Another power plug mishap.....

[FF]

Surface area is only part of the amperage passing ability, the ampacity of the material used as contacts determines how hot it gets.


Copper , as always is best.


Suggested Ampacities - IEWC

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SUGGESTED AMPACITIES (All Types of Single Conductor Insulation) ... Current ratings for different conductor materials may be calculated by multiplying the ...

 

[mvweebles]

Good thread. Given my 15 year boating coma, I didn't know SmartPlugs existed. Will be installing as part of my refit.

Question - conventional wisdom on dielectric grease on prongs of shore power plugs? I would think a good thing as long as it isn't slathered so thick that it creates a path for electricity across face of plug. Any comments against?

 

[psneeld]

Practical Sailor I believe recommended its use like many manufacturer instructions and found many of the conductive greases to contain ingredients not suitable for salt water use.

 

[caltexflanc]

If you've got the space, a Glendinning Cablemaster solves this and many other issues on the boat side.

 

[syjos]

Good thread. Given my 15 year boating coma, I didn't know SmartPlugs existed. Will be installing as part of my refit.

Question - conventional wisdom on dielectric grease on prongs of shore power plugs? I would think a good thing as long as it isn't slathered so thick that it creates a path for electricity across face of plug. Any comments against?

Dielectric grease will reduce corrosion but it is not conductive.

I use MG Chemicals 846 Carbon Conductive Grease. It is a carbon-filled, electrically conductive grease. It lubricates, reduces contact resistance, repels moisture and inhibits corrosion.

 

[diver dave]

... the ampacity of the material used as contacts determines how hot it gets.


Copper , as always is best.

...

Pure copper contacts on the twist lock would cause far more fires. The ampacity is only part of the story. Contact pressure is important. You need alloys like yellow brass or even better, phosphor bronze to improve the plastic yield limit of the arrangement in a twist lock.
Now, on a straight blade design, like dryer, stoves, RV plugs, etc, the story changes. Now, the design is a bit easier, and you can use higher conductivity contact surfaces, teamed with even a stainless C spring to maintain high mating forces.
For quite a while, I used an AMP system aboard that had high Cu content blade contacts, gold plated, with stainless steel parts to keep the contact pressure high. High conductivity, high corrosion resistance, and high contact forces team up to make a reliable, although somewhat expensive, system.

 

[Redhook98]

Update - I replaced the inlets with the new SmartPlug receptacles. No issues, fit like a glove and very easy. maybe 20 minutes each all told. Nice product. I cut the power cables back to install the new ends and found the detriment to all, black brass wires. Even though these cables were only about 6 months old, water had intruded into the cables somehow and had caused corrosion in the wiring (turned black, not bad enough for green/powder). Your plain run-of-the-mill Marinco power cables are not tinned wiring. Nor do they appear to be as water-proof as originally led to believe (on both ends). By the time I cut it back to expose shiny copper, the cables were a bit to short for my comfort. I installed the ends to get me up and running, but ordered new SmartPlug 30a cables off Amazon. Decided on a new Y-Adapter while I was at it. And enough CAIG DeOxit Marine Dielectric grease to slather up the entire boat.



Funny enough but the older shore power cables he wired the boat with (receptacle-to-panel) are actually 8 gauge (not the normal 30a 10 gauge) and were in considerably good shape (i.e. all shiny, no sign of water intrusion into cables).



I'll post better pics of the receptacle I removed. Pretty nice meltdown.

 

[Redhook98]

Last update. Here are the parts after R&R.

 

[Olebird]

That is really ugly! Rather be lucky than good!! You dodged a bullet!

 

[FoxtrotCharlie]

Wow, that's scary. Our boat is 50 amp, 120. So I have an adapter for 50 amp, 220 pedestals - works great, and I love the heft of the 50 amp plugs. No issues so far. I have a voltage monitor in the saloon and with two 15k a/c's running, along with water heater... we rarely get over 36-37 amps continuous. Propane range in the galley. Glad you are all safe!

