The equivalent resistance of several devices connected in parallel is given by
where
are the resistances of the various devices. We can see that every time we add a new device in parallel, the term 
increases, therefore the equivalent resistance of the circuit 
decreases.
But Ohm's law:
tells us that if the equivalent resistance decreases, the total current in the circuit increases. The power dissipated through the circuit (and so, the heat produced) depends on the square of the current:
therefore if there are too many devices connected in parallel, this can be a problem because there could be too much power dissipated (and too much heat) through the circuit.
where
But Ohm's law:
tells us that if the equivalent resistance decreases, the total current in the circuit increases. The power dissipated through the circuit (and so, the heat produced) depends on the square of the current:
therefore if there are too many devices connected in parallel, this can be a problem because there could be too much power dissipated (and too much heat) through the circuit.