Low voltage overload protection
Electrical safety tutorial
Low voltage overload protection
We are now going to learn the different concepts related to low voltage overload protection.
Low voltage trip
If the line voltage drops to an abnormally low value, the electrical machine is damaged or unable to start service. Due to the low voltage, the shunt coil on the starter final contact hold solenoid disconnects the motor from the line. After the line voltage is restored, the motor resumes operation. The release of low voltage is unexpected and dangerous. To protect machines, low voltage protection must be provided.
Low voltage overcurrent fault
In low voltage condition, temperature protection is called overcurrent protection. There are three major causes of overcurrent. The causes are listed below -
By equipment overload
The overload condition occurs when the equipment is subjected to more than its rated value. This results in excessive heat production.
By short circuits
If there is a connection between the line-to-line or line-to-neutral conductors, this causes a short-circuit. This generates a temperature higher than the designated ratings.
Through earth faults
If electric current flows from a conductor to an uninsulated l, an earth fault occurs.
The current flows in the circuit according to the demand of the loads. If the amount of current increases and exceeds the rated value of the electrical equipment, the system is overloaded. The wires or cables may not withstand the higher current. The wires heat up and even melt the insulation. This leads to the risk of fire. Therefore, a protection contre overloading is necessary to avoid such accidents.
Causes of the overload condition
Here are the different causes of the overload condition -
Misuse of extension cords and multiple adapters on the same circuit.
Running too many devices at once.
When more electricity is used as an electric decoration.
The following image shows the overuse of the extender -
The following image shows how a fire hazard is triggered due to overload -
Signs of low voltage overload
Now let's see the different signs of low voltage overload. Here are the different signs -
- Flickering lights
- Sparks from appliances or wall outlets
- Hot switch plates
- Dimming lights, televisions
- Reduction of motor speed
To avoid such problems, fuses and miniature circuit breakers are used as protection devices. In the event of a fault, the fuse should burn out and the circuit breaker should open the circuit.It is also important to protect the conductors as well as the equipment against higher currents.
Each cable has a rated current, which is the maximum safe current capacity of the cable. This current load capacity depends on the following factors -
Material - Aluminum or Copper
A structure - Individual conductor or grouped conductors
Medium path - In the open air, laid earth, or near the ovenhot or inside a well ventilated room, etc.
The fuse or circuit breaker should be chosen according to the cable size. When the fault current reaches the fuse, it will blow. This gives a temporary overload condition to the cable. The cable must withstand momentary overloads for a very short time. A little overheating cannot create a dangerous level. This is called the Slow Hit Protector.
Fuse and circuit breaker can protect the cable. However, these are not sensitive to protect a small-use device plugged into the circuit. Therefore, these protection devices are built into the devices to protect against overload. External fuses are used in the main service panels or subpanels, but the equipment fuse or circuit breakers protect every part of the electrical equipment that securesise the system.
The following image shows the thermal fuse inside a motor -