I was wondering how much resistance you would need when connecting the 5v to analog to ensure that no short circuit would be created?
Thanks
Do you mean an analog input (to the ADC)? Which Arduino board? The input resistance (to ground) on the mega328 on an Uno or Nano, for instance, is 100 Meg Ohms so a short to ground is not possible and no resistor is needed as long as the voltage will not exceed Vcc.
I think that @Clusk needs to explain a little better. What do you want to protect? The Arduino or the device that is measured? Or both?
A 0.001 Ohm resistor is in theory no short but practice is different.
The Arduino pins are input in your scenario so will not cause shorts (see reply #1). You can short the pins (without doing harm to the Arduino); you might however do harm to the device that you're measuring.