Circuit Breakers vs Fuses

[autobonrun]

I'm making the modification to my dash lighting this weekend by adding a fuse to the inline wiring. In an earlier post, it was mentioned that a circuit breaker would be better than a fuse.

Other than money, is there a reason why fuses are used rather than circuit breakers in cars? I know fuses are faster. Is there a safety reason or are circuit breakers too slow? It would be nice just to reset a breaker rather than changing fuses.

Has anyone done a wholesale replacement of their fuse panel with a breaker panel?

[dickster]

is that right?

in a house in the uk circuit breakers are much faster than fuses.

thats all thats used generally in new builds

maybe totally diff. in cars

the dickster

[critter]

Most aircraft use circuit breakers NOT fuses!

[autobonrun]

Originally posted by richardnelson
is that right?

in a house in the uk circuit breakers are much faster than fuses.

thats all thats used generally in new builds

maybe totally diff. in cars

the dickster

I was going from memory that fuses are faster, but your statement has me rechecking my memory. I found an excellent site that gives info on fuses, breakers and wiring. After reading, I'm going to hold up installation of the fuse on my lighting circuit until I can find the best place to put it. The site brought up an excellent point; the fuse should be installed as close to the voltage source as possible. The wire from the voltage source to the fuse is not protected from short circuits so it should be as short as possible. The fuse can only protect if the sc current passes through it. So placing the fuse behind the panel would protect short circuits in the panel wiring, but not in the lead wire.

The pages also briefly discuss the fact that enclosed fuses are better in harsh environs like under the hood of a car. This may explain why breakers are used in houses, not cars.

http://www.eatel.net/~amptech/elecdisc/fuses.htm

http://www.eatel.net/~amptech/elecdisc/cirbrakr.htm

[RoninLB]

I may/some times reply in "cave man" attitude. Some things leave no room for cheap/good enough. My humble '77 has a 8 breaker marine panel. If you want an explanation I can do it later. All CB are in use. Fires are a horror waiting to happen.

[Doug Zielke]

I don't subscribe to the notion that a circuit breaker is "better" than a fuse. A fuse is always the first line of protection in any electrical distribution system with potentially high fault currents.

You may have a circuit breaker panel in your home, but somewhere down the distribution system, there are many, carefully engineered fuses providing vital primary protection.

A circuit breaker may or may not be "faster" (to trip) than a fuse. It all depends on the individual component. When you have circuit breakers behind a main fuse, you can have serious coordination problems that can lead to protection failures.

So...if you are going to replace a fuse with a CB, you better know the electrical characteristics of the circuit and protective devices before you burn something up. Once again, why is it that we think we know more than the people who designed and built our cars?

[autobonrun]

Originally posted by Doug Zielke

So...if you are going to replace a fuse with a CB, you better know the electrical characteristics of the circuit and protective devices before you burn something up. Once again, why is it that we think we know more than the people who designed and built our cars?

I agree with your first sentence 100%. However, I have no problem questioning any older design. Questioning does not mean you think you know more than the designers. It just means you recognize that technology has changed and improved in the 22 years since your car was built. What didn't or couldn't work then may now. What wasn't available then may be now. But as you mentioned, you must know what you're doing.

I consider researching these type questions part of understanding the design underlying the car. However, taking your statement and mine together, if circuit breakers were the way to go, the new Porsches would most likely have them.

[aseem]

When we are talking household electrics both circuit breakers and fuses are available with several characteristics. Typically CB's are available with "fast", "medium" and "slow" characteristics. Similar for fuses. (for 220V systems anyway).
When it comes to 12V auto or marine electrics I'm not so shure. I never really checked at the autosupply if fuses are available in several "speeds".

As far as I know both CB and fuses are set out to do the same job: to "trip" if the current increase beyond the fuse value e.g. 10amps. The max load for any given circuit is calculated and given a fuse (or CB) to match. If the current increase beyond this value, there is a short or a malfunction somewhere, and the fuse snaps to prevent fire and/or any further damage.

