Inverter Wiring Question

[BozDMAX]

I have been using an inverter for the last couple of years to run the laptop and charge the phone while I drive. I want to permanently wire the thing instead of using the lighter plug hookup and got to wondering about some basic electical theory that I thought I would let you guys take a crack at.

1) We know that electricity really flows from the negative terminal of the battery to the positive.

2) So why is it we always "fuse" the positive wire coming to a device. Wouldn't it make more sense to fuse the wire "before" the device so that the fuse would blow before the electricity arrived at the load?

3) Yes, I know that electricity flows really fast (186,282 MPS) and that it probably doesn't matter a whole lot anyway, but is it just a matter of tradition or is there a real good reason to fuse the red lead instead of the black one?

[David Utz]

We had a tractor that was positive ground and the fuses were on the negative leads. The fuse can go anywhere in the circuit. It makes the most sense to put it on the leg that is not grounded to the chassis and as close to the power source as possible. This will protect not only the device but the wiring as well. The fuse doesn't care which direction the electrons are going, only that the number of them going past stays below the set limit. If to many flow past, it overheats and melts the fuse.

[BozDMAX]

Understood, but the "power source" is really the NEGATIVE terminal of the battery, not the positive terminal that the electrons are flowing toward.

I guess you could say the + terminal "sucks" the electrons...

Which brings me back to my question, unfortunately - why not fuse the grounded leg?

[pgreen]

Let me have a crack at this one....

Since the vehicle is negative ground, you always want to fuse the positive lead. This will protect the wire and the device.

If you fuse the neg. lead, it will protect the device as long as the case of the device isn't also grounded. But, if the pos. wire rubs through the insulation (say through a hole in the firewall?), there's nothing to prevent the wire from becoming a toaster wire. The fuse on the neg. wire of the device will not see any increase in current (probably a decrease) if the pos. wire shorts to ground between the battery and the device.

Let me know if this makes any sense!

[BozDMAX]

This does make as good of sense as anything I have heard, and would also explain why the fuse should be as close to the + tap as possible - to reduce the length of wire that is unprotected.

Thanks for taking a shot at the question.