 

[FF]

"on a straight blade design, like dryer, stoves, RV plugs, etc, the story changes. Now, the design is a bit easier, and you can use higher conductivity contact surfaces, teamed with even a stainless C spring to maintain high mating forces."


The other advantages are the cost is minor they could be replaced for 15 years at the price of a "marine" unit, , every time the plug is pulled it is self wiping , and the straight flat copper of the plugs is easy to clean .


Finally they work really well at internal load transfer. A socket for the dock power source and one more socket for the noisemaker and one more for the inverter makes switching sources both easy and safe.
Really simple to understand too!

 

[diver dave]

Finally they work really well at internal load transfer. A socket for the dock power source and one more socket for the noisemaker and one more for the inverter makes switching sources both easy and safe.
Really simple to understand too!

Very interesting idea. In my industry, lots of old timers don’t trust circuit breakers or switches with their life. Fuses and disconnects “in the pocket” are trusted. In the really old days, knife switches were trusted. Because you can witness the open status. I don’t see much of those anymore; certainly a hazard on board a moving boat. [emoji15]

 

[Stillwater]

Yeppers

I have to toss a red flag...does anyone have a reference that says a 30A boat circuit is not rated for 30A continuous? And don't reference NEC stuff.

Nope. You can run 30 Amps All day. That's why Hubbell Refuses to provide a current rating. They've heard that arguments before. So on a nice 95 degree day in Florida, with 85 percent humidity you can run 'er at 30 Amps all day, assuming you've calculated all inrush specs on your motors and pumps, with variances for peak power spikes during switching operations which of course can spike to (in the case of air conditioners) to 300% briefly during cycling which of course will be pushing your little 30 Amp connector to over 40 Amps. Yep, that's why Hubbell stays out of it.

 

[Joe Pica]

Not only must one clean the shore cord contacts you should periodically remove the mount screws in order to inspect the connections on the back side of the boat side female plug to the feeds to the panel. Those back side connections are not sealed so are exposed to the elements(salt air) and readily corrode adding to the totality of accumulated resistance. When adding up all the resistance of the many connections in these complex circuits. Test ohms to appliance. The circuit is only safe if all these connections have perfect connectivity without adding resistance.

 

[Tellico Bob]

Back 1n 2017 prior to moving my boat from Nashville to Knoxville I completed an up grade to my shore power setup by switching out my existing 50 amp 240 volt twist lock connectors. The existing plug and socket showed no signs of overheating. My concern was that I didn't feel the connection was as tight as I thought it should be. I installed a new 50 amp Smart Plug. Biggest mistake I ever made. Four days into the cruise I had to order a replacement and have it shipped to a marina I would be at in a couple days. The Smart Plug was showing signs of overheating. I contacted Smart Plug and without a yes, no, or maybe they shipped me a replacement. Since they did not want me to return the bad plug I cut it apart to see what failed. I feel the 50 amp plug is a bad design but the 30 amp is a great design. I have seen several 50 amp Smart Plugs fail, I have had two. I have switched back to a twist lock type and have had no problems. I now check the connection at least once each week for heat and found no temperature rise. Somethings can't be improved on.

 

[Teakettle15]

Stupid question from a guy trying to learn...why didn’t the breaker trip? I thought that was the point of breakers (either in the shore power stanchion or on the boat’s panel).

 

[rslifkin]

Stupid question from a guy trying to learn...why didn’t the breaker trip? I thought that was the point of breakers (either in the shore power stanchion or on the boat’s panel).

Breakers will trip to protect against an overload-induced meltdown. But unless there's a thermal cutoff in the plug, it's possible for increased resistance due to corrosion to cause a meltdown. Basically, with the corroded plug, the contacts make more heat than normal and can get hot enough to cause a meltdown while operating below the rated current limit (so the breaker never sees a problem and doesn't trip).

