fuses 5mm x 20mm heating w/low current

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RRonke

Member
Location
Lincoln,NE
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

Senior Member
Location
Chicago, IL
Occupation
EE
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:


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

Member
Location
Lincoln,NE
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!
 
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