Shore power connector dies at a good time, sort of.

So, if you have read my other thread about my heat exchanger dying, I'm in the "what's next mode". I'm on the boat day before yesterday to continue flushing my engine. I start cooking breakfast and half way through, my range top quits with an error msg. I look at the breakers, ok, I look at the incoming power and oops, I have one 120v leg and the other is reading 30v a/c. So I wiggle and twist all my connectors (I have 3, pedestal, boat and extension) on my 50 amp cable. Still 30v. So, I disconnect my extension, and there it is, burned contacts. Must have gotten water in at the last rain. But, to be sure I check at the pedestal and indeed I have 120v on two legs. Good news is I was there and I checked the my charger and I was on the inverter. If I was not to be there for some time = depleted batteries, spoiled food, etcetera. Ok, start the generator, two 120v legs. I Charge the batteries but I had to go home and leave it on inverter. So, yesterday I check Lowes, they have a new female 50 amp connector for $65 but special order only. I check Home Depo, same price, same situation. Well I need one now, local electrical warehouse, no gots. Crap, off to West Marine and I get to spend $129 for the same thing. Well anyway no easy task replacing the old one. Tried to take it apart, no dice. Had to cut the cable and install the new one. But the new expensive one is not anything close to the water proofing of the old one. It works but now I get to spend more to buy the heavy cover for water proofing. My mechanic opines that as soon as one thing is fixed, the next will break. He suggests I don't fix the next non-critical problem otherwise for sure the next shoe will drop.

What does the end that it plugs into look like? It may be burned too and if it is it may burn your new plug. It can keep bouncing back and forth if you don’t change both sides at the same time.

One 120v leg has too much power going thru it. My guess is your loads aren't balanced between the 2 legs. A new and socket may end up the same.

Comodave said:

What does the end that it plugs into look like? It may be burned too and if it is it may burn your new plug. It can keep bouncing back and forth if you don’t change both sides at the same time.

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The male end looks fine. No issues

RickyD said:

The male end looks fine. No issues

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Maybe you caught it in time.

When you are done with installing/wiring the new plug, check the resistance with your multimeter, end to end of the 50 ft cable. Check each of the 4 wires. Resistance should be less the 0.2 ohms which is as low a my fluke meter typically reads. If is is more you need to check both ends and make sure the wire is clean and bright an not clamped on to the wire insulation. I coat the wires after wire brushing clean with dielectric grease before assembly into the plug.

Do yourself a favor and buy the smartplug. Marine How to site has a great article on the 1930's technology of your plug. After replacing three of the burned ends, I switched to the smartplug and after a year, I no longer have any issues. You don't need the whole cable and the boat side outlet matches up with the old outlet.

Cleaning the prongs and dielectric greasing them will help by keeping moisture out.
n they have trouble.

Coil from the plug/prong end. The socket end has some serious protection, the plug end does not.

Bending those prongs back does not always work. Just a suggestion.

Mac2 said:

Do yourself a favor and buy the smartplug. Marine How to site has a great article on the 1930's technology of your plug. After replacing three of the burned ends, I switched to the smartplug and after a year, I no longer have any issues. You don't need the whole cable and the boat side outlet matches up with the old outlet.

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The Smartplugs are definitely good hardware. And for boats with 30A connections, I'd consider them a very, very good upgrade. The 30A NEMA L5-30 connectors aren't adequate for the abuse they take in a marine installation. However, the 50A 125V and 50A 125/250V connectors (NEMA SS-1 and SS-2) are much, much heavier duty and generally perform well unless damaged. For these applications, the Smartplug is less of an upgrade.

rslifkin said:

The Smartplugs are definitely good hardware. And for boats with 30A connections, I'd consider them a very, very good upgrade. The 30A NEMA L5-30 connectors aren't adequate for the abuse they take in a marine installation. However, the 50A 125V and 50A 125/250V connectors (NEMA SS-1 and SS-2) are much, much heavier duty and generally perform well unless damaged. For these applications, the Smartplug is less of an upgrade.

