What is difference between overcurrent and overload protection?
ANSWER: Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. Overload protection is a protection against a running overcurrent that would cause overheating of the protected equipment. Hence, an overload is also type of overcurrent.
Where are overcurrent protection devices required?
Overcurrent protective devices, or OCPDs, are typically used in main service disconnects, and in the feeders and branch circuits of electrical systems for residential, commercial, institutional, and industrial premises (Figure 5.3). Figure 5.3. Overcurrent protection devices include circuit breakers and fuses.
How many overloads are required in a 3 phase motor?
three overload
Since 1971, The National Electrical Code® has required three overload protective devices for the protection of three-phase motors, one in each phase. Diagram showing two overload devices protecting a three-phase motor.
How many percent is apply in overcurrent protective device maximum?
430.32 specify that overload protection device be sized between 115\% to 140\% of the motor nameplate current rating.
What are the two types of overcurrent?
The three major categories or types of overcurrent are overload, short-circuit, and ground-fault.
Does fuse protect from overload?
If excessive current flowed through the wires they would overheat and eventually start a fire. A fuse or circuit breaker prevents this by ”blowing,” or breaking the circuit, when an overload occurs. The higher-rated fuse will allow more current to flow than the wires can safely handle, causing overheating and fire.
Which protective device will not operate due to over current?
A breaker is designed to protect the equipment and wire. A breaker of too much amperage will not turn off the electrical supply in the event of an overcurrent draw. A breaker that is too small will turn off the power before the maximum current is drawn by the unit.
What is an over current relay?
Overcurrent relay. An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. The ANSI device number is 50 for an IOC relay or a DTOC relay.
What are the two basic types of overload relays?
The two basic types of overload relays are as follows:
- Thermal overload relay.
- Magnetic overload relay.
How do you calculate motor overload current?
Divide by the rated full load current from the motor nameplate. This will be the load factor for the motor. If the motor current is 22A and the rated full load current is 20A, then the load factor is 22/20 = 1.1. This means the motor is overloaded by 10\%.
What happens if an overcurrent protective device is oversized?
Undersize your overcurrent protective device (OCPD), and normal operations might become impossible. Oversize your OCPD, and the whole place might burn down. It helps that, for a given circuit, conductor sizing and OCPD sizing begin with the same two steps.
What is the difference between overload and short circuit protection?
Overload protection typically operates on an inverse time curve where the tripping time becomes less as the current increases. Short circuit protection is protection against excessive currents or current beyond the acceptable current rating of equipment and it operates instantly.
How many over current relays are required for a single line?
The general practice is to employ a set of two or three over current relays and a separate over current relay for single line to ground fault. Separate earth fault relay provided makes earth fault protection faster and more sensitive.
How to discriminate adjacent over-current relays?
These over-current relays need to coordinate with each other such that the relay nearest fault operates first. Use time, current and a combination of both time and current are three ways to discriminate adjacent over-current relays. Over-current Relay gives protection against:
How do you adjust the operating time of an overcurrent relay?
The operating time of an overcurrent relay can be moved up (made slower) by adjusting the ‘time dial setting’. The lowest time dial setting (fastest operating time) is generally 0.5 and the slowest is 10.
What is the main application of long time over current relay?
The main application of long time over current relays is as backup earth fault protection. (D) Directional Over current Relays When the power system is not radial (source on one side of the line), an over current relay may not be able to provide adequate protection.