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Will a DC circuit breaker trip due to high voltage (exceeding voltage rating) or will it only trip because of high current? For example, if you have a 40 Amp DC circuit breaker which also has a 32 voltage rating would you have to keep the amperage below 40 and also keep the voltage below 32? Or do you only have to consider the amperage not going above 40?

The reason I ask this is because someone else on here asked if an AC circuit breaker will trip because of voltage and the answer was no. An AC circuit breaker will only trip due to high current and can't even detect voltage. I was also hoping this applies to DC circuit breakers as well. Does anyone know the answer to this?

Chris U
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    As a design goal all your components and assemblies have to have a rating greater than the actual supplied voltage. So if you now have 48 (more when full) volts then you need to make sure all your breakers, controllers and motors are all able and designed to be able to cope with the higher voltage. – KalleMP Oct 25 '18 at 06:39

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You need to keep the voltage less than 32V, but not because the breaker will trip if you go higher than that.

The problem is that if the voltage is too high when the breaker trips, it might not be able to stop the current because of arcing.

Dave Tweed
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  • If I have a 48 volt lithium battery, will this be way too much? The reason I'm asking all this is because I have an electric scooter with a 1600 watt motor that has been having problems with 40 Amp fuses in the battery connector (which runs from the lithium battery to the control board) getting melted and ruining the battery connector. I'm tired of having to order more and more battery connectors so I figured a 40 Amp DC circuit breaker (with a 32 voltage rating) would solve the problem.Am I wrong here? I wanted to ask before I possibly do something to cause damage. – Chris U Oct 25 '18 at 01:40
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    A fully charged 48V lithium battery will go up to 53V. – Zy Gan Oct 25 '18 at 03:35
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    Changing a fuse into a circuit breaker is unlikely to solve the problem. There's a good chance you'll ruin the circuit breaker instead of the battery connector, which sounds like a bad tradeoff. Or maybe both get ruined. The fuse is not your core problem, something drawing overcurrent is. – Niko Kiirala Oct 25 '18 at 11:10
  • Thanks for helping me thus far. Here is the link for where I bought the scooter......... http://www.bigtoysusa.com/evo1600welectricscooter.aspx and here is the link for where I bought the lithium battery.......... https://www.aliexpress.com/item/1800W-20Ah-48V-eBike-Battery-For-18650-Cell-Built-in-50A-BMS-Lithium-Battery-48V-With/32812989387.html?spm=a2g0s.9042311.0.0.376b4c4dWLezw9 Can you tell from the specs from both links why this is happening? Can you tell me what the best solution for me to do is? – Chris U Oct 25 '18 at 12:13
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Circuit breakers do not "know" the voltage of the circuit they are used in, so cannot trip based on that voltage - they only trip on over-current.

However, they are designed and rated to operate correctly (trip cleanly) only up to a certain voltage - using a 32 volt breaker on a 120 volt circuit may result in the breaker arcing when it trips (likewise, using a DC-rated breaker on an AC circuit, or vice versa, may result in faulty operation.)

(GFCI and AFCI breakers may be more sensitive to voltage than normal breakers)

Peter Bennett
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  • Please allow me to explain what I'm trying to do because I have a few more questions....I have an electric scooter with a 1600 watt motor. I swapped the lead acid battery that came with it for a 48 volt lithium battery. I have been having problems with 40 Amp fuses melting inside the battery connector which runs from the lithium battery to the control board (which has a voltage rating of 32.) So today I purchased a 40 Amp circuit breaker with voltage rating of 32. My questions are 1) Will this work and not cause damage? 2) Will this slow down my scooter? 3)Do you all have any better ideas? – Chris U Oct 25 '18 at 01:33
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    What was the original battery voltage? Applying 48 volts to a system designed for 32 volts may cause all sorts of problems and/or damage. – Peter Bennett Oct 25 '18 at 01:40
  • I'm not sure exactly what you mean by original battery voltage but the lithium battery is 48 volts, the motor is 1600 watts and the control board has a voltage rating somewhere around 33 volts – Chris U Oct 25 '18 at 01:43
  • The circuit breaker is rated for 32 volts if that's what you mean....? I'm not sure what you're talking about with the 32 volts. – Chris U Oct 25 '18 at 01:45
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    @ChrisU If you apply 48 volts to a control board with a voltage rating of "around 33 volts" then be prepared for severe hardware damage, blown fuses, and dangers of fire/overheating. You've literally exceeded the voltage rating of it, it failed in some undesired way, and that failure caused your fuse to melt. – nanofarad Oct 25 '18 at 02:05
  • @ChrisU: you said "I swapped the lead acid battery that came with it for a 48 volt lithium battery". What was the voltage of the original lead-acid battery? A circuit breaker rated for 32 volts DC SHOULD NOT be used in a 48 volt system - it might possibly work, but the manufacturer says it should only be used up to 32 votls, so NO guarantee. – Peter Bennett Oct 25 '18 at 03:10
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    @PeterBennett The nice thing about going outside the specs of breaker is that they work fine initially, until they suddenly stop working fine and burn everything. – Jeroen3 Oct 25 '18 at 07:18
  • Thank you for your answers, here is the link for where I bought this scooter and well as the link for where I bought the lithium battery. The lead acid battery (that originally came with the scooter) that I swapped out was also a 48 volt..... http://www.bigtoysusa.com/evo1600welectricscooter.aspx https://www.aliexpress.com/item/1800W-20Ah-48V-eBike-Battery-For-18650-Cell-Built-in-50A-BMS-Lithium-Battery-48V-With/32812989387.html?spm=a2g0s.9042311.0.0.376b4c4dWLezw9 – Chris U Oct 25 '18 at 12:07
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    @ChrisU: fuses and circuit breakers should only blow on fault conditions. If yours are blowing frequently, this is a sign of bad design. Also, fuse holders and connectors should be suitably rated for the current they normally carry, and should not be damaged in normal use. – Peter Bennett Oct 25 '18 at 15:06
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The answer to the question is no. A beaker does not measure the voltage in the wire as it has no specified reference to measure against. There is a voltage across the terminals when they are open and this would be the working voltage (perhaps higher with unexpected over voltages) and it would have a voltage referenced to the chassis or other adjacent conductors (of relevance for the insulation withstand) though these are not used as a reference.

The voltage ratings on breakers are due to safe switching voltages without detrimental arcing and contact erosion AND insulation withstand capability.

The first rating is not important unless the breaker is open or operated (manually opened or closed or opened due to fault) as it relates to the contact gap (and speed of operation, gas or vacuum fill or quenching systems) and not to the closed circuit.

The second rating (less often even mentioned) is the insulation resistance and may be 500V on even low voltage breakers and exceeding this with respect to external surfaces, adjacent poles or mounting hardware will result in unintended breakdown that could easily cause fires.

These ratings are different for DC, AC, HF and will be affected by relative humidity and atmospheric pressure unless the breaker is a fully sealed unit.

As mentioned in my comment:

As a design goal all your components and assemblies have to have a rating greater than the actual supplied voltage. So if your battery now has 48 (possibly more when fully charged) volts then you need to make sure all your breakers, controllers and motors are all able and designed to be able to cope with the higher voltage.

KalleMP
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