The Offshore Voyaging Reference Site

Two More Shore Power Safety Upgrades

One of the first things I had to fix on our new-to-us J/109 was the shore power system, to reduce the risk of it hurting, or possibly even killing somebody.

I documented that process in this article, which also attracted a huge amount of shore power safety wisdom in the comments.

Since that first article on the subject, I have upgraded the safety of the shore power system in two more ways that I will detail in this article.

By the way, I’m also working on an electrical system checklist, covering shore power and battery supplied systems, to pull all this together.

And I have not forgotten that I promised to share detailed drawings and a bill of materials for the new DC system I designed for the J/109. I have one more article on the whole lithium thing to get through and then we will get to that.

On with the show:

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Matt Marsh

Insurers are getting wise to the issues with incorrect AC panels. Our boat came with an old residential panel, the kind you’d use for a garden shed. I flagged it at the initial viewing as “that’ll need replacing,” the surveyor noted it as “not compliant”, and the insurer said “we agree, you can’t plug it into anything until the panel, ELCI, and breakers are brought up to current ABYC specs”.

We are still on NEMA L5-30 for the cord, and it is quite adequate for low power use (we draw maybe 5-10 amps on average), but you are absolutely correct thst NEMA twistlocks of any size become very problematic in continuous use at anywhere close to their nominal rating. And that goes doubly so in a corrosive environment. Our Coast Guard boats switched to SmartPlug a while ago and they seem to be very happy with it. And I’ve switched the larger machines in my labs to IEC pin-and-sleeve connectors from Hubbell and Mennekes, which I’ve seen used on larger boat and small ships as well.

Alastair Currie

I too had a Marinco shore power connector and found that it had burnt connections and twisted wires. It’s not fit for purpose, either rating, usage or for a marine environment.

I fitted a stainless Ratio Electric shore power inlet, in 2013 and it looks as good as new today.

My own shore power is standalone, totally separated from boat electrics, with the boat switch panel and the mains power consumer unit on different bulkheads. I have a standard consumer unit, with a primary RCB, then MCBs for my ring main, water heater and fridge. The earth cables are wired via a galvanic isolator. Most of the cables are run in trunking, but not all.

Dave Warnock

I have installed a 32 amp socket and plug from Victron:
Victron Energy Power Inlet stainless steel with cover 32A (2p/3w) – SHP303202000

Our boatyard is only 16A anyway so no experience yet with higher current.

Star Tracker

Funny story, I’ve been going back and forth a bit with Victron a bit lately, did you know their Galvanic Isolator is not ABYC compliant? Ironic for a product being sold in N America, I was going all Victron when I noticed this. Otherwise superb products generally and very attractive prices.

Dave Warnock

Could you elaborate on how it isn’t ABYC compliant and if it is possible to install it in an ABYC compliant way?

Earl Waltemyer

I like Victron stuff a lot but you can’t assume their kit is ABYC compliant. Their Lynx system doesn’t meet ABYC overcurrent requirements for large battery banks. Their LiFePO4 batteries aren’t A-13 compliant (regarding certification to construction standards).

Matt Marsh

I am fairly sure that the Victron part in question is a standard IEC 60309 type 332B6 inlet with the gender of the alignment key flipped to force you to use the same vendor’s cord set. Those can, indeed, carry 32 A @ 250 V in continuous duty.

Its cable is, quite oddly, colour coded black (which usually means 480-500 V AC) on the boat end, despite being colour coded blue (200-250 V AC) on the shore end and having the pin and keying pattern for 200-250 V AC 1PH on both ends.

I might note that, in marketing literature, SmartPlug only ever seems to be compared to NEMA twist-lock plugs (against which it is undeniably superior). Apart from the integrated thermal shutoff, which could be implemented in an IEC connector as well, SmartPlug’s advantages over IEC 60309 – if any – would appear to be relatively minor.

In general, British connectors seem to be massively over-engineered, continental European ones are well-designed and appropriate for their purpose, and North American ones tend to be barely-meets-code copies of a thing from 1938 that won acceptance by being somewhat less likely than its predecessors to burn down factories.

Alastair Currie

I use the 32A Model as the boat is wired with USA colour code wires, black, green and white and are a much larger diameter than U.K. sized systems. I use a flying lead between the 32A plug and U.K. plug. The 32A plug pins are much larger in diameter than the 16A pins on the shore power cable.
The Ratio plug is a tight fit, it takes a bit of force to slide the socket over the pins. It must be bottomed out as a cam lock ring then compressed the seal. Compare this to the 16A plug, much looser, with spring loaded cap lock.
Most EU, U.K. round pins are significantly oversized for their rating, I understand.

