Fuses - hdbk10920186

DOE-HDBK-1092-98

9.6.2 FUSES

Fuses are temperature-sensitive, current-sensing elements that are generally used as short circuit

protective devices in individual electrical chassis. The fusing characteristic, or opening time versus

current, must be within the safe time/temperature characteristic of the device being protected.

Designers must carefully consider the load requirements in the fuse selection process, particularly

when high surge currents may be encountered during initial turn-on. Operating time/current

characteristics of the various types available can usually be found in fuse manufacturers catalogs. A

fuse's interrupting current capacity must also be considered when connected to a power distribution

system having a significant fault current capacity.

The voltage rating on a fuse shall be equal to or greater than the device's operating voltage.

In general, cartridge fuses should have a disconnecting means on the supply side, (NEC Section 240-

40), and shall not be connected in parallel unless factory assembled and listed as a unit (NEC Section

240-8).

9.6.3 CIRCUIT BREAKERS

A chassis or cabinet shall not employ circuit breakers as "on/off" switches unless rated for the

application by the manufacturer.

9.6.4 POWER INTERLOCK DEVICES

Cabinets and equipment having potentially dangerous currents and/or voltages present should have

a means of controlling access, or a power interlock device designed to interrupt the power to the

cabinet. Provisions shall also be made to discharge any stored energy, such as in capacitors or

inductors, to less than 50 volts within 10 seconds when the safety interlock is opened. Interlocks may

not be used as a substitute for lockout/tagout. (29 CFR1910.333(c) and ANSI/ISA S82.01-1988,

Section. 9.3.5.2)

9.7 DISCONNECTING MEANS

All enclosed electrical/electronic equipment shall be provided with a means for disconnecting it from

each external or internal operating energy source. This disconnecting means shall disconnect all

current carrying conductors.

9.7.1 GENERAL

Interlock systems are not a recommended disconnecting means for cabinets and equipment having

potentially dangerous currents and/or voltages present. (See Section 9.6.4)

Permanently connected equipment and multi-phase equipment should employ a switch or circuit

breaker as means for disconnection.

9-12