Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

For all anglers who like to go afloat to catch their fish
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Duncan Holmes
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Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Duncan Holmes » Mon Jun 10 2019 14:43

Circuit Protection

The level of current or amps drawn from the battery are restricted by the resistance within the components in the circuit. If the circuit is connected but there is a very low resistance the current flow becomes restricted by the battery, this is what happens when a short circuit occurs. Short circuits happen when there is direct connection between positive and negative, through a component failure or damage (missing) insulation.

The battery will be capable of delivering amps much higher than the wires attached to it can safety manage, and the wires will start to heat up. What effectively is created is a long thin electric heater running around the boat and is likely to start a fire. It is important to include either a fuse or resettable circuit breaker within the circuit, this will disconnect the circuit if the current flow is higher than rating on the fuse or breaker. To calculate the size of breaker required add up the maximum current of each connected component and select the next size up of breaker or fuse, with a minimum of 1.25 times the total current draw. If you are running multiple high draw components such as electric outboard and anchor winch, it is better to split the circuits with multiple breakers, otherwise the breaker/fuse size will be higher than cables can manage.

The breaker/fuse should be positioned as close to the positive terminal of the battery as possible to reduce the length of cable that is unprotected. Cables between the breaker/fuse and the component should be sized to match the breaker between the cable and the battery, this may mean you have more than one fuse/breaker or combination of both.
Components should have a fuse/breaker the next size up from the rating of the component.

Calculating Cable Sizes

Cables should be sized correctly to ensure that the required current can flow safely and efficiently. Referring to the water analogy cables act like the pipes in a water circuit, a small pipe restricts flow, a small cable restricts current and causes voltage drop. If the cable restricts too much current it will start to heat up and if it gets hot enough will melt the insulation, either causing a fire or a short circuit.

At a minimum a cable should be sized to safely carry the current, but it is better to size the cable to also reduce volt drop as this leads to a more efficient circuit and increased battery usage. Ideally a 3% or less volt drop will give good efficiency. As cable length increases the resistance in the cable increases, therefore the cable size must increase to offset this.
Cables are sizes are referred to using different measurements, it is important not to confuse the actual diameter of the cable with its cross-section area of the copper conductor. For cable sizing, information and description of cable sizes measurements, see the following link.

https://www.12voltplanet.co.uk/cable-si ... ction.html

Positive and negative cables should be identical size.

Switch Gear

As well as a circuit breaker, the circuit should also include at least on isolator or switch to enable quick disconnection of the circuit if required.
Something like this is ideal for small open boats

https://www.12voltplanet.co.uk/marine-b ... nuous.html

Dependant on the complexity of the circuit and how many components are attached it maybe convenient to use a fused switch panel. The panel can be supplied using a larger cable that is suitable for the total load and the distance from the battery. Inside the panel are fuses or breakers, which allow the cable size to be dropped suitable for the attached component.
Something like this is ideal for small open boats

https://www.12voltplanet.co.uk/6-way-wa ... panel.html

All switches should have a current rating at least 25% higher than the component will draw.

The diagram below shows the cable sizes, and breaker fuse ratings on my simple small boat set up.

Boat Circuit.png
Good Wiring Practice

Boats create a lot of vibration so it is important to use tight fitting connections and cable protection to avoid circuit failures. All exposed metal contacts should be covered, ideally with shrink tubing or plastic/rubber covers. When routing cables through bulk heads, rubber grommets should be used to protect the cable insulation from wearing on the edge of the cut out.

Ideally positive cables should be red and negative cables black, but if you only have one colour a red or black marker should be put on the cable at the connection point.

As part of a maintenance schedule, screw down connectors should be checked for tightness, loose connectors cause arcing and reduce efficiency in the system
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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Danoutdoors » Mon Jun 10 2019 15:04

Top stuff, thanks for sharing all that Duncan๐Ÿ‘

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Kev Berry » Mon Jun 10 2019 15:09

Very helpful Duncan :thumbs: :dizzy:

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Cyprio » Mon Jun 10 2019 15:44

Great threads Duncan :thumbs:

Forum Admin should make them sticky threads for the boat section :cool:

Save using the flakey search function to find them as they slip down the board.

Andy

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Edward.P.A.C » Mon Jun 10 2019 16:05

Cyprio wrote: โ†‘
Great threads Duncan :thumbs:

Forum Admin should make them sticky threads for the boat section :cool:

Save using the flakey search function to find them as they slip down the board.

Andy
+1 :thumbs:
Awesome thread(s) Duncan. :cool: :handshake:

And all that is why I'll pay someone (qualified marine electrician) to do my electrickery.....cos as far as Im concerned its all "white mans magic".....confused as fook.com
Last edited by Edward.P.A.C on Tue Jun 11 2019 13:11, edited 1 time in total.

