A fault current is an unintended, uncontrolled, high current flow through an electrical system. Fault currents are caused by very low impedance short circuits. These may be shorts to ground or across phases. The resulting high current flow can result in overheating of equipment and conductors, excesses forces, and at times even serious arcs, blasts, and explosions. Causes of faults include things such as lightning strikes, animals, dirt and debris, dropped tools, corrosion, and human error.
Fault current calculations are based on Ohm's Law in which the current (I) equals the voltage (V) divided by the resistance (R). The formula is I = V/R. When there is a short circuit the resistance becomes very small, and that means the current becomes very large.
If the resistance was zero, then the calculated fault current would go to infinity. However, even copper wire has some resistance; it is not a perfect conductor. Determining the fault current involves knowing the total resistance from the power source to the location of the fault.
Fault Current Calculations Are Required :-
Knowing the available fault current is important when selecting protection devices, however it is also required by code. The National Electric Code (NEC) 110.24(A) states:
"Service equipment in other than dwelling units shall be legibly marked in the field with the maximum available fault current. The field marking(s) shall include the date the fault current calculation was performed and be of sufficient durability to withstand the environment involved."
This means there must be field installed labels on electrical equipment, such as service entrance equipment, that gives the available short-circuit fault current. This allows the Short Circuit Current Rating (SCCR) of the equipment to be easily compared with the maximum available fault current.
Any time there is a change in equipment the fault current calculation must be redone. This is specified in NEC 110.24(B):
“When modifications to the electrical installation occur that affect the maximum available fault current at the service, the maximum available fault current shall be verified or recalculated as necessary to ensure the service equipment ratings are sufficient for the maximum available fault current at the line terminals of the equipment. The required field marking(s) in 110.24(A) shall be adjusted to reflect the new level of maximum available fault current.”
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With these Fault Current Calculator we can calculate the following parameters :-
1. Fault current at Transformer
2. Fault Current at main panel
3. Fault Current at sub panel
4. Fault current at distribution Board
5. Fault level at diesel / Gas Generator
6. Fault Level at Transformer side
7. Fault Level at main LT panel Side
8. Fault Level at LT sub Panel Side
9. Fault Level at Distribution Board side
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