In electrical installation, what's the difference between OVERCURRENT and OVERLOAD protective devices?

Answer 1

Overcurrent protection is designed to protect the distribution system.

Over current is when there is a an excessive flow of current in an electric circuit which exceeds the rated capacity. There are numerous causes such as a surge, crossed wires or short circuit when can cause the high current flow. The trip setting is usually set at a point well above a normal operating point (15-20%). Currents at this level require a quick response to protect the system while providing a buffer to allow breif current excursions to prevent nuisance trips

An Overload protection device like that found in a motor controller/starter is designed to protect the motor (electrical device). The current flowing to the motor passes through a bimetallic heater. As current increases the amount of heat produced by the heater increases and a heat increases so does the amount of deflection of the bi-metallic strip. Eventually the heat causes enough movement of the bi-metallic strip to trip a disconnect mechanism.

Overcurrent protection devices have an inverse current time relationship. Meaning that a small overload will take a longer time to trip the motor OR a high current flow will take a shorter time to trip. Overload applied to a motor need not be an electrical fault but may include mechanical problems. Additional mechaical loading from a faulty bearing, or placing too much weight on a conveyor for example will trip an overload device.

Answer 2

overcurrent is power fluctuations from the supply company like when a line gets hit by lightning

overload is when an end user device like a washing machine develops a fault then the rcd will cut out to prevent electrocution

Answer 3

Over current generally means that you have a higher voltage than recommended. ie. 120 volt device and you have 125 line voltage
Over load is when your wiring is rated rated at ie. 20 Amps and you are drawing 25 amps from that circuit