Shore power short

[SeaDogAK]

When I came to the boat today, the shore power was out. I eventually figured out that the breaker on the power supply on the dock had tripped. I unplugged the shore power cord, plugged it back in, and reset the breaker, and there was a big scary flash that fried my shore power cord and the area around the plug. Pictures attached.

I disconnected shore power and fired up the generator, and it charged normally and supplied AC through the inverter without any apparent problem. No breakers tripped on the boat at any point.

My question is whether the problem is a short or some other problem on the boat, or a problem with the power supply on the dock. I’m an ignoramus when it comes to electrical issues. Does anyone have any ideas?

 

[Comodave]

The L5-30 plug set is notorious for overheating and burning like your photos. It can be cused by poor connection and the consequent heat buildup. I would replace the power cord and have the marina change out the socket in the dock pedestal. Also check the inlet on the boat for any signs of overheating. If so replace it too.

 

[Aguyinak]

The same thing happened to me on Friday

Mine did the same thing on Friday, though not nearly as bad, and we caught it before the breaker tripped. These plugs are notorious for this and it typically is due to an overload on the neutral, as yours appears to be. My connections were tight, I use dielectric grease and my calculated load did not exceed 30 amps, yet it still happened. I also spent part of my afternoon today cutting off old plug ends and installing new.

 

[Comodave]

While the breaker is rated at 30 amps it should not be used at more than 80% or 24 amps for any amount of time. The connector was designed back in the 30s and is a rather poor design, but unfortunately is on a bazillion boats. Maybe look at a Smart Plug inlet and cord set. The contact area on a Smart Plug is about 20 times as great.

 

[SeaDogAK]

So what does it mean if there is an overload on the neutral?

 

[Aguyinak]

I agree with what Comodave is saying regarding connected load, unfortunately 24 amps is not quite enough during the winter here. I don’t know what it is about the neutral and why it often is the location of the short.

I am going to put together a 50 amp setup for next winter, and I am definitely going to look into the smart plug. Thank you Comodave!

 

[Comodave]

Check out marinehowto.com for a great article about shore power plugs.

 

[twistedtree]

Keep in mind that a Smart plug will only address the cable to boat connection. I think the weakest link in these systems is the shore receptacle. You may take care of your plug ends, keep them greased, and replace them when they are looking bad. But nobody is looking at the shore receptacle until it's blow out like yours. Every time there is a contact arc because someone plugs in an old plug, or a dirty plug, or a pitted plug, it's going to pit the receptacle. And once the receptacle is pitted, it's more prone to pit your plug. So it's crappy condition is contagious.


In this case, I'd start by replacing both the plug end and the receptacle. Check the receptacle with a meter, and check your shore cord with a meter just to be sure there aren't any shorts. And definitely check the connection at your boat end.


If it works for you, switching to a 50A cord is a good approach. They are substantially better connectors, and much less prone to problems like this.

 

[Iggy]

I had the same problem. In my case the receptacle was more burnt and after it was replaced it happened again.

The fix was the wires from the buss bar in the tower were corroded up to the receptacle.

 

[Chuck34]

Just a heads up…
NEVER connect/disconnect your shore power cords with anything on in the boat. If you do, you activate a small electrical arc. Over time all those little arcs add up to serious burn marks on your connections, both male and female, which cause serious problems.
Either nothing on in the boat or shore side breaker off when you connect/disconnect. Make it a habit.

 

[twistedtree]

Just a heads up…

NEVER connect/disconnect your shore power cords with anything on in the boat. If you do, you activate a small electrical arc. Over time all those little arcs add up to serious burn marks on your connections, both male and female, which cause serious problems.

Either nothing on in the boat or shore side breaker off when you connect/disconnect. Make it a habit.

[emoji106]

 

[tiltrider1]

Smart plug now makes shore receptacles, cords and boat sockets. Talk to your marina about allowing you to replace the shore receptacle with a smart plug version. If you succeed there then up grade all three parts. You will need an adapter to plug in anywhere else but this should prevent your problem at home.

 

[Comodave]

But even if you still have the L5-30 connector on the dock and the Smart Plug on the boat you have moved the likelihood of a fire from the boat end to the dock end. I would much rather have a fire on the dock than on the boat.

 

[Endeavor GB 32]

+1 on Smartplug. When we seatrialed our boat the dock end of the plug was already bad. First order of business after completion of purchase was to install Smartplug receptacles fore and aft and put a matching plug on the cord. Also +1 on Comodave, rather have a fire at the pedestal than the boat. But as we are now in a condo slip that we own, I will inquire if the marina would install a Smartplug receptacle on my ped if I provide it. Time for L5-30 connectors to go the way of the Dodo.
Regards,
Scott

 

[DennisB1]

Has the plug dropped into the salt water. Corrosion on the plug pins or on the inter pin to wire connection cause resistive heating which you see on your plug hot pin. If dropped into the bay you need to think about replacement.

 

[Nick F]

Quote
" . . typically is due to an overload on the neutral. "
Unquote

I belive this could be a little misunderstood. As the poster said (further down) the current was less than 30 amps, so was was NO overload. Also, the current would was almost certainly the same in the live pin.