A "slow" CB or fuse allows the current to rise above the fuse value for a period, while a "fast" fuse will snap. With motors in the circuit you will need a "slow" fuse, or an oversized fuse as motors draw a lot more current when starting up than when it is running.

[RoninLB]

To start with, the 911 electrical system leaves much to be desired. Doug doesn't have to subscribe to any notion I may put forth. If I see a design that I can improve, I'm going to do it. I like marine circut breakers because there is no chance of the "fuse" becoming a source of an elec. fire in a fuel atmosphere and a magnetic type CB reacts instantaneous in short circuits. Fire prevention is the main job of this "weak link" in wireing. There are 2 types of this "weak link". Thermal and magnetic do the job differently. Thermal devices react to heat, magnetic devices react to a magnetic field created by excess amperage. CB can be a combination of the two. Some CB offer what is called "ignition protection" and some CB don't. "ign. pro" is the ability to prevent a fire by its operation. Fuses react to heat and offer no "ign pro", you can argue that the fuse glass does offer "ign. pro". The glass fuses we may use are not vapor proof. Environmental heat or cold may be an issue because fuses "trip" due to heat. The same fuse used in Canada in winter time will "trip/open" at a different load than if the fuse was in Florida in the summer time. The "weak link" design in our cars is a factor of manufacturing production. CB has been around for many, many years. If you are comfortable with a group of in line fuses, fine. If you want instantaneous protection with a short, which I define as 10 X current capacity of wires[properly sized] and vapor ignition protection, which may be important, then use vapor proof CB. The amperage limit on CB is not the design of the CB but the cost of high current CB. Standard/any fuse is cheap. In big electrical distribution systems the cost is the limiting factor, not the design. Knowing the electrical characteristics, slow blow/ fast blow of the "weak link" is a consideration on multi "weak link" circuits, no big deal.
I use Blue Sea Systems vapor proof magnetic 8 position CB panel. Part no. 8023, about $120. I mount it in front of the windshield washer pump next/close to battery in the space between the battery and spare tire. It's low, easy to access, not in the way, safe, and a pleasure to have. Installation is idiot proof. I also use marine grade wires which are higher quality, more abrasion resistant, and must meet higher standards than automotive wires. Any soldering is done with Radio Shack 4% silver that does not have any lead in it. The CB I use comes with 15 amp CBs but can accept different sizes. The more complicated the circut and the more expensive the electrical device the more I want the best. Did I mention safety again yet?? IMO vapor proof magnetic CBs are safer than fuses.

[Doug Zielke]

No comment.

[island911]

Originally posted by Doug Zielke
No comment.

LOL
Well said Doug!
Besides, what would YOU know about Fuses CB's et al.

I'm thinking I need to update mine to GFIC. It's much more Modern and, keep in mind, that 12V can really get-ya if those wires touch your tonge

[stormcrow]

I agree with you Ron. I don't know if you are aware of it or not, but the marine industry does use CB's in most pleasure boats. As you have stated, the marine industry standards are a lot different because of the enviornment that the equipment/components are exponsed to.

If CB's were not safe to use on gasoline boats, then they wouldn't be used. Knowing how a product works is also a plus. The information you provided about the CB's will surley educate a lot of us on this board about them. They are defnintely different than the household CB which I think a lot of members here think of when you say Circuit Breaker including myself.

Thanks for the info.

Steve

[RoninLB]

Storm/Steve...thanks for the acknowledgement..Under my sign in name is Long Beach, N.Y. LB NY is a sandbar, literally. Lived on the ocean my whole life. 75-100 miles offshore w/8-12 ft. seas in a 30 ft boat are routine. Grew up $@a!ing boats at 12 years old. This CB stuff is local knowledge. A better/wilder topic is electrical grounds. The only way I know about Bald Eagles is to hear local knowledge from the Washington/ Oregon men. I want to earn my keep around this board. And I don't want to be boring. All I offer is what I see thru my eyes, not only what the books say. If I don't come across as sweet and nicey, to bad. Maybe snorting salt air has been corrosive on my little brain.