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I am using the 50 amp cord. Melted three at the plug-positive prong. Last incident started to burn the wood liner on my steel boat (which probably saved me). My boat was designed to run on two 50's but my dock only has one 50 amp plug. This could be part of the problem.

DennisB1 said:

When you are done with installing/wiring the new plug, check the resistance with your multimeter, end to end of the 50 ft cable. Check each of the 4 wires. Resistance should be less the 0.2 ohms which is as low a my fluke meter typically reads. If is is more you need to check both ends and make sure the wire is clean and bright an not clamped on to the wire insulation. I coat the wires after wire brushing clean with dielectric grease before assembly into the plug.

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Thank you for this.

Mac2 said:

I am using the 50 amp cord. Melted three at the plug-positive prong. Last incident started to burn the wood liner on my steel boat (which probably saved me). My boat was designed to run on two 50's but my dock only has one 50 amp plug. This could be part of the problem.

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If you've melted several and it's not down to a bad connector that hasn't been replaced, I'd be taking a serious look at the overcurrent protection in your setup to make sure you're not overloading the connectors.

rslifkin said:

If you've melted several and it's not down to a bad connector that hasn't been replaced, I'd be taking a serious look at the overcurrent protection in your setup to make sure you're not overloading the connectors.

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The breakers were tripping properly. I only found the problem when I unplugged to go cruising. I have zero issues now after switching to the smartplug. My breakers tripped several times last night trying to keep the boat warm and have all the christmas lights on. I checked the smartplug and it was barely warm-no signs of overheating. Huge difference.

I would try not to go over 50' with any power cord. What I have seen happen, is that corrosion builds up on the socket and wiring in the tower. I have had to cut back the wires to the socket and install a new socket. Between the two there is too much resistance.

Keep in mind that as the brakers get older they don't trip as fast. They get stiffer to the point were you cant move them due to the corrosion.

Iggy said:

Keep in mind that as the brakers get older they don't trip as fast. They get stiffer to the point were you cant move them due to the corrosion.

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I've also seen old breakers get weak and trip too easily. In general, old, well used breakers (especially those out in the elements) are always a bit suspect.

A couple of fundamentals:
1. In an electrical circuit, the result of electrical resistance is heat.
2. The heat generation that caused the damage shown in the photos in post #1 will only trip the pedestal circuit breaker if the melting/burning of the plug is so extensive that a short circuit in the plug/inlet interface is created.
3. In my experience the Post #1 damage was caused by high resistance at the plug. This resistance was created in the wire to plug connection or the connection between the shore cord plug and the boat's shore power inlet either because of corrosion in the cord plug or inadequate plug/inlet engagement.
4. The Marinco plugs were designed in the 1930's for use in factories. As such, they were designed to comply with the NEC and carried a continuous use rating of 80% of their capacity.

IMO, it is highly unlikely that loads powered by the panelboard caused a load imbalance between the loads on the L1 leg and the loads on the L2 leg caused the problem. Any imbalance, if it occurred, was created by high resistance in the plug/inlet "system".

At one time I had a five-gallon bucket of burned cable ends and a few burned inlets for boat show viewing. There were no SmartPlug cable ends or inlets in that bucket.

I have put SmartPlugs on my last 2 boats and love them. They are the way to go.

My concern with SmartPlugs is that if I DO have a problem with it, and am in a remote area, my chances of getting a new Smart cord, and associated receptacles is a lot lower than being able to get a standard Marinco cord or plug. . . . .

So the "solution" would be to carry spares . . . . . .

A spare SmartPlug cord is around $800.00. And SmartPlug ends ($180.00 to $250.00 EACH) . . . .

My spares budget is not unlimited, and a Marinco cord as well as Marinco replacement ends are about 1/3rd the price of the SmartPlug (per SmartPlug's website).

And I'm still not convinced that the SmartPlug is any better. I recently helped a boater replace his SmartPlug receptacle (He paid over $200.00) after it overheated and burned. . . . He had the new cord ($800.00 including tax) on order. He was NOT a happy camper . . . . or rather boater.

slowgoesit said:

My concern with SmartPlugs is that if I DO have a problem with it, and am in a remote area, my chances of getting a new Smart cord, and associated receptacles is a lot lower than being able to get a standard Marinco cord or plug. . . . .

