Factory Aux switch fuses - other than factory fuse rating

[Sweetums]

Pretty sure my dip-shit uncle would take a look at the blown fuse and try to use a .22 cal round instead.

I'm so glad we are using blade style now instead of the old glass or Bosch style. Much lower chance of some moron just shorting the terminals with whatever they have lying around.

I think you were reading chorky's post wrong -
He was suggesting using a fuse with a SMALLER rating so it would blow faster.

Some of us connect wiring to our aux switches that is smaller than the aux switch rating.
If that aux switch can handle 40 amps and the aux switch WIRE from the factory can handle more than 40 amps - you are good to go.
So then you do what I've done - run a longer run of wire a size smaller to a load.
You don't want to keep that 40 amp fuse in there, so you drop the fuse down a size.
He's talking reducing the fuse size to match any smaller wiring.
Some of us connect loads smaller than the switch is wired and fused for. Maybe a light kit that comes with wires a size smaller - if you leave that 40 amp fuse in there, you'll blow your new wiring. Forget the lights - go by what the wiring you just installed can handle.
You run wires that can handle 30 amps back to a 20 amp load in the back and connect it to the 40 amp aux switch circuit, you should not leave the 40 amp fuse in there, you should fuse for that wiring that handles 30 amps. Go 25 for example.

Fuse to protect the wire. That's what he's saying.
A lot of us run smaller loads on the 40 amp circuits, and have smaller wiring connected to the aux wiring.
If you match or exceed the factory wire sizes, no reason for a change at all.
If you keep the exact same gauge or one size larger wire gauge run from the aux switch pigtail wire over to the load - no reason to change the fuse.

This is what he said and he's 100% right -


REDUCE fuse size. That means the FUSE blows even faster.
Say the aux switch 40 amp is 14 gauge just for simple numbers.
You connect a smaller wire going to a 20 amp load and the smaller wire can only handle 30 amps - he's saying take out the 40 amp fuse and drop to a 25 amps fuse.
Fuse blows first because the new wire can handle 30 amps, and the factory wire handles 40 amps.

Sorry, that's what I was trying to say. The fuse should always be the first to blow - it should blow before the wire melts or the device is damaged.

The fact that we are still using fuses is a bit nuts, that could all be done solid-state these days by having the computer monitor current and just turn the circuit off if it goes outside spec. Physical fuses are an anachronism.

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[ecidiego]

Pretty sure my dip-shit uncle would take a look at the blown fuse and try to use a .22 cal round instead.

lmao

 

[chorky]

The fact that we are still using fuses is a bit nuts, that could all be done solid-state these days by having the computer monitor current and just turn the circuit off if it goes outside spec. Physical fuses are an anachronism.

This would be awesome but I think it would increase cost significantly. I mean I have two of the switch pros systems and they were $650 each, and each one only offers 8 power ports... But it is the way of the future. Kinda a double edge sword though I think because fuses are, in some cases, easier to diagnose. I am conflicted on it myself. I absolutely LOVE the super small footprint of the switch pro system as compared to a similar fuse/relay system. But it is definitely more complicated and would require some pre-though by a designer. Maybe Jeep will offer something like it in the future!

I think you were reading chorky's post wrong -
He was suggesting using a fuse with a SMALLER rating so it would blow faster.

This exactly. Thank you for clarifying in case what I typed might have sounded confusing.

And, to take it a step further, this situation can be expanded to apply to all sorts of things, not just aux fuses. Even aftermarket items in general. For example, the water pump I have came with a fuse rated at I think 15 amps. But the maximum draw for the pump itself is only 7 amps, with an average of 3.5. And the wires of the pump itself are pretty small, maybe 16 ga. So when wiring it up, I set the amp cutoff of the switch pro system to 10 rather than 15. A similar situation could be done for my Engle fridge, which comes with a 10a fuse and appropriate wiring, although the maximum draw it can have is 3.5 - so one could use, say, a 7.5a fuse just for that safety buffer. But as Bill said - fuse circuits to appropriately protect your wiring, and ensure the wire is appropriate for the type of load.

 

[Mash5]

I think the OP is right on with sizing the fuse to protect the smallest conductor in the circuit. I see no reason or problem that could be caused by "right-sizeing" the fuse for what you have connected to it.
One thing that probably is not relevant but may be interesting is that fuses have two ratings. The one most are conversant with is the nominal rating such as 15a. The second is time. To fully categorize a fuse you need to look at chart of blow time as current over time. Some are very fast and others are slow. At 15a for instance a standard auto style 15a fuse may not blow for several seconds or even minutes where as at 20a it may be only a fraction of a second, and at 50a it would be effectively instant.

 

[ShadowsPapa]

That is until your brother-in-law uses your truck and finds that fuse blown and thinks he's helping by putting one back in rated what the panel says.

That would be my luck.

There's only 2 people who would ever use my truck - and neither of them would ever use any accessories (or better not be in a situation to need them)
My wife would be the first - and she'd never use any aux switches let alone do anything with a fuse - it would be up to me to resolve it, and my son - same thing.

One can also make a small decal to go over that legend.

 

[ShadowsPapa]

Pretty sure my dip-shit uncle would take a look at the blown fuse and try to use a .22 cal round instead.

I'm so glad we are using blade style now instead of the old glass or Bosch style. Much lower chance of some moron just shorting the terminals with whatever they have lying around.


Sorry, that's what I was trying to say. The fuse should always be the first to blow - it should blow before the wire melts or the device is damaged.

The fact that we are still using fuses is a bit nuts, that could all be done solid-state these days by having the computer monitor current and just turn the circuit off if it goes outside spec. Physical fuses are an anachronism.

