Fuses for Fishfinder wiring.

Since i am completely clueless when it comes to wiring, all i can find in a slo-blow fuse is the round type, I have 10ga wire that i am running to a 6 circuit blu sea box. I was told to be sure to install a 3 amp fuse (i think this is right) on each head unit wire. I have the type that use the blade type of fuses. I have 3 amp fuses but i dont see that they are slo blow? are these ok.. The helix 7 say 3 amp the 12 says 5 amp in the installation.
Also do i need a circuit breaker between the battery and the 6 circuit box?

thanks

any time you connect to a battery you want a fuse (or breaker) as close to the connection as possible. An inline fuse holder works great. Your main fuse that supplies power to your fuse panel needs to be rated to support a little more than the sum of all the devices you will use. The helix 7 says use a 3 amp fuse, the actual draw of the 7 is probably 1.5-2 amps and will say in the specs for the device. You get the main fuse size by adding the actual draw.
Ultimately the fuses are only to protect the wire from becoming hot knives and catching fire when something shorts out.
If it was me I would get a blade style fuse panel on amazon and put a 25amp main fuse at the battery and a bunch of 10-15's in the panel for your devices. You can always use a little bigger fuse, but you cant go smaller. If your device itself fails having a perfectly rated fuse is extremely unlikely to save the device as a fuse pops because the device already failed. Dont let people scare you, this isnt rocket science but you alway always ALWAYs want to use fuses. Even a single fuse at the battery would be sufficient for safety, but if one device or wire fails all your devices would go out which is why you break them down with individual fuses.

Remember that the primary function of a fuse is to protect the wire itself - not the electrical devise.

You do not need a slo-blo fuse. I discarded the 3AG fuse holder on my Helix, and wired to my Blue Sea fuse panel using a 4A blade fuse. I am an EE and consider this to be perfectly fine, and it has been so far (months).

You must take the size and length of the wire in consideration.

FYI, wire length has nothing to do with fuse/breaker rating. Wire gauge size only. The length of the wire has to do with how much voltage is dropped due to the copper losses. I used 8 AWG tinned copper marine wire from the battery & breaker (40A) to the Blue Sea panel. Almost no voltage drop.

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Originally Posted by jawjatek

FYI, wire length has nothing to do with fuse/breaker rating. Wire gauge size only. The length of the wire has to do with how much voltage is dropped due to the copper losses. I used 8 AWG tinned copper marine wire from the battery & breaker (40A) to the Blue Sea panel. Almost no voltage drop.

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You are right. I was thinking voltage drop. That's what happens when you get old.

ok, going to try this today. i got a 6 circuit blade style fuse panel with negative terminal. I am going to mount within 1 foot of the battery. I am going to connect to battery with 8ga battery terminal wires. I am going to put a 40 amp blade style inline fuse on power side. I am going to connect 1 echomap 93sv, 1 helix 12, 1 helix 7 di gn2, 1 helix 7 combo si/di gen 3n and a panoptix livescope to the blade fuse. i have 3 amp fuses fir the helix 7 and 5 or 7.5 amp fuses in the fuse panel for the helix 12, echomap and livescope black box.
I am also considering adding a second battery in parallel to double capacity. if so i am going to connect them with 4ga battery cables

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Originally Posted by crappiejim

I am also considering adding a second battery in parallel to double capacity. if so i am going to connect them with 4ga battery cables

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If you are going to add a 2nd battery, then do yourself a favor and buy a Perko battery selector switch (with one, two, both, off). That way, you have only one hot feed into the terminal block plus you have the ability to isolate each battery separately or turn off all power drains from your battery.

These are going in a front rod box and i really dont have a place to mount. If i found a place, how exactly is it wired.

There is a diagram here:
1-2-BOTH Boat Battery Switch | Blue Sea 6007 | New Wire Marine

Basically, the Common terminal goes to your fuse block (and/or outboard if that is what you are powering) and the two other terminals go to each battery's hot side.

how far can that switch be from the batteries and the fuse panel? What gauge wire would I need for say 3-5 feet?