So the "solution" would be to carry spares . . . . . .

A spare SmartPlug cord is around $800.00. And SmartPlug ends ($180.00 to $250.00 EACH) . . . .

My spares budget is not unlimited, and a Marinco cord as well as Marinco replacement ends are about 1/3rd the price of the SmartPlug (per SmartPlug's website).

And I'm still not convinced that the SmartPlug is any better. I recently helped a boater replace his SmartPlug receptacle (He paid over $200.00) after it overheated and burned. . . . He had the new cord ($800.00 including tax) on order. He was NOT a happy camper . . . . or rather boater.

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When I changed to a Smart Plug, at the boat to shore cord connection, I saved the old Marinco boat end. Then when my Smart failed, which the original design was prone to do, I swapped back to the Marinco connection, used my spare that still has its original Marinco end and contacted Smart for a replacement. That arrived within a couple of weeks, so I again did the swap, and now have the second generation Smart, without the prone to failure issue of the first. I also still have the old Marinco unit.
Scot, change to the Smart Plug, get the second generation unit, and save the old Marinco unit. Check with your insurer. Some offer a rebate if you change to a Smart. Mine did, though that was several years ago.

koliver said:

When I changed to a Smart Plug, at the boat to shore cord connection, I saved the old Marinco boat end. Then when my Smart failed, which the original design was prone to do, I swapped back to the Marinco connection, used my spare that still has its original Marinco end and contacted Smart for a replacement. That arrived within a couple of weeks, so I again did the swap, and now have the second generation Smart, without the prone to failure issue of the first. I also still have the old Marinco unit.
Scot, change to the Smart Plug, get the second generation unit, and save the old Marinco unit. Check with your insurer. Some offer a rebate if you change to a Smart. Mine did, though that was several years ago.

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Koliver,
I had an early 50amp Smart Plug fail. I hadn’t heard about issues. Is there information available on that?
Thx

I am considering an upgrade to Smart Plugs.
But this blog post shows the problem on the dock end... not on the boat end.
I believe the Smart Plugs only affect the boat's end of things. Correct?

In any case, here is how I solved my problem (without spending $100s on new cords):

https://shellerina.com/2022/11/11/shore-power-cord-fix/

It is tough to say exactly what the caused of the resistance which caused the heat / failure in this case. In this case it was on the dock end... but still... not a comforting thing to see.

It's worth noting, a high resistance scenario, which could come from a poor connection, pitted contacts, water intrusion or failure to fully engage connections, will not trip a circuit breaker.

The burned contact in this case is the neutral. That could be from one of the above causes, however, if the neutral fails entirely you end up with a "dropped neutral" which could be very dangerous, it often leads to fires.

To be on the safe side, you should call in an ABYC certified electrician to check the current flow on the neutral with a variety of loads on, but ultimately everything.

Mac2 said:

Do yourself a favor and buy the smartplug. Marine How to site has a great article on the 1930's technology of your plug. After replacing three of the burned ends, I switched to the smartplug and after a year, I no longer have any issues. You don't need the whole cable and the boat side outlet matches up with the old outlet.

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Thank you I did a little looking into it at first but I will again as the "new" connector cover is hard plastic with a thin rubber washer to keep water from creeping down the cable and into the connection. My old one had the heavy rubber cover which finally failed. I have no confidence that my new system is "waterproof".

Turning Point said:

Koliver,
I had an early 50amp Smart Plug fail. I hadn’t heard about issues. Is there information available on that?
Thx

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I learned of issues when I called Smart Plug to get a replacement. My failure was at the boat end of the 30 amp cord. The original SP had an automatic reset feature, that was prone to failure and actually failed on mine. The next generation don't have that feature and have also lost its attendant failure rate.
I haven't heard of any failure prone 50 amp plug, but I don't have one, so why would they tell me.
They couriered a new SP to me, all at their expense.