Check your T fuses with an infrared thermometer while under Inverter load.
As part of an electrical upgrade, installed a Blue Sea 225amp T-fuse on Blue Sea holder between new 2000w inverter and new Blue Sea rotary isolation switch.
All 3/8" terminals were initially set with a torque driver to 35 ft-lb which seemed very light; hand tightening averaged 55-75 ft lb which I ran with.
Operations testing with infrared heat gun monitoring elicited
severe heating at one fuse terminal closest to Inverter. Ambient 76F, wiring 76-78F, and terminal climbed to
147F. Shut it down, removed, inspected. Good mating of surfaces, good torque, no interferences from heat shrink. Good lug crimp. Wires closest to inverter did not heat up at all. Tight bend in photo is undesirable but did not create an issue.
Here is what I saw on removal: apparent coating on the T Fuse lug surfaces- either a lacquer or shop oxidation; and transfer of this surface material to mating surfaces on the (chromed?) Fuse holder. Compare with the bare metal exposed by the serrated lock nut.
I sanded ALL surfaces with 400 grit paper, reinstalled and torques, and tested satisfactorily.
Nearly NO heat rise. Thank goodness.
Quite clearly this coating on the fuse was creating enormous resistance!
I have written to Blue Sea technical support querying what coating they use if any, and whether they have encountered counterfeit materials for sale on
Amazon where I bought this.
I am not happy with the Blue Sea fuse holder: the terminal posts are embedded in plastic and are NOT BONDED to the plates. Looking straight down at end of terminal bolt you can see a slight gap between it and the terminal plate.
Strangely the hot point was at the terminal nut points closest to the fuse on the 'outbound' inverter side. The opposite side of nut was far less hot, and adjacent surfaces barely hot at all. This suggests that in addition to plate-to-plate contact, current is trying to flow up the bolt and touching only a handful of thread edges creating severe resistance. If the terminal post was welded or threaded through the baseplate this issue would probably not occur.
I am aware the use of the infrared thermometer on various angled surfaces may create some artifact readings. I played around quite a bit with monitoring different surfaces from different angles, and came up with fairly consistent results.
@rfuss928 kindly weigh in on this issue.
Per internet search, there are counterfeit rotary Blue Sea switches however this one appears genuine. No findings on fuse.