Technical 175 amp fuses???

The latest American Autowire kits include their #510476 "Alternator and Main Power Connection Kit" which is composed of 25ft of 6 gauge SGX wire, and two 175 amp (!) mega-fuses and holders. The recommended connection scheme puts one fuse between battery and alternator, and the other fuse between battery and fuse panel. Seems to me that by the time the fuses blow, the wiring would history, especially the kit's 10-gauge wire that feeds the panel. Just looking for comments here.

I couldn't determine how to post one page of a pdf here, so please check out pdf page #21 for the sub-kit's diagram.

Ah, just figured out how to do it:

https://smhttp-ssl-87263.nexcesscdn...ck_Classic_Update_Second_Design_3.pdf#page=21

 

Its to protect from a dead short in the alternator diode pack and main power to the fuse box. Its the last line of defence for the electrical system.

 

But a 175 amp fuse is not going to protect the 10 gauge main panel feed wire. Seems like a 30-40 amp fuse would be better for that, or even a #14 fusible link.

 

Guys seem to think you need a fuse everywhere, but when the fuse size is 3X the wire ampacity (#6) or 6X (#10), there isn't any protection going on no matter what BS they use for justification... It's a way to extract more money from you and just adds a couple more failure points to the harness.

 

I have no idea what current a 10 gauge wire is suitable for, but for the curious it shouldn't be too hard to use a couple of lengths of such wire with a 175 amp fuse to short a battery, and see what happens. Just make the connection some distance away from the battery, and have a backup plan for how to disconnect it all, if the fuse doesn't blow.

 

THANK YOU, SIR. Shades of the fusible link in my 1977 Cadillac.

Ben

 

I'm installing this setup in a 66 Olds 442. I also thought the 175 amp fuses were pretty large to actually protect anything. But, it is what the man bought.

 

It takes the place of a fusible link. Most cars built to the later end of the era had a fusible link, you cannot imagine haw many I have bypassed over the years because the damned things let go just past the last pig farm in the middle of the night.

 

We use 175 amp circuit breakers with 2 gauge battery cable for lift gates on the rear of box trucks. Don’t worry, Murphy clearly states a $200 picture tube on a TV will protect a 50 cent fuse by blowing first.

 

I think it’s a false sense of security. I guess it’s possible with a direct short to ground the fuse could pop and stop current flow, but I’d still think the wire would (at least the insulation) show signs it needs to be replaced.
Would/could it stop a meltdown in the harness? My instinct says no, but I’m not going to go pick up a fuse and wire it up and test it out either.
What I would do is contact the manufacturer and get the run down, ask them the questions and how they came up with a 175 amp fuse, what tests were done, results etc.

 

I would have been fired for wiring something that way. The 10 ga. wire is going to turn into a fusible link long before that 175 amp fuse even wakes up.

 

Don't look at it when it blows, or it will be like looking at an arc flash.

 

I installed these on a friends truck. The main fuse block feed is tied to these fuses. Your think is this main fuse block feed needs to fused. With smaller rated fuse? Thanks

 

Why does the fuse block need to be fused? Think about it.

 

IAW google, max current for awg 10 wire is 30 amps
awg 3 wire is 150 amps

 

Keep in mind that 175 amps is arc welding current, and you better be using 1/4" or larger rod and welding 1/2" or more thick material. Turn your welder to that and just try welding on your car... Can you say 'swiss cheese?'

Want a visual representation of what can happen? Remove your battery-to-starter cable and substitute a piece of #6, then turn over the motor with the coil wire lifted. It will probably liquefy the insulation; it may catch fire. Switch to #10, that will catch fire.

Realistically, neither of these things will likely happen. In the case of a catastrophic accident with extreme damage to the front of the car solidly pinching the wire between two places, the fuse MIGHT function but I wouldn't bet the farm on it. You'll have other, more serious issues in any case.

What's far more likely is some damage to the insulation allowing the conductor to rub. This is stranded wire, those individual strands will melt far short of 175 amps, so if it continues to rub it will eventually burn the wire in half and/or melt the sheet metal away. If any flammable vapors or liquids are present, these 'small' arcs can start a fire.

Fuses are there to protect the WIRE, and MUST be sized to the wire's ampacity. As #10 is rated at 30 amps and #6 at 60 amps, that fuse is grossly oversized and will offer zero protection. It's this thinking is why I personally would never use a store-bought harness as supplied.

A 175 amp fuse requires a 1/0 cable....

