fuses 5mm x 20mm heating w/low current

[RRonke]

I have 2 240 volt radiant heaters each pulling 7.1 amps that are fed through 12 amp inline fuses. I ran 10-2 NM w/grnd to a single positive off 20 amp controller then added 4 square 2 1/8” box to fuse and reduce wiring to 2 runs of 14-2. My customer called a month later after measuring fuse holder temperature of 140 F. I changed fuse holders from inline to cabinet mount and measured. 30 degree increase after 2 hours continuous running. No fuses have ever blown and wires are not hot. Does anyone know if heat gain can be eliminated or reduced at fuse holders by switching to a 1 1/2” cartridge fuse 15amp?
Thanks for any info..

 

[synchro]

Some amount of fuseholder heating is to be expected due to contact resistance at the fuse-to-fuseholder interface. Littlefuse recommends operating a fuseholder at no more than 60% of its current rating because of variations from the UL test conditions that occur in practical usage, in order to prevent excessive temperatures from occurring:

https://stevenengineering.com/tech_support/PDFs/28FUSECP.pdf

140°F is 60°C, and that seems a little high. A 30°F rise is about 16.7°C which would only be a ~42°C temperature level with a 25°C ambient, and so I would not be concerned about this.
Both the contact resistance and the element within the fuse itself will produce heating, and so some temperature rise is inevitable.

 

[RRonke]

Thanks for the quick reply Syncho and the Steven engineering site reference. Since the fuse holders are 15 amp the 60% guideline would put the draw within guideline limits. Now I just need to reassure the customer!