Shore Power – SmartPlug vs. 1938

No Mincing Of Words…

This is an ordinary day for me and it brings to mind that saying, a picture tells a thousand words…

Rant Warning:

AS A MARINE ELECTRICIAN I TRULY DESPISE THIS ANTIQUATED & ARGUABLY UNSAFE STANDARD FOR SHORE POWER PLUGS/SOCKETS ON BOATS!

The regulatory & certification organizations that over see this, such as UL, NEC, NFPA, NMMA & the ABYC should all be ashamed that they continue to allow this standard to continue in the marine environment.

There I said it.. Whew….. So why do I dislike it so much? Lets examine this further…

• When this plug standard began life it was back in 1938. I can’t imagine that Harvey Hubbell III ever intended this to be used on boats, inches from the ocean, back when it was conceived..
• In 1938 houses had cloth covered wire and no safety ground for 120V outlets
• In 1938 we did not even have seat belts
• In 1938 GFCI outlets were not even a thought in an inventors mind
• In 1938 lead paint was the rage and asbestos was in everyday use.
• In 1938 there were NO SAFETY STANDARDS for electrical safety on docks or boats.
• In 1938 safety testing for marine use never even existed.

How many other critical electrical items do you use in your house or boat that have remained virtually unchanged since 1938..?

Suffice it to say we have been grandfathered into a substandard and marginally adequate plug & socket combination for marine shore power cord/plug/receptacle use. This twist-lock standard would likely never gain approvals under today’s stringent electrical safety standards but we have it due to grandfathering. Safe? Read on and decide for yourself…

Untinned Wire

Here’s a prime example of where tinned marine wire may have bought this owner a bit more time. A new run of 10/3 triplex tinned marine wire was in order. The black oxidation on this wire can also lead to or create high resistance. When in doubt, it’s best to also replace the feed wire from the new AC inlet to the AC panel.

If your wire run between the AC shore inlet to the AC main breaker, at the AC panel, is more than 10′ wire feet, not as the crow flies, then you will want to install a second 30A or 50A double pole breaker.

A main AC breaker on a boat needs to interrupt both the AC WHITE/NEUTRAL & AC BLACK/HOT wires, and be located quite closely to the AC shore inlet (10′ or less). Single pole main breakers (hot only) are not used in the marine AC systems despite many builders doing so in the 60’s 70’s & 80’s.

Need More Convincing?

When word got out, in my Hall of Fail article, that I was a huge fan and proponent of the SmartPlug pictures came flying in from all over, pictures of burned twist-lock plugs. I am certainly not alone in my dislike for this antiquated & unsafe standard.

I have far too many images of burned twist-lock plugs to show them all so I chose this one to be a good representation.

Photo courtesy: A. Mazon

A NEMA L5-30 Socket

In order to dig deeper than we’ve ever seen before, into this antiquated standard, I bought a NEMA L5-30 socket. This is the standard used for 30A shore power on boats here in the USA and elsewhere.

In order to make these points clearer I chose to destroy this socket by cutting it open to give a full look into why they are so dangerous.

SITE PLUG: Here is a prime example of where your support comes in handy. I paid for this socket out of my own pocket. Support for this site through my donate button (end of this article) help keep this site FREE and the in-depth brutally straight forward articles coming your way. Keep in mind that I don’t have advertisers I need to worry about offending so I can actually be honest in my writing.. Do your part and help support MarineHowTo.com.

I Cut The Plug Open And Exposed The Actual Sockets

My goal here was to show exactly why or how this standard can result in so many boat or marina fires. In this picture we can see the contact area between pin and socket. Not too much is there? The green headed screw is the grounding/Earth terminal but they all have about the same contact surface area.

Socket Riding On Spot Dimple For Contact Area

Please do yourself a favor and blow this image up. This is the result of just 1-2mm’s of movement and the dimple riding up and out of the hole in the pin..

Let’s go over some of the major issues with this standard that lead to safety issues.

