# Should I use an in-line fuse?



## DuckNut (Apr 3, 2009)

8ga wire is pretty stout stuff to wire in a flimsy little fuse, not to mention the increase of resistance from the connection and you could be giving yourself fits.

A marine breaker would be better.


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## topnative2 (Feb 22, 2009)

The motor is fused.


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## firecat1981 (Nov 27, 2007)

The motor should already have a fuse block under the cowling, no need to add more points of failure. 8 guage seems a bit on the light side for me, I'd step it up to at least 6 for that long a run.


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## c_ronius (Mar 16, 2010)

The fuse on the motor protects the motor,but not the wire run between the battery and motor.

A fuse/breaker should be used as close to the battery as possible, in combination with the fuse on the motor.


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## topnative2 (Feb 22, 2009)

Never ever saw one .................never


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## c_ronius (Mar 16, 2010)

Because you are unfamiliar with it does not make it inaccurate. I have seen many.

It protects a short in the wire from starting a fire. This protection is not provided by the fuse on the motor.


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## topnative2 (Feb 22, 2009)

I agree, never stated it was inaccurate just that I have never seen one which is also accurate.I was thinking more in the line of unnecessary.However, it did make me think.So, Below is a link to a good read which "supports" both ideas.
Safety is a good thing and better safe than sorry.

http://www.12voltplanet.co.uk/fuses-guide-uses.html


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## jfboothe (Dec 19, 2012)

Not familiar with the Yammie, but for my ETEC there is no requirement or need to put a fuse between the battery and the motor per the Evinrude Installation and Predelivery documents


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## DuckNut (Apr 3, 2009)

ABYC Standards for CPD (Circuit Protection Device) placement. Measurements are maximum lengths between the point of connection and the CPD. All 7" dimensions may be increased to 40" if the conductor is enclosed in a sheath or enclosure in addition to the wire insulation.

https://www.jamestowndistributors.com/userportal/document.do?docId=108

Wire sizing
http://assets.bluesea.com/files/resources/reference/20010.pdf


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## jfboothe (Dec 19, 2012)

c_ronius said:


> The fuse on the motor protects the motor,but not the wire run between the battery and motor.


I am not sure I understand this? If there is a high amp fuse on the motor in the starting circuit, it protects the "circuit". Meaning if the fuse opens (blows) the circuit it completely open between the battery and the motor.


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## c_ronius (Mar 16, 2010)

I also have my outboard directly to battery switch, without a breaker. Using the oem installed wires.

Unless the oem wiring is 12' long, it will have to be extended in this case. This extra wire creates a different circuit than oem designed. I would think this would void the oem recommendation to connect directly to the battery without additional wire protection.

If I read correctly the link referred to by Ducknut shows a fuse would be necessary over 72"?


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## c_ronius (Mar 16, 2010)

jfboothe said:


> I am not sure I understand this? If there is a high amp fuse on the motor in the starting circuit, it protects the "circuit". Meaning if the fuse opens (blows) the circuit it completely open between the battery and the motor.


What if a short occurs (accident or outboard malfunction) in the wire. regardless of whats connected on the end. imagine a 10 ft, 8 gauge wire connected to a battery, touch the leads together and you'll be welding.


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## jfboothe (Dec 19, 2012)

c_ronius said:


> What if a short occurs (accident or outboard malfunction) in the wire. regardless of whats connected on the end. imagine a 10 ft, 8 gauge wire connected to a battery, touch the leads together and you'll be welding.


So in that case why does it matter if the wires are 4 foot, 12 foot or 20 foot? As part of the installation, the wiring should be protected from chafing and shorts. Just like the terminals of the battery are required to be protected so if you drop a wrench on them it doesn't weld everything together. I understand what you are saying, but I don't see it as necessary and if you do put another fuse in there, make sure you carry a spare.


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## jfboothe (Dec 19, 2012)

Here is some additional information also from James Town Distributors based on ABYC recommendations. It would seem the jury is out and while some think it's a good idea, others don't recommend it. Interesting

https://www.jamestowndistributors.com/userportal/document.do?docId=109

_If more current flows in a wire than the wire is rated to handle, the wire can heat up, its protective insulation can melt, and the heated wire can start a fire. This overcurrent condition can occur, for example, when a short circuit occurs. Fuses and circuit breakers are used to limit the amount of current that flows through circuit wires. *Except for those wires that are intended to carry starting currents, every positive wire in the DC main power distribution system must be protected by a fuse or circuit breaker.*

Notice that wires intended to carry engine-starting currents between the batteries, the switch, and the starter, are not required to have main-circuit-protection devices installed.

