480.7 DC Disconnect Methods. Maximum Available Short-Circuit Current.

The DC circuit breaker circled in red serves as the DC disconnect switch for this bank of storage batteries. The maximum available short-circuit current derived from the stationary battery system and the date the short-circuit current calculation was performed must be field marked at the DC disconnect.
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The DC circuit breaker circled in red serves as the DC disconnect switch for this bank of storage batteries. The maximum available short-circuit current derived from the stationary battery system and the date the short-circuit current calculation was performed must be field marked at the DC disconnect.

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 short-circuit current derived from the stationary battery system and the date the short-circuit current 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).

2014-2017 Code Language:

480.7 DC Disconnect Methods.

(D) 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) Maximum available short-circuit current derived from the stationary battery system

(3) Date the short-circuit current calculation was performed

(4) The battery disconnecting means shall be marked in accordance with 110.16.

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480.7 DC Disconnect Methods. Maximum Available Short-Circuit Current.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Which of the following is true of the DC disconnect in a stationary battery storage system where the available short-circuit current derived from the battery system is 19,000 amps?

A: It must be marked with the minimum AIC rating.
B: It must be factory marked with the maximum available short-circuit current.
C: The required field marking on the disconnect must state that the available short-circuit current derived from the battery system is 19,000 amps.
D: It must be factory marked with the AIC rating of the storage batteries.
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