LV voltage Fuse co-ordination

[Brickeletric]

I think this may be a silly question but here it goes. I mainly worked with MV fuses and coordinating those types of system know I have been tasked with some 600V and 480V work and would like to know how fuses curves works for class J and Class cc fuses. I’m use to seeing a minimum melt time and a total clear time. When I look at LV fuse all I get is a melting time curve. How do you go about being selective with you system? Do you just make sure that the fuse you selected has a lower melting time then the fuse upstream of that one?

 

[dpc]

They coordinate the same way, it's just that the LV fuse suppliers are too cheap to provide the min melt and max clearing time and just give something called "average melt", if they give you anything.

You just need to allow some additional margin between fuses. The Bussman or Shawmut websites should have some documentation regarding coordination between fuses of similar type. There are some rules of thumb.

 

[pauliwood]

Dpc, it's more of a competitive issue regarding min melt and total clearing times. They publish avgerage melt curves as you said, and to get your min melt and total clearing, I believe it is +/- 10%. Has been awhile, you could confirm that Brickeletric by calling either of the fuse companies Dpc mentioned.

Also, if you are using all of the same manufacturer in your facility, both companies provided selectivity charts in the applications section of their catalogs. It gets a little gray on coordination when you have a mix of fuse suppliers, as most people do. Then you would need to overlay fuse curves to ensure proper selectivity. However, both Bussmann and Shawmut are close in there premium fuse line, so you'd be very close to being selective if Shawmuts catalog says you have selectivity between their Class J AJT80 and their Class CC ATDR60 (just an example, don't have chart in front of me)

If you had the Bussmann LPJ80 and the Shawmutt ATDR60, chances are you'd be selective as both manufacturers have similiar fuse characteristics. Again, you'd want to draw out the min melt and total clearing to ensure this.

Both companies have a good applications department and would help you with a phone to them.

Regards,

Paul