Selecting the right fuse

[drkidd22]

Hello,
I'm working on a project that will use a resistive heater to warm water up to 50C. I'm trying to select the correct fuse.
The mains voltage where this can be installed may vary between 210VAC to 250VAC.

Heater Specs:
Rated Voltage (VAC) 240
Rated Power (W) 1000
Calculated Rated Current (A) 4.17
min HTR Resistance 53
max HTR Resistance 61.3

I think a 5A fuse should do it like (GDC-5A), but not sure if it's enough de-rating. That fuse also has a breaking current of only 50A and might be too low in case of short. Another thing I was going to use is a fuse holder (FPG4) and connector (15-31-1066) which I believe are sufficient.
What ya guys think?

 

[KeepItSimpleStupid]

I would not have a problem going to 6.3 A, but I think a 5A SB would work fine.

If your using a SCR/TRIAC controller, I would re-think it. In that case I would use a standard blow fuse at probably 1.5x the min load and use a very large I2t fuse like 25 A. I worked with our own custom tantalum resistive heaters in a vacuum and by using controllers that had current limit and a large I2t fuse (25 A) an 3A fuse on a 120 VAC, max 200 W load. Usually the 3A fuse blew first and we saved $30 a fuse. I made sure that the current limit was in place and a fuse was rated for the load.

 

[dr pepper]

Heating elements can have lower cold resistance, this needs to be taken into account, have you measured the current at switch on?
The fuse rating needs to be slightly over this, if your not using phase angle control that is.

 

[drkidd22]

No I have not measured inrush current yet, I will try to do that.
Thanks.

 

[schmitt trigger]

"In that case I would use a standard blow fuse at probably 1.5x the min load and use a very large I2t fuse like 25 A."

That is a very sensible approach.
The smaller fuse would protect against minor overloads, but would not reliably clear a solid fault to ground. That requirement would be met by the larger secondary fuse. High fault current-clearing fuses are more expensive, and you don't want to be replacing them often.