It is best to have the disconnect switch as close to the battery as possible to protect the entire wire circuit if the battery shorts out ...

Remember ... the most likely place for a short is at the battery or the battery itself - breakers, switches and fuses will only protect things “downstream” of the protective device installed ... (thus the need for the first protective device as close to the battery as possible) ...

I’ve seen many boats wiring from the battery to a fuse panel with thinking only of protecting electronics devices - with no thought of protecting the wire between the battery and the fuse panel ... (wire fire hazard if the battery shorts) ...

If it is not feasible to install the disconnect switch within a short distance (I think ABYC standard is like 7” between the battery and the first protective device) - then it is possible to add a circuit breaker at the battery post ... this protects the wire from melting if the battery shorts (regardless of “if” there is a disconnect switch installed or where the disconnect switch is installed in the wire circuit) ...

It is good practice to have a circuit breaker at the battery post with heavy wire thru the disconnect switch and on to the Buss bar fuse panel. ... Then use correct fuse sizes and wire sizes for the individual electronics device(s) runs ...

This practice protects everything “downstream” of the battery post ...

Here is info for marine wire size per length of run ...
Marine Wire Size and Ampacity | West Marine

Rickie

Quote:

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Originally Posted by rnvinc

It is best to have the disconnect switch as close to the battery as possible to protect the entire wire circuit if the battery shorts out ...

Remember ... the most likely place for a short is at the battery or the battery itself - breakers, switches and fuses will only protect things “downstream� of the protective device installed ... (thus the need for the first protective device as close to the battery as possible) ...

I’ve seen many boats wiring from the battery to a fuse panel with thinking only of protecting electronics devices - with no thought of protecting the wire between the battery and the fuse panel ... (wire fire hazard if the battery shorts) ...

If it is not feasible to install the disconnect switch within a short distance (I think ABYC standard is like 7� between the battery and the first protective device) - then it is possible to add a circuit breaker at the battery post ... this protects the wire from melting if the battery shorts (regardless of “if� there is a disconnect switch installed or where the disconnect switch is installed in the wire circuit) ...

It is good practice to have a circuit breaker at the battery post with heavy wire thru the disconnect switch and on to the Buss bar fuse panel. ... Then use correct fuse sizes and wire sizes for the individual electronics device(s) runs ...

This practice protects everything “downstream� of the battery post ...

Here is info for marine wire size per length of run ...
Marine Wire Size and Ampacity | West Marine

Rickie

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I appreciate the response but I don’t understand. I don’t know what it meant by protective device. I guess this is just too complicated for me. What is the ABYC equals 7A in your response. Is that 7 feet


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A protective device is a circuit breaker, a disconnect switch or fuse ... a device that protects the wire circuit running to the electronics stuff ...

The ABYC (American Boating and Yachting Council) standard is less than 7 inches between the battery and the first protective device (there can be more than one protective device in a circuit) ... and that still leaves 7 inches of wire unprotected if the battery shorts out (which is why I recommend a circuit breaker at the battery post to not leave any part of the wire circuit unprotected) ...

Rickie

Not sure what you mean by "the battery shorting out". If this happened internally to the battery there would be no current in the wire, and no device would protect anything. The protection is for the much more likely scenario when a short (positive wire touching negative wire) occurs downstream of the battery due to a pinch, cut, or collision with something that damages the insulating plastic. The wires then conduct way too much current and get smoking hot, causing an electrical fire. This is why the main or first breaker needs to be close to the battery, and sized appropriately for the wire gauge.

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Originally Posted by jawjatek

Not sure what you mean by "the battery shorting out". If this happened internally to the battery there would be no current in the wire, and no device would protect anything. The protection is for the much more likely scenario when a short (positive wire touching negative wire) occurs downstream of the battery due to a pinch, cut, or collision with something that damages the insulating plastic. The wires then conduct way too much current and get smoking hot, causing an electrical fire. This is why the main or first breaker needs to be close to the battery, and sized appropriately for the wire gauge.

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You are correct ... My word formulation is not as easy to understand as yours ... thank you

Rickie