1- Round plugs need to twist in order to lock into place. To facilitate this locking feature dimples are used to create the detente so you know the socket is in place.

2- Due to the fact that this standard relies on twisting to lock the plug into the socket the fit of the round plug into the female socket is more sloppy than it should or could be and allows movement between socket and plug. Shore cords weigh a lot and the cord alone can cause strain to the plug & socket, forget waves, boat movement or people stepping or tripping over the shore cord etc…. It is very rare that a shore cord is properly supported to strain relieve the plug & socket.

3- We are trying to use this on boats and boats move continuously….

4- Even just 1-2 millimeters of movement between the plug & socket can cause the dimple to ride up out of the hole and create even less contact area than this already poor design has.

5- There are no seals on this plug standard thus it is very easy for corrosion to set in on the pins & sockets and create yet even more resistance.

6- The socket clamping mechanism/spring clamping feature is made from material just 1mm thick.. It does not take much pressure or offset torquing to loosen a 1mm spring clamp and cause it to provide even less pressure for good contact. Over time the female spring mechanism tires, becomes weaker and the plug fits loosely and no longer snaps or clicks into the detentes…

Actual Contact Area NEMA L5-30 Socket

I needed a good way to show the actual contact surface area of the clamping socket on a NEMA L5-30. I grabbed some sheet metal the same thickness as the plug pin and inserted the socket over it.

I then slid it back and forth thus creating a corresponding mark on the sheet metal showing the actual contact area. The results were, well, shocking..

It should be noted that this was not the dimple side but the non-dimpled side.. Do you really want to run 30A through that?

My Computer Seems To Be Taking Over

Really, I am not uploading these, my computer is just so full of them it keeps puking them out… (grin)

Okay, Back On Track….

The contact area that was scored into the sheet metal was just about the same width as a US dime..

HOLY COW !!!!!!

Are you beginning to see the reason why so many of these plugs and sockets lead to melt downs, boat fires or entire marina’s burning down? The entire contact area here is but a 1.3mm X 2.7mm and 1.3mm X 2.4mm area often trying to handle 30A of current.

Smart Plug 30A
Back of Pin Contact = 16.4mm X 8.5mm = 139.4 sq mm
Front of Pin Contact = 6mm X 8.5mm = 51 sq mm
Total Contact Area = 190.4 sq mm

Twist-Lock 30A
Back of Pin Contact = 1.3mm X 2.7mm = 3.51 sq mm
Front of Pin Contact = 1.3mm X 2.4mm = 3.12 sq mm
Total Contact area with dimple locked in place = 6.63 sq mm

IMPORTANT: Due to the curved shape of the twist-lock measurements are as near as can be made without going to impressions on transfer paper. The Smart Plug pins are flat thus measurements are far easier. Still the difference in contact surface area is huge.

Insert Contour

With the last two images you can easily see why the two actions required for connecting this plug, insert & twist, leaves us with very, very, very little contact surface area.

The Male Pins Are Thicker

Here I’m measuring the pin thickness of a NEMA L5-30 “marine grade plug” made by Marinco. It measures about 1.77mm thick.

Let’s Examine The SmartPlug

This is the back of a SmartPlug 30A inlet. This is the original style plug which has now been updated, and further enhanced for ease of installation, but the basics are the same.

In order to wire the AC shore inlet you will need to first remove the rear cover plate. This is a simple one screw deal. Once the plate is removed the inlet can be wired.

This new SmartPlug 30A inlet is purposely designed to use the same mounting & hole pattern as the twist-lock standard 30A marine inlet. It will fit the old location regardless of whether the original inlet was plastic or metal. This makes the installation & conversion to a SmartPlug simple.

BLACK = 120V HOT

The SmartPlug makes installations as easy as it possibly can be. Even the clamping screws are color coded to the corresponding wire colors. This is the clamping screw for the AC BLACK/HOT wire.
In this photo we are looking at the side of the 30A shore power inlet.

