15 amp fuse hex window

[dougcorena]

Can anyone explain why a 15amp edison type fuse is the only one with a hex window. 20 amp and up all have round windows. This is a question that I was asked and I have no clue. I know there is a logical answer so any answers would be appreciated

 

[bphgravity]

Re: 15 amp fuse hex window

This is a code requirement per 240.50(C). The section states that the hexagonal configuration is for distinguishing 15-amp rated and lower fuses from those of higher than 15-amp. I do not know the history of this requirement or the logic of the hex shape?

 

[jmc]

Re: 15 amp fuse hex window

I'm old, but not that old, but I recall an old-timer telling me that the different shapes on edison base fuses was so that one could tell that the ampere rating was while in the dark.???

 

[dougcorena]

Re: 15 amp fuse hex window

well i'm actually looking for the theory reason to it and no its not so that you can tell it in the dark sorry JMC. I've tried that and was shot down on that answer. Reason being is you cant feel the window.

 

[jmc]

Re: 15 amp fuse hex window

Doug: If u go back far enough 15 amp fuses had a hex configuration on the perimeter back in the old day. Take a look in some of the old electrical books such as "Practical Electrical Wiring" by Richter and Schwan. Also check older edition of 1965 NEC Section 240-20(C). I know that they existed and I may have some in my cellar of antique artifacts.
John M. Caloggero

 

[iwire]

Re: 15 amp fuse hex window

We should all be familiar with JMC from these books.

Books