I'm building a 5 V and 4 A circuit that will be in contact with the body.

How can I know if this amperage, in case something goes wrong, will not be a problem for my health or my life?

  • \$\begingroup\$ well, your body and the intended circuit form a current divider. Hence, the amount of current flowing through you will depend on the voltage of the supply. Not on how much current it's currently supplying. For example, a supply pushing 5A through a 100mΩ resistor will not be dangerous to you, at all – that only requires 0.5 V, and your skin resistance will be high enough to not allow for dangerous current to flow through you. Now, pushing 5A through a 1 kΩ load will require 5 kV, and that will pretty much kill you,because then your body resistance isn't high enough to avoid significant current \$\endgroup\$ Nov 19 '18 at 9:35
  • \$\begingroup\$ But. this question has been asked in various forms here before: Search for "do volt or ampere kill me" and similar. \$\endgroup\$ Nov 19 '18 at 9:35
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    \$\begingroup\$ which part of your body? if it is your external skin and you stop when it gets uncomfortable there will be no harm. \$\endgroup\$
    – Jasen
    Nov 19 '18 at 9:38
  • \$\begingroup\$ Something else you need to consider: If the 5V and 4A are coming from a line powered power supply (you plug it into an outlet in your home) then you may be exposed to higher voltages that can kill you. \$\endgroup\$
    – JRE
    Nov 19 '18 at 12:09
  • \$\begingroup\$ If you are connecting it to your body, do not power it from an outlet. From your question, you do not have the knowledge and experience needed to design and build a line powered device that can be safely attached to a human being \$\endgroup\$
    – JRE
    Nov 19 '18 at 15:15

You can't hurt yourself with 5V DC voltage. Hazard for a human is considered at more than 30V (If I'm not mistaken).

  • \$\begingroup\$ Human body resistance varies by multiple orders of magnitude depending on conditions. Any capacitance or inductance in circuitry gives 'DC' a limited meaning at best when changing current distributions (as when you suddenly touch different parts of the circuitry). Hard and fast safety advice is seldom good, it's worse when that advice is that something is safe, it's unacceptable if it has to be qualified by "if I'm not mistaken". \$\endgroup\$
    – DonFusili
    Nov 19 '18 at 12:19
  • \$\begingroup\$ This type of question is where you don't "want to be mistaken" and trust random people on the internet who don't back their answers with references though. \$\endgroup\$
    – pipe
    Nov 19 '18 at 13:47
  • \$\begingroup\$ Bottom line is that you CAN"T kill or hurt yourself with 5V, even if you aaply them directly to your heart. The part where I'm not sure is 30V or 34V. \$\endgroup\$
    – drdm
    Nov 19 '18 at 14:40
  • \$\begingroup\$ @drdm "if you apply it directly to your heart from a nicely behaving element such as a battery". OP is working with a 4A circuit that is supposed to be in contact with the body. This kind of circuitry tends to have a lot of inductance. Inductance leads to lag of current adjustment. The time for 4A to do something bad to your body is expressed in microseconds. The time for transients to settle in typical inductive circuitry that comes in contact with a human body is expressed in nanoseconds. That's not enough backoff to my liking for something that can kill you. \$\endgroup\$
    – DonFusili
    Nov 20 '18 at 8:23

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