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Lets talk circuit breakers vs. fuses
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Gross Polluter Offline
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Post: #1
Lets talk circuit breakers vs. fuses
I forgot what thread it was over on TB where I noticed Eric was talking about fuses being better than circuit breakers in high current automotive applications. I was sort wanting to get his input on it, and others' for that matter. Away from the TB riff raff of course.

I'm particularly interested in discussing this subject because I just recently started to use breakers in favor of fuses in automotive applications. One of the big things right now is applications where I have multiple fuel pumps running in parallel. With these applications I tend to favor running individual relays for each pump but one common protection device for the entire pump array. I do this because if we lose a single pump at WOT then I'd rather have the system shut down as a whole than lose fuel flow and lean out at high loads. On street cars I usually tie the injector circuit in with the fuel pump so the fuel system shuts off entirely in the event of an overload.

In these applications I tend to rate the protection device about twenty percent above maximum operating capacity. As a simple example, my 2JZ setup shares a common 30amp protection device for the fuel pump, ECU, and injectors. At maximum operating capacity that entire circuit draws about 22 amps, roughly 73% of the protection device. I began having issues with standard ATO style fuses. They would get hot and melt the holder over time. The holder would eventually fail and cause a great deal of resistance rather than just opening the circuit. This happened a few times and every time it was the fuse that was getting hot and not the wires that ran to the holder. I got fed up and switched to Tyco aviation grade circuit breakers. These style breakers have very low internal resistance compared to a fuse so I can run a greater tolerance to the circuit opening point without generating excessive heat or resistance. I've found similar results running the Bussman 150amp breakers.

Additionally, it's much easier for my customers to simply reset a circuit if they're out in the middle of nowhere instead of being stranded without a replacement fuse. Obviously we design things so this never happens. But, I've had an influx of catastrophic failures recently as a result of poor work from other shops, most notably stereo shops that are less than sufficient at safely running high current cables.

But, it's entirely possible I may be missing something here. So what gives? What makes a fuse better than a circuit breaker?

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01-14-2013 09:41 PM
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WindowsBreakerG4 Offline
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RE: Lets talk circuit breakers vs. fuses
At least in a house application, breakers get weaker every time they blow, I assume the fuses are the same?

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01-14-2013 10:01 PM
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Gross Polluter Offline
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Post: #3
RE: Lets talk circuit breakers vs. fuses
I don't know about the Bussman style high current breakers, but the Tyco aviation breakers are rated for open and closing operation just like a switch. I forgot the cycle life off the top of my head, but most of the aircraft I've worked on didn't didn't specify a replacement interval for circuit breakers. For something that's disconnected routinely for inspection purposes, I doubt they get weaker as a result of cycling. That's not to say they don't get weaker as they blow, however.

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88 245 - 2JZGTE VVTi powered, MS3X/MSGPIO controlled
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01-14-2013 10:07 PM
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scottyd Offline
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RE: Lets talk circuit breakers vs. fuses
I thought a lot of the race cars use circuit breakers?

I always use a Maxi Fuse for the E-Fan with a 960/850 relay

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(This post was last modified: 01-14-2013 11:43 PM by scottyd.)
01-14-2013 11:43 PM
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badvlvo Offline
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RE: Lets talk circuit breakers vs. fuses
Ok, before we go down this path lets lay out the scenario where fuses are better

But I can't take too long, I'm waiting to cause another epic 740atl meltdown. If I can get him to lose his shit again I'm popping a bottle of champagne tonight.

ONLY in car audio would I consider fuses as the only way to go, and that's ONLY on the high current side of things like the power supply to the amps. Fuses blow at a more consistent amperage, and when they blow they completely break the circuit by the nature of their design. High amperage car audio style breakers can stick, or not completely break the circuit, or they will break at lower current than rated. I have even had one that would break if I hit a bump the wrong way.

They also withstand the vibration of a HUGE system better, like 150db sound systems. The vibration alone will trip the breaker.

When you have a 1/0 or larger cable as a potential short, and you are trying to pull 300a through it the length of your car you want the protection, and you don't want premature failure when competing, or even just playing it loud.




OK, now that we have that out of the way........



If you are melting your fuse holders the connection would be suspect. Anywhere you are concentrating heat there is poor conductivity.
Your solution of the breaker is a good one if it solves the problem, and I have done similar myself.

For example, I had a truck that would blow the tail light fuse if I had the trailer connected and would have the brakes on for more than about 1 minute. This sucked in traffic, in LA, at night and in the rain with Matts car on the trailer. The solution, a breaker originally used for the AC system that would plug right in the box in place of the fuse. It never overheated or gave me any shit for the next 2 years I owned that truck, and it still hasn't burnt to the ground as far as I know.

For applications other than high amperage usage such as car audio I see no problem with breakers. I have used them in a few race cars we have assembled, nothing like popping a circuit and only having to push a button to reset rather than finding a fuse to replace it.



When I wire circuits I tend to go a little overkill. If the circuit pulls 30a I wire it to handle 50a and fuse it as such. Heat builds resistance and can rise the amperage load seen at the fuse or breaker. I'm no electrical engineer so I can't explain in the technical detail, just what my hack ass has learned over the years of building charging systems and other shit. The fuse protects from a short and insures the amperage being drawn doesn't exceed the capability of the wiring or connections.


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01-15-2013 12:11 AM
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Gross Polluter Offline
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RE: Lets talk circuit breakers vs. fuses
(01-15-2013 12:11 AM)badvlvo Wrote:  The fuse protects from a short and insures the amperage being drawn doesn't exceed the capability of the wiring or connections.

Precisely. This is how it is written in the Federal Aviation Regulations, which I follow as a guideline when building cars. The fuse or breaker is there to protect the wire from failing and not the device wired to it.

I have a feeling the fuses I was using may have played a role in the failures I was personally experiencing. After analyzing the mode of failure I observed that it was always the fuse filament that would get hot and melt over time. The actual terminals that the fuse slid into never got hot or arc'd over or anything of the like. I'd consider it an isolated incident, but one is enough to justify switching over to breakers.

But, as I said, if I missed something I wanted to know.

(01-15-2013 12:11 AM)badvlvo Wrote:  Clear as mud?

Crystal clear. Thanks for the input!

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88 245 - 2JZGTE VVTi powered, MS3X/MSGPIO controlled
98 XJ - Stock(ish)
01-15-2013 12:55 AM
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badvlvo Offline
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Post: #7
RE: Lets talk circuit breakers vs. fuses
You were right on target with your conclusion.
Breakers are the way to go in many applications and I plan on replacing all of my fused circuits in the 244 with breakers.
The 850 will have a couple huge fuses, but 400a each isn't much I guess.

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01-15-2013 02:24 AM
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745 TurboGreasel Offline
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RE: Lets talk circuit breakers vs. fuses
(01-14-2013 10:01 PM)WindowsBreakerG4 Wrote:  At least in a house application, breakers get weaker every time they blow, I assume the fuses are the same?
My garage has the screw in residential fuses, and they are definitely a lot weaker after they blow. I have to drive all the way to the hardware store, and hope they restocked since I last bought all of themFacepalm


Aside from that, spade terminals pretty much suck and melt out their holders.
in their engine bay fuse boxes Dodge and Ford use the screw in ones like PAL or ANL.
http://www.nxtbook.com/nxtbooks/waytek/catalog224/#/122 (LONG LOAD WARNING)
breakers start a few pages right. I got some big screw down bad boys when I put the 400A controller in the golf cart http://www.evparts.com .

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01-15-2013 05:56 AM
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