 

Sounds like they are using the concept that a lot of newer cars have. A block with a bank of relays and fuses close to the battery or a large gauge cable from the battery where the switches in the car trigger indivdual relays on that bank to operate various systems and the fuse block inside doesn't have to handle a lot of amps nor do the switches handle a bunch of amps. The electric fan, AC, sound system and the occasional power window or seat movement may be drawing 60 continuous and up to 80/100 amps for a short period but no wiring in the car is carrying over about 30 amps max. Then you get over in the big boom audio brigade and they have those 150 amp fuses to the big amps but those are totally isolated from the rest of the electrical system and on their own circuits outside of the power feed from th alternator to the battery that they draw power from.

 

There is a fuse craze going on since a few years. Especially with those mega fuses.
Folks double and tripple fusing everything but the kitchen sink these days.
Just look at the factory fusing of a random 50s/60s car - how many fuses do you see on anything that is going on in the engine bay, or fused fuse boxes?

Heck my 41 Chevy had one fuse in the light switch and that was it.
They didn't burn down by the dozen back than.

If anything, I would be way more concerned of those cheap China fuses from your local supermarket or Homedepot, that are often way out of specs.

 

Some modern alternators have an output of 150 amps. Maybe not the cheap clone 70s GM stuff in the hotrod market but actual modern day OEM parts, to fuse this output you need a much larger fuse. It would make sense that if you ate making a hook up kit you would need to cater for a modern alternator. You can over think this as much as you want but the logic seems pretty simple to me. I run a 45A alternator and have a 50A maxi fuse between the alternator, battery and main fuse box and i carry a spare.

Modern cars are smothered in fuses because it reduces the wire gauge and connector sizes used in the harness.

 

Thanks for all the responses!

The Chevy pickup on which I'm installing the AAW harness has worked just fine for 54 years with its original #12 wire protected by a #16 fusible link. I did replace the link in the mid-90s. I can't remember why, but it wasn't because it had blown.

For the past 20 years or so, the alternator has been a 12SI model, which is either 66 amps or 78 amps -- can't remember which . For some reason, the original #12 wire from battery to alternator has survived and shows no signs of overheating, even though the alternator had to charge more than one nearly-dead battery.

So, I think I'm going to "step up" to #10 wire and a #14 fusible link right at the battery. The routing is such that I can easily convert to #8-wire and a fuse in the future. I doubt I'll ever use any components from that AAW charging kit, certainly not the mega-fuses and holders. That #6 wire would probably work as a battery-to-starter cable on a small, low compression engine.

 

Those fuses are a plague. These came out of the automotive audio sector which is really the only legitimate use for them, for fusing the power supplies to monster amps. As was mentioned above, these circuits are stand-alone and not integrated into the main harness.

There's still a lot of misunderstanding on what needs to be fused and why. What I don't get is why the aftermarket harness industry has gotten onto this particular bandwagon. Is it a case of cynicism, playing into their customers paranoia/ignorance while making a quick buck or do they share that ignorance? Neither answer is a comforting thought.

There are two reasons for using overcurrent protection, assuming that sound engineering is used (a very large assumption where the aftermarket is concerned, and misplaced faith IMO). Again, in both cases it's to protect the wire against damage and that's the overriding reason. Reason one is in the event the connected device fails and presents a short-circuit potential that can cause a damaging overcurrent. The fuse will disconnect the device, both protecting the wire and stopping the short in the device from causing a fire. Fuses are NOT used to protect the device! If it's going to fail, a fuse won't prevent that. At best, it may limit device damage but generally not enough to 'save' it.

Reason two is to protect the wire from short circuit in case of damage to the wire itself. This is why it's critical to carefully route and install your harness to protect it from physical damage as much as possible. Again, fuse size MUST match the wire ampacity, the more the fuse size exceeds the wire ampacity the less protection you have. When the fuse size is multiples of the wire ampacity, you have essentially ZERO protection.

The next thing to understand is not all circuits present as a short circuit hazard if the device fails. Lighting is one of them. When a lamp fails, you may see a very brief current spike but once the filament burns in half, that hazard is gone. But lighting is traditionally fused, the reason for that is the lights are located where wire damage in the event of an accident is high, so protection for the wire is needed, also to prevent fires if the fuel line is compromised. Ignition is another circuit that fails to 'open'. Ask yourself, what happens when you leave the ignition on but the motor isn't running? The points burn and you may see a coil failure but that's it. Inside-the-distributor electronic ignition? The cheaper versions will fail also under the same conditions, the better ones will auto shut-off. Even the 'box' style will fail open. Fusing this is fine, but all you're protecting against is physical damage to the wire.

