protecting wiring with fusible link, circuit breaker, or fuse?

[Guest Jeff_Miller]

Perhaps I'm just being paranoid but I was thinking of going one extra step above using a battery disconnect and adding a modern approach to protecting wiring by putting a fusible link, circuit breaker, or big fuse on the 10 gauge wire that runs from my starter to the ammeter on my 1936 Buick Special. It is this 10 gauge wire that feeds all the electrics in the car short of the starter motor.

My wiring is original and although it looks to be in good shape I can't help but think how brittle it might be. I think that if I added something like a 50 Amp sacrificial fusible link, breaker, or fuse that I would have a little more protection from an electrical fire while driving down the road. The lights are 15A and the generator only puts out 25A so it seems that 50A should be sufficiently large to take spikes and yet burn fast enough that the rest of the car should be safe if a short happens.

Has anybody else done this or have any opinion about doing it?

Jeff

[Dwight Romberger]

Model T owners have been puting a 20 amp fuse in that wire for years. I put one in when the wiring under the dash (next to the gas tank) in my '26 caught on fire.

In my 1936 International Pickup I just finished rewiring, I installed fused switches on everything except the horn and the wire to the ignition switch.

My '30 Buick will have a small hidden six fuse panel to protect everything except the wire from the battery to the starter.

Dwight

Edited February 20, 2013 by Dwight Romberger (see edit history)

[Guest WEB 38]

The model a venders sell a very nice one I have one on mine (fuse holder) Bill web 38

[Daves1940Buick56S]

Hmmm, I would not do what you are proposing. You are putting a single fuse in the line for all the power in the car, including lights and ignition. In engineering we call this a single point of failure (SPOF) and they are to be avoided. For example, you are cruising down a 2 lane road and decide to pass a slowpoke, so you slam it back into second, pull around and...the fuse goes and you got nothin' with a Mack comin' straight at ya. Whole new category of bad day. Also, at night you will lose not only your ignition but the lights as well.

Take a good look at the wiring schematic and the wiring diagrams in the shop manual. If you want more protection for the circuits *other* than the ignition and head/tail lights (don't know the '36 in particular, but the lights are hopefully protected by a circuit breaker in the switch), add in-line fuses appropriate for the max draw as close to the power source as you reasonably can, probably near the ammeter. If the wiring in the "unprotected" parts looks bad, repair or replace.

Cheers, Dave

[Guest pfloro]

In my opinion, adding one or more fuses for over-current protection is a good idea.

I understand the concept of a 'single point of failure'. However, what are the odds of a properly sized fuse in a quality fuse holder which has been solidly wired into the circuit failing... Failing, this is, when an over-current has not occurred. However, I do like Dave's idea of separate fuses located in the individual circuits. This would spread out potential failure points.

I used a 30A cartridge type fuse in a solid holder when I added higher wattage (80/100) headlights in my '84 Toronado. A 30A relay switched a direct feed from the alternator through this fuse to power the headlight circuit. The headlight dimmer switch only powered the relay coil.

At least in the later '70s - '80s, GM used a fusible link in the main power distribution circuit. It was connected to the starter motor battery stud and directly fed part of the bulkhead connector. I accidentally shorted this circuit to ground while 'playing around' the alternator. Most of the car's circuits went dead (headlights worked but no cranking or ignition)...! That certainly was a SPOF. Ouch!

Paul

Edited February 21, 2013 by pfloro (see edit history)

[Daves1940Buick56S]

Paul:

I agree the odds are very low of a failure but it is not zero. And Jeff was concerned about shorts in his wiring, so it is not unreasonable to say that it might happen while under way, and if the ignition circuit is past the fuse you've got a dead engine. Risk management is especially important with this old iron, we have to be wary about putting ourselves or anybody else in harm's way when it can be avoided. I always say I don't want my last concious thoughts to be "well THAT was stupid." I am not trying to be an old nag but I sure don't want anyone to get hurt.

And bad on GM for having that fusible link where it was! Definite fodder for lawyers I would reckon...

Cheers, Dave

[Guest Jeff_Miller]

Well this is an interesting discussion that I started

I am familiar with the GM fusible link implementation and indeed that is the exact type of implementation I am looking for. And yes, I know the pain it causes when this SPOF occurs because I was stranded on the side of the road in the middle of the night in the middle of WI once when that fusible link blew on my 1984 Fiero. There was nothing wrong with the car other than the fusible link but I still appreciate the concept that had there been a monster short in the vehicle wiring that the link would have gone before the car torched, potentially with me in it.

