Another power plug mishap.....

[Redhook98]

Well, it was bound to happen. In 30 years of boating, I have never had a power plug issue, until this weekend. I was overdue I guess. All we had on was one 12k btu Heat/AC unit and a 1500w bilge heater on that side. Ran all day just fine. Went in for dinner and came out to no power. This is what I found. Nice. Normally two heat/AC units would be on that side, plus microwave and one of the water heaters (plus battery chargers, plugs, etc).



Bought a full set of SmartPlugs to replace both connectors on both sides of the boat and on the cables. I have four total power input plug areas on the boat.


I was lucky. This could have been bad.

 

[rslifkin]

That looks like a 30A plug. Those things are total pieces of crap IMO. A 12k A/C unit on heat cycle plus a 1500w heater should be about 21 amps of load, so not overloaded. Anything over 24 amps on a 30A (80% rule) on a continuous basis would be considered overloaded, however. Short bursts up to 30A are fine though.

Personally, I'd say all inputs on any boat should be either Smartplugs or 50A twist locks. Personally, I prefer 50A shore power inlets in general as you get to use the much more robust 50A connector on the shore end unless they only have 30s available (and then you use an adapter). 50A lines are heavy to carry, but not much worse than 2x 30A (which is common). And IMO, the more robust connectors are worth it.

 

[Comodave]

Yes, you are very lucky that you caught it when you did. It could have happened overnight when you were sleeping.

We put Smart Plugs on our boat 2 years ago and have not had any issues since. I agree that about 24 amps is all you want to draw for any period of time on the 5-L30 plugs. Unfortunately when people see that it is rated for 30 amps, they think that 30 is ok all the time. The 5-L30 has very little contact area for 30 amps.

 

[psneeld]

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...unless there is a direct connection to boat shore power supplies.

 

[tiltrider1]

30 amp plugs can not handle 30 amp continuous. In fact anything over 24 amps will eventually end up like the pictures above. It doesn’t take much corrosion to cause excess heat. As the heat builds the female socket looses its grip, which creates more resistance which creates more heat which can lead to a boat on fire. The above pictures were close, lucky there is still a boat. If you are going to continue using these old style 30A plugs you need to inspect them every month. I bet if the above plug had been inspected a month earlier you would have seen discoloring around the positive prong on the male plug.

Boats that need to pull 30A continuous need to switch to 50A plugs.

Can’t answer Psneeld about a reference to 30A plugs being rated or not rated for 30A continuous. I can only reference people to a long list of boat fires that started at a 30A plug.

 

[Lou_tribal]

Personally, I'd say all inputs on any boat should be either Smartplugs or 50A twist locks. Personally, I prefer 50A shore power inlets in general as you get to use the much more robust 50A connector on the shore end unless they only have 30s available (and then you use an adapter). 50A lines are heavy to carry, but not much worse than 2x 30A (which is common). And IMO, the more robust connectors are worth it.

Why?
I have a 30 amps and that is far enough for what I need knowing that I never have more than 15 to 20amps load at any time. This all depends on how much energy hungry one is.

L

 

[psneeld]

And 100% of every failure I have seen was probably corrosion/bad connection in the plugs, not because of their ratings...not the wires unless damaged and not the CBs.


Proof is worth a 1000 posts of dock talk....anyone have actual PROOF or some reliable recommendation?


If the setup is not foolproof...then what IS the acceptable continuous rating...as corrosion, looseness,etc could do the same at many different amp draws...why not limit them to 15A as safe?

 

[rslifkin]

Why?
I have a 30 amps and that is far enough for what I need knowing that I never have more than 15 to 20amps load at any time. This all depends on how much energy hungry one is.

L

The 50a plugs have more contact area. And with the outer shell, they lock in much more securely, so there's less risk of the plug shifting and causing bad contact.

For the 80 percent rule, look at the circuit breaker specs. Most say 80 percent is the continuous rating. Most non marine electrical codes say the same. As a rule, that's the safe option unless the breakers and connectors are explicitly rated for 100 percent continuous load. Wiring is easy to size for the desired continuous load, so that part isn't much of a concern.

 

[psneeld]

Agree the Smart plug for 30s and either for 50s is a quantum leap in terms of plug security.

 

[Capt. Jon]

Appears psnead is correct. Nowhere in the installation literature does it say that the 30 amp marine cable cannot carry its rated load continuously. it actually says just the opposite. Below is a link to the installation paperwork. Refer to section 3. Its a short read and very informative.


https://hubbellcdn.com/installationmanuals/WIRING_PD1343_INSTALLINST.pdf

 

[syjos]

I run 30 amps from shore power a lot and have never had a burnt or melted plug. No furnace so we run electric heaters during the winter.

