Shotgun Fuse mystery-advice please

[KPTIM]

Voltage drop across a higher resistance connection does NOT increase current.
The higher the resistance the lower the current.
Simple Ohms law.
Current (amps) = E (voltage) / R (resistance).

But,
The higher resistance will cause more heat to be generated across the poor higher resistance connection.
Power (watts) = I^2 (current) x R (resistance).

When the fuse holder starts to fail such as from corrosion and starts to become a poor connection or higher resistance connection it generates more heat and will eventually burn up.

Keep the fuse holder clean and periodically service with dielectric grease.

[oscarvan]

So after re-reading this thread I want to add that a fuse will (should) only blow/burn when there is a current through it. The power company can go to 10,000 volt, unless there is a path through the fuse to a user there is no current. If something inside shorted out allowing the current there would be evidence of same.

So...... was there ever more light shed on this mystery?

[jmooney]

I would suspect that the wiring behind the fuse holder is corroded. Pull the stainless steel steel panel that holds the inlets and fuse holders and have a look . I replaced my wiring and used blind lugs on the wires . I replaced the fuse holders with new and never had a problem with fuses since , that was almost 20 years ago. Also 3 a/c s on one fifty amp cord is a lot , especially if the water heater , battery charger , or ac fresh water pump cycles on .

[oscarvan]

Also 3 a/c s on one fifty amp cord is a lot , especially if the water heater , battery charger , or ac fresh water pump cycles on .

On a 125VAC/50A service yes. On 220VAC/50A as long as it's balanced, ie two AC's on one leg the other and the WH on the other it works fine. I do it all day long. Never see more than 30A on each leg.

[carolinacoast]

Fair question about an update from nearly 3 seasons ago. Good news, no new issues. Updates: 2 other boats became near sinkers from electrical issues. Dockmaster left. Both boats now sold and gone.
everything disassembled and checked, then recent insurance survey, all good. No claim, just time. I suspect a marina issue caused all of these problems.
smartplug definitely runs less temp on same load, even on much older cord. 2 ac's , no heater, outback charger, pulls less than 30 amps.
My conclusion was there was too much running on one cord in a hot environment back then, and no capacity for voltage spike/drop. That led to an amp draw change. Fuse replacement with breakers are the best choice, but just not necessary in this case. Not a liveaboard. Thanks for checking. Is agism a thing against boats too?

[Pascal]

On a 125VAC/50A service yes. On 220VAC/50A as long as it's balanced, ie two AC's on one leg the other and the WH on the other it works fine. I do it all day long. Never see more than 30A on each leg.

Down here you can’t survive running just two ACs... right now I m pulling 39amps just for air con leaving just 10 amps for everything else. An often overlooked issue is the load on the neutral wire. My chillers and air con pumps are 240v so the neutral only carries about 5 amps from the 120v air handlers and maybe 10 amps from the house loads. On boats with 120v air cons (whether self contained or splits) the neutral wire and pins will be carrying well over 50amps. That’s why it s often the neutral wire or pins that burns up

Ideally I need to add a second cord to my boat so I don’t have to worry about tripping breakers when running everything. I ll do it at some point, I just hate having to deal with a second cord when leaving the dock.

[rwaldrop13]

Down here you can’t survive running just two ACs... right now I m pulling 39amps just for air con leaving just 10 amps for everything else. An often overlooked issue is the load on the neutral wire. My chillers and air con pumps are 240v so the neutral only carries about 5 amps from the 120v air handlers and maybe 10 amps from the house loads. On boats with 120v air cons (whether self contained or splits) the neutral wire and pins will be carrying well over 50amps. That’s why it s often the neutral wire or pins that burns up

Ideally I need to add a second cord to my boat so I don’t have to worry about tripping breakers when running everything. I ll do it at some point, I just hate having to deal with a second cord when leaving the dock.

All of my AC units are 220/230 volt, with corresponding pumps. However, PO recommended going to double cords at some point. He had wired in a smartplug on the port side, but used welding cable to make a cord - it fried the smartplug at our first marina (which we left 2 hours later and cancelled lease). I haven't had time to start digging into electrical beyond replacing old Crusairs with modern self-contained units. Most of my panel gages don't currently work, but I knew when purchasing Pau Hana we were getting into a semi-project boat. As I replace equipment I try to replace wiring but its not easy. All new AC's and pumps have new wire.

[Pascal]

I installed LED meters from Blue Seas in my new panels. I love them. I can monitor them from the helm or from the couch