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Old 01-08-2022, 11:45   #1
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Arcing in 30 amp shore power cord? (Picture)

Hello from Florida:
Plugged in my 30 amp cord to run the 10,000 BTU A/C: Strong smell of burnt something.
Disconnected the cord and noticed black soot marks on the female end.
Cleaned the male contacts (They were already clean, no corrosion, but black from the arcing)

Different day, different marina AND different cord, same result: Arching and burned smell.
What is going on?
(No breakers popped on the boat or on the dock pedestals, the A/C was working normally.)

A short in the vessel's 110 volt system? (If so, breakers should have popped)
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Old 01-08-2022, 12:10   #2
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Re: Arcing in 30 amp shore power cord? (Picture)

Interesting that this happened to you twice with all different connections. Had that not been the case then I would have said this was either corropion at one of your shore power connections or a surge (or power on when connecting).


Since that is likely not the case here, you need to look further into your boat power systems. Do you just have a single connection on your boat? Had you been running other items on shore power (not the AC unit) prior to this event? When was last time you used the AC prior to the event?


Something changed and you need to think backwards and write it all down to find a link.


EDIT - have you looked inside the on-boat connector to see if there is corrosion? Is it possible one of those connections is loose? I know many are often potted which makes that inspection impossible. I also know from reading other stories that the back of plug connection on the boat is often suspect for the cause of this arcing.
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Old 01-08-2022, 12:46   #3
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Re: Arcing in 30 amp shore power cord? (Picture)

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Originally Posted by GreenWave View Post
Interesting that this happened to you twice with all different connections. Had that not been the case then I would have said this was either corropion at one of your shore power connections or a surge (or power on when connecting).


Since that is likely not the case here, you need to look further into your boat power systems. Do you just have a single connection on your boat? Had you been running other items on shore power (not the AC unit) prior to this event? When was last time you used the AC prior to the event?


Something changed and you need to think backwards and write it all down to find a link.


EDIT - have you looked inside the on-boat connector to see if there is corrosion? Is it possible one of those connections is loose? I know many are often potted which makes that inspection impossible. I also know from reading other stories that the back of plug connection on the boat is often suspect for the cause of this arcing.
Yup, single connection.
Besides Air condition there is an inverter/battery charger as well as 110 volt outlets, but none of that is has been used in a long time because the solar panels keeps the batteries topped of.

I have not looked inside yet, it will be next step, but pain in the rear to unscrew and inspect..

Nothing has changed, no new installation or repairs, no nothing, it just started this one day when I was going to run the air condition overnight.
(I run it once a month to keep everything fresh and lubed)
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Old 01-08-2022, 13:02   #4
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Re: Arcing in 30 amp shore power cord? (Picture)

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Originally Posted by CSY Man View Post
Hello from Florida:
Plugged in my 30 amp cord to run the 10,000 BTU A/C: Strong smell of burnt something.
Disconnected the cord and noticed black soot marks on the female end.
Cleaned the male contacts (They were already clean, no corrosion, but black from the arcing)

Different day, different marina AND different cord, same result: Arching and burned smell.
What is going on?
(No breakers popped on the boat or on the dock pedestals, the A/C was working normally.)

A short in the vessel's 110 volt system? (If so, breakers should have popped)
Not a short or other problem in the system, it's more likely something marginal in that specific connection. If the burning and charring has happened with two different cables, then the common element is the male AC connection on the boat. It might be deficient somehow: dirty, worn, etc.

And also, try to measure the highest AC current drawn by your boat when that AC is running hard, etc. Those connectors might be rated for 30A, but that's under perfect conditions. We all know that those connectors have often been problematic.
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Old 01-08-2022, 13:03   #5
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Re: Arcing in 30 amp shore power cord? (Picture)

You could put a voltmeter on your boat connection and check for any resistance/continuity issues?
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Old 01-08-2022, 13:09   #6
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Re: Arcing in 30 amp shore power cord? (Picture)

These yellow Marinco cables and connectors are made according to a standard established around 1930, nearly 100 years ago. You are not alone with this problem with these connectors. An internet search will turn up hundreds of these.

There is a replacement male/female connector from Smartplug that has been designed to overcome all the problems and improve contact surface to pass current for all the AC and other consumers on modern boats that did not exist in the 1930’s. It fits the same hole and screwholes.

I am myself a satisfied customer of Smartplug, no other stakes.
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Old 01-08-2022, 13:40   #7
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Re: Arcing in 30 amp shore power cord? (Picture)

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Originally Posted by sailormed View Post
These yellow Marinco cables and connectors are made according to a standard established around 1930, nearly 100 years ago. You are not alone with this problem with these connectors. An internet search will turn up hundreds of these.

There is a replacement male/female connector from Smartplug that has been designed to overcome all the problems and improve contact surface to pass current for all the AC and other consumers on modern boats that did not exist in the 1930’s. It fits the same hole and screwholes.

I am myself a satisfied customer of Smartplug, no other stakes.

