What is prospective fault current?

What is prospective fault current?

The Prospective Earth Fault Current is the maximum current that could flow between Live conductors and Earth. The higher of these two values will be noted down as the Prospective Fault Current (PFC).

Where is the highest value of PFC in an installation?

Heads up: The PFC will always be the highest at the origin of the installation as the impedance/resistance is always the lowest there. So as a rule if it’s not too high at the mains it will be okay everywhere else.

Where is Pfc measured?

PFC is conducted at the origin of the installation, such as at the main switch or at other switchgear connected directly to the tail from the electricity distributor’s metering equipment.

Why do we measure prospective fault current?

A PFC test calculates the current that will flow in the event of an earth fault; i.e., Line to Earth. It is important that we conduct the tests to make sure that the protective devices installed within a circuit are rated at the correct breaking capacity.

How do you calculate maximum prospective short circuit current?

So the transformer is 500 kVA, we convert to VA by multiplying by 1000 and then divide by the square root of three x the nominal voltage, 3 phase of 400 V. Now, to calculate the Short Circuit Current, multiply the rated full load current by 100 and then divide by the actual percentage impedance of the transformer.

Which current value is maximum during fault?

For single phase circuits, the maximum fault current is between the phase and the neutral and in three phase circuits it is when all phases are shorted (symmetrical current). The total impedance is that with operating temperature 20οC (lower temperature means lower resistance).

How do you calculate prospective short circuit current in single phase?

In this case, the PSC can be calculated by multiplying the single phase reading by the square root of 3 or 1.73. Therefore in the example above, the PSC would be 3000 x 1.73 = 5190 A or 5.19kA.

What is the difference between PFC and PSCC?

includes the short circuit of Phase(line)/Earth aswell as the obvious Phase/Neutral path. PFC is the larger value of PSCC (prospective short circuit current) and PEFC (prospective earth fault current).

What is prospective current in fuse?

The prospective current is defined as the value of current which would flow through the fuse immediately after a short circuit occurs in the network. Melting time of fuse or Pre-arcing time of fuse: This is the time taken by a fuse wire to get broken by melting.

Why are we required to calculate the value of prospective short circuit current at points in the distribution system?

To select devices like circuit breakers and fuses that will protect the circuit, you need the PSCC value. Such devices must be able to sustain the PSCC to provide a reliable protection. If the breaking capacity or interrupting rating of the protective device is too low, the PSCC may destroy it or cause an electric arc.

How many AMPS is a phase to neutral fault?

The next fault is less severe, basically a fault between two phases that reduces the current to about 87%, so 12,570 A. A short circuit to earth on a Multiple Earthed Neutral (MEN) system is the equivalent of a phase to neutral fault, and the current is further reduced by the impedance of the earthing system between the fault and the neutral link.

What is the maximum prospective fault current for an electrical panel?

In such circumstances, the maximum prospective fault current should be recorded as 16 kA in the relevant part of the electrical certificate or report, and undertaking prospective fault current testing at any point in the installation would be considered unnecessary.

When do I need to carry out prospective fault current testing?

In some cases, prospective fault current testing may need to be carried out at other relevant points in the installation, particularly at the furthest points, to confirm that the fault current is sufficient to cause operation of the protective device before the permitted limiting temperature of any conductor or cable is exceeded (Regulation 434.5.2).

What happens when a cable is exposed to a fault?

As shown by the calculations in Fig 2, the cable is exposed to a higher fault current at position (A) than at position (B). However, a fault occurring at position (B) represents the most onerous condition because the lower fault current leads to a longer disconnection time, which results in a higher let-through energy I2t.