Correct switch location in a circuit

John K

Hello,

I was wondering what the correct location of a switch is in a circuit. I thought I read/heard that you should switch the side of a circuit closest to ground, is this right? What if you switch the positive side?

Thanks,
John

SPENCE

I am not shouting. I have been able to read and type all caps much easier for over 55 years.

John. It depends on the circuit. On very low voltage circuits there is not much of a safety concern but on high voltage there definatly is.

On high voltage never break the ground side. Always switch the hot (none ground) wire. Also always fuse the hot wire, not the ground.

Generaly i would do the same for low voltage.

The only none standard situation i can remember is working with jumpering a auto with a dead battery. Hook up the hot jumper on each end. Then hook ground jumper on ground terminal on one battery and on the last connection make it to ground some safe point away from the battery so if there is a explosion, you will be somewhat removed from the battery.

Safe switching or as the arrl, amateur radio handbook has advised for many many, years. "switch to safety"

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73
spence
k4kep

Paul Baker

Assuming you are working with low voltages (5V is low), it depends on what type of polarity of the switch you want. There is an active low configuration where a resistor ties the line to 5V and the switch is connected ground, so when the button is not pressed the line is high, when it is pressed the line is low. The other configuration is active high, where a resistor is connected to ground and the switch is tied to the other end of the resistor and 5V, when the switch is not pressed the line is low, when the switch is pressed the line is high.

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·1+1=10

John K

Hi,

Thank you for your replies. Ok, so only switch the hot (positive) side. Now, maybe I can learn a little more. I have searched all over on the internet for an explanation on that, but could not find it. Is the reason for locating a switch on the hot side is that it will be under the least load?? As current flows from ground to positive, and·components between the switch and ground would have some current across them, that means that the current drop on those components would present a smaller load across the switch contacts??

John

John R.

Assuming that there are no "secondary" devices involved (transistors, relays, etc.) it will not make a diffrence on switch load.

The reson to switch the "hot" side on any "power" circuit is that the ground side is just that, "ground", and if there is a leak, generally, it is less dangerous.

By switching the "hot" side, you remove any power, and minimize (never eliminate, but minimize) the chance for high power shorts and other nasty type events. Basically, the closer to the source you tie off the power, the better off you are.

This applies to power. In fact, for "power" it is "code" to switch the hot.

As Paul noted, for logic circuits the rules are different, largely because of the low voltage level. Even then, as a general case, the closer to source you switch off the power (hot or positive), the more you reduce the chance of inadvertant failure...

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John R.

8 + 8 = 10