The final amount of Available Fault Current (AFC) at a given point depends on several factors and can change by modifying any one of them. The following items are all characteristics of the circuit that need to be considered when selecting equipment ratings according to NEC^® 110.10:

• Length of wire. A longer run of wire will result in less AFC at the end of the run of wire than the same type and size of wire installed in a shorter length because of resistance.
• Size of wire. In most cases, the larger the wire, the less resistance which means higher AFC at the end of the run of wire.
• Type of wire. Copper is a better conductor of electricity than aluminum which means using a copper wire where aluminum was specified, results in a higher amount of AFC at the end of the run of wire.
• Raceway or cable. Conductors in a cable will have a different AFC value at the end of the cable run than the same type, length and size wires installed in a raceway.
• Type of raceway. Installing conductors in a ferrous metal raceway will result in a lower amount of AFC than the same size, type and length of conductors installed in a plastic raceway because of the current that will be lost through induction on the metal raceway which does not occur with a plastic conduit.

When the electrical utility company provides an AFC value at the service equipment, it will be based on the type, size and length of service entrance conductors installed from the secondary spades of the utility transformer to the service equipment. As well, they will consider the number of parallel runs and if the conductors are installed in a plastic or ferrous metal raceway.