Electrical safety: Low voltage fuse classification

by | Mar 13, 2018 | Electrical Safety

Electrical safety: 

Low voltage fuse classification (0-600V)

In this blog, the different classes of fuses used in industrial electrical installations will be presented.

Fuses are protective devices installed on an electrical circuit to protect it from overcurrent. When the circuit current exceeds a certain value during a given period, the fuse can melt passing to the liquid state under the effect of heat, it therefore interrupts the circuit to protect it. To protect the circuit effectively, the fuses are characterized by class. One class differs from another by one or more letters. Each fuse class is distinguished by the electrical and physical characteristics of the fuse, such as the maximum time required for it to melt during overcurrent, the maximum current for a fault or the interrupting capabilities as well as the physical dimensions.

Classes L, J, RK, K and CC are of the HRC type and are regularly used in industrial electrical installations. While class H is different from other classes, it includes fuses that do not have high interrupting capabilities. According to the code, they are old fuses. There are also other existing classes.

Class H does not have a high rupturing capacity (HRC) and does not limit the fault current. The nominal voltage is 250 to 600 V and the breaking capacity is 10 kA. This class is not recommended, and it is suggested to replace it with HRC class fuses. In addition, class K1 fuses have a higher interrupting capacity and a fault current limitation. The interruption capacity is 200 kA and it is possible to interchange a class H fuse with a class K1 fuse without modifying the electrical panel.

Class L have a high rupturing capacity (HRC) and are used for switchboard mains and feeders, large motors branch circuits and power circuit breakers. The nominal current can vary between 601 A and 6000 A, the nominal voltage is 600 V or less and the interruption capacity is 200 kA.

Class J have a high rupturing capacity (HRC) and are used for new installations. The fuse block takes up less space in the panel, is less expensive, and provides superior protection for motors, heaters, and transformers. The nominal voltage is 600 V or less and the interruption capacity is 200 kA.

Class RK1 have a high rupturing capacity (HRC) and offer a better degree of limitation of the fault current than the class RK5. It is regularly used for upgrading power circuits of the RK5 class. The class RK1 is the equivalent of class J. It protects motors, transformers, switches. The nominal current can vary from 1/10 to 600 A, the nominal voltage is 600 V or less and the interruption capacity is 200 kA.

Class CC have a high rupturing capacity (HRC) are used for small motors, transformers, solenoids and inductive loads. The nominal voltage is 600 V or less and the interruption capacity is 200 kA.

Class K1 have a high rupturing capacity (HRC) offers a better degree of limitation of the fault current than the others (K5 and K9). The nominal voltage is 600 V or less, and a class K1 provides an interruption capacity of 200 kA, whereas class K5 and K9 have an interruption capacity of 100 kA and 50 kA.

It should be noted that each fuse switch disconnector must use identical fuses and the same company. If this is not the case, in the event of a short circuit, there may be faulty triggering of the protections caused by the time delay as well as the limitation of the current which may differ according to the manufacturer.

 

Some questions, contact us!

 

Bibliography :

Amp-Trap 2000 : Gross Automation, www.ferrazshawmutsales.com

Littelfuse : POWR-GARD, www.littelfuse.com

Ferraz Shawmut CRS : Gross Automation, www.ferrazshawmutsales.com

TRI-ONIC TRS: Gross Automation, www.ferrazshawmutsales.com

IEEE std 242-1986: 5. Fuses

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Intervention Prévention Inc.

Intervention Prévention concentrates its operations in the field of work safety, offering specialized services following Standards CSA Z462 – Workplace Electrical Safety, CSA Z460 – Control of Hazardous Energy: Lock-out and Other Methods, and CSA Z432 – Safeguarding of Machinery.

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