My Buick was originally equipped with a single 30 Amp fuse on the lighting circuit. I will be replacing that implementation with a fuse block and pulling the ignition, lights, and new fuel pump and fan off into separate fused and relayed circuits that will each be fused at much less current than the 50 Amp I am thinking of putting on the main feed from the starter. Doing this should protect those individual circuits and let them blow before I lose the 50 Amp and everything else.

With the 50 Amp fuse I am talking about it can carry current that is more than 3 times larger than the 15 Amps the lights might draw and easily 2.5 times the capacity of what the car might possibly consume. Unless the fuse is faulty, it blowing indicates a significant issue in the wiring that most likely would torch the car.

So I think it comes down to deciding if a SPOF that is hinged on a modern electric fuse that can be easily replaced on the road is worse than trusting in wiring that if it took greater than 50 amps would likely torch the car, or at the very least, render the car irreparable on the road. We each get to make our own decisions but for me, the fuse seems like the right idea.

Jeff

[Dandy Dave]

Fuse or no fuse. I have seen wires from charging systems that were heated to the point that the copper had broken down and had enough resistance to cause heat without blowing a large fuse first. Also, I have seen the copper turn green in spots also contributing to a, "loss of flow." If you are Afraid of old brittle wire. (And you should be.) Be safe and replace it. Dandy Dave!

[Mark Shaw]

I am with Dandy Dave on this one....

[Guest Jeff_Miller]

It is hard to argue against fixing a problem vs. masking it with a backup. I just ordered the engine and dash harness which will set me back 3 weeks but clearly I won't need to worry as much about the wiring. I'm still thinking it is a good idea to have the backup fuse though.

Jeff

[Dwight Romberger]

After having two vehicles catch fire while I was driving them, new wires are a must for me. Almost anyone can do it, and with reproduction harrnesses and bulk wire any car can be wired.

Good choice Jeff.

Dwight

[superbuick]

OK, everyone has a valid point. But I agree with a fuse link on the main power supply. I have worked on cars for 35 years and they have been factory installed on most or all the cars built during that time. A fuse that would is rated above 50% of your greatest possible load would be safe for driving and help prevent possible electrical fires. I own and drive 7 prewar Buick's and so I will have an unplanned problem a couple times a year. And they are never real fun but most of the time an easy fix, but that's what I signed up for with these vintage cars. However I get cars in the shop with blown fuse links that are an easy fix after that short is found.

If you burned a fuse link installed as you described, then you have a big short and not having one will only buy you a few extra seconds of time before a big melt down and possible electrical fire.

As Mark said- if you are aware of several bare or crumbling wires , then plan on ordering a new harness. And all of us should unhook the battery on these old cars when stored in our garages and under our house.

- Steve Fisher

[Dandy Dave]

I agree that it is good to have fuses for those times when a dead short happens. But it is not 100 percent fool proof on old broken down wiring. When a piece of wire gets heated from a dead short the wire will loose its ability to conduct the flow of electricity and will act like a Nichrome oven heater element. This is what has happened when you find a bunch of wires melted together and you were lucky enough not to loose the whole vehicle. If a wire has decayed to the point that some of it has turned to a green powder, and there are maybe half of the strands left that have a substantually reduced ability to carry the current, then you will have a "Hot Spot". This happens most often in high demand, or high flow areas like the charging system. It is a lot like turning on an electric oven, the element gets red hot and yet the breaker or fuse in the panel will not blow because the resistance is less in the oven. It is more common on older vehicles with old wiring. I have seen this more than once in over 40 years of wrenching for a living. Dandy Dave!

Edited February 22, 2013 by Dandy Dave (see edit history)

[bigvic]

Hello, just rewired my 28-58 and most of the wiring runs thru flexible conduit, it takes a little persistence but with some help and digital pics you can rewire your car. You have to remember the age of the rubber insulation (RW) and how brittle it is. The cloth covering hides alot. A fuses purpose it to protect the circuits based on the wire size (gauge) which depends on what there feeding headlights, tailights or horns..So with respect to original wiring you should use the smallest fuse where possible. If a fuse ( sized correctly) keeps blowing, then you have a problem, it's doing it's job. That 50 amp fuses would only protect the primary circuit not the secondary circuits