IMPORTANT: If you are uncomfortable with AC wiring, and do not understand the differences between HOT, NEUTRAL and GROUND, please hire a competent marine electrician to do this install. AC wiring and wiring mistakes can kill you..

SILVER = 120V WHITE/NEUTRAL

The silver screw is your AC 120V WHITE/NEUTRAL wire.

I apologize for the tape residue but some of these pics were taken in 11F weather and the tape did not want to come off cleanly.

Oh My, Another One

Apparently my computer has a mind of its own today and these images just keep seeping from my image database… Sorry, I will try not to let it happen again.. (wink)

Robust

In my experience nearly everything about the SmartPlug is extremely well thought out and constructed specifically for the marine environment. This 30A inlet is highly polished cast, not stamped, 316L stainless steel. If you break the cover off a Smart Plug inlet you’re also going to have a nice hole in your boat… (wink). The gasket for keeping it water tight is also very well designed and engineered.

Innovative Designs

The guys at Smart Plug like to think outside the box and come up with very well designed equipment. This is their new set screw design for clamping the inlet wire.

One of the issues with some inlet designs is the resulting damaging & molesting of the wire strands when clamping them.  You also can’t easily drive a standard set screw directly into finely stranded wire without fracturing it. This is also against the ABYC safety standards.

To combat these issues the guys at SmartPlug came up with a floating & rotating head for their set screw design. This prevents fracturing the wire strands and creates incredible clamping force on the wire to create a good electrical connection.

I experimented with these set screws in my shop to see how they performed.. I clamped a 10GA UL1426 wire under one of the clamp screws 35 times. After 35 inserts and removals only two very small wire strands broke. This is pretty incredible when you consider you will only ever do it once or perhaps twice at the most.

These Were Brand New Plugs

When I called SmartPlug, during the research phase of this article, I spend many hours or sometimes weeks researching before I delve into a detailed article, I asked about independent testing and temp scanning.

They told me that Cascade Thermal Imaging, Inc. of Redmond Washington had in fact conducted some independent, third part thermal imaging tests on the Smart Plug.

I was then able to convince them to send me this thermal image of two brand new plugs & inlets, both 30A. One is the circa 1938 NEMA L5-30 twist-lock standard, most boaters are using today, and the other is a SmartPlug.

These plugs and inlets were both 30A versions run at 28A or 93% of the face value rating. They were loaded to 28A for 1.5 hours at an ambient room temp of 72F..

I think the image speaks for itself and represents pretty much what I see in the real world. When you look at the temp spread you can see a 23F rise in temperature, from the ambient air temp, on the circa 1938 NEMA L5-30 plug standard. Loaded identically, the SmartPlug yields just a 4F rise from ambient room temp.

I am playing devils advocate here, but there may be differences in the plug casings and how they transmit heat? My gut instinct is that I suspect 1.5 hours should be sufficient to get any heating at the plug/socket juncture to the surface of the plug.

Keep in mind that a 30A NEMA L5-30 circuit should never be loaded to this level for long duration’s. This was 28A in a controlled testing environment with brand new specimens. Even at this 93% of rating level the Smart Plug handles the current in a far better manner. I suspect if the NEMA L5-30 standard were tested today, to today’s standards, it would have never gained approvals.

I regularly measure plug temps with my infrared thermometer and also see this in the real world. Here in Maine we do have a fair number of boats that winter over, many of which use electric heat.

I will say it again, portable electric heaters can be VERY, VERY dangerous even on well maintained cord sets and inlets because they draw immense current. Please be careful using electric heaters.

The max continuous level at which you want to load any shore power circuit is 80%. Keep in mind this is when they are new and with clean tight connections. As the connections age corrosion can set in and this can create high resistance, especially with the highly susceptible 1938 twist-lock standard.

