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The 2011 National Electrical Code introduced a new Article. 110.24 - requiring a LABEL on non-dwelling Electrical Services indicating both the date and the Maximum Available Fault Current (MAFC) calculation at the Line In Terminals of the Main Overcurrent Protective Device. The Formula is relatively simple once the Electrical Contractor obtains the FAULT DUTY (Also termed Maximum Fault Current) from the Utility. This data represents the Transformer KVA Rating, the voltage at the secondary and the Per Unit Impedance at the Secondary terminals of the providing Transformer. MAFC is then calculated considering the Type of Wire from the Transformer terminals, the type of raceway utilized, and the Number of Sets of Service Entry Conductors associated with the installation.
The formula for a typical 3 phase 4 wire Service is:
Sq Root of 3 X L (Wire Length) X I (Short Circuit Current Utility provided) DIVIDED BY:
C (Constant) X n (Sets of SE Conductors X E (Line to Line Voltage XF Secondary)
This answer is termed Calculating the "F" Factor. F factor is then simply compared to a Chart to find a multiplier "M". {Always Less Than One (1)}
This multiplier M is times the XF SCC. This answer is the Maximum Available Fault Current. Note that the type of raceway, PVC or Metallic, the type of Wire, Copper or Aluminum, the number of "barrels" will affect by inductive reactance or impedance of the conductors, by lowering, to a small degree, the SCC at the
providing transformer. The most difficult number in the formula is the Constant "C", which must be obtained from an outside source such as Cooper Bussman's Point to point AFC calculation chart. Both "C" and "F" > "M" are located in the
Point to point Guide at Cooper Bussman. Electrical Inspectors will verify the MAFC Calculation and the Date of the Calculation when the Electrical Contractor places the required label on the Service Equipment, per NEC 2011 110.24
Keep in mind the Service Equipment (SUSE Rated) must have a SCCR Rating on its manufacturers plate. The SCCR (Short Circuit Current Rating) Must be higher than the Maximum Available Fault Current at it's Service Line in Terminals.
August 22, 2011 B. Head Certified Electrical Inspector, All Structures.
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Which means Pfc = Nominal Voltage / Impedance
It's Ohms Law
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How do you calculate earth fault current value by knowing the setting in electromagnetic relay?
trh
How do you calculate rated kva of a circuit breaker?
You don't calculate the rated kV.A of a circuit breaker; it's determined by the manufacturer. It's important that a circuit breaker's rated kV.A exceeds the fault level kV.A at the point where the circuit breaker is located, otherwise it may fail to interrupt a fault current and, possibly, self destruct.
What are symmetrical and unsymmetrical faults?
the fault in electrical transmission line which give rise to symmetrical fault current is called symmetric fault. e.g; L-L-L-G fault. the fault in transmission line which give rise to unsymmetrical fault current is called unsymmetrical fault.e.g; L-L , L-L-G , L-G fault to solve the unsymmetrical fault, the fault current can be represented by sum of the sequences--zero phase sequence , +ve phase sequence , -ve phase sequence. where L:line G:ground
How do you detect a fault current?
Put cheese on it.
Why fault current can be extremely high?
Because the impedance to current flow is very low.
How do you calculate maximum earth fault current?
transformer max earth fault current
How do you calculate internal fault loop impedance?
by calculating the loop current
How do you calculate earth fault current value by knowing the setting in electromagnetic relay?
trh
How do you calculate 3 phase earth fault loop?
You can't have a three phase earth fault, you can have a phase to phase or a phase to earth fault. If you want the potential phase to earth fault current it will be your voltage times your impedance. If you want the phase to phase potential fault current then you should just double the above result.
What is the surge current limit for a 40 A MCB?
A 40A MCB is a circuit breaker. The surge current limit is protected to 250A 8/s0uS. The limitation capability of a circuit breaker is that characteristic whereby a current less then the prospective fault current is allowed to flow under short circuit conditions.
What is fault inception angle?
It the angle between fault current and voltage at the point where the fault occurs.
What is a fault record?
fault records gives complete information about a fault,i. fault current magnitude,type of fault,fault phase details,etc.with time stamping.
Is it advisable to let a prospective employer call your current boss for references even though the job is not guaranteed?
Don't have a prospective employer call your current boss. If your current boss knows you're looking for another job, he/she could fire you! The prospective employer should realize this. Feel free to give earlier job references, of course.
How do you claculate thee Earth fault current level at different different voltage level?
T calculate the fault current level at different voltage levels with the formula F = V / sqrt(P) / ((L x R / 1000) ^ 2 + (L x X / 1000 + V / (A x sqrt(P))) ^ 2) ^ 0.5 + 4 x M + 5 x N. The letter V is the circuit voltage, P is the number of phases, L is distance from the source feeder to point of interest, R is resistance of feeder, A is available fault current, M is total fault current contribution of induction motors, and N is total fault current contribution of synchronous motors.
How do you calculate rated kva of a circuit breaker?
You don't calculate the rated kV.A of a circuit breaker; it's determined by the manufacturer. It's important that a circuit breaker's rated kV.A exceeds the fault level kV.A at the point where the circuit breaker is located, otherwise it may fail to interrupt a fault current and, possibly, self destruct.
What is the reason for using a neutral current transformer on a transformer?
A current transformer is primarily used at the neutral point of a transformer for earth fault protection. A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply of electricity to the transformer.
How do you detect a fault current?
Put cheese on it.