 

[Mike3888]

Guys new to this stuff. When I inspect the old style plugs should i put any type lubrication on the plugs/posts?
Thanks Mike

 

[tadhana]

The Smart Plugs are not immune to problems. There have been several fires. The issue is workmanship. The wire connections are screw terminals. When you put it together you torque it down and then leave it for half an hour or so and then re torque them. And then after a month or so check the torque again. If the connection is not tight, tight tight, it will become a high resistance connection. As others have said, resistance=heat.

We've used Smart Plugs for several years and have found another weakness. The OEM Hubble and Marinco ends are potted. The Smart Plugs are not. Our plugs are on the transom. We used to keep the plugs attached all the time, with the locking mechanism tight. this was acceptable and endorsed by Smart Plugs. But on the transom you get a lot of salt spray and mist. The attached pictures show salt bridge which built up inside one of my plugs after 2 years and 12,000 nautical miles. The plugs were not running warm. The problem showed up when we tripped the ELCI device at a marina we have stayed at many times. The boat next to us also had a smart plug so I asked to try his cord. It did not trip the device. When I took the Smart Plug apart there was moisture inside and a bridge of salt between the hot and ground. .

 

[Mike3888]

Thanks much. I have the old style plugs. we are new to the larger boat seen and I was wondering what I should be looking for when I inspect the plugs. I have a 50 amp pedestal with a Y to 2 30 amp cords and connectors to the boat itself. Our plugs on the boat are about mid ship and don't get a lot of spray but still would like to know what to look for and if we need to lubricate the plugs?

 

[syjos]

Guys new to this stuff. When I inspect the old style plugs should i put any type lubrication on the plugs/posts?
Thanks Mike

Yes, See post #65

 

[diver dave]

The Smart Plugs are not immune to problems. There have been several fires. The issue is workmanship. The wire connections are screw terminals. When you put it together you torque it down and then leave it for half an hour or so and then re torque them. And then after a month or so check the torque again. If the connection is not tight, tight tight, it will become a high resistance connection. As others have said, resistance=heat.

We've used Smart Plugs for several years and have found another weakness. The OEM Hubble and Marinco ends are potted. The Smart Plugs are not. Our plugs are on the transom. We used to keep the plugs attached all the time, with the locking mechanism tight. this was acceptable and endorsed by Smart Plugs. But on the transom you get a lot of salt spray and mist. The attached pictures show salt bridge which built up inside one of my plugs after 2 years and 12,000 nautical miles. The plugs were not running warm. The problem showed up when we tripped the ELCI device at a marina we have stayed at many times. The boat next to us also had a smart plug so I asked to try his cord. It did not trip the device. When I took the Smart Plug apart there was moisture inside and a bridge of salt between the hot and ground. .

Looks like little baby busbars inside. On large busbars, both the material of the bolts and the torque is highly critical. The bolt thermal expansion needs to be close to the busbar expansion factor.
I might be tempted to pot such a plug; Haven't seen one up close yet though.
This picture is a great example of conductive condensate, and lack of creepage distance to accommodate.
My parents lived in a home a block from the ocean; one day a garage outlet strip spontaneously caught fire with zero load. Same issue.

 

[TemptUs]

I’m getting ready to retire from 45 years as an electrical power engineer and a boater for 39 years. The limitation on the amount of current a thermo-magnetic breaker will carry is based on how it is used in the circuit. Breakers will carry their handle rating in open air but are limited to 80% of handle rating due to the heat they generate when enclosed. The same is true for conductors.
The cord set plugs can be affected by corrosion but most often plug burnouts are due to not completely twisting the connection and holding the plug in place with the locking ring. The contact surface is reduced when the plug is not fully engaged, especially the neutral connection.
I’ve replaced multiple 30A plugs over time due to these issues. I just purchased a boat with a 50A cord set and noticed some burning starting on one of the plugs. I changed to a 50 A Smart Plug and have had no problems since.
It’s all about contact surface and being able to lock the plug in place. Smart Plugs do both well. Switch to these new connectors and forget worrying about them burning up. When you hear it snap into place you know you have a good connection.
Also remember to close the receptical cover on your boat to help keep it free of contamination.

