# A very basic thing in electrical circuits that has confused me for weeks

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Hi Everyone , I am new to this forum. Infact its my first time ever being on any kind of forum.
I need your help on a very basic concept of electrical circuits that is confusing me alot and has shattered my basic concepts.

The question is :
In circuits we often tend to ground the negative terminal of a battery ( DC ). So the positive terminal is at higher potential.
Why do we connect FUSE on the positive terminal side & why do we connect LOAD on negative terminal side.
Because the direction of electronic current is still from negative terminal to positive terminal. So the fuse should have been on the negative terminal side of a battery.

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#### telectrix

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are you referring to vehicle electrics?

#### davesparks

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The negative path in a vehicle can be through any and all bodywork metal so it would be impossible to ensure that the fuse is in the circuit if it was inserted into the negative as much of the current could bypass the fuse

#### darkwood

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If the fuse was on the Negative side and operated it would leave the circuit live still with a PD to ground... putting it on the positive side ensure tht when a fuse operates the associated circuit has no potential to negative/ground in your example removing the risk of shocks or fires from possible faults, the shock risk is minimal when discussing SELV (safety extra low voltage) like found in cars etc for instance but you would still want the fuse to de-energise the circuit with reference to ground.

#### ruston

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The fuse would have to be at the component , It would mean that fusing at a central point such as a 'fuse box' would be very costly to manufactures as it would mean double wiring.

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@darkwood - but wont the current pass through the load first when we place it on negative side which means if there is any fault i-e any high currents ( short circuits ) the current would pass through the load before it could pass through fuse. Making the load vulnerable to damages ?

#### davesparks

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No, because the same current will flow through all points at once

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@telectrix - the video i was watching was about cars but my question is a general question. Just like in any electrical schematic we see a fuse connected to a hot wire ( in series to a source ). Whose basic purpose is the safety of equipments. But as the current flows from neg to pos in DC why dont we connect a fuse on negative terminal side ?

#### davesparks

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It doesn't matter from a current flow point of view where the fuse is, it breaks the circuit and stops the flow of current wherever it is.
The same current flows throughout the whole circuit up to the point at which the fuse blows

#### darkwood

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@darkwood - but wont the current pass through the load first when we place it on negative side which means if there is any fault i-e any high currents ( short circuits ) the current would pass through the load before it could pass through fuse. Making the load vulnerable to damages ?
I build controls systems so I spec' to different regs than that of vehicles so are we assuming we are discussing vehicles here as you never said the scenario.
If we are discussing cars then removing the raised potential against the chassis is safer and when you say a fault would go through a load then why if it was say a short before the load to the chassis it wouldn't flow through the load as it follows the path of least resistance.

You fuse the section where the raised potential would be against the common or ground (chassis) be it strapped + or - design.. A battery at the end of the day is eg 12v and it doesn't matter which side you strap to the chassis by design the feed side of all the loads becomes the raised potential against the chassis be it positive or negative source and its this that needs fusing to ensure all potential (with respect to the ground/chassis) is removed from the wiring in a fault or overload condition.

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Davesparks - the current would pass through the load first which if very would damage the load ( and most of the power would be lost ) which means less current will flow through the fuse making the fuse worthless ..

#### davesparks

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Davesparks - the current would pass through the load first which if very would damage the load ( and most of the power would be lost ) which means less current will flow through the fuse making the fuse worthless ..
No it won't, the current passes through the whole circuit at the same time. Current does not diminish, get used up or lost throughout the circuit. The total current flowing out from the negative terminal of the battery will return via the positive terminal of the battery.

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Thanks alot davesparks and Darkwood
It was really helpful. I think i getting the point now.

#### Lucien Nunes

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As above, the fuse is in whichever side of the circuit is not connected to the common or grounded terminal of the supply. This is because modern practice dictates that we ground the neutral so reliably, that there is negligible chance of it becoming live with respect to true ground, hence no need to fuse it. It does not matter whether it is positive, negative or one side of an AC supply, the fact it is solidly grounded avoids the need for a fuse. Single-pole fusing in the line / 'hot' side only, gives the benefit that when a fuse fails it will always disconnect the load from the 'hot' side.

So in household single-phase AC supplies in the UK, that's the line conductor (the neutral is grounded). In modern cars it's DC positive as the negative is grounded i.e. connected to the chassis (for compatibility with electronics), although historically the positive was grounded and fuses were in the negative.

If neither side of the circuit is grounded, then all conductors must be fused. Examples include domestic 240V circuits in the USA (which are centre-tapped to ground, making both sides hot at 120V), and single-phase circuits derived from 3-phase delta, such as shipboard power and historically in mainland Europe for domestic supplies, which also have neither side grounded and must be fused in both lines.

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@Lucien Nunes - Your detailed reply is really appreciable and helpful to me. You described it in really simple words [emoji106]

But what If a short occurs at the positive side of a battery before the fuse ? Wont a very large current pass through load because the load is on negative side and there is no fuse on its side ?

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