Which wire is generally switched, hot or ground?

[skeeter_ca]

As they say current does flow - to +. I think the biggest reason they "usually" switch the postive side is in case the component or wire shorts to ground it will not work if it is interrupted on the positive side. If you had a vehicle with a positive ground you would want to switch the negative side of the circuit. It's all relative. Alot of computers and such usually ground the negative side of the circuit to turn on a component to keep arcing to a minimum.

skeeter

[rleffler]

As they say current does flow - to +. I think the biggest reason they "usually" switch the postive side is in case the component or wire shorts to ground it will not work if it is interrupted on the positive side. If you had a vehicle with a positive ground you would want to switch the negative side of the circuit. It's all relative. Alot of computers and such usually ground the negative side of the circuit to turn on a component to keep arcing to a minimum.

skeeter

As Skeeter mentioned, there are always exceptions. For example, in the Vertical Products product line, most of the switches are logic switches and all the switch does is provide a path to ground. The signals the controller to enable and apply power to that specified circuit.

[vaflier]

Have I been misinformed in electronics 101. ????. I was taught that current in a DC system flows from positive to negative, due to the fact that the + or positive battery terminal has an excess of electrons and the - or negative terminal has a deficit of electrons. In other words the flow would be from excess to deficit. Was this not correct ??????.

[rwanttaja]

Have I been misinformed in electronics 101. ????. I was taught that current in a DC system flows from positive to negative, due to the fact that the + or positive battery terminal has an excess of electrons and the - or negative terminal has a deficit of electrons. In other words the flow would be from excess to deficit. Was this not correct ??????.

Yep. Remember, electrons have a NEGATIVE charge. Having a lot of them doesn't produce a positive terminal.

Ron Wanttaja

[Dave Stadt]

Have I been misinformed in electronics 101. ????. I was taught that current in a DC system flows from positive to negative, due to the fact that the + or positive battery terminal has an excess of electrons and the - or negative terminal has a deficit of electrons. In other words the flow would be from excess to deficit. Was this not correct ??????.

You were misinformed. Gazillions of negativity charged electrons hang around the negative terminal looking for a way to get to the positive side. The positive terminal has the deficit.

[Neil]

You may have been thrown off track by someone talking about how to wire the master solenoid. As a rule the master solenoid is mounted as close to the battery as possible. The battery cable to the solenoid is kept very short this way. Also a jumper wire goes from the battery post on the solenoid to one of the trigger post. The other trigger post goes to the master switch and then to ground. This is done so that a minimum amount of wire in the airplane is hot when the master is off. All the master switch does is ground the trigger post to engage the solenoid.

[1600vw]

I could have gone into the the theory that the flow from a battery is from - to + but we do not practice this theory. If I would have said electricity flows from - to + everyone would have said I am wrong. But in theory this is correct.

But we switch the + just like I said and why. To kill the power and not to switch or kill the ground. If anything goes to ground you still have an closed circuit. But if you switch the + or the positive and something goes to ground you still have an open circuit. Simple. The flow of electrons is a complete different subject in itself.

But here in America we practice that electricity flows from + to - or positive to negative.

Tony

[1600vw]

Yep. Remember, electrons have a NEGATIVE charge. Having a lot of them doesn't produce a positive terminal.

Ron Wanttaja

Also remember its not the negative charge that will bite you but the positive charge that will bite you. This is why when you go to unhook a battery terminal you unhook the negative first.

Tony

[njones]

Guys, direction of current flow is not the issue - there is no reason tied to any laws of physics that defines which wire should be switched. Safety, standardized design methods and ease of debugging are the main factors that drive why things are done a certain way.

We commonly call the power supply (battery) terminal that is connected to the frame "Ground" (but in fact "Chassis" or "Circuit Common" is a better term since it isn't actually connected to the earth). And we commonly call the call the power supply (battery) terminal that is connected via fuses and switches to various loads "Hot" or "Supply".

Because many systems use (-) common, it's common to hear people calling (+) "Hot" and (-) "Common" or "Ground" - while this is true on (-) common systems, it's very good idea to NOT get into this habit because it can lead to mistakes if you ever work on a (+) common system.

There is no practical difference between a system with (-) "common" with (+) fused/switched and (+) "common" with (-) fused/switched. As some have already posted both types of systems are out there. That being said, there are a few cases where there is a good (electronic) reason for using either (+) or (-) common.

The vast majority of North American systems use (-) common, and unless you have a particular piece of equipment (rectifier/regulator for example) that needs to be (+) common, then it's probably better to stay with (-) common because that's what most people expect to see.

$0.02

[Matt Gonitzke]

Also remember its not the negative charge that will bite you but the positive charge that will bite you. This is why when you go to unhook a battery terminal you unhook the negative first.

Tony

Only true for negative ground. If it is a positive ground system then you'd remove the positive cable first. The ground is removed first so that you can't short the positive terminal to ground with the wrench (on a negative ground system).