.


Frankly

Well not really. You want the circuit protection device as close to the power source as possible.

Having a fuse or breaker somewhere midstream will not save you if there is wife chafe or something between the source and the breaker/fuse. That will cause a fire hazard in the run between the source and the chafe if it goes to ground.

[flightlead404]

Originally Posted by stormalong

Somehow my pictures didn't make it into my post above. Here they are.

I get a little chubby for wiring installations like this

[flightlead404]

Originally Posted by flightlead404

Well not really. You want the circuit protection device as close to the power source as possible.

Having a fuse or breaker somewhere midstream will not save you if there is wife chafe or something between the source and the breaker/fuse. That will cause a fire hazard in the run between the source and the chafe if it goes to ground.

WIRE chafe, not wife chafe, although that can be bad also

[Frankly]

Originally Posted by flightlead404

Well not really. You want the circuit protection device as close to the power source as possible.

Having a fuse or breaker somewhere midstream will not save you if there is wife chafe or something between the source and the breaker/fuse. That will cause a fire hazard in the run between the source and the chafe if it goes to ground.

Don't think you understand the differences between the basic electrical terms: overcurrent, short circuit, and ground fault.


Frankly

[Lake-Effect]

Originally Posted by Frankly

A circuit can be protected at any point along the path for overcurrent...

Nope. The protection device (fuse, breaker) must be located somewhere between the source of power and the "drawer" of current, whether it's the expected load, or an accidental load, like a short or a wiring error. So, obviously, the closer the protection device is to the power source, the more wiring is protected.

An overcurrent situation that happens upstream of the protection device won't trip that device.

[Frankly]

Looks like you suffer from the same affliction as flightlead.


Frankly