I recently bought some Fuse Holders. Sometimes these Fuse Holders get warm/hot. Someone suggested the fuse might not be properly connected at the terminal.
Is there a reason why I'm getting a warm/hot Fuse Holder?
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Yes, either: the fuse or terminal is loose which increases the resistance and causes it to get hot
the terminal or holder is too small and it again gets hot due to the current and resistance.
Whatever the cause, it needs to be corrected - wires of sufficient size, clean and tight terminals and a quality fuse holder.
In electrical circuits heat in any part of the circuit is always the product of the Resistance in the element and the Current flowing in that element multiplied by itself (i.e. squared.)
For example, if the resistance across the fuse holder and fuse is 1 Ohm, and the Current flowing in it is 2 Amps, then the heat generated in the fuse holder and fuse will be: 1 Ohm x 2A x 2A = 4 Watts. This would feel warm or hot to the touch.
Here is a link to a Wikipedia article on Joule Heating - https://en.wikipedia.org/wiki/Joule_heating
If you want to try and diagnose the problem yourself, and if you have a Digital Multimeter [DMM] or an analogue electrical tester, you could try and measure the Resistance across the whole fuse holder and fuse. If you can, test for current flowing by connecting the ammeter, in series with the fuse holder and fuse while the power is flowing. Ensure the ammeter is set for DC amps if that is what is flowing in the fuse.
In short, either high Resistance (Ohms) or high current (Amps), or both, will produce Joule heating (heat).