At the time of a short-circuit, a direct connection is formed between two points in the circuit that are not supposed to be connected. This creates a path of least resistance, bypassing the other components of the circuit.

Option 1: "Reduces substantially" - This option is incorrect because a short-circuit actually causes an increase in current, not a decrease.

Option 2: "Does not change" - This option is incorrect because when a short-circuit occurs, the flow of current changes drastically due to the new low-resistance path.

Option 3: "Increases heavily" - This option is correct. The short-circuit creates a path with very low resistance, allowing a larger amount of current to flow through. This increase in current can be dangerous and can potentially damage the circuit or cause other hazardous situations, such as overheating or electrical fires.

Option 4: "Keeps on fluctuating" - This option is incorrect because a short-circuit does not cause current to fluctuate. Instead, it creates a stable, low-resistance path for the current to flow through.

It is important to note that short-circuits can be extremely dangerous and should be addressed and corrected as soon as possible to prevent any damage or harm.