Most often, the main source of the Available Fault Current (AFC) also called available short-circuit current is the electric utility company. Other sources can be PV systems, generators, and storage batteries.
For stationary storage battery installations, NEC® 480.7 requires specific field marking at the DC disconnect which includes the maximum available fault current derived from the stationary battery system and the date the calculation was performed.
Knowing the maximum amount of AFC that the battery system can produce is the first step in determining proper ratings of equipment supplied by the battery system.
See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).
2020 Code Language:
480.7 DC Disconnect Methods.
(F) Notification. The disconnecting means shall be legibly marked in the field. A label with the marking shall be placed in a conspicuous location near the battery if a disconnecting means is not provided. The marking shall be of sufficient durability to withstand the environment involved and shall include the following:
(1) Nominal battery voltage
(2) Available fault current derived from the stationary battery system
Informational Note: Battery equipment suppliers can provide information about available fault current on any particular battery model.
(4) Date the calculation was performed
Exception: List items (2), (3), and (4) shall not apply to one- and two-family dwellings.
2023 Code Language:
480.7 DC Disconnect Methods.
(F) Notification. The disconnecting means shall be legibly marked in the field. A label with the marking shall be placed in a conspicuous location near the battery if a disconnecting means is not provided. The marking shall be of sufficient durability to withstand the environment involved and shall include the following:
(1) Nominal battery voltage
(2) Available fault current derived from the stationary standby battery
Informational Note: Battery equipment suppliers can provide information about available fault current on specific battery models.
(4) Date the calculation was performed
Exception: List items (2), (3), and (4) shall not apply to one- and two-family dwellings.
Which of the following is true of the DC disconnect in a stationary battery storage system where the available fault current derived from the battery system is 19,000 amps?
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