I examine and clean the prongs with electrical contact cleaner monthly. I also spray the cleaner into the female cord plug openings while holding the prong with the openings facing down to drain. A Scotchbrite pad is sometimes used for thorough cleaning of the male prongs.

The wiring from the shore inlet to the breaker and panel is #8 instead of the standard #10. In order to mitigate any possibility of the area around the inlet getting hot or burning, the inlet is mounted on a flush mount steel electrical box that is enclosed on the back side to contain any flames.

During the winter when we are away for couple months and heater use is high, I use a shore power cord with three ring terminals instead of the female plug and direct connect it to a terminal block inside the electrical box.

I'm in the process of installing a temperature sensor on the back side of the shore inlet wired to a solenoid that will open when the temperature gets to a certain point. I have to experiment and see what the high temperature open point will be.

The first generation Smart Plug had the safety feature of opening the circuit when the inlet became hot. That feature was discontinued since the breaker they used would reenergize automaticaly when the temperature dropped introducing a safety hazard.

The lack of a high temp cutoff on the newer Smart Plugs sort of reduces the safety aspects. It still has positive clamping and more contact surface area than standard plugs. But the contact area on Smart Plug still needs to be kept clean.

 

[Comodave]

Check CMS marine web site. He did an article about it. The contact area on twist lock connector is incredibly small.

 

[psneeld]

But they ARE adequate...like the Hubble link says...it's not the materials that are the problem...its the connection, corrosion, etc....


And thus why 30A standard are the most likely to overheat...because they are not easy to keep tight for a myriad of reasons.

 

[boathealer]

Agree with psneeld. I have never seen one of these melted contacts (including one of my own!) that was NOT due to corrosion. As I wrote in another post....

Corrosion on contacts equals resistance. Resistance on contacts means voltage drop and more current being drawn by onboard devices. Higher current through a resistance equals heat. Lots of heat equals melted plug. Guess which terminal had the corrosion?

Keep those shore power contacts CLEAN (both sides). Dielectric grease does help keep corrosion at bay.

 

[FF]

By switching to the 240V 50A range plugs the copper contact area is increased 400% or more.

Yet to see the all electric live aboard folks melt one. Any Big Box store , priced right.

They are not "water proof" , never seems to matter.

 

[syjos]

But they ARE adequate...like the Hubble link says...it's not the materials that are the problem...its the connection, corrosion, etc....


And thus why 30A standard are the most likely to overheat...because they are not easy to keep tight for a myriad of reasons.

I agree that dirty contacts and corrosion is the cause of burnt inlet/outlet.

The inlet and the female plug should be cleaned and inspected regularly and at the first sign of corrosion or overheating, replaced.

If the locking ring doesn't tighten the plug, replace the ring.

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.

 

[sunchaser]

I have to agree with PSN and others on this. The 30 amp cord "scorched" issues I've seen are relegated to corrosion, abuse or old tired connectors. All bets are off when breakers on either side don't trip properly.

An all too common, and ignored, occurrence is running electric heaters and thinking that is the load. Then in the dark of night the wind blows down a tree somewhere kicking off power for several hours. Once power restored your big inverter charger kicks on overloading the already challenged cord set. Which is why I try to stay at less than 1/2 of 30 amps with electric heat during the winter.

 

[Codger2]

Agree the Smart plug for 30s and either for 50s is a quantum leap in terms of plug security.

I switched to the SmartPlugs when they first came out and have had both 30 & 50 amp plugs.

 

[Redhook98]

The funny thing is I do maintenance all the time. My years in the Navy has taught me to be pretty anal on this point. It was a fairly new cord (about 5 months old), I used dielectric grease and the rings were seemingly tight. My Portuguese Bridge door opens onto those two power connectors and I am wondering if someone on a recent cruise had opened it a little carelessly and hit them. It's a heavy door. Either way, it was a bad connection and somehow that got worse. Luckily it burned itself out. New SmartPlugs and cables on the way.

 

[Gulf Comanche]

Had a similar almost disaster as shown in the OP’s pics. Switched to Smartplug and both ends run cool to the touch. But, pulling the female side from the boat is no picnic, I thought it was supposed to be easy.

 

[High Wire]

Just curious if a smoke alarm went off. If not you should seriously consider placing one in the compartment.

 

[CMS]

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...unless there is a direct connection to boat shore power supplies.

The L5-30's are "rated" for 30A but the NFPA/NEC stipulate that on a continuous basis, defined as longer than 3 hours, the "max continuous" is 80% of 30A or 24A. This applies to household outlets too. They may be 15A rated but are 12A max continuous under the codes.. NEC/NFPA covers to the dock pedestal so a max continuous of 24A on a 30A service applies.

