What is the available fault-current (AFC) at the terminals of the transformer?
You’ll need this information to determine your overcurrent protection coordination, as well as order the right transformer. This transformer has a 2% impedance. Don’t confuse this with your system impedance, which is a different quantity. We normally express system impedance in ohms. If someone has already done a network analysis on your project, you may have a value shown as the admittance, expressed in units called siemens. To convert to ohms, invert the value ohms and siemens are reciprocals of each other. AFC=FLA of transformer/Z AFC=217.31A/.02 AFC=10,865.5A Solution: The AFC at the terminals of the transformer is 10,865.5A. Sizing elements of each feeder Before you can order switchgear, you need to determine what size breakers you will need for each feeder. You also need to determine conductor ampacities. Remember, you must select conductors rated for MV application. Feeder No. 1. (684.65A) The OCPD for the panelboard will be 700A. Why would the breaker not be smaller than 684.65
