Fuse Types

[mityeltu]

I am moving into a new position as a metrology engineer and I am reading up on the standards that I will need to be familiar with in that role. I am currently reading the UL 248 series and I have a question. In UL 248-1 the following is stated:

2.2.7.7 Branch circuit fuse
A fuse which is suitable for protection of distribution systems, wiring, or equipment. Examples of branch
circuit fuses are Classes R, J, L, T, and CC. A supplemental fuse, intended to protect equipment only, is
not a branch circuit fuse.

Question: Why would other type fuses (say class K) NOT be good for branch circuit protection as opposed to the other classes listed?

 

[JoeStillman]

It isn't plain from the language that the list is complete. The word "Examples" implies a subset of the complete list.

 

[ron]

It isn't plain from the language that the list is complete. The word "Examples" implies a subset of the complete list.

Agreed. I think that they just gave examples of fuses to try and explain that there are Branch circuit fuses and NOT Branch circuit fuses (supplemental fuse, intended to protect equipment only).

Usually the supplemental fuse is inside and part of the listed equipment and not in the jurisdiction of the NEC rules.

 

[petersonra]

Question: Why would other type fuses (say class K) NOT be good for branch circuit protection as opposed to the other classes listed?

The real reason is because UL says so.

I seem to recall that according to UL branch circuit fuses are required to be rated at least 250VAC and be able to interrupt at least 5 kA, among other things.

Supplemental fuses are typically used to protect individual pieces of equipment while BC fuses protect branch circuits and feeder circuits.

 

[zxfabb]

It isn't plain from the language that the list is complete. The word "Examples" implies a subset of the complete list.

Exactly, if you check out Bussmann's catalog, you would find Class H, Class K and some more in the category of "Branch Circuit Rated Fuses".