These requirements cover Class T fuses for use in accordance with the National Electrical Code, NFPA 70.
A Class T fuse has a maximum current rating of 1200 amperes, and a voltage rating of 300 volts a-c to ground and a maximum current rating of 800 amperes and a voltage rating of 600 volts a-c.
Class T fuses are of the nonrenewable cartridge current limiting type and have an interrupting rating of 200,000 amperes rms symmetrical, with peak let-through currents and total clearing amperes-squared-seconds specified for the individual case sizes.
These fuses are intended for use with fuseholders that will properly receive Class T fuses, but will not receive fuses of any other type. The 300 volts knife blade-type fuses rated not more than 600 amperes are for either clip mounting or bolted-in installation. The 300 volt fuses rated more than 600 amperes and the 600 volt knife blade fuses are for bolted-in installation only.
A product that contains features, characteristics, conponents, materials, or systems new or different from those in use when the standard was developed, and that involves a risk of fire, electric shock, or injury to persons shall be evaluated using the apprropiate additional component and end-product requirements as determined necessary to maintain the level of safety for the user of the product as originally anticipated by the intent of this standard.