This exception is based on the notion that the starting battery would have just enough power to handle starting the engine, and the wiring would be appropriately sized such that the full capacity of the battery would be unlikely to overstress the wire. It was also assumed that the batteries would be very close to the engine.

Some modern installations violate some or all of these assumptions with very large house banks that may include an emergency cross connection switch, making them part of the starting system. The house banks may be some distance away from the engine in different compartments. *Some experts believe that all circuits on a boat should be protected - including the start circuits. However, at this time, this is not an ABYC recommendation.*
_


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## c_ronius (Mar 16, 2010)

jfboothe said:


> So in that case why does it matter if the wires are 4 foot, 12 foot or 20 foot? As part of the installation, the wiring should be protected from chafing and shorts. Just like the terminals of the battery are required to be protected so if you drop a wrench on them it doesn't weld everything together. I understand what you are saying, but I don't see it as necessary and if you do put another fuse in there, make sure you carry a spare.


Because a 20 foot wire is 20 times more likely to fail than a 1 foot wire. Manufacturers and the boating industry allow a few feet here and there, so the 6' pigtail off the outboard, the short connections between batteries, and some other things are allowed to be unprotected. Still does not make it safe.

Every inch of wire leaving the battery is potentially a short. By interrupting the circuit close to the battery you cut off the power at the source.

There are countless ways a boat could encounter a shorted wire. Wire rubbing insulation in poorly assembled pipework, rodents eating away insulation, pinching or dropping a metal object onto the wire. The list is near infinite.

To me it seems common sense, and a inexpensive breaker or fuse allowing a bit more safety in my boat is a good thing. I don't care what oems or the industry does. This info is not new to the boating world, and is common place in many other 12 volt applications.

I have seen wiring from many oems chuck full of safety issues. Just because it is all lined up, and made pretty with zip ties, does not mean it is proper or safe.


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## yobata (Jul 14, 2015)

The small battery I will be using is only 15#. I decided to place it under the rear deck and use the OEM pigtail that is 6'. 

If I go ahead and add a fuse, can you recommend one? What amp fuse, the CCA recommended by Yamaha for this motor is 245. Do I get a 245amp fuse? That's a big fuse!

@DuckNut mentioned a marine breaker instead of a fuse. They also have the resetable ones. Which option should I go with?


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## c_ronius (Mar 16, 2010)

yobata said:


> The small battery I will be using is only 15#. I decided to place it under the rear deck and use the OEM pigtail that is 6'.
> 
> If I go ahead and add a fuse, can you recommend one? What amp fuse, the CCA recommended by Yamaha for this motor is 245. Do I get a 245amp fuse? That's a big fuse!
> 
> @DuckNut mentioned a marine breaker instead of a fuse. They also have the resetable ones. Which option should I go with?


I'm no expert, but I know you will not need a breaker that big. I'm not sure of the relationship of the battery requirements vs breaker size, but I have successfully used a 120A breaker on a relocated battery in a automotive application. I would imagine somewhere in the 50-100 range would work for that small motor. It will depend on the wire properties, temperature, etc...

One way to know for sure is to connect an ammeter while starting under various conditions. I believe the standard would be to add 20% onto that for your breaker.


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## firecat1981 (Nov 27, 2007)

I can tell you from experience that a 50 amp breaker will pop everytime you try to crank the motor. No offense but electrical work should not be done by theory. ABYC standards are pretty strick and tested meathods. If you really have a question call pacer group, they will tell you what's needed.


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## MariettaMike (Jun 14, 2012)

It is my opinion the OP should use a secured battery switch as near to the secured battery as possible. Turn the switch off when the boat is stored.

Don't put overcurrent circuit protection on starting circuit because that will just be more of a nuisance than a true help for preventing electrical fires. Just don't bury your fire extinguisher under your wiring harness, and you should be fine.

It is more important to secure and protect the battery, switch, and wiring so it doesn't move or get hit by things that move than fusing the starting circuit.


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## DuckNut (Apr 3, 2009)

Agree with Mike. Do not use one for starting circuit but use one for EVERY other circuit.


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## yobata (Jul 14, 2015)

Thanks guys! I ordered a battery switch made by Blue Seas Systems


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