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Author Topic: Fuses on Circuit breakers....  (Read 1211 times)
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« on: May 24, 2013, 08:04:46 AM »

This one is for the electrical gurus in the room.

My Buffalo has 6 circuits up front that have glass fuses connected between the wire and the circuit breaker. All of these circuits are for the various lamps and lights on the bus. The glass fuses are all 30amp and the circuit breakers vary with one being 5amp, 2 are 8amp and 3 are 10amp. See attached image.

I'm hoping someone more knowledgeable than I can explain the logic of this set-up because I'm not seeing it.




P8M4905A-1308, 8V71 w/V730
Custom Coach Conversion
Greenville, GA
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1980 MCI MC-5C

« Reply #1 on: May 24, 2013, 04:16:09 PM »

I tried hard to come up with a legitimate reason for having high amp fuses in the load path with a low amp breaker.  All I could come up with is the obvious - minor overload, resettable breaker so you can change a lamp or whatever, major overload the fuse blows and you can find the short.  The problem with that is the breaker will blow before the fuse every time.  So the fuse becomes a last ditch protection for the major overload and the breaker failing.  \maybe the fuse is fast blow while the breakers are slow blow.   Maybe that is the answer but it's all I can come up with.


1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Tatamagouche, Nova Scotia
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« Reply #2 on: May 24, 2013, 05:34:49 PM »

Breakers have a quality known as interrupting capacity. Fuses do too. If the available fault current exceeds the interrupting capacity of the breaker the contacts may weld together. Guess what happens then?
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I'd rather be lucky than good.

« Reply #3 on: May 24, 2013, 08:36:51 PM »

The problem with those resettable breakers is they keep resetting even though your fault hasn't necessarily cleared.  Eventually the breaker fails and you have a fire. The fuse prevents that. Manually resettable breakers would be a simpler solution, bit it works as is.

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Rick A. Cone
Silverdale, WA
66 Crowny Crown "The Ark"
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« Reply #4 on: May 25, 2013, 10:58:07 PM »

These auto resetting type breakers were once used on older light aircraft and later banned and replaced by fuses for the above posted reasons.

However, that doesn't explain the huge different differences in ratings on your bus.

Ash Flat, AR
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