The problem is the poor design of the twistloc type plugs/receptacles. They don't make good contact. Poor contact leads to heat generation which, in turn, makes the contact even worse and generates even more heat. The heat affects the surface of the pin, but it also weakens the "spring" force of the receptacle so that it no longer firmly pinches the pin of the plug (reduced contact force). Both of these effects cause increased contact resistance.

Often a plug starts to show discoloration around a pin long before final failure as seen in the photos.

As also well mentioned above, any deterioraton of the pin surface can trigger this degradation mechanism. As stated, this initial deterioration can be caused by the sparking when a plug is inserted or removed with the power on, or by saltwater corrosion (dropping the plug in the sea).

 

[sparky66]

A bad connection should not cause a breaker to trip due to overload. If the pedestal breaker is an ELCI breaker, then it is possible that it tripped because of the arcing making a carbon trace between hot and neutral or ground.

 

[SeaDogAK]

Interestingly, when the harbor replaced the outlet, they told me exactly the same thing happened to another boat just a few boats down, at almost exactly the same time. Makes me think there was some kind of power surge or brownout or something.

 

[sparky66]

Your type of failure is simply a bad connection. Nothing else. If overload, breaker would have tripped and/or 2 of the 3 connectors would have been damaged.

 

[Caballero II]

But even if you still have the L5-30 connector on the dock and the Smart Plug on the boat you have moved the likelihood of a fire from the boat end to the dock end. I would much rather have a fire on the dock than on the boat.

That's exactly what I did when my 40 year-old 30 amp boat inlet plug fried. I was running an electric floor heater during the cold this winter when some fluctuations occurred that puzzled me at first, but the a/c units continued to work. The next day I found that I had no a/c power from the shore pedestal, and the display on my Magnum inverter/charger read "A/C Overload". Checking both boat and shore plugs, I found the 30 amp female plug on the boat side fried. I ordered up the Smart Plug cord with boat Smart Plug receptacle, standard dock side 30 amp male plug on the shore end. I could try to get the marina to change out to Smart Plug receptacle, but that's a job for another day.

 

[adornato]

twist to lock

You would be surprised at how many individuals who plug in the L5 30 amp plug
don''t know you TWIST it to the right to lock it in the socket. I would say the majority. Which allows the plug to move, slide back and arc building up resistance and heat.

 

[Caballero II]

You would be surprised at how many individuals who plug in the L5 30 amp plug
don''t know you TWIST it to the right to lock it in the socket. I would say the majority. Which allows the plug to move, slide back and arc building up resistance and heat.

Well, maybe. But that was not our problem, or anyone else's that I have talked to. The twist part doesn't make it a particularly more robust system, and as far as I can tell, most people understand the twist part. I think it's an archaic system due for a remodel.

 

[SeaDogAK]

Well, maybe. But that was not our problem, or anyone else's that I have talked to. The twist part doesn't make it a particularly more robust system, and as far as I can tell, most people understand the twist part. I think it's an archaic system due for a remodel.

Agreed. Without a retaining ring, which my pedestal doesn’t have, a twist doesn’t hold the plug tightly.

 

[Comodave]

Even if you twist the connector and use a locking ring the L5-30 still only has 1/20th the contact area that a Smart Plug does. That is what the real problem is, not enough contact area for the current being carried, the burns and overheating are symptoms of the problem.

 

[twistedtree]

If I were going to change my boat connection to replace a 30A inlet, I think I would use one of the industry standard IEC pin and sleeve plugs that are used world-wide, rather than a proprietary Smart Plug. The 32A version would be a perfect fit.

 

[mbevins]

If I were going to change my boat connection to replace a 30A inlet, I think I would use one of the industry standard IEC pin and sleeve plugs that are used world-wide, rather than a proprietary Smart Plug. The 32A version would be a perfect fit.

https://www.ecmweb.com/content/article/20892323/a-brief-guide-to-pinandsleeve-devices

 

[rslifkin]

I agree that the L5-30 connectors just aren't robust enough for shore power use. The NEMA SS-1 and SS-2 connectors used for 50 amp are much better. They have more contact area, but they also have an outer sleeve that keeps things seated tighter and makes for better contact. The L5-30 relies entirely on the pins, so they move more, the contacts wear and get loose, and they fail.

For 30A, the IEC or smart plug connectors are much better. For 50A, I'm less convinced that the smart plug connectors offer much improvement.

 

[High Wire]

…[/INDENT]I’m an ignoramus when it comes to electrical issues. Does anyone have any ideas?

Time to call in a professional.

 

[Iggy]

I total agree that the L5-30 just does not cut it.

But I think some of the problems go back to the pedestal. The 10 gauge wire from the buss bar to the L5-30 is just copper wire. After a few years its starts to corrode which add more resistance and the plug heats up. At lest this is what I have found. Once I replaced the whole unit, plugs, breakers and wires. It comes in a whole assembly my problems were solved.

 

[Nepidae]

Shore power

When we bought our boat I read about boat fires.

The power cords were ugly with dirt and there was some singing.

I did some research and found SmartPlug (https://smartplug.com/).

I changed out both the boat connector and the shore power cords.

FYI, most boat fires are electrical in nature and shore power needs to be top notch. Company stands behind their product.

Great investment for boat safety.