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When does a fuse or circuit breaker blow

mrel

Jul 2, 2008
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Hello
Did a test on lithium 12 volts 100 amp hour battery ,hook wire from positive terminal to a 25 ampere circuit breaker and the other end of circuit breaker to negative terminal of the lithium battery .
The question (1) is the wire got hot But the circuit breaker did not trip, why circuit breaker did not trip?
Question (2) Did the same hookup but instead of using circuit breaker use 20 amp fuse holder and the fuse did not trip why?
El
 

Externet

Aug 24, 2009
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Because the current did not reach 25 nor 20 Amperes. The 100A is/was the supply capability of the battery; not what it 'puts out' Did you measure the voltage of the battery when you connected it ?
 

Keonte45

Aug 29, 2022
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The answer is quite easy. It just means that the current flowing through it didn't reach the max (20 or 25 Amp).
 

mrel

Jul 2, 2008
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Because the current did not reach 25 nor 20 Amperes. The 100A is/was the supply capability of the battery; not what it 'puts out' Did you measure the voltage of the battery when you connected it ?
So try to find right circuit breaker or right fuse to use for my solar panel have two 100 watts solar panel connected in parallel to double the ampere output and using mppt controller and 100 Ah battery .
Now back to my experiment since post the setup experiment the circuit breaker and fuse did not blow ,but the wire connecting to circuit breaker and fuse start smoking so breaker or fuse Did Not blow that mean could start fire .
What will right size circuit breaker or fuse to use in case short breaker or fuse blow( where answer)?
el
 

Harald Kapp

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Nov 17, 2011
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You'll have to consider at least two parameters:
  • Max. amperage of the combined solar panels. To protect the solar panels from overcurrent the external fuse or circuit breaker should be rated at max. the amperage the solar panels can deliver.
  • Max. amperage of your wiring. This is the usual function of a fuse or circuit breaker: protect the wiring from overheating (or even fire) in case of a short circuit.

The max. amperage of a wire depends on the material and of course the diameter/AWG (link to information). If your wiring is rated below the max. amperage of the solar panels, then this defines the upper limit for your circuit breaker or fuse.
 

Externet

Aug 24, 2009
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A breaker or fuse protects wiring. Does not protect a DC current source as a solar panel.
If a wire inside a panel opens from overcurrent; the wires inside that panel are under what is needed, it is a poorly designed panel.
The opening of a wire in a solar panel under load likely produces arcing instead of a 'spark' leading to :

1662484744497.png

A fuse/breaker cannot avoid the arcing fire from an open circuit within a solar panel.
If you want safety, better install solar panels on metal roofing. A breaker would have to be DC rated and be used for disconnection.

Your original post mentioned Li.ion battery; not solar panels. And 100Ah as mentioned is not the Amperes you believe it is.
 

crutschow

May 7, 2021
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The question (1) is the wire got hot But the circuit breaker did not trip, why circuit breaker did not trip?
Question (2) Did the same hookup but instead of using circuit breaker use 20 amp fuse holder and the fuse did not trip why?
Either the wire was too small gauge or the battery couldn't deliver that much current.
 
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