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Why do we use a fuse/circuit breaker on both the DC positive and negative wires


Tariq
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For example, in an automobile ( as far as I know), there are fuses in only the positive supply wires and not in the negative, is it because pretty much the whole car is the negative side.

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Hi Tariq

I am sure your assumption is pretty much correct. Most automobiles have chassis on negative (0v). Some older automobiles  are positively grounded(+). The negative can be joined to many instruments and therefore will carry current for more than one instrument. The positive wires are normally single or grouped together from an instrument and go to the fuse box and protect them before going to the battery. Negative wires can be joined or taken from various places and can aid in the wiring to reduce the volume of wiring of a automobile.

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On 2021/04/03 at 12:14 PM, Tariq said:

For example, in an automobile ( as far as I know), there are fuses in only the positive supply wires and not in the negative, is it because pretty much the whole car is the negative side.

I have noticed the same. A fuse on both the positive and negative wires right by the battery

There is no technical reasons to so.

You only want to have a fuse as close to the source as practical possible. A fuse only on the positive would provide the required protection.

 

I guess one reason is that the fuse isolators that is commonly used is also used in AC applications where you want to disconnect both the Live and Neutral.

But even there you can use a fuse on the live and a link in the neutral.

 

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25 minutes ago, Jaws said:

to have a fuse as close to the source

curious... what do you see as the source? the battery providing electrons to the inverter or the inverter charging the battery? 'tis a potential problem, maybe... somewhere else someone had a fuse at the positive end of the battery as well as a fuse on the positive end at the inverter... that may not be the worst option...

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Not necessarily true that only fusing the positive would provide the necessary protection. If your positive terminal was earthed the fuse wouldn't fail if there was a fault current from the negative terminal to earth. In most systems you earth one of your potentials and then your protection can safely be installed on the other potential. Quite a few inverters earth the negative battery DC or recommend it, but not all, so it is safer to have a fuse on both lines in case your equipment is set up differently.

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