Volts push Amps through Ohms. Ohms Law. With low volts (20V) and high resistance (your skin) you end up with low current (harmless). The main danger would be from fire or burns if you run 1 A through a wire (or unintended conductor) that can't handle it.

How many Volt is harmful?

In industry, 30 volts is generally considered to be a conservative threshold value for dangerous voltage. The cautious person should regard any voltage above 30 volts as threatening, not relying on normal body resistance for protection against shock.

What is the lowest voltage you can feel?

The minimum current a human can feel is thought to be about 1 milliampere (mA). The current may cause tissue damage or fibrillation if it is sufficiently high. Death caused by an electric shock is referred to as electrocution.