Overload protection & overcurrent protection

None - Overload is a situation which occurs in a basically healthy circuit but where the load is drawing excess current. An overload operates the "excess" or "overcurrent protection" device.

On a balanced 3 phase load, the 3 phases are monitored for equal loading and if one phase overloads or the supply to one phase is lost (single phasing) then an imbalance will occur thereby operating the overcurrent protection.

Traditionally overcurrent protection is provided by thermal or thermal/magnetic elements, but later devices use small toroidal current transformers like RCDs.

Short circuit protection either between phase - phase or phase to neutral or phase to earth occurs in a defective circuit and the low impedance fault path results in very high currents. This operates the short circuit device (fuse or circuit breaker) instantaneously

Enough said here good post.

Good one

Overload-Defines limit of circuit capacity for particular circuit.( You can not increase the load beyond this spec)

Over current- Fault condition, to Isolate & limit the fault

Am i right?

There is however a difference between overload and short circuit protection. Typical overload protection is of a more exact nature with closer margins and is finer tuned than a circuit breaker and the device doesn't necessarily perform well under real short cct conditions.

For that, the circuit breaker, operating both thermally and magnetically, is much more rugged and can usually interrupt thousands of amps without being blown of the wall. It usually has a short circuit interruption rating depicted in kA. It is however not well suited for motor overload protection as it can take a considerable time before reacting on small overload levels.

I once saw a video of a 60A tp 5kA circuit breaker, under test, coming out in a ball of flame at a test short cct current of 70kA. And they claimed it still worked afterwards!

There is something called Arc Flash or Arc Blast... Take a look at Ralph Lee's equation in the 1980s... There is a very big difference in Overload portection and Overcurrent protection... Badly designed Overcurrent protection can KILL people....

This doubt is good, over current flows when there is an over load.

Ultimately any protection circuit senses the current flowing through the load and when it exceeds certain limit it will set an alarm or just switches the circuit off.

But, Over current need not to flow through load only.A system can draw over current when some thing get short circuited with in the system. Such over current shall be sensed at power input of the system or at some suspicious node within the system, not at the load. This Could be a over current protection.

NEMA defines overload as when a device (such as an electric motor) is driven beyond it's design rating causing the device to draw more current. This will result in thermal tripping of the protective device. (Typically an overload relay for a motor.)

Overcurrent is the result of a short circuit. Which is why breakers and fuses have an AIC (ampere interrupt current) rating.

Contrary to what others have said here, they are not the same.

Sudh--

You may not have access to the National Electrical Code used in the USA. Its first sections are definitions.

"Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor . . ."

"Overload. Operation of equipment in excess of normal, full-load rating . . . A fault, such as a short circuit or ground fault, is not an overload."

The two terms are similar, but different because "overload" refers to the effects of this load, and names damage or dangerous overheating, while "overcurrent" simply relates to the ampacity of a conductor.

Hope this helps--JMM