3

Has anyone ever accidentally or inadvertently connected connected the supply port with the ground port with a wire?

Does Arduino provide internal safety to prevent the circuit board from shorting out?

6

There is some protection.

When powered from the USB port, the UNO has a 0.5 A fuse. This is a self resetting fuse that will trip when the current is high, and reset when it cools back down. These fuses are great for peripherals that might be exposed to occasional "oops". See the data sheet for more details of the part on the UNO.

When powered from the PWRIN plug, the voltage regulator provides some protection. The device on the UNO contains over current and over temperature protection, which is common for regulators such as this. The device will get very hot, and the protection will activate to limit the current (see datasheet for details). By design, the regulator chip should protect itself from being destroyed.

So to first order, if you by mistake connect the +5 on the header to GND, all that will happen is Vcc will be reduced to near zero Volts.

The caveat is that a small spark can be generated when you make this short to ground, especially if you have a bunch of capacitors on Vcc. That spark may cause a voltage transient that could damage a pin.

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