Dick Stevenson

Hi John,
I have been using Smart Plugs for years now and have been very happy with them. Much more secure and no danger of the plug coming loose in the receptacle and arcing, as I knew could occur with the older style plugs: their “twist-lock” never seemed to lock very securely.
Marinas would do a good deed for their customers were they to install Smart Plugs on their pedestals. My observation on shore power cords is that the most damage occurs at the marina receptacle end of the cord by inadvertently getting the plug doused in salt water. If that occurs, the plug needs to be taken apart and well serviced or there will be trouble down the road (I know what I do, but I am no expert, so I hesitate to go further with suggestions.)
One observation on the picture in your article: it looks like the receptacle is on a surface that is tipped. I had a similar install, and found that water migrated into the case of the smart plug receptacle and puddled there and tripped the marina’s GFCI . I built an angled plinth of g10 to return the mounting surface to vertical and re-mounted the Smart Plug. As added insurance (and a bit of ascetics) I the covered it with an “umbrella” of Sunbrella. No problems since then.
BTW, I had occasion to call Smart Plug where the owner/designer answered the phone and was very helpful and informative and pleasant to talk with.
My best, Dick Stevenson, s/v Alchemy

Torsten Hansen

Hi s/v Alchemy, Our new-to-us Norseman 447 has the same negative angle inlet and I want to thank you for adding another task to the refit 🤓. While I am at it, I want to also thank you for taking the time to add your always informed comments on the various forums.

Hoping to see you there one day,

Torsten, S/V Scout

Dick Stevenson

Hi Torsten,
Thanks for the kind words.
I hope and expect you will very much appreciate your new to you Norseman 447. Alchemy is also a Bob Perry design (a Valiant 42) and BP’s boats generally take good care of their crew.
And it would be nice to share an anchorage.
My best for a good re-fit and some safe cruising, Dick Stevenson, s/v Alchemy

Mark Devlin

error in last para above summary – current is same at both shore & boat end of shore power cable

Ian Cameron

Easy way of isolating AC…Measure the size of your panel and buy a plastic rectangular food container, the kind with water-proof snap-on lid, to fit. Cut or saw off the bottom. Hold down box with small stainless L brackets. Drill holes in sides for running wires. Now you have easy access just by removing the lid.

Star Tracker

Blueseas makes a cheap and cheerful backing cover for most of their panels, nice and easy to run cables under, it’s what I have used in the past on many panels for exactly the reasons you identify, and nobody can argue that the panel maker doesn’t make an appropriate cover. However I like your G10 idea far better, I’m copying it as part of my system redesign for my boat! Side note for the tupperware: To meet ABYC rules, you could simply install a screw in either corner where the lid locks, I would bet it will cause more grief than it’s worth down the road however especially as insurance is getting more cautious, and I’d hate to be chatting with an adjuster while they look at an AC panel fire and the melted tupperware!

Ian Cameron

The first generation of Smart Plugs had flimsy plastic grips for holding the cable. Mine shorted out when it was accidentally pulled. Make sure yours is the upgraded version. I had an electrician wire the new improved one just to be sure.


The Smart Plug looks like a great upgrade, thank you!
Another contributor to power cord connector degradation is pulling the plug before turning the supply breaker off. If any inductive loads are active when the plug is pulled, then an arc will occur and that means part of the plug contact has been vaporized. Anything with a motor or solenoid is an inductive load, which includes fans, dehumidifiers, and the LPG supply solenoid. The breaker is designed to absorb the inductive load dump, the power cord connector is not. Unfortunately, in the marinas I’ve sailed from, pulling a hot plug is not an uncommon practice. And, insult to injury, the hot, unattached power cable is often left coiled on the dock waiting to fall into the water and pose an electrocution hazard!  

Star Tracker

I find that asking if they bathe at home while making toast usually gets the idea across effectively, if it’s boat neighbours near my personal boat, especially since a toaster would be on a 15A GFCI breaker in the bathroom! First lesson every employee gets on a dock is the boat end is never unplugged before shore end under any circumstances, breaker off or not, and how to politely explain why to owners. Then when you go to unplug the boat end you have a visual cue that no power is present even if you want to leave the cable behind(a couple wraps around the power pole and the rest of the cable on the finger for return is my preference).

Ben Garvey

Love the smartplug – another satisfied user here… but it must be hurting your weight feels John – that is not a light unit!!

Ben Logsdon

I despise the standard NEMA twist lock plugs. The threads on the locking ring are forever trying to cross-thread. Thanks for recommending the SmartPlug. I’ve put it on my winter to-do list.