[autobonrun]

Thanks Ron. This is good information. I think I'll just hold off on my modification and take a good look at the entire electrical distribution system; I have noticed insulation on several of the wires at the fuse box that are burned. I think the sealed CB's you speak of are hermetically sealed. At least that's the term we use in my industry for switches, etc that are sealed from the environment in a wax-like enclosure. From what I read on the web site I attached, there should be either a main fuse or CB located right at the battery to protect the main feed to the distribution panel from a SC. Did you install one on yours?

By the way, who distributes the Blue Sea Systems?

[RoninLB]

Auto...I don't think there is a breaker from bat. to fuse panel. Some systems may have a fuseable link, a wire that opens under high current, comes in different sizes. I didn't install anything between bat. and panel. That would be important if that wire got grounded, the branch circuits from panel should be protected. I did install a bat. terminal that has a wing nut to attach my ground cable for quick disconnect. I use it routinely. I'm always in motion doing electrical upgraded. I have done the lighting circut, which is important. I put elect. seats on CB also. My attitude is that there is 2 systems to look at. 1 system will/should only be a problem in a crash. The other will be a problem due to poor design or electrical device problems. I figure the lighting circut is poor design and elect. seats are possible device problems due to high current and switches/motors that can fail. The more you look at a circut the more complicated it may become. Elect. blower motor circuts may need attention. The dash lighting circut is another question mark. I would like to install a pulsing CB on main feed to headlight sw. which, IMO is a possible problem. I love the after market radio amp that has a fuse 1 ft from amp and 8 feet from bat. Whatever electrical device that is expensive should have protection to protect the cost of the device. The stock ground system for engine starter is a known weak spot. I will be adding another ground wire from starter to both transmission mount bolts. Loctite has a anti seize that is called Graphite-50 that I hope to use there that is 2X as conductive as copper anti seize.
The best thing about working on the electrics is that you walk away with clean finger nails. Also a decent meter is the Fluke automotive volt/ohm/amp/rpm/heat temp. meter than can be found on sale for $200. A mail order marine supplier that is OK is M&E Marine in Camden, NJ. 1-800-541-6501 or you can check out www.memarine.com Blue Sea Systems is not the cheapest mfg. of CB panels. Even the cheapest marine CB panel is better than fuses. I like the quality of Blue Sea. My attitude on this electric stuff may be over kill, but that's my problem.

[dickster]

all i know is that if i were in an electric shower that shorted while i'm under the water i'd be glad i had circuit breakers, and probably dead if i had fuses. or so i have been told.

i have no wish to find out!!!

and the reason they're not used in cars?? cost versus safety risks??

the dickster

[304065]

I don't think you find them in cars for a couple reasons:

The first is cost of the breaker v. the fuse: checking my Aircraft Spruce catalog, a decent a/c breaker, like a Klixon, starts at about $10, whereas I just bought an assortment of fuses for $2. Even assuming you bought them in massive quantity like an auto manufacturer does, they're still more expensive.

Before I saw the light I had 4 other cars made by a company in Munich- the power windows had a circuit breaker in series: I suppose they intended this as a safety feature, e.g. the CB trips when the motors begin to draw excessive current as they try to close on an inflexible object like somebody's arm. But this is the only time I've seen them used in an automotive application.

The second point, and I think I put this in an earlier post, is that when a fuse blows it requires you to stop what you are doing and trace the fault in the circuit, otherwise you will just keep blowing fuses. The ability to rapidly reset a circuit breaker is a temptation to some to rapidly reset it after it blows without identifying and fixing the cause. Which is fine, if you have done something like run your air compressor and garage heater and soldering iron on the same 15-amp circuit, like I did a few weeks ago. But not so good, if you don't resist the temptation, like an old flight instructor I had, to reset the landing gear pump circuit breaker in a C172RG immediately after it blows, saying "don't worry about it." Needless to say there were no further lessons from that guy: somebody who doesn't even wait for it to COOL before loading it again is asking for an onboard electrical fire.

Autobonrun, I agree with your strategy of fixing the electrical issues (burnt insulation) first- check my other post for the source of original wire and connectors for this.