I generally don’t recommend loading a NEMA L5-30 30A circuit to more than 70% of its face value rating, especially in the marine environment. This means approx 21A on a 30A circuit. If you want to push it to 80%, and feel safe about that, the number is 24A. As a marine electrician I do not feel safe about that with the 1938 NEMA L5-30 plug standard.

WARNING: If you want to push beyond a 21A load on a 30A twist-lock you are doing so at your own risk.

Field Install Plug & Inlet

Here we are looking at the 30A field install/retrofit plug and a 30A inlet. There are four points of positive locking between the inlet and the plug:

1- Right & left push lock connectors which are similar to the locking mechanisms found in cordless drill batteries. They are SS and lock into very thick and robust notches in the sides of the inlet

2- The front portion of the lid, nearest the hinge, positively locks into the plug body.

3- The back portion of the lid locks positively into the plug body.

Rather than creating my own video SmartPlug has already done this:

The Lid Also Has Gasket

Here is the lid gasket. When not in use this gasket keeps the pins drier..

This image also shows just how thick and robust the plastic of the plug body is. This is not an accident. The robust nature of the inlet is part of the design. It needs to be robust to handle the marine environment and loads imposed by a moving boat. It also creates a nice wide gasket mating surface and a very solid area for the positive locking devices to lock into.

Another Safety Feature

When Ken, the owner of SmartPlug, set out to design this product he wanted to incorporate a thermal-breaker into the inlet body to prevent melt downs, boat and marina fires due to high resistance. It was not good enough to just design a better plug & inlet, he wanted to design a truly safe product. Should be simple right?

Wrong…..

It seems that no thermal breaker existed that could work in this type of application.

• Problem number one, design and build a thermal protection system for the SmartPlug 30A inlet.
• Problem number two find a company that can make it to SmartPlug’s stringent specifications and quality standards. They finally settled on a design for the thermal protection system and then found a company to manufacture it. This company is not Chinese, as one may assume, but rather a German company where labor costs are quite high.

It should be noted that the vast majority of this system is made right here in America and I like that.

• The tinned wire used in the cord sets is made here in America
• The thermoplastics used in the SmartPlug are all made in America
• Assembly is all done here in America with US labor
• The thermal breaker is made in Germany using comparable wages to US workers.
• The stainless used in the SmartPlug does come from China but only out of necessity. If US Made, the product would sit in US shelves because it could not be built affordable and could not be competitive. Ken tried his hardest to manufacture it all here in the US which is more than most companies will even attempt these days.

The Additional Safety Feature:

Inside the body of the 30A inlet is an epoxy potted thermal breaker that will trip at 200F. This is below the melting point of the wire jacket. Once the inlet has cooled it will automatically re-set at 110F so you don’t lose bilge pumps etc..

No other shore cord system, in the world, incorporates this innovative safety feature. It will prevent the high resistance melt down images you have already seen so many of here and could save lives, entire marinas and boats.

IMPORTANT: There are some in the industry who feel an auto-resetting breaker, of any kind including thermal, is not safe. This mind-set & origin stems from breakers re-setting into a dead short, and I agree 150% with this. However resetting automatically into a dead short is not the same as a high resistance thermal shut down.

REMEMBER HIGH RESISTANCE CAN CAUSE A FIRE AND NEVER TRIP A STANDARD CIRCUIT BREAKER.

Up until now we have had no shore power thermal breakers that trip on high resistance / temperature just on overload of the circuit or an imbalance such as an ELCI (basically a whole boat GFCI)..

The argument the opponents (most likely the manufacturers who don’t care about safety) propose is this:

Boat owner’s Darrell & his other brother Darrell awake in the middle of the night to no boat power.. Darrell & Darrell find no electricity at the AC panel. Darrell #1 opens the AC panel at the same exact moment the thermal breaker re-sets and gets zapped.

