Fuses - hdbk109220040153

DOE-HDBK-1092-2004

When used at a point on a circuit, a surge arrester should be connected between each

ungrounded conductor and ground.

For power line applications, MOV manufacturers recommend a varistor be used with a fuse that

limits the current below the level that MOV package damage could occur. In general, circuit

breakers are not recommended for this application since circuit breaker tripping is too slow to

prevent excessive fault energy.

Consult the manufacturer's application data sheets for more information.

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

240.40), and shall not be connected in parallel unless factory assembled and listed as a unit

(NEC 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 should also be made to discharge any stored energy, such as in

capacitors or inductors, to less than 50 volts within 5 seconds when the safety interlock is

opened. Interlocks may not be used as a substitute for lockout/tagout. [29 CFR 1910.333(c)].

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.

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