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Fuses

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Tresguey

New Member
i recently purchased a electric fan for my car. and the instructions stated to install the fuse on the ground side not positive side. why is that? :?:
 

stevez

Active Member
Whatever you do - do not allow the conductors or wires supplying the positive side (hot, the not ground side) to be unprotected in terms of overcurrent. The overcurrent protection must be sized to protect the wires - in case of a short to ground. Maybe this other fuse is just to protect the fan.
 

Tresguey

New Member
the instructions state to go direct from 12 pos batt. to the first leg of the toggle switch from the other leg of the switch go to the pos side of the fan. then tie in the ground side of the fan to the inlilne fuse and ground direct to chasis ground.
 

heathtech

New Member
Tresguey said:
the instructions state to go direct from 12 pos batt. to the first leg of the toggle switch from the other leg of the switch go to the pos side of the fan. then tie in the ground side of the fan to the inlilne fuse and ground direct to chasis ground.
This makes absolutely no sense to me. To qualify this, the fuse would still do the job if the fan motor developed a short in the windings, because current is equal throughout a series circuit. However, if for some reason the positive lead were to touch ground incidently, the fuse would be negated from the circuit! The battery would have a dead short with no protection. I would consider buying another fuse holder and an equal value fuse to put on the positive side as well. it couldn't hurt, and will give you double protection without violating the manufacturers specs.
 

_3iMaJ

New Member
My initial guess would be because current flows from ground to positive. But as I said thats just my best guess.
 

Tresguey

New Member
it just seems strange to me. i call the manufature and they told me it doesn't matter what side the fuse is on. positive or negative.
 

stevez

Active Member
Quite often the switch to operate fans, lights, etc, is on the ground side - often because the switch that operates the device has a contact closure to ground - maybe so that just one conductor is needed. I'd put the fuse as close to the battery as possible and make sure that the fuse safely protects everything in the circuit.
 

heathtech

New Member
_3iMaJ said:
My initial guess would be because current flows from ground to positive. But as I said thats just my best guess.
Yes, this is "theoretically" true, but, a fuse offers the best protection when it is placed on the positive or hot side of the load, not the ground side. As I stated earlier, if an internal short occured in the fan motor, yes, the fuse would blow regardless to where you put it in the circuit, but, say for instance another TYPE of short occured : Example/ the positive wire of the fan became brittle and the copper exposed, and this wire touches a chassis grounded metal panel or bolt, a short would develop from the battery to ground, totally bypassing the motor and fuse and elemenating the effectiveness of the fuse, and a fire could start! Where, on the other hand, as Stevez pointed out, if you locate the fuse as close to the battery as possible, you reduce the amount of wire that is not fuse protected. If this same short occured, the fuse would be BETWEEN the positive terminal and ground, and would open. So, the engineers who suggested that it doesn't matter where the fuse is located are fools.
 

zevon8

New Member
heathtech and stevez have summarized this very well, especially regarding the point of fusing close to the battery to leave as little unprotected wire as possible.

Many vehicle circuits are "lowside" switched, meaning the ground side is switched on and off. This has two desired results. One, this simplifies any electronics in the circuit, since switching is referenced to ground, and two, since the switch side of the wiring is often the longer run of wiring, exposed to more hazards, the worst that can happen if the wire shorts to chassis is the device turns on.

In all my vehicle installations at work, the fuse is always located directly at the battery, or inverter/generator, protecting the wiring, which is really the point of the fuse anyways.
 

Oznog

Active Member
Tresguey said:
i recently purchased a electric fan for my car. and the instructions stated to install the fuse on the ground side not positive side. why is that? :?:
Perhaps the people who wrote the instructions have no idea what they're talking about? Just a theory. What kind of electric fan is this? Got a brand/model #?
 

Dean Huster

Well-Known Member
If this is an Asian import, you're probably the victim of the instructions. In the Chinese factories, the boss shouts out to his employees in Chinese, "Who knows English?" The first employee who shouts "McDonald's" gets the job of writing the instructions they include with the fan. I've never figured out why they don't hire an English-speaking person who knows a little Chinese to do the job.

Dean
 

zevon8

New Member
LOL, I think Dean Huster may be on to something... My all time favorite is this one device we buy at work that has a prominant red label on the battery cover that reads:

IMPORTANT ! Insert batteries in the opposite direction as shown on label and in the instructions.

Yes, it is made in China, and of course if you don't follow the instructions, the device becomes a paperweight, no reverse polarity protection.
 
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