While, in theory, this could possibly happen, it is about as likely as Rosie O’Donnell beating Lance Armstrong in The Tour de France. At least Darrell & Darrell were still alive to open the AC panel & not cooked medium rare in their sleep…

Follow me for a moment please;

The same few folks (ABYC members & even instructors) & competitors of the SmartPlug arguing against the thermal-breaker in the SmartPlug 30A inlet have zero issues with auto-transfer inverters which can create the same exact Darrell & Darrell scenario they paint above, and use, to argue against the innovative and significantly safer SmartPlug..

Once such competitor actually argues out one side of their mouth against the thermal-switch then out the other sells piles & piles of auto-transfer inverters…. Blatant hypocrisy? You bet…

Follow me again please;

Darrell #1 goes to the dock pedestal and physically unplugs the shore power cord. He yells down to Darrell #2 “Okay-dokey it’s safe now.” Darrell #2 opens the AC panel and ZAP………!!!!!!!!!!!!!

Oops, the inverter transferred AUTOMATICALLY without requiring a manual-reset to produce 120V AC.…… D’oh.

It is insanity to argue against the thermal-breaker in the Smart Plug 30A without also arguing against auto-transfer inverters, especially if they want to use the Darrell & Darrell argument….

Like anything common sense should rule the day, but too often common sense is being waved bye-bye to out the back window of the school bus.. We now have a safer mouse trap & a better mouse trap but it will always get hung up with second guessers & direct competitors proposing poorly thought out & grossly hypocritical supposition like I just outlined. You will have to decide what is safer for your vessel.

EDIT: SmartPlug has decided to offer a version of the 30A inlet without a thermal breaker to be in compliance with the ABYC standards against auto-resetting. Now if we could just get all those inverter manufacturers to… Aw $hit, I give up………

A Shill….?

Rant Warning:

It recently came to my attention that some, within an organization I support fully, namely the ABYC, have told people that this article is a direct marketing piece for SmartPlug and that I am a shill for SmartPlug? If this level of immaturity keeps up I will begin naming names and I will call you out. Enough with the lies already, please grow up..

This is flat out bovine dung and a 150% LIE!

Lets stop the BS here and now. I find this level of immaturity, by people who should know better, utterly disgusting and the lowest form of low. Grow up!

FACT: I make no compensation from SmartPlug, I do not sell it on this site and I have specifically & purposely not become a direct dealer so as to not impede or negatively impact the importance of this article. I believe in the dire seriousness of these issues 150%.

FACT: This article was written by me and of my own volition. I did not need any prompting and am only doing what 2000+ other good marine electricians should have done long ago. By that I mean calling out the sheer safety concerns of a left over, grandfathered & arguably dangerous standard from 1938 vs. today’s technology designed from the ground up to minimize the exact issues the twist lock standard is fraught with.

FACT: SmartPlug had nothing to do with this article other than to offer heat sensing images and answer about 1000 pestering questions from me. I wrote this from my own physical experiences and from what I firmly believe, as a marine electrician, is safer.

FACT: I receive nothing from SmartPlug, zero, zilch, NADA. I buy my Smart Plug products through regular wholesale or retail organizations such as Hamilton Marine, Sailboatowners.com, Defender etc.. I don’t even buy direct from SmartPlug. I do this purposely and by design to eliminate any potential for being called a shill.

FACT: The only compensation I’ve made from this article has been from the “DONATE” button in this article. This site is 100% FREE and reader supported, not industry supported in any form shape or manner.. To date I have made less than it cost me to write this article due to the cost of buying the supplies etc. then destroying them. (EDIT: 2/24/16 I have now made $245 in net reader donations on this article after paying off all the parts and pieces used or destroyed in the article.)

FACT: I personally believe in this product and SmartPlug had nothing to do with my writing of this article. Twist-Lock failures, marina fires and the safety of my fellow boaters are what drive my motivation.

FACT: What have I received from Smart Plug? Exactly one warranty replacement, a 30A 50′ shore cord for a customer who had one fade to a paler shade of orange. This was a very early cord and they subsequently added more UV inhibitors in later production runs. The customer benefited, not me.

Rant off… (grin)

Good luck & happy boating!!