This leaves two more circuits where the only protection you can realistically accomplish is against wire damage, and there's plenty of obstacles in your way. The first is the charging circuit. Alternators and generators fail to 'open', every time. They don't present a short-circuit hazard to the wire, it is physically impossible for them to produce more current than they're rated for or cause a high-current short from an internal failure. The problem here is that output varies and virtually everyone 'cheats' on the size of the output wire from the alternator. Up until the advent of these larger alternators, these had no overcurrent protection from the factory. Then fusible links started showing up in the output wire. Those were NOT short circuit protection, their only purpose was to protect the wire from overload because it was too small at the brief but recurring high charge rates. Install a bigger, correctly sized wire and it's no longer needed, but the OEMs calculated the link was cheaper than the right-sized wire. The aftermarket has now carried this concept to the point of stupidity. It should also be pointed out that if you're trying to protect the charging output wire against physical wire damage, you'll need TWO fuses, one at each end. A fuse only functions if the short is downstream from the fuse, or put another way, it has to be installed at the point of origin of the current. As the charging system output wire is being fed from both ends (alternator at one end, the battery at the other), a single overcurrent device can only protect half of the circuit at best.

Last but not least, the feeder to the fuse panel. The first thing to realize is the OEMs cut every corner they can, and it's all about reducing costs. But they carefully design their harnesses taking that into consideration, so by and large those are safe, reliable harnesses. The aftermarket cuts all the same corners, throws in a few more, but sells these as 'universal' harnesses which may or may not be adequate for your vehicle. The issue with panel feeds is very similar to the charging system output wire; you don't have a steady load. The load will vary widely, depending on what's 'on' at any given time. Again, this is a place where most harnesses 'cheat' on the size of the wire. You shouldn't have to worry about device shorts, those should be on individual fused circuits of their own in the fuse panel. So that leaves overloads and physical wire damage. If you're going to try and fuse this, you'll need a fuse that will withstand the maximum peak current that can occur. If using an actual fuse, there's very little wiggle room; the fuse needs to be sized at 125% of peak current to prevent nuisance tripping. You'll have a bit more latitude with a fusible link, but if you end up with an overcurrent rating that's a multiple of the wire rating, you don't actually have any protection. This is my biggest beef with the aftermarket harnesses, their too-small panel feeds. Unless your vehicle is pretty bare-bones, a #10 feeder is seriously inadequate IMO.

I would use that #6 for the alternator output and skip the link and the fuse. One issue with 'cheating' the wire size down is it introduces excessive voltage drop at higher loads, even if those loads could be considered 'safe'. The same problem exists with the panel feeder. This represents lost power and generates heat. This is particularly important if using a 'one wire' alternator. The three wire alternators the OEMs use have a 'sense' circuit connected 'upstream' (usually at the ignition switch or fuse panel) that measures voltage at that point and adjusts output to insure full voltage in the main harness. One wire alternators lack this.

In electrical, too big is always good (except for fuses!), too small is when problems appear.

 

@Crazy Steve , I discussed these uses for the maxi fuse with the American Auto wire guy (the boss) at Louisville one year.
The conclusions we came to were similar to yours, in that the Maxi fuse doesn't provide insurance if the wires are sized correctly.
I don't know why they decided to make this part of their wiring kit, but it was added after my rod was built using their product.

 

So the correct answer to my question is cynical greed apparently....

 

In the one country in the world famous for ridiculous and crazy expensive lawsuits I can see why people would want to throw everything and the kitchen sink at extra safety if there's any chance it can reduce the risk of ending up in court - and as long as you can make the customer pay for the "improvement" there's no downside for the seller anyway.

I'm not quite sure how you guys dare to do anything more risky than breathing over there.

 

I just mount the panel and run the wires wherever it says to on the wire.

I like fuses.
Replaced a 120 amp fuse once cause someone hooked up the battery backwards. Was a lot easier than replacing whatever was last in line in the system.

we would add circuit beakers to the high load stuff at work. Fans, AC….
why? Cause the boss said so.

 

I believe most people think that the fuse is set up to protect a component. Let’s face it , the fuse is set up to protect the vehicle. You can change a component, a section of wiring, but you cannot change the facts that somebody died in a car fire.