 

[tadhana]

Thanks much. I have the old style plugs. we are new to the larger boat seen and I was wondering what I should be looking for when I inspect the plugs. ....The easiest way to check is to put your hand on the plug when you are pulling a heavy load. The plug should feel the same temperature as the surface next to it. A temp gun is also mighty useful, If the plug is 10 degrees warmer than ambient, it is time to fix it. Remember to check both ends of the cord. . Any time you disconnect, you should inspect carefully for any discoloration in either side of the connection. .

 

[TemptUs]

I agree with your hand test as it will uncover a problem prior to a failure. I noticed the hotter plug by hand before I noticed the beginning of a plug failure. You will see plug failure as a browning or blackening of the yellow plastic along the edges where the blade enter the cord plug.
You will only use smart plug(s)on the boat end of your cord(s) and the boat receptical(s). (Get the SS cover plate). You are not to monkey with the connection at the dock pedestal as this is not part of your boat. Of all the burnt power connections I have seen is always on the boat and not on the dock end which jives with my opinion that most problems are due to operator error. (Failure to fully twist the plug and locking the plug in place with the locking ring) we can see the wear on our dock lines due to the movement of the boat, but don’t check our electrical cords.

 

[rhoulio]

Don’t overlook the thought that if one is making their own connections inside the connector (Not a factory molded plug), and the screw holding the wire down was not tightened properly, it will gradually become looser and looser as it expands and contracts due to heat created from the load. You will end up with a higher resistance connection meaning more heat where there should be very little. If tightening stranded wire under a screw (in a connector or at the breaker), tighten it down and then physically wiggle the wire back and forth and you can then re-tighten more as the strands move around and settle into place. You will find you may obtain another full turn or more depending on wire size and number of strands.
If you are pulling close to the limit of a 30 amp plug, then a 50a would be a much better choice.

 

[Steve DAntonio]

Statistically speaking, most boat fires are the result of shore power faults. One observation from the photo, the back of those inlets are supposed to be covered/insulated, you should do that on the replacement, even if it's a Smart Plug, their inlets lack full insulation without an enclosure. If you can see a energized screw, it should be covered.

For some time I've recommended smoke alarms be installed above shore inlets, again statistically speaking it's high risk.

More on shore power overheating here https://stevedmarineconsulting.com/october-2011-newsletter/

(In Taiwan)

 

[syjos]

Don’t overlook the thought that if one is making their own connections inside the connector (Not a factory molded plug), and the screw holding the wire down was not tightened properly, it will gradually become looser and looser as it expands and contracts due to heat created from the load. You will end up with a higher resistance connection meaning more heat where there should be very little. If tightening stranded wire under a screw (in a connector or at the breaker), tighten it down and then physically wiggle the wire back and forth and you can then re-tighten more as the strands move around and settle into place. You will find you may obtain another full turn or more depending on wire size and number of strands.
If you are pulling close to the limit of a 30 amp plug, then a 50a would be a much better choice.

Connecting stranded wire directly under a screw is not recommended. Crimp a ring terminal to the stranded wire then place that under the screw.

 

[clyde]

i would go to the local ace hardware, and buy a new 30 AMP plug to replace the bad one! worked for me...clyde

 

[DrissZougari]

I do not understand why people think that, switching to the so called smart plugs or to 50A plugs should solve their issues or prevent the above damage.
- Do not waist your money on these plugs because the dock side will still be the same 30A.
You can save your boat however, a fire on the dock is pretty much the same. Also, you are still at risk inside your power panel or somewhere else that is not visible on the boat.
- Please, do not replace your 30A connectors and shore power cables to 50A. You need to know that all your wiring inside your boat is still designed for 30A system.
- the best item to add to your boat and to protect it is a current meter for every 30A (or a single gauge with a switch). Boats are designed for 80% continuous draw however, system do get old and the current draw will most likely to go up. Proper maintenance of your systems and proper power management (80% rule) is recommended.
Monitor you current draw to protect your boat.