Just silly question, but not clear for me. For example, I have some device with 20A DC consumption. I have to connect this device to power source by some multicontact connector, 20 pins for example. Each pin can carry 2A of DC current.

How much VCC and GND contacts I should use to handle 20A to the device?

Variant 1: 10 VCC pins and 10 GND pins, because connector should pass 20A through VCC pins to the device and then return the same 20A to the power source by GND contacts

Variant 2: 5 VCC pins and 5 GND pins, because each pin can handle 2A, so 2A*(5vcc + 5gnd) = 20A

  • 1
    \$\begingroup\$ Current flows in a loop. If 20A is flowing, it is flowing anywhere in the loop. Vcc contacts - 20A, GND contacts- 20A \$\endgroup\$
    – Kartman
    Apr 30 at 13:23
  • \$\begingroup\$ Your variant 2 is a power calculation which is not applicable to this situation. \$\endgroup\$ Apr 30 at 13:36
  • 1
    \$\begingroup\$ Also most of those "max current" ratings assume you are not using all pins at their limit at the same time, so some additional current overhead and perhaps testing is called for. \$\endgroup\$
    – vir
    Apr 30 at 16:09

Variant 1 is correct as far as the maths goes.

5 VCC pins and 5 GND pins, because each pin can handle 2A, so 2A × (5vcc + 5gnd) = 20A.

That's like saying "I have a container that has five inlets and five outlets. Each inlet has 2 L/s going in and each outlet has 2 L/s going out. Therefore the total (water) current = 2 L/s * (5 in + 5 out) = 20 L/s. It's not. It's just 5 x 2 = 10 L/s in and the same out.


simulate this circuit – Schematic created using CircuitLab

Five inputs with 2 A each = 10 A. Current out = current in.

As @vir has pointed out, while the individual contacts may be rated at 2 A there may be total current rating as the sum of the contact resistance heating may have to be taken into account.


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