Both Short circuit and overload protection devices protect motor circuit from over current.
Over current or excess current is a situation where a larger than intended electric current exists,which leads to excessive generation of heat and risk of fire or damage to the equipment.
Why Short circuit / Overload protection is required ?
- Prevent damage of equipments
3.Protection in place can prevent downtime and maintenance.
Short Circuit Current -
Short circuit is very huge. (x100 s of rated current).
Short circuit causes instant damage.
Must be cut immediately.
Always a fault,not normal.
Current is more than rated,but not much.
Causes overheating by time.
Causes damage over time.
It is very common to happen.
Must be cut after a period,not instantly.
Differences between Short circuit vs Overload protection.
Overload protection is a protection protection against a running over current that would cause overheating. Overload protection typically operates on an inverse time curve where the tripping time becomes less as the current increases. This means an overload relay isn’t going to trip on momentary or short-term over current events that are normal for the piece of equipment it is protecting. For example some equipment may in create inrush currents as it starts up. These inrush currents typically last only a few seconds and rarely cause a problem. So overload relays are used in a motor circuit to protect motors from damage caused by prolonged periods of over-current.
A short circuit occurs when current travels along an unintended path. Often where essentially a no or a very low electrical impedance is encountered. So short circuit protection is protection against excessive currents or current beyond the acceptable current rating of equipment and it operates instantly.As soon as an overcurrent is detected the device trips and breaks the circuit.