In many tutorials and guides they use the 5V pin, the GND pin and a GPIO pin to control a servo with a JR-plug. In these guides, they didn't use any other components (I.e. resistors) in between. Now I am wondering if this is safe to use for my pi, because I've read on many websites that the GPIO pins can handle a maximum of 3.3V.

Does this maximum of 3.3V apply to the GND pins? Is the GPIO pin in danger to be fried because if the voltage? (-> What can I do to make that circuit safe?)

P.S.: I've tried to measure the voltage that goes through the cables when the servo is attached in its original position, an RC-car, the results were: about 5V in + and -, about 300mV in the signal cable. These results may be completely wrong as I am new to this topic.

Technical details (may be translated inappropriate, please look at the measuring units): • operating voltage: 4,8-6 V • Rotation Speed: 0,2 sec/60° at 6 V • Rotation force at 6 V: 60 Ncm
• JR-plug

  • Voltage doesn't go "through the cables". "Does this maximum of 3.3V apply to the GND pins" makes no sense. Rather than asking vague questions about electric current, ask about WHAT YOU ARE ACTUALLY TRYING, describing actual components and connections, plus software you may be using.
    – Milliways
    Dec 17, 2016 at 22:16
  • @Milliways This "voltage goes" fault is more of a language fault as I am not a native English-speaker/-writer. With "Does this maximum of 3.3V apply to the GND pins?" I wanted to ask whether a voltage >3.3V on a ground pin would break the Pi. Also, I am describing that I want to control a servo and that I am worried about connection faults that could break the board; in this early stage I haven't used any software.
    – traxam
    Dec 17, 2016 at 22:34
  • Voltage on a pin makes no sense. Voltage is a potential difference BETWEEN 2 points - normally between (what is commonly referred to as) Ground and some other point. You CANNOT put a voltage ">3.3V" or any other BETWEEN Ground & Ground. Most servos use PWM as control, and need to be connected to a specific pin on the Pi.
    – Milliways
    Dec 17, 2016 at 23:06
  • @Milliways Oh, I must have got that wrong... Thank you!
    – traxam
    Dec 22, 2016 at 13:15

1 Answer 1


Ground in a DC circuit refers to either an actual earth ground (i.e., 0 volts vs. anything) or a common ground for different components that may be working at pretty much any voltage relative to it.

I think what you would really want to be concerned with on the Pi is the amperage, if the "common ground" to the Pi is the primary ground for whatever you are connecting -- but it is hard to imagine how an arrangement like that is possible without intending to do so and jumping through hoops to accomplish it. My point here is if you wanted to fry the Pi that way you probably could, but only if you actually wanted to (by shorting a high amperage supply to ground through it).

Anyway, a common ground between between circuits running at different voltages is fine (and necessary, if there is any other connection between them). This doesn't automatically make every circuit using it safe, it just means that using a common ground doesn't by definition make it unsafe.

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