How Do You Know the Right Fuse for Your Circuit Protection Needs

 

BY: Shane Weaver

How Do You Know the Right Fuse for Your Circuit Protection Needs

 

BY: Shane Weaver

Class T

Choosing the Right Fuse: It's About Class

What are the differences in fuse “classes”?  Why are fuses divided into “classes” and what standards do they need to meet? All good questions. Today, the playing field for circuit protection contains a huge range of fuses designed specifically for all different types of power systems, so the old methods of fuse classification just wouldn’t cut it. Today, we have the classes, which are designed to meet safety standards put forth by agencies such as UL (Underwriters Laboratories) in the United States, CSA (Canadian Standards Association) in Canada, and ANCE (Asociación Nacional de Normalización y Certificación del Sector Eléctrico) in Mexico. Keep in mind that these standards are constantly updated, so while we can provide a basic overview, it’s important to consult the latest iteration when starting a new project.

LPS-RK Series Substitute for Class H

What do the Classes Reflect?

A fuse fits into a certain “class” based on certain physical specifications and certain performance requirements (ie. how many volts it is rated for, or how many amps it is able to interrupt). If a fuse meets a certain standard, it will fall into that “class” as laid out by the associations mentioned before.

Glossary of fuse terms:

Time Delay: also known as a “slow blow” fuse, this type will allow a brief surge in electricity before the fuse actually blows. For certain types of electrical appliances, this can be more beneficial than a typical fuse which blows as soon as too much current is drawn through it. For devices such as electric motors and fluorescent lights, which consume a greater amount of energy when initially turned on, a time delay fuse will allow them to continue operating without resorting to a higher rating of fuse. A fuse must meet certain requirements to be labeled “time delay.”

Current Limiting: the process of imposing an upper range limitation on the amount of current that may be delivered in the interest of protecting the circuit.

Interrupt Rating: defines the capacity of a fuse to withstand fault current without being destroyed or severely damaged.

 

Class T

So, What are the Classes?

Here’s a rundown of the different classes of fuses, their characteristics, and other unique information:

 

CLASS CC

Voltage Rating: 600 volts
Amp Rating: 1/10 amps thru 30 amps
Interrupt Rating: 200,000 amps
Dimensions: 13/31" x 1-1/2"
Notable Features: non-renewable, current limiting. May be labeled “time delay” if meets requirements. Designed with a “rejection” feature that lets them to be used in rejection fuse holders and fuse blocks that reject fuses with lower voltage and interruption ratings.
Designed For: protecting components sensitive to short-time overloads, non-inductive loads, and protecting motor circuits from short circuiting.

 

CLASS G

Voltage Rating: 600v and 480v
Amp Rating: 1 amp thru 60 amps
Interrupt Rating: 100,000 amps
Dimensions: 13/32" diameter with a length between  1 5/16" and 2-1/4"
Notable Features: non-renewable, current limiting. May be labeled “time delay” if meets requirements.
Designed For: lighting and appliance panel boards equipped with special fusible-switch units.

 

LPS-RK Series Substitute for Class H

 

CLASS H

Amp Rating: 1 amp thru 600 amps
Interrupt Rating: 10,000 amps
Notable Features: not current limiting, renewable and non-renewable versions available. Renewable Class H’s cannot be time delayed, but non-renewables can. An older style of fuse, they are often misapplied in the electrical industry (ie. exceeding the minimal interrupt rating in an industrial plant, or installing more than one link in a renewable fuse).
Designed For: general purpose branch circuits, lighting circuits, and protecting non-inductive equipment (ie. electric ovens and resistance heaters).

 

CLASS J

Voltage Rating: 600v
Amp Rating: 0 amps thru 600 amps
Interrupt Rating: generally 200,000 amps, up to 300,000 amps available
Notable Features: current limiting. Not interchangeable with other classes. May be labeled “time delay” if meets requirements.

 

CLASS K

Voltage Rating: 200v and 600v
Amp Rating: 0 amps thru 600 amps
Interrupt Rating: 50,000; 100,000; or 200,000 amps
Notable Features: non-renewable, not current limiting. Interchangeable with Class H fuses.

 

CLASS L

Voltage Rating: 600v
Amp Rating: 601 amps thru 6000 amps
Interrupt Rating: 200,000 amps with up to 300,000 amp versions available
Notable Features: non-renewable, current limiting. May be labeled “time delay” if meets requirements.
Designed For: protection of feeders and service entrance equipment.


 
CLASS R

Voltage Rating: 250v and 600v
Amp Rating: 1/10 amps thru 600 amps
Interrupt Rating: 200,000 amps
Notable Features: non-renewable, current limiting. May be labeled “time delay” if meets requirements. Shares outer dimensions with Class H fuses, but rejection feature prevents fuses with lower interrupt ratings from being used when coupled with special Class R clips, though they can be used with rejection & non-rejection clips.

 

CLASS T

Voltage Rating: 300v and 600v
Amp Rating: 0 amps thru 1200 amps
Interrupt Rating: 200,000 amps
Notable Features: non-renewable, current limiting. May be labeled “time delay” if meets requirements.
Designed For: protecting feeders and branch circuits as specified in the National Electrical Code.

 

And there you have it. Hopefully, this simplifies these things (as much as a complicated issue like fuses can be simplified), at least a little bit.

 

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