Fusible link - minimum wire length???

[buening]

I have a situation where I'm wiring up a fan controller that is rated at 50a and uses a 10ga power wire with a 14ga fusible link. The problem is the controller is mounted right next to the distribution block, so I don't need a very long supply wire. Does anyone know of a minimum wire length for the fusible link? I'm probably looking at 6" total wire length and was thinking 3" of power wire and 3" of fusible length. I'm tempted to not even use a fusible link due to the short wire length, but then the system isn't fused. I know the theory behind the fusible link, but don't understand how the length of wire comes into play when it comes to the wire heating up.

 

[apollard]

I've never seen a guideline for this, but maybe Mid will chime in. However, all the factory fusible links I've seen were around 6 inches, so when I did mine for the alt feed, I used that length.

 

[Midlife]

No help from me...sorry!

 

[buening]

The link that was provided in the kit is about 6" as well. I tried a google search but nothing mentions anything about length, just the 4 wire sizes less.

 

[Horseplay]

I'm no electrical engineer but question why you would not use a fuse instead. I have never liked the idea of fusible links. Putting something in place which would react as they do seems dangerous to me. I say wire it up, measure the draw at peak and normal operation and install the appropriate fuse.

 

[apollard]

A fuse IS a fusible link - both are designed to blow when heated excessively by current. No difference in function, it's the automotive sector that considers them different. A fusible link wire is designed to be used inline without a separate holder, and contains mayhem in the high temp wire insulation. A fuse is designed to contain the mayhem in it's casing - but, I've seen ANL fuses launch the casing, with just melted metal in between. Not sure how that is safer than a fusible link. Fuses are more easily replacable - a reason they are sometimes not used, since people have a tendency to replace them w/o fixing the fault.

 

[buening]

From what I understand, the fusible link acts as a very slow burning fuse. A normal fuse would blow much quicker, and maybe it has something to do with the high initial amperage draw from a fan motor that a fuse isn't used with this kit? Regarding the fusible link, the way I understand it is the wire heats up when an overload or short occurs, and once it heats up enough the wire will separate to break continuity in the circuit. The wire jacket/insulation is rated for higher temperatures than standard wire, so to allow for this heat.

I sent an email to Brian at DC Controls to get his take on this. He is an electrical engineer and should be able to provide some light on the situation. If he wanted the system fused I would assume he'd tell the end user to fuse the system, but instead he provides a fusible link. It may just be a cost thing, as a fuse holder may be more expensive to supply than a fusible link.

I do like not having a bulky fuse holder, streamlining the wiring aesthetics. It'd look kind of goofy having an inline fuse coming off a distribution block that is also part of a fuse block. Unfortunately the fuse block utilizes standard size fuses and are only rated up to 30a, so I can't just wire it into that fuse block. Chalk it up as a learning experience, as I had initially intended using the fuse block for that controller (among other things).

 

[Horseplay]

A fuse IS a fusible link - both are designed to blow when heated excessively by current. No difference in function, it's the automotive sector that considers them different. A fusible link wire is designed to be used inline without a separate holder, and contains mayhem in the high temp wire insulation. A fuse is designed to contain the mayhem in it's casing - but, I've seen ANL fuses launch the casing, with just melted metal in between. Not sure how that is safer than a fusible link. Fuses are more easily replacable - a reason they are sometimes not used, since people have a tendency to replace them w/o fixing the fault.

I understand how each works and the similarities. I'm not an electrical engineer but I am very well versed in things electrical. Your descriptions of each are accurate but I would argue (from experience) there is a much higher chance of fire etc. with a fusible link than a fuse, hence my initial response. I would wager that cost is the reason for the link as opposed to the fuse as the proper fuse and holder would surely cost a bit more. Both can and will do the job, just for me with as much money as we all put into these cars, I'd feel better with a fuse of the proper type and rating.

 

[Grabber70Mach]

Re: Re: Fusible link - minimum wire length???

From what I understand, the fusible link acts as a very slow burning fuse. A normal fuse would blow much quicker.

I thought that was the intent (purpose) of a slow-blow fuse. They are designed to accept the higher current (start-up current) for a short duration, then act as a standard fuse to protect the circuit.

Sent from my DROIDX using Tapatalk

 

[apollard]

I understand how each works and the similarities. I'm not an electrical engineer but I am very well versed in things electrical. Your descriptions of each are accurate but I would argue (from experience) there is a much higher chance of fire etc. with a fusible link than a fuse, hence my initial response. I would wager that cost is the reason for the link as opposed to the fuse as the proper fuse and holder would surely cost a bit more. Both can and will do the job, just for me with as much money as we all put into these cars, I'd feel better with a fuse of the proper type and rating.

See, my experience is the exact opposite. Although, I've only had one fusible link blow, but lots of high amp fuses.

 

[buening]

DC Controls recommended using only the fusible link cut down to the length I needed and not use any 10ga wire, so that is what I did. FYI