I know you are a smart , thinking person, so I was like, hmmmm.......... one of us is missing something here?

LOL - aluminum foil wrapped around the glass fuse, a screw or bolt that fits into the clips, yeah, seen that!

Pretty sure my dip-shit uncle would take a look at the blown fuse and try to use a .22 cal round instead.

For some reason, I seem to recall seeing something similar back in the 70s. I thought it clever but stupid. At least the thing was spent, was just the brass - otherwise you could feel a tingle in your foot if that circuit got hot.

 

[ShadowsPapa]

I think the OP is right on with sizing the fuse to protect the smallest conductor in the circuit. I see no reason or problem that could be caused by "right-sizeing" the fuse for what you have connected to it.
One thing that probably is not relevant but may be interesting is that fuses have two ratings. The one most are conversant with is the nominal rating such as 15a. The second is time. To fully categorize a fuse you need to look at chart of blow time as current over time. Some are very fast and others are slow. At 15a for instance a standard auto style 15a fuse may not blow for several seconds or even minutes where as at 20a it may be only a fraction of a second, and at 50a it would be effectively instant.

You likely recall the slow-blow BUSS fuses of the past, as opposed to those with a spring that ensured a fast blow.
There are reasons and places for both. Some loads are transient and you don't want a blown fuse for a load that lasts 2 or 3 seconds and the wire never exceeds the thermal ratings.

Wire ratings include more than amperage - length, temperature.....

 

[Lost1wing]

There's only 2 people who would ever use my truck - and neither of them would ever use any accessories (or better not be in a situation to need them)
My wife would be the first - and she'd never use any aux switches let alone do anything with a fuse - it would be up to me to resolve it, and my son - same thing.

One can also make a small decal to go over that legend.

I would make a decal. If a system was designed for a X amps and X amps is in the manual and on the cover, wiring on that circuit should be rated for that rating. A lower rated fuse is fine. But like I mentioned earlier, Murphy will visit one day and put the size fuse that the book says.

 

[Lost1wing]

I know you are a smart , thinking person, so I was like, hmmmm.......... one of us is missing something here?

LOL - aluminum foil wrapped around the glass fuse, a screw or bolt that fits into the clips, yeah, seen that!



For some reason, I seem to recall seeing something similar back in the 70s. I thought it clever but stupid. At least the thing was spent, was just the brass - otherwise you could feel a tingle in your foot if that circuit got hot.

It was in one of those Darwin award stories. Fuse blew and replaced with a 22 round. What caused the fuse to blow was still an issue, so the 22 round was acting like a fuse and warming up. It got warm enough that the round fired and shot the driver. Funny story anyhow.

 

[ShadowsPapa]

I would make a decal. If a system was designed for a X amps and X amps is in the manual and on the cover, wiring on that circuit should be rated for that rating. A lower rated fuse is fine. But like I mentioned earlier, Murphy will visit one day and put the size fuse that the book says.

My tendency - normally - is to go up in wire size - in part because I'm extending length. I just prefer more than necessary.
But in cases of a light set - for example, that includes their own wires to the light or whatever, unless you rebuild their harness, they use only what's necessary in wire size to feed the draw of those lights.
So you have a choice - fuse holder where the lighter wire starts, or drop the fuse size for the whole thing, or replace all of their smaller gauge wires with larger.

 

[Lost1wing]

Pretty sure my dip-shit uncle would take a look at the blown fuse and try to use a .22 cal round instead.

I'm so glad we are using blade style now instead of the old glass or Bosch style. Much lower chance of some moron just shorting the terminals with whatever they have lying around.


Sorry, that's what I was trying to say. The fuse should always be the first to blow - it should blow before the wire melts or the device is damaged.

The fact that we are still using fuses is a bit nuts, that could all be done solid-state these days by having the computer monitor current and just turn the circuit off if it goes outside spec. Physical fuses are an anachronism.

Actually, just a few years before I retired, an aircraft company started using solid state circuit breakers. The tech could open the circuit, open and lock the circuit and last open, lock and tag a circuit. You could work on the system and actual replace the card for the circuit with a new one. It would still be locked out by another module.

Nothing to do with this post, but I think we will see more of it in the coming years.

 

[Sweetums]

It's already here, the Cybertuck uses 48 v architecture with computer controlled "breakers".

 

[Blaster11]

Sorry, but I don't care what your certification is in but if ALL my wiring is good to 40 amps and my items are only going to pull say 15 amps max , then I am not fusing it for 40 amps.... I am going to fuse it for 15 amps. No way am I going to have a component fail and allow it to pull an excessive amount of current and cause a fire....I will just carry an extra fuse but I am not going to burn my ride down! We will just have to disagree on this one.

 

[chorky]

Wire ratings include more than amperage - length, temperature.....

This right here! Lots of people neglect this factor. As well as where the wire is - inside, outside, by a hot engine or not, etc.. Lots of factors

 

[ShadowsPapa]

No way am I going to have a component fail and allow it to pull an excessive amount of current and cause a fire....I will just carry an extra fuse but I am not going to burn my ride down!

Yeah, I guess you just do whatever - it works, but it's not how fires start.
If the device fails, it won't start a fire unless the draw is too great for the wire - then if that's the case, the fuse goes.
It's not "certifications" - it's 50 years auto wiring/electric experience.
Still, whatever. As long as you feel good about it and the fuse will blow before the wires get hot, it works.

No matter what you call it - the end result is exactly the same as we've been talking about - preventing melted wires. Semantics.

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