Shotgun Fuse mystery-advice please

[carolinacoast]

In 10+ years of owning our Hatt, I have burned, not blown, two (2) 240 volt 50 amp shotgun fuses at the power inlet, both in the last 6 months in the same marina.
After the first, I had a great mechanic/electrician replace the source 2 plugs with smartplugs. New cords, and use 2 when entire family onboard.
No breakers have blown. Also(and maybe unrelated) 6 months prior I did also have electrolysis cause 10 month failure on a raw water pump with no source identified. Assumed it was from another marina in another state. not confirmed.
After the electrolysis incident, the water was checked by marina electrical contractor and no stray current identified.

After the first fuse burn, the pedestal was changed. SO, I got the call Friday evening that I had another smoking fuse, in the same exact location on the OTHER side of the boat(below inlet on right). No one onboard, no breakers blown, 3 of 4 ACs set to 77. Those should easily run on a 50/240 amp cord and circuit.
Got to the boat, spun it around with gen on, pulled all 4 shotgun fuses to double check thing, checked with ohm meter, sprayed with corosion spray, installed 2 cords on 2 different pedestals. Spent the night , all seems fine.
On the burned fuse, was able to unscrew the metal fuse holder and burned dust just poured out. Cap was melted through, no fire. The first fuse to burn was a time delay, this one was a 1 time green 50 amp.

With a marine electrician checking the pedestals 2X, a marine electrician replacing my first fuse holder, and installing smartplugs, and checking supposedly everything, I get the same burned fuse on the other side within months with a light load or less. Corosion is not the cause. No arcing on the male or female side of the smartplug cord. Intermittent low voltage from the pedestal as a cause?

I am the only one on this particular dock using 50 amp 240 volt power. others use 50 amp, but 125 volt. I have checked the power at the pedestal, and watched a marine electrician do the same, so now I'm thinking I need a way to track the power at the pedestal to prove a bad transformer or spike from the power company side. My other thought is that I have something on the boat starting to fail that is drawing too many amps, but why no breaker pop, and a fuse burn??

So, gremlin experts, please share your thoughts. I'm baffled, and no one around the docks seems to have a great suggestion, other than,"your boat is old...." I want to figure this out, and quiet those knuckleheads. Thanks in advance.

 

[Boatsb]

What is the power at the pedestal? What is it on board with a medium load?

Why replace the old fuses with the same when there are much better systems for circuit protection.

I'm installing 2 32 amp 230 volt (European vessel) this week.

 

[oscarvan]

I'm with Boatsb here..... take the pyrotechnics out and put some proper protection in there and THEN start trouble shooting if there still is a problem.

 

[Boatsb]

On adding 2 of these.

https://www.googleadservices.com/pa...MIjvH4-uvj3QIVg7XACh1ShwCrEAQYASABEgLhf_D_BwE

 

[Pascal]

Get rid of duses and replace with breakers. Too many hatts had had damage becase of 70s technology. Often you can install the fuse inside the within a couple of feet of the power inlet. For instance on most MY you could install the breaker in the ER just under the shore power inlets and still be within a couple of feet.

Marinco makes a shore power breaker installed inside a standard waterproof cover that matches the other ones.since nowone use phones anymore, you can pull the old phone inlet and put a breaker in that hole

 

[carolinacoast]

Thanks Guys. Breakers in ER underneath makes a ton of sense. Will post a pic once completed.

 

[Boatsb]

Look at the blue seas 3120. I believe that's what I installed on another boat. There's other versions for different use. The 230 volt ones are not always in stock because they're European. You need the 240 volt ones

If you dont use a transformer and bring in 50 amp 125/250 volt then the 3119 works.

 

[doc g]

I remember an explanation that was brought forward about Hatteras using the fuses, a breaker trips when there is too much current but can do nothing when there is a bad connection that is generating heat, which is a low current situation, thus the fuses. My '81 61 CMY had them , my '99 74 SDMY doesn't .........Pat

 

[Pascal]

Doesn’t a bad connection lower voltage thus increasing amp tripping the breaker?

Recently I had what can be called a bad connection on a 100amp plug which was causing the boat side breaker to trip. Replaced the plug and trimmed the end of the wires and the breaker no longer trips.

 

[Phasma2128]

Voltage drop across a resistive connection increases current draw

 

[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