What's new
What's new

fuse types


Oct 22, 2014
Does anyone have any good resource for understanding fuse types? If I'm reading it correctly, NFPA 79 only allows CC, J, CF, or T fuses if you want to protect a power circuit to use <14 ga wire. But some motor controllers recommend ABC fuses, and we've use AGC in the past. I like the little fuses, as they don't take up much room in the cabinet, but I also like thin wire.


Jan 27, 2021
Fuse sizing is not nearly as easy as it would seem it should be. I have seen some nice guides published by fuse manufacturers and distributors. Unfortunately, none of them make the topic simpler and the branding jargon makes the topic more confusing.

Normal operating currents, open circuit voltage and the amount of energy the fuse must be capable of interrupting in an overload condition are the fundamental factors.

The best thing to do is look at the data sheets for each fuse type. There are multiple categories of fuses with different characteristics under each class - time response, interrupt ratings and voltage.

ABC fuses are for low voltage applications and have limited ability to interrupt circuits where large amounts of energy must be dissipated.

Wire choice is determined by required ampacity, temperature, number of conductors in a cord, raceway or conduit and insulation type.

Generally speaking, 14 gage is limited to 15 amps.

I chose to standardize on type CC midget fuses inside of control cabinets. These are good for our 480VAC mains and go to 30 Amos and cover most systems we have. The holders are compact. I use FRS-RK5 cartridge fuses for disconnects 60 amps or less and blade type RK5 fuses above 100 amps.

I do not use 14 gage wire - it is a code problem waiting to happen. I do use 18 gage for control circuit applications where the circuits are energy limited.

Bill D

Apr 1, 2004
Modesto, CA USA
The big switches and breakers have to use compressed air to blow out the arc or the plasma flow will simply bypass the wide open disconnect. For smaller power levels it is not unknown for contacts to be welded shut so they can not be disconnected.
A family fried lost a lot of appliances including tv's and stoves when a 12kv line dropped onto his 240 volt supply line. Fuses exploding blew the fusebox door open. I think the breaker panel door stayed closed. Lucky not to burn the house down. The power company repalced the appliances.
Bill D