Star Tracker

Some insurance used to offer a discount if you switch to smartplug, always worth advising them and see if it’s still a thing! That’s how much money it saves them in claims. If keeping twist lock, I like to examine both ends when I de-winterize, any charring or heat damage = stop use until taken apart.

Alan Bradley

You can avoid the aggravation of installing the plug and it’s troublesome strain relief if you buy the SmartPlug receptacle and the new SmartPlug pigtail, a four foot adapter from the SmartPlug to the old-style cord. The pricing is similar, the molded strain relief is far superior, and your shore power cord becomes 4 feet longer. I know it’s an additional connection point, however you only have to make the connection once and securely attach the two together with the threaded, locking sleeve that is common with the old-style cords.

SmartPlug Pigtail.JPG
Alan Bradley


Point taken however, I have two shore power cords: the shorter one now has their plug, so it’s dedicated to the SmartPlug receptacle; I use the longer cord with the pigtail when I need more length and can still use it’s NEMA plug when to join the two cords in the event I need even more length. I’ve been in that situation several time.

Steve D

John, why not make a clear cover, Plexi for instance that’s very common, for the AC gear, so you can inspect it when opening the panel?

Like everyone I too like the Smart Plug, however, I have had a handful of overheat events, all of which SP has warranted. One feature I don’t care for is the screws they use to make contact with wires. ABYC standards prohibit direct bearing screws, SP gets around that by making the screw tips rotating, which I don’t care for, I’d prefer a floor plate. I’m not sure there’s anything that can be done at assembly to mitigate this. Again, I’m a SP fan but wish they’d change this.

Lying Krestof Island, Alaska.

James Rambo

Only smart plug for me from now on. Totally agree on the slippery soap!

Star Tracker

On the smart plugs:

  1. Silicone spray is your friend for the install, spray inside the boot, and on the yellow sheath where you want it to slide in, if old wire, clean the yellow sheath first with MEK, Lacquer thinner (or MEKP if stuck in California/WA I think now too), then wipe the whole cord down with 303 Aerospace protectant.
  2. The “tool” it comes with to get the wire through the boot is bloody useless, however putting a light bevel on the yellow sheath takes a few seconds with a file or bit of sandpaper or even a knife blade if you are confident in not nicking the conductors or yourself, that and silicone spray makes things much much easier.
  3. After you do 5-10 of them, it is a 15 minute job but cursing is still required. Yes instructions are essentially worthless for measurements etc, ironically they work better on the bigger size from what I remember(been a few years now). I simply keep a favorite caliper with me when doing it, and measure the lengths. Side note this caliper is the best thing on a boat since sliced bread. It’s brass, short, no dial or moving parts except the one slide, and it isn’t chasing thousandths, instead it has nice clear legibly printed fractions, blunt tips so it can’t poke you in a pocket and costs less than 10$ from Lee Valley. Very handy for everything from rigging to lines/anchor chain. Much easier than regular caliper or tape measure.
  4. I like to waterproof the connections after install(tighten screws, go do something else for 20 minutes, come back, snug again, usually you’ll get another 1/4 turnas the multi strand seems to settle in somehow, which is a big deal after years of use with slightly less than perfectly snug connections) then coat with Dialectric grease or corrosion spray. Many like to put it on things before install, but I find it doesn’t make sense and often causes problems to put something designed to block electricity on wires before making a connection.

Other thoughts on them: If you locate your outlet facing aft and don’t wrap the cord on things, even in the worst case of someone motoring out, or the boat breaking free, the cord will tend to release without much damage. Side load it and the same issues as the twist lock can occur.

Question: has anybody managed to make a smart plug copy with that brilliant LED setup Marinco came up with some years back(1 LED for power, 1 for incorrect polarity, one for excess current on the AC ground). They never became popular but I would love to figure out how to build that same set of LEDs to install at the shore inlet for easy diagnosis and confirmation of limited stray current risks.

Jack Chadowitz

In Europe the connectors, (plugs and sockets) have round pins with lots of surface area. The outlet cover acts as a clip to hold the plug in place. The 16amp connector is smaller than the 32amp connector. The connectors are industrial grade not marine grade but work well. The socket on the boat side is often in a locker, for example on the Jeanneau 36i.

My only criticism is that the connectors are sold separately and not as made up cables. So you often see a 32amp plug with a cable rated at 20amps maximum or a 32amp to 16amp pigtail.

A recipe for disaster. Should the cable have a partial short on deck, maybe trapped between sharp edges, current less than 32amps but greater than the cable’s current rating will cause the cable to heat up and eventually burn along its length becoming a long fuse. The circuit breaker will trip when enough insulation burns away to cause a direct short. Meantime you have a long length of cable on fire on a wood or fiberglass deck.