Was just going to bring Smartplug into the conversation. Last year when I had a Marinco style connector do just what the OP's did, I converted. Best money I have spent for the boat other than that countertop ice maker!
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Old 01-08-2022, 14:02   #8
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Re: Arcing in 30 amp shore power cord? (Picture)

Replace, not just clean the inlet. It is 20 years old and has to have some damage from the short. This may not be the root cause but is now damaged. Replace the cord or at least a foot or so if installing replacement cord end. Shutoff everything on re-connection and then energize 1 at a time while monitoring amp load to see if something else is a problem

We have a pile of damaged cords in the shop - have seen several boats have issue in a weekend when power was marginal.
A help is to fill female plug ends with dielectric grease to block moisture. Have seen energized cord dropped in momentarily without tripping but don't recommend it as a test.
Smart plugs are as others suggest an alternative if you have a spare boat buck or 2 but can complicate your setup if transient and using different cords.
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Old 01-08-2022, 14:08   #9
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Re: Arcing in 30 amp shore power cord? (Picture)

Replace the male end. And cut back the cable untill good. It’s probably melted inside. Abd will just keep hearing new cords.

Both ends need to be changed so often
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Old 01-08-2022, 14:16   #10
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Re: Arcing in 30 amp shore power cord? (Picture)

Quote:
It fits the same hole and screwholes.
This is important..
I have heard of Smart Plug but no personal experience with it.
I am selling the boat, buyer is lined up and survey scheduled for next week.
I am tempted to just replace the male plug if the cables inside seems ok, and call it a day. ($99 Marinco)
The buyer can always replace the female end OR he can go for the Smart Plug.
I will tell him and the surveyor what is going on.
Thx guys. (and girls)
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Old 01-08-2022, 14:18   #11
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Re: Arcing in 30 amp shore power cord? (Picture)

We experienced the same problem some years ago. In our case, we replaced the receptacle the cord plugs into and the cord. The receptacle went bad which damaged the cord. Our current practice is we replace the receptacle every three or four years.
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Old 01-08-2022, 14:41   #12
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Re: Arcing in 30 amp shore power cord? (Picture)

I'm agreeing with everyone that it's the male end in your boat's shore power hookup that has failed.

It is the common denominator; I doubt it's the AC, any heavy electric load would have done the same thing. It's good you were monitoring the situation. Consider all the cycles of wear it has sustained over the years - imperfect connection between those prongs (either from dirt, corrosion, or material wear) will generate arcing and melty bits, as you discovered. It's not a hard fix and even a drop in replacement is fine.

Thankfully naval architects and yacht builders work in harmonious concert to anticipate life cycles of wearable parts to keep them easily accessible for routine maintenance by marine engineers and boat owners.

Oh wait what did I just say nevermind.
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Old 01-08-2022, 18:08   #13
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Re: Arcing in 30 amp shore power cord? (Picture)

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Originally Posted by thesaltytar View Post
I'm agreeing with everyone that it's the male end in your boat's shore power hookup that has failed.

It is the common denominator; I doubt it's the AC, any heavy electric load would have done the same thing. It's good you were monitoring the situation. Consider all the cycles of wear it has sustained over the years - imperfect connection between those prongs (either from dirt, corrosion, or material wear) will generate arcing and melty bits, as you discovered. It's not a hard fix and even a drop in replacement is fine.

Thankfully naval architects and yacht builders work in harmonious concert to anticipate life cycles of wearable parts to keep them easily accessible for routine maintenance by marine engineers and boat owners.

Oh wait what did I just say nevermind.
Ha, you hit the nail...

Yes, I will lay down on my back, wiggle my head in and underneath the coamings, grab a philips screw driver and try to remove the piece.
Stay tuned..
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Old 01-08-2022, 18:36   #14
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Re: Arcing in 30 amp shore power cord? (Picture)

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What is going on?

Common problem. The cord end has failed and you will have to replace it. You are probably better off replacing the whole cord unless it's in great shape, because the cost of replacing the end is close to the cost of replacing the whole cord. Check prices and decide for yourself.


Two things happen over time to the brass contacts inside the end. They corrode, and they lose their springiness. This leads to a high-resistance connection that overheats even at power levels the cord is supposed to be able to handle. The overheating causes further loss of "springiness" and the problem cascades. Because there isn't a short or overload, breakers don't trip.


All connectors fail this way with age and use, especially in a salt environment. Time will tell whether the "Smartplug" is a substantial improvement -- it's a new enough product that we don't really know yet.


The overheating you have experienced can lead to fires in some cases. The shore power inlet and cord are supposed to be made of materials that will not burn but materials quality varies. Boats, and lives, have been lost. You are fortunate that you caught it before things got to that point.


There have been various product proposals for a shore power connection with a temperature sensor that will disconnect the boat in the event of overheating, before there is a risk of fire. I'm only aware of one that made it to market and it was withdrawn due to problems with build quality.
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Old 01-08-2022, 19:41   #15
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Re: Arcing in 30 amp shore power cord? (Picture)

This is not going to help your problem but might others that read this thread. A few weeks back I was working on my boat (mostly cleaning interior surfaces). I was running the 12,000 BTU AC to keep the interior bearable. After a few hours I got off the boat and always unplug the shore power cable from the dock connection. I noticed the 30 amp connector was warmer that typical. Checked the boat end and it was normal. I applied a coating of Alnox(electrical joint compound) to the male pins and plugged/ unplugged it a few times. Connector temperature returned to normal and has remained so on multiple AC days.

Get a tube, mine must be 30 years old and has been smeared on a lot of electrical connections over the years.


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