Why Noram Chose to Develop Duralim HRC Fuses (over CBs)

Noram embarked down the “protection road” by developing either circuit breakers (CBs) or current-limiting fuses (CLFs). After careful review of its users’ and specifiers’ list of desired core performance requirements for electrical protective devices, the Duralim HRC fuse was born.

Core Performance Requirements

General Purpose—One Device for All Applications. Both CBs and CLFs can be used as general-purpose devices if the proper types and ratings are chosen. Certain application decisions or compromises may have to be made in order to achieve a general-purpose capability.

For example, a CB’s frame size may have to be increased to ensure that adequate inter- rupting rating (IR) is achieved for systems with high fault levels. A CLF with time-delay overload characteristics could be employed to permit the same fuse to be used for not only feeder protection, but also full backup motor protection.

Noram came to the conclusion that for this requirement (general purpose), a time-delay CLF with high interrupting capacity (IR 200 kA) provided an excellent means to protect main, feeder, and branch circuits with both noninrush and inrush circuit characteristics.

High Level of Protection—Overload and Short-Circuit. In the overload region, both the CB and the CLF can provide protection, assuming that the proper device and rating are pro- vided for the specific application. In the short-circuit region, certain advantages arise with the high-rupturing capacity (HRC) fuse over that of the CB, due to the CLF’s high level of current limitation. Although current-limiting CBs are available, they are generally larger than standard breakers, more expensive, and significantly less current-limiting than HRC class J fuses.

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