Yes, a 175 amp fuse is way too big. I just looked at one of my aviation books. A #6 wire is rated at 70 amps max with a 6 foot or less run. Once you go longer, such as a battery relocated to the trunk, the amp rating drops to 50 amps.

Yes crazy Steve is right, 175 would become a very serious problem. Can you change the fuse to 100a? I would be more comfortable with a different fuse.

 

Seems to me that if #12 wires for charging and panel feed worked fine for all these years, then #10 should be an extra margin of safety. The truck is pretty much "bare bones". No power windows or locks, no audio amps, no electric cooling fans. But, yes, there is always the alternator which is at least 66 amps.

One of the problems with #6 wire is trying to route it. It's absolutely anaconda-like! I want to use the plastic wiring gutter than runs across the radiator support. It carries the "charging" wire and passenger side light wires. No way will the #6 wire fit in the gutter. However, I think I'll give the #8 wire another shot. Easier to do it now instead of later.

 

Decided to use #8 wire for the charging circuit. It will be routed from the battery to a distribution block. From there, a #8 wire goes to the alternator and #10 to the fuse panel. In addition to a fusible link near the battery to protect the #8 wire, someone above suggested using a fusible link to protect the #10 wire. I think that's a good idea, so I will determine a way to mount it. Glad I'm retired and have time for re-thinking my plans. Here in Texas, my friends would say I spend most of my time "fixin' to think about things."

On a related note, I found a reasonably-priced source for cross-linked wire on eBay. I'm using SXL with its thicker insulation, but the source also sells GXL (thinner insulation but more flexible). The price for 25 feet is 20% less than other sources, and shipping is free instead of $12-$16. Don't know if I'm allowed to post links to eBay, so I'll just tell you the store name is "Premium Cables and More."

 

We wanted to clear the air here. There has been quite a discussion on this subject without folks understanding the engineering that went into the decision to use the Mega Fuses in many of our kits. I am a site member here, and also work at AAW as one of the design engineers. The 175 amp Mega Fuse (not Maxi Fuse) is used in many OE GM, BMW, Audi, VW, etc. applications to protect the main circuit to the energy center (Fuse panel). We chose these because when a fusible link blows, it can create quite a mess, and in some instances, even cause a small fire. The fuse serves 2 purposes: 1. To protect the main feed in the case of a catastrophic failure (EG: a front end collision that shorts the main feed to ground). In this instance, that fuse will blow in .5 seconds. 2. To protect the main feed in the case of a slow overload (a gradual draw over what the system's capabilities are). They are rated at 175 amps because they are intended to be mounted out under the hood just as in an OE application where the industry standard under hood temperature is understood to be 200-250 degrees F. With that temperature in mind, that fuse degrades to about 110 Amps. This information was well researched with the engineers at Little Fuse who manufacture these fuses. A 10 gauge GXL/SXL wire is capable of handling about 103.5 amps before degradation begins. 103 amps would be an extremely high draw in most any vehicle, and would only happen on very rare occasions or builds.

Placing the Mega Fuse holders inside the car or in the trunk, are not suggested for 2 reasons. By mounting the fuses in the passenger compartment (cabin or trunk), in the case of any type of failure, you are now bringing a hi-tension, unfused 12V battery lead into the vehicle and allowing the unprotected circuit to enter the cabin instead of leaving it outside of the vehicle. Extremely bad idea. Also, by mounting them in the cabin, where the air temperature is ambient, the fuse is now rated too highly to properly protect the system. That is why we suggest, just as the OE applications are done, to mount them out under the hood close to the battery, starter and alternator. This allows for the circuitry to be fused properly, and in the case of a catastrophic failure, keeps any instance of a fire outside of the cabin or trunk.

As far as placing the alternator on a fuse, that was done as a safety issue in case the alternator shorts to ground, and yes, although rare, that can happen. Probably overkill, but not a bad thing.

With all this in mind, we chose these fuses because they are very clean, and when they blow, there is no mess and no cutting of wires to re-splice as with fusible links. Simply fix what caused your problem, open the mounting case, and replace the fuse.

All of this was done with keeping the safety of our customers and the integrity of our product in mind. We certainly could have continued to use fusible links, but the safety and clean installation that these fuses just makes for a much better product.

 

You aren't really fusing the fuse block, you are fusing the power going to the fuse block. It's there to protect the wire between the battery and the fuse block. However, 175 amp does seem excessively high.