Final answer:
An excessive current in a phase causes the heater to heat up to a higher temperature than intended, potentially causing it to malfunction or become damaged.
Step-by-step explanation:
When an excessive current flows through a heater, it causes the heater to heat up to a higher temperature than intended. This can lead to the heater malfunctioning or even becoming damaged. For example, if a heater is designed to operate at a certain temperature, but an excessive current flows through it, the heater may heat up to a much higher temperature, which could cause it to melt or become damaged.