AVOID Electrical Issues! - Battery Terminal to Fuse Length EXPLAINED - Car Audio

When you install an aftermarket amplifier you need to run a power wire from the vehicle's positive battery terminal to the amplifier. Somewhere along this wire you must include an inline fuse in order to properly protect the wire. A commonly used suggestion is to keep the fuse "within 18 inches of the battery", but is this actually the best suggestion? Why does the fuse need to be close to the battery anyhow? Let's dive in!

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[pockets]

fun fact, that 18" number came from competition rules way back in the day. it is an entirely arbitrary number. It just sounded like a good idea to the guy that wrote the rule. Yes the closer the better, but that 18" gave enough room for different circumstances.

[matthysharmse]

Thanks for this explanation. Makes way more sense than just following the mainstream without knowing the reason of why

[phlix]

Excellent point made at 2:50. The whole point of the guidelines (such as ABYC E-11.10.1.1.1) is to place the overcurrent protection device as close as practically possible to the power source to protect the rest of the wire run, and the maritime ABYC's (American Boat and Yacht Council) recommendation of no more than 7" is so strict since having a boat fire while out at sea can be an extremely life-endangering event.
In the maritime industry, Blue Sea Systems has a product called MRBF (Marine Rated Battery Fuse) Terminal Fuse Blocks, part numbers 5191 and 2151, that make it such that the terminal you bolt your cable's lug to is itself fused, ensuring the whole cable run itself is protected. The fuse options range from 30A - 300A. The only drawback would be that you'll need a standard battery post to marine style battery stud adapter (or use marine deep cycle batteries that already have threaded stud connections), and you'll have to crimp on lugs to the cable before connecting it to the MRBF. This makes for a very robust setup that should be impervious to long term vibration exposure (either in a boat's engine room with a big diesel motor, or in a high SPL competition vehicle).

[jaredwoodward]

I've always make a bracket that if possible straight off one of the battery tie down brackets/strap then keep the first part of the power supply lead as short as possible between the battery terminal and the major fuse for the whole system. Then always secure the cable after that fuse with stand off cable tie mounts if possible every 6 inches. Where the cable passes through bodywork or trim panels use an appropriate rubber grommet. I've been doing this since the mid 90's and have never expirienced any cable failures/ shorts.

[ScottGunMag]

Thanks, it’s basically common sense which isn’t always common. I may not ever do another audio system, but regardless, I enjoy learning from your channel. Thanks!

[trin]

As a consideration, why not use one of KnuKonceptz fused battery terminals instead of a block fuse in line?

[centralcoaster]

My car has a positive terminal with a few large fuses and potential mounting points in there. Even my short section is protected 👍

[marcushelweg]

A good rule of thumb that i have learned as an electrician, always fasten your cable to the point you are no longer able to grap the wire and pull it. if that requires a lot of cable ties, so be it.
Also ALWAYS tighten the connector screw to the specefications of the manufacture, so if it says you gotta tighten with 5nm. then no more or less. they have tested that to make sure the wire is not loose so i can't vibrate itself loose or you dont over tighten it and can over time break each strands of wire in the cable wich in result makes the cable diameter smaller wich results in the wire not being able to handle the same amount of Amps.

I hope this comment helps, at least i hope Marc will read this and agree with me on this :)

[TheMustachioedJames]

One more (minor) consideration, I try to keep the run to the inline fuse as short as possible, but you should also make it long enough to make the bends it needs to make without stressing. That extra inch or two you cut away does no one any good if you have your cable bent in a hairpin that stresses your compression fit terminal lug and/or your fuse terminal.

[FOXCRFRIDER]

Mounting the battery and fuse holder to the same part, as in bracket or tube is ideal. That way they vibrate together.

[Luminous.Dynamics]

What about a fuse holder that has one end that bolts directly to the battery terminal? Like with a copper lug straight to batt from fuse holder, no wire on that side

[MrMoparNoCar]

Is it crucial to have a 2nd fuse block for a 2nd battery setup? thanks

[jdmjesus]

Safe routing and mounting is more important than how short it is. If you need to go a bit longer to avoid sharp or hot things, then do it. It is a good rule though. Extra sleeving on the un fused section is always good too.

[JA]

18” is a lot in my opinion. The shorter you can brake that circuit the safer you car is. Some times fuses fail and terminals get hot and can go unnoticed until the point of failure the less unprotected the greater the risk of fire

[chncerpau]

Great video! Do the same rules apply to distribution blocks? My shop owner insists that you don't need a fuse at the distribution block because the main fuse protects the whole thing, but that doesn't make sense to me. TIA!

[richeygoldberg]

Who decided on 18"? Why not 16" or 20"? The hard limit of 18" has always been a kind of made up number. You need to be as short as possible when taking the mounting location of the fuse in to consideration AND any objects that could damage the wire and short out.

[Polk]

@CAF can you make a video of installing a secondary battery

[Sweetaccord]

Never liked the fuse with set screws that grind into a wire. Even adding a wrap or other. Best are ring terminal style fues.

[jg]

So could I install the fuse as close as possible to the start of the positive wire near the battery and there would be no issue other than fitmet issues ? Do you recommend as close as you can ? is there different recommendations for different size wire I need to add a inline fuse to 16 gauge wire for heated grips

[motoboy]

I watched quite a few of your vids for guidance in installing my basic system of a 8" powered sub, 4x50W compact amp, and four door speakers. I've heard the 18" rule from many sources. To me, it seems that 18" is an arbitrary distance. What are the calculations showing that 18" should be the maximum distance from the battery? Why not 12", 20", 27.3", 74mm, etc? Thank you for your professional and informative videos!