Fuse Safety

[Greynomad]

How's this for electrical engineering?
The wiring on my $300 portable air-compressor sacrificed itself to ensure the 30A $2 fuse did not destroy itself...

Fuse.jpeg

[T1 Terry]

How's this for electrical engineering?
The wiring on my $300 portable air-compressor sacrificed itself to ensure the 30A $2 fuse did not destroy itself...

Fuse.jpeg

Very common Ray, blade fuses are only suitable for loads under 25 amps, really 20 amps for a continuous load. The problem is the poor contact area between the fuse and the connector on each end, not enough area to carry high current so the resistance inherent is such a poor design creates heat build up. The only 2 places for the heat to escape is through the fuse itself and the wires each end, so they both over heat and start to melt. To add to the problem, over heated copper becomes oxidised and creates a resistance all of its own adding the problem. Sort of fortunately, oxidised copper has a low melting point so finally the heat causes the wire to melt and the circuit is broken.
The fix, cut the oxidised wire off, get a "Midi" fuse and holder and using good quality crimp connections on the cables attach the cables to the fuse holder, the problem will not occur again. However, if the crimp connections are not god ones the melted cable will reoccur because the high resistance joint problem will still be there. Don't be tempted to solder the wires before crimping them or using solder in place of a terminal, the high resistance joint that could occur with simply melt the solder and create an even worse joint....... I have a lot of examples in my show and tell pile where this has happened and many were performed by so called "professionals" or people who charged money to do a sub standard job. I won't go any further into that topic as it gets me wound up big time, the quality of work these days rarely meets the "tradesman like" level that was expected in the past

T1 Terry

[Lance]

From a contact surface area viewpoint, how does all that work considering the std blade fuse, the Mini and now the Micro fuses ?

[Greynomad]

T1,
Wotsa "midi" fuse/holder look like?

[Busman]

Midi is your normal blade fuse size, there are micro ones as well, but the contact area is soooo small, you would only use for VERY light loads, and the big ones are much bigger than midi. I have one of the larger ones in my current testing meter, you put the ends into where the fuse goes and it tells you exactly how much DC current is being drawn. It is protected by a 60 amp jumbo blade fuse.

[Greynomad]

Could I instal one of those tubular-looking fuse holders and use a glass-tube 30A fuse?

[BruceS]

Ray I suggest you take a look at those manual resetable 'fuses'. (is resetable a word?)
I've got a couple here I use in testing circuits that blow fuses.
Doesn't cost much to just push a button!
Something like these.
http://www.ebay.com.au/itm/5-pcs-15A-am ... SwJQdXDJOT

[T1 Terry]

This is a Midi fuse holder and fuse http://www.ebay.com.au/itm/MIDI-FUSE-KI ... OSwQ59ZX8f~ the surface area on each end of the fuse and the fact the cable lug comes into direct contact with the fuse solves the high resistance joint issues. Good for up to around 150 amps after that a mega fuse and holder is required http://www.ebay.com.au/itm/MEGA-FUSE-KI ... Swx3NZX9Vs
We were using the ANL fuses used in some of the plastic tube type holders http://www.ebay.com.au/itm/ANL-FUSE-HOL ... Sw2gxYsSmD but after issues with cable connections getting hot and screws not holding in the muck metal gold plated bodies we switched to Midi & Mega fuses. The 5AG big glass fuseshttp://www.ebay.com.au/itm/5AG-Glass-Fuse-Hold ... Sw0vBUd4~M also had issues with the muck metal gold plated bodies and poor contact causing them to melt so we stopped using them very early in our system builds.
Mini blade fuses actually have a better contact area than the standard blade fuse, but 25 amps is still the upper limit before problems start to occur.
If you want never ending headaches with false circuit breaker tripping due to heat build up be my guest, simply putting a massively over rated circuit breaker to get around the problem negates the whole purpose of using it in the first place.
About the only ones that truly work on DC current are the NoArk circuit breakers, maybe a bit big for the purpose here though http://www.ebay.com.au/itm/32A-DC-Break ... SwBahVZRGO. These are the way to go for solar protection before the controller, 40 amp or even the 63 amp for a big system using 6 B&S cable or heavier but I tend to stay with the 40 amp units as this works well combined with 6 B&S cable when it comes to voltage drop, 63 amps creates excessing voltage drop over longer 6 B&S cable runs

T1 Terry