diy solar

diy solar

mrbf/anl vs class-t

John Frum

Tell me your problems
Nov 30, 2019
I watched this video
a while back and posted about it.
If memory serves @Hedges expressed some doubt as to the validity of the test.

I "wonder" if the fuse opened without sustaining an arc because it took a few more milli-seconds to trip.
Therefore the voltage dropped enough that the MRBF fuse could quench the arc.

Some of that has been answered (,

Maybe a visual will help.


And these are just the small fuses. Imagine what happens in a short circuit condition that's not limited by those small wires. 8AWG! That's tiny. I would dare you to repeat that same test with 4/0 wire if it weren't so unsafe. He is NOT demonstrating extremely high-current disconnect. He's focused on fuse versus NO fuse.


The most inportant, to me, is the Class T fuse. This is a very fast acting fuse with a high arc interrupt rating that
should be put on the positive side of the battery bank. Everything should
pass through this fuse. A Class T fuse has the meltable (fusible) link but it also has a filler that
melts when the fuse blows and flows between the end caps (on fuses under 100 amps) or tabs
(on fuses of 100 amps or more). The filler helps to prevent an arc jumping inside the fuse body.
When properly sized and installed, in a dead short it will clear the short and remove the batteries from
the system.
When the fuse or circuit breaker is not rated high enough to handle the battery bank, the arc can
continue through the device (jumping it) like it was a piece of solid metal.
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My experience with ANL versus class T was interesting

I had a 250 amp ANL fuse that blew on me... The weird thing is I wasn't even really pulling 250 amps through it

I assumed that maybe I hadn't gotten something tightened all the way down or even that it was a bad fuse so I replaced the fuse and went on about my business the next day the same thing happened

This time I managed to get to it within seconds of it blowing as I happen to be in the compartment working

What I found was the fuse was extremely hot as were the wires around it

I thought maybe the fuses I was using possibly had an incorrect rating or something of that nature.

So I decided to try run a 500 amp fuse just to test and see what would happen... The exact same thing happened... The fuse blew

But here the fuse was oversized by 100%!!!

(Just to clarify I did this in a very controlled environment standing by with a fire extinguisher)

Then I tested it with no fuse... Again I had my fire extinguisher... Everything worked just fine

Then I took everybody's suggestions and I converted over to class T fuses... I went back to a 250 amp fuse and have not had any trouble since

It turns out that not all ANL fuses are made the same... I've been told that a lot of them are cheaply made and used on the car audio market... And as such they're just not good at handling high inrush currents