1. Is it true that wires or PCB traces contain inside capacitance of pico Farads?
If its true, than how come that they dont create a cut-off in DC circuits?
Two conductors running in parallel IS a capacitor, but a very small one.
They DO create a cutoff for DC, which is quite fortunate, as otherwise you could just as well solder all your components to a single plate of metal.
In high frequency it becomes a real problem, but as the saying goes: If someone gives you a lemon, squeeze it and make lemonade.
So, in high frequency (UHF and beyond) circuits, that capacitance (and the likewise inescapable inductance) of PCB tracks are turned into components - Striplines is used quite a bit in UHF and in micro wave circuits you need specialized programs to design your PCB, where parameters for the PCB carrier material . like thickness and dielectric constant, has to be entered to calculate the components. A microwave filter can be made with just a PCB and no further components besides what you create by the parasitic capacity and inductance - perhaps the word "parasitic" shouldn't be used in those applications though.
2. In my PCB there are traces that carry 220Vac and 16Aac, 50HZ and 60Hz frequency.
Is it considered a high frequency, such that parasitic capacitance between close traces can significantly influence the circuit?
No, it's considered pretty low in the audio frequency spectrum, so you won't have a problem with parasitic components in close traces... However, anyone using close traces in a mains voltage PCB should be shot by sight
(or at least electrocuted
), since they're endangering other peoples life (by electric shock or by fire etc.).
There should be an absolute minimum distance of 10 mm between mains voltage and low voltage circuits and at least 3 mm between any two points of mains voltage tracks