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Duncan Holmes » Mon Jun 10 2019 17:50

Thanks gents, got a couple more parts to finish off, and I will be able to give an update on the the lithium once its had a winter in the boat.
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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Mike J » Tue Jun 11 2019 11:04

Hi Duncan.
Great post as its a minefield especially for anyone just starting out.

I assume you are a professional and only wish to advise using the best products available but it might be an idea to include a few of the cheaper alternatives to what are to many, are overpriced marine components?

Eg; domestic switches, oversized auto wire, soldering connections, filling basic heat shrink with hot melt glue, installing low cost fused switches on a board mounted inside a food container that has a sealed waterproof clamp closure, the use of paint-on electrical sealant https://www.force4.co.uk/starbrite-liqu ... black.html

I have also used different coloured (automobile) wire for each circuit to enable fast tracing should a fault occur and need solving while afloat.


Ben a Sticky would be perfect.

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Cyprio » Tue Jun 11 2019 11:40

With respect Mike and not wanting to darken this thread, :no: which should be made a sticky. :thumbs:
If you use the correct materials for the job, install the correct guage wire for the circuit & plan where the cable runs, securing along the way. You wouldn't need to fault find.
Theres no place for domestic switches bodged into Tupperware containers on a boat. I'm sure you wouldn't
Get a safety certificate with that sort of install.
Marine wire may be expensive but it is not the same as auto wire or domestic cable.
The strands are tinned to assist in corrosion resistance, the cable insulation and construction of the core is
Designed to allow a flexible approach to your install allowing the cables to follow the contours better than
Standard stiffer cables.
You don't need to fill heatshrink with glue as they now make it with or without glue..

Ps
Happy for the mods to delete these last two threads.
I think there an insult to Duncan for the time and
Goodwill that he personally donated to help those who would like a better understanding of boat electronics.
Cheap is not always best and for those who are not the best with wiring only want to install once!
Andy๐Ÿ˜ก

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Duncan Holmes » Tue Jun 11 2019 12:41

Mike J wrote: โ†‘
Hi Duncan.
Great post as its a minefield especially for anyone just starting out.

I assume you are a professional and only wish to advise using the best products available but it might be an idea to include a few of the cheaper alternatives to what are to many, are overpriced marine components?

Eg; domestic switches, oversized auto wire, soldering connections, filling basic heat shrink with hot melt glue, installing low cost fused switches on a board mounted inside a food container that has a sealed waterproof clamp closure, the use of paint-on electrical sealant https://www.force4.co.uk/starbrite-liqu ... black.html

I have also used different coloured (automobile) wire for each circuit to enable fast tracing should a fault occur and need solving while afloat.


Ben a Sticky would be perfect.
I'm not a professional in Marine Electronics, and have no vested interest or links to any of the links I posted. I was previously been a professional in DC electrics in another field, designing and building DC systems up to 1000v. Sure I would only ever advise that someone uses the correct components for the job, marine electrics are designed to cope with constant vibration and damp environments, domestic and automotive equipment are designed for completely different environments.

Having been called as an expert witness in a fire that was caused by use of AC designed switch gear used in a DC circuit, I would strongly advise anyone from using "domestic" products in boat electrics. DC electricity is a completely different animal from AC and potentially far more dangerous, a fire on a boat is a very bad way to end your days fishing.

I am sure there are plenty of boat electric "hacks" that can be used and I am sure that would be an interesting thread and useful to some, but they aren't something I am going to recommend or discuss, especially in writing, on an open forum.

Your use of different coloured cables for different components is a very valid point and certainly in more complex installations using wiring looms or on larger boats this would be good working practice, however on small basic systems that perhaps have 4 or 5 circuits at most it would be a bit overkill.
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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Will Smith » Tue Jun 11 2019 22:09

:thumbs:

Will.

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Ben » Wed Jun 12 2019 12:38

Iโ€™ll sticky them now ๐Ÿ‘๐Ÿผ

Although maybe over time there should be a sub-forum called Boat FAQs
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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Ben » Wed Jun 12 2019 12:41

So detailed, thanks for doing this Duncan
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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by Mike J » Fri Jun 14 2019 07:13

Thanks for your response Duncan.
I agree with your advice especially from a professional viewpoint.
Perhaps the securing of all wiring is something you may wish to consider?

Fires on boats do happen and its not unusual for our lifeboat to rescue 2-3 crews each summer when someones pride and joy starts to burn, the last, a newly constructed 8 man cruiser, was barely a mile from the quay when a fire sunk it before anying could be done but save the crew.

Experience of battery isolation switchgear suggests some can be suspect, but not so with Vetus or Blue Sea components.

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Re: Basic Electrics for Boat Anglers - Part 4, Cables and Breakers

Post by ranabat » Mon Jun 24 2019 09:51

Duncan ,
Thank you for the time and effort you have put into that.
Very much appreciated.
Dave G

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