1941-1948 Ford ignition Resistor & (fuse)Breaker Assembly

[SoCalCoupe]

Anyone still using the original style ignition resistor and lighting breaker assembly? Think they're safe?


Anyone using this replacement style ignition resistor and lighting fuse block assembly? What size fuses are you using?

[fordor41]

to size the fuse connect a multimeter (amp reading) to the circuit you want to size. with that circuit energized, you will know the amp draw. example, meter reads 5 amps use a 5 amp fuse or maybe 7 amps. sometimes you may have to go a bit oversized to take in account for initial surge in the circuit as it is energized.

[petehoovie]

Originally Posted by SoCalCoupe

Anyone still using the original style ignition resistor and lighting breaker assembly? Think they're safe?


Anyone using this replacement style ignition resistor and lighting fuse block assembly? What size fuses are you using?

[V8COOPMAN]

Originally Posted by fordor41

to size the fuse connect a multimeter (amp reading) to the circuit you want to size. with that circuit energized, you will know the amp draw. example, meter reads 5 amps use a 5 amp fuse or maybe 7 amps. sometimes you may have to go a bit oversized to take in account for initial surge in the circuit as it is energized.

Fuses & circuit breakers are not designed to protect the item(s) that are powered in a circuit, such as lights and radio. Fuses and breakers are used to protect the smallest conductor (wire) in a given circuit. DD
.

[Tinker]

You mean I can't put in my house a 14-2 wire on 20amps breaker? Well at least the old 6 volt wiring it larger then the 12 volt stuff. I'm agreeing with you if your wondering.

[V8COOPMAN]

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Originally Posted by Tinker

You mean I can't put in my house a 14-2 wire on 20amps breaker?

240.4(D) of the "NEC" says unless specifically permitted in 240.4(E) or 240.4(G), the overcurrent protection shall not exceed 15 amps for 14 AWG. You also must remember that eons ago when the "smart" guys started putting the NEC together, they also took "Romex" 'de-rating' into consideration. DD
.

[Tinker]

Maybe why I would use a 12-2 awg wire on a 20 amp circuit.

[rotorwrench]

Household type wiring doesn't well compare to lower voltage automotive type wiring due to the differences in the voltage and type of conductor wire even though they both do the same basic job.

I use a chart in the FAA advisory Circular AC43.13-1B chapter 11 for advice on aircraft and automotive type wiring. Chapter 11, section 4, page 11-15 has a chart (Table 11-3) that illustrates acceptable fuse and circuit breaker ratings for the given conductor wire sizes in current use. This chapter also has information on wire sizes depending on load and distance of run (resistance) of the conductors for selection in a given circuit. This is the FAA bible for aircraft repair and it relates directly to automotive uses as well. Fuses and circuit breakers are not in the same category so it pays to know what an acceptable circuit breaker rating would be versus a fuse rating on any given wire gauge size. Here is a link to the current book. https://www.faa.gov/documentLibrary/...-1B_w-chg1.pdf

[SoCalCoupe]

Originally Posted by rotorwrench

Fuses and circuit breakers are not in the same category so it pays to know what an acceptable circuit breaker rating would be versus a fuse rating on any given wire gauge size. Here is a link to the current book. https://www.faa.gov/documentLibrary/...-1B_w-chg1.pdf

Thanks for the assist thinking this through.

Interesting. The 1940 Ford had all the lighting with multiple gauges in parallel from a single 60 amp circuit breaker. In 1941 they split it up into rear lights and headlights plus some miscellaneous lighting.


Not positive what the gauges of the wires are, and I don't want to remove the insulation, but I saw somewhere that they used 10, 12, and 14 gauge wires. Found a source selling cloth covered wire and it looks like coverings are usually associated with a particular gauge. Looking at my lighting wires, the headlight wire is yellow with a red tracer suggesting 10 ga. The rear lighting is red with a yellow tracer suggesting 12 ga. Based on the FAA chart a 40 amp circuit breaker would be used with a 10 ga and 30 amp with the 12 ga. That's in the ball park with Henry's 60 amp circuit breaker running them in parallel.


The chart says 30 amp fuse for 10 ga. and 20 amp fuse for 12 ga. so that's what I'm going to run. It doesn't protect the 14 ga. wiring for accessory lighting running in parallel with the headlights, but I can't help that. That's the way it's designed.

[Zeke3]

I don't think the 1940 circuit breaker was rated at 60 amps, that is too high a value to protect the circuit wiring. I think it was more like 30 amps.

[fordor41]

Originally Posted by V8COOPMAN

Fuses & circuit breakers are not designed to protect the item(s) that are powered in a circuit, such as lights and radio. Fuses and breakers are used to protect the smallest conductor (wire) in a given circuit. DD
.

true, the fuse/CB protects the wire but you have to know the amp draw for the entire circuit to size the fuse. I thought that was the original question

[V8COOPMAN]

Originally Posted by fordor41

true, the fuse/CB protects the wire but you have to know the amp draw for the entire circuit to size the fuse.

You REALLY have to know the amp draw for the entire circuit to properly size the CONDUCTORS (wire). DD
.

[rotorwrench]

The conductor wire gauges were selected to carry the current loads for any given circuit. The cars current output is reflected in the power generation capability of the generator design. It wasn't until the early 1950s that Ford started using generators with more than 35-amp capacity. Most systems are designed so that the generator load doesn't exceed 80% of it's capability as a general rule. There are certainly exceptions but most of those are special applications that would be special order like police and emergency vehicles.

The key thing to remember is that the circuit protective device it to protect the conductor wire and not the load. You can use a smaller rated fuse or circuit breaker than the conductor will rate but you can't use a larger rating or it will not protect the wire. Conductor wires burn very quickly when directly shorted to ground.

Auto electric systems have two types of circuits. One is intermittent contact type. The other is the continuous type. Starters, horns, and brake lights are intermittent. The rest would more for continuous operations. I remember driving at night and in cold weather in the old 51 Merc when I was young. The heater and lights were on and usually the radio as long as it was working. If you hit the brakes to stop, the lights would dim somewhat. The car has a standard 35-amp generator and a group 2 capable 6-volt battery. The saving grace was that if you slowed below governor speed, the overdrive would kick out and save some energy if you had to hold the brakes on a hill.

[fordor41]

Originally Posted by V8COOPMAN

You REALLY have to know the amp draw for the entire circuit to properly size the CONDUCTORS (wire). DD
.

agreed, but the question, as I understood it, was FUSE size. You can have grossly over sized wire for the amp draw but you still need to size the fuse to handled the amp draw in that circuit.