The ground fault interrupter on the dock, if there is one will not trip. The breakers in the boat will also not trip.

The basic rules are that the breaker or fuse must be close to the source of power and must trip at an amperage less than that of the ratings of any cables, wires or equipment downstream.

Arne Mogstad

I believe the connectors you’re referring to, is the CEE17 industrial plugs and sockets. They are extensively used in farming and industrial environments, and on the dock-side. I have never heard or seen them delivered in a “factory-molded” way to the cable, as you say. They are fairly good when mounted correctly, but are not waterproof (IP 44). I have however not heard any unsafe issues (heat, broken earth connection, etc) with them ever. But I guess it is possible if you don’t know what you’re doing when you mount them yourself.


I switched the boat end of my 30amp shore power to Watertight Nickel Plated Pin and Sleeve. Either Hubbell or Leviton are quality choices but it is pricey at $500 for the receptacle and the inline outlet.The contact surface area is massive and it will handle the full rated amperage continuously without failing. These Pin & Sleeve style connectors are standard on super yachts and commercial vessels but most cruisers don’t realize they come in 30amp single phase models suitable for the boat side of the shore power connection. Unfortunately the shore side will remain a Hubbell Style Twist lock but we have moved the point of failure to the dock pedestal and away from the boat and its occupants. I work in the entertainment industry and we abandoned the twist lock blade type connectors years ago. They’re not designed for what amounts to a permanent connection when someone is at the dock for weeks at a time.Hope this adds another option for folks looking for something other than the almost 100 year old Hubbell Twist.

Krist Van Besien

This looks like a CEE connector (and that is indeed what AFAIK the big boats use). Yellow, because 120V, (240V are blue)

Aaron Grogan

Locking NEMA plugs/connectors have their problems, but at least they’re a multi-vendor standard. If we’re going to replace them, we should be using IEC 60309 connectors, which are also multi-vendor, widely-deployed, and address the problems with locking NEMA connectors. SmartPlug seems like a scheme to introduce an inferior proprietary connector that the world didn’t need, then gradually expand its installed base and profit accordingly.

The IEC 60309 system covers every imaginable voltage/phase/frequency use case up to 690 V / 125 A and from DC to 500 Hz. Some IEC 60309 products are rated up to IP69K and have features to prevent connection and disconnection under load.

Aaron Grogan

IEC 60309 pin & sleeve connectors are the most common type of shore power connection in the 50 Hz world, and are also commonly used for 100 A service to larger yachts in North America, so this discussion is not merely theoretical.

IEC 60309 products come with instructions too.

I haven’t done an exhaustive search for 30 A 125 V IEC 60309 inlets that are compatible with the “Hubbell” hole pattern, but there appear to be some options, so I don’t think this is a case of perfect being the enemy of the good. In the worst case, an adapter plate or some minor glass work could be required, so I’ll give you that, but if people stopped promoting SmartPlug and instead promoted IEC 60309, more options would undoubtedly emerge.

I question the motivations of the SmartPlug people. Any entrepreneur looking to sell an alternative to locking NEMA inlets would almost certainly have become aware of IEC 60309 connectors early on their business development process. A scrupulous entrepreneur might then set about developing IEC 60309 inlets that work well with the “Hubbell” hole patterns found on many 60 Hz yachts. Instead, for some reason, the SmartPlug people set out to market a proprietary connector. Greed-driven deliberate incompatibility is both anti-customer and a waste of natural resources.


To add to my comment regarding the Pin and Sleeve below. Here’s the male L5-30 I used for the shore side of the cable. Honestly one of the highest quality versions of this type of connector I’ve seen.

Washdown Turn-Lock Connector
Grounded Three-Blade Plug, NEMA L5-30

Iain Dell

Hi John – I appreciate this is an older thread but I came cross something (almost) the hard way that could add to your safety dialogue. My shore power stopped working but as there was still current in the cable I wasted ages trying to track the fault down. However, it turned out to be serious abrasion of the cable itself that was the issue; it could have gone from being an inconvenience to a threat to life pretty quickly.

Being a near-electrical dyslexic, I never knew there were two types of cable: HO7 and ‘arctic’. All I knew was that I could buy 25m of cable for £30 from Amazon or for £150 from an electrical specialist for the same length. I’d guess that the vast majority of ordinary boaters out there know as as much about cable choice as I did, and given the number of cables you see draped over anchors, cleats etc, this hazard is pretty widespread.

‘Buy cheap – pay twice’ is a good axiom, but in this case it could be ‘buy cheap – leave more in your Will’….