An explanation of the interrupt rating for circuit breakers and fuses

In extreme cases a fuse carrying an excessively high current can vaporize and the metal can be deposited on the base of the fuse block in a way that permits it to continue to carry current. Similarly with circuit breakers, if the level of fault current goes above a certain level the circuit breaker can become inoperable while still conducting current. Fuses and circuit breakers all have an interrupt rating as a measure of their ability to cope with these circumstances. For any given device the interrupt capacity may be different for AC and DC current and for different voltages. 

For DC Systems of 12 or 24 volts the primary circuit protection (Main fuse or breaker next to the battery) is required to have an Interrupt capacity of 3000 Amps for battery banks from 650 CCA (cold cranking amps) up to 1100 CCA capacity and 5000 Amps interrupt capacity for larger battery banks.  Secondary circuit protection is permitted to have a lesser interrupt capacity on the assumption that the primary circuit protection will blow before the secondary one is permitted to carry such a large fault current, the allowable range is from 750-3000 amps interrupt capacity depending on battery size.

For Lithium battery systems the highest AIC available is usually required.  Class-T fuses have an AIC of 20,000 amps.

For AC systems of 120 Volts the requirement is 3000 Amps interrupt capacity for both main and secondary circuit protection.  For 240 volt systems the requirement is 5000 Amps interrupt capacity throughout.

The detailed ABYC standards are summarized in Table IV of ABYC standard E11

This is an interactive blog, feel free to add your questions or comments.

There is little or no available data on the available short current data from lithium batteries.  This may be because everyone if afraid to measure it.  Not having the correct information makes selecting the right fuse more difficult.  I am told that future versions of the ABYC standard will include a way to calculate the short circuit current without having to actually measure it. The answer is probably going to be the same; lithium batteries are capable of a very high current and so only the best fuses will be appropriate.  This will make it clear that Class-T fuses need to be used, and that a fuse for each battery will be required.