 

[oscar]

The 30 amp cord "scorched" issues I've seen are relegated to corrosion, abuse or old tired connectors. All bets are off when breakers on either side don't trip properly.

And therein lies the part most people don't understand. Breakers are only designed to protect against current exceeding the allowed value.

Corrosion will start creating the heat at a MUCH lower value because it INCREASES the RESISTANCE. Basically what you have is a miniature space heater inside your plug.

The fire will start at a MUCH lower current flow than the max. A space hater runs at 7-15 amp, think of the heat it creates..... The breakers will happily let that through while the fire starts, and they will be operating as designed.

 

[Bacchus]

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...unless there is a direct connection to boat shore power supplies.

psneeld
First to admit I'm no expert but here is my interpretation - feel free to let me know where I am incorrect.

I don't understand how you can discard NEC...
My thinking is NFPA/NEC applies to marinas. So isn't the power pedestal governed by these standards. My interpretation is that OCP (overcurrent protection) specifies that a branch circuit (pedestal in a marina) should be protected as follows (emphasis mine)...

"Branch circuits. The requirements for branch-circuit overcurrent protection are found in Section 210.20. The general requirement is to size the OCP for no less than 125% of the continuous load and 100% of the noncontinuous load. The NEC definition of a continuous load is a load where the maximum current is expected to continue for 3 hours or more."

If you do the math I think that says you can only draw a continuous load of 80% of the OCP. If a 30A outlet on the pedestal protected by a 30A breaker it seems that 80% is the max continuous load that should be placed on the circuit.

I don't see this specific reference in ABYC but again my thinking is that if applied to the pedestal it would be redundant to aging impose the 80% aboard the boat. I do see the 80% referenced in many marine related sources as a practice. I do agree that if it is non-continuous the OCP can be 100% of the non-continuous load.
Here's the full reference that elaborates on the above.
https://www.csemag.com/articles/understanding-overcurrent-protection/

Edit: I see I'm a slow at typing and CMS has weighed in with his opinion.

 

[O C Diver]

When redoing the 30 amp inlet on my charter boat, I installed it near the transom, under the gunnel, with the inlet facing down. Over the next 20 years, the contacts have remained corrosion free as they are protected from weather and and water would fall away from the contacts. The cord gets attached 75 t0 100+ times per year, which helps clean the contacts. Because the cord hangs straight down, I believe there is less adverse loading on the socket and plug.

Ted

 

[rslifkin]

Because the cord hangs straight down, I believe there is less adverse loading on the socket and plug.

This is a good point. My inlets are a couple inches above deck level, so I get similar strain relief from the cords coming nearly straight out and resting on the gunwale.

 

[psneeld]

The L5-30's are "rated" for 30A but the NFPA/NEC stipulate that on a continuous basis, defined as longer than 3 hours, the "max continuous" is 80% of 30A or 24A. This applies to household outlets too. They may be 15A rated but are 12A max continuous under the codes.. NEC/NFPA covers to the dock pedestal so a max continuous of 24A on a 30A service applies.

OK....thanks, that was what I was looking for

 

[rslifkin]

Plus, safety issues aside, sticking to the 80% rule means that you're unlikely to cause a nuisance trip of the breaker from any small variable loads that are easy to forget about (like a refrigerator, etc.).

 

[psneeld]

But I think that's exactly why there is the NEC safety factor built in the way it is....and for companies to say why their gear is rated for their "labeled" amperage.


It would be rare to actually draw 30A continuously for 3+hrs. Many of the biggest draws on a boat shore power intermittent once cooled or heated.


At any given time there is WAY OVER rated appliances plugged into any household circuit. If everything in the circuit is rated/engineered properly and the CB works as advertised...it pops long before you overload the wiring or outlets. (unfortunately we know of many CB issues that make this debatable but really at that point all safety becomes debatable if overcurrent protection is unreliable)


Same should apply to shore power.... running a boat at 30A with things like ACs, heaters, water heater, or whatever....as long as you keep the total 30A total per units....you should be OK as none should be running continuously...if they are they are either undersized or like Hubble recommends about feeling outlets and cords to see if they are warm.

 

[diver dave]

I find the CMS report compelling. As an engineer in the electrical/electronic space for the utility industry, the most impressive piece of data is the heat rise IR picture, using brand new twist lock and smart plug. A 24 deg rise in exterior temperature of a brand new 30A twist lock system is, to me, entirely unacceptable. You must also realize that the IR camera is seeing the outer thermoplastic, not the metallic contacts inside; those will be far higher. And, this was, IIRC, at 27 Amps.

I am in the middle of a dock electrical design at my new home. It HAD involved a 30A twist lock, which I have purchased already. I'm not positive what I will do, but the 30
A NEMA system will not now exist on my dock.