Smart Plug -- Wow!

[bobatkins]

Originally Posted by Paul L

Bobatkins,
Thanks for the detailed post mortem. Bummer for you, but enlightening for others. A couple of questions:
1. Do the xray pics show the thermal breaker?
2. Any thoughts on why the thermal breaker didn't trip early enough?

1. Do the xray pics show the thermal breaker?

As seen in the x-rays which were taken from every position (I only posted two of the 6 images). The wires are connected directly to the lugs/pins. I see no device of any type that could interrupt the flow of electricity and that would be capable of carrying a 30A load between any wire and the associated pin - do you?

2. Any thoughts on why the thermal breaker didn't trip early enough?

Maybe because there wasn't any thermal breaker to trip? Or at the very least a faulty/ineffective design. The advertised thermal safety device failed to do the job.

[bobatkins]

Originally Posted by s/v Jedi

The big points to get right: use ferrules and clamp them down really tight. This is the 50A inlet, which has allen key screws.

Galvanic corrosion will happen between ANY dissimilar metals over time - especially in a humid marine environment whether using clamped, super high quality ferrules or not.

[bobatkins]

Originally Posted by Jammer

First of all, thank you for sharing this difficult sequence of events so that others may learn and protect themselves.


Engineering is hard and it is nearly impossible to know the safety and reliability of a new product until it has been in the field in quantity for years. This is why I have never been a fan of the Smartplug -- I've seen it as replacing a horse we don't like with a horse we don't know, as the old adage goes. (For clarity, I have no financial or other stake involved here)


For those looking for a better alternative to the NEMA twistlock and the Smartplug I would recommend pin and sleeve connectors:


https://www.elecdirect.com/pin-sleev...re-splashproof


These follow international standards and are available from several manufacturers. They have been in widespread industrial use in wet environments for decades and are the accepted standard for larger shore power connections (over 50a). I believe that the extensive track record this connector family has augers well for its safety. Their main drawback is cost.


I also agree with @bobatkins that it is curious why the ABYC standards do not require connections to be made in a fireproof enclosure as is the case with residential, commercial, and industrial wiring governed by the NEC and codes derived from it.

While the pin and sleeve connectors appear to be more durable for solving the connect/disconnect wear problem - the same issue being solved by the SmartPlug. They also have the same dissimilar metal issues:

Pins & Sleeves: Nickel Plated Brass
Sleeve Force Ring: Zinc Plated Steel
Terminal Screws: Nickel Plated Steel

Copper wire being held in place against Nickel Plated Brass with Nickel Plated Steel screws will eventually result in galvanic corrosion and a high resistance connection.

The standard Marinco receptacles and plugs are all copper lugs and screws. There is no possibility of galvanic corrosion between the inside copper wire and the pins/lugs/screws of the receptacle. I so wish I had thought about this before I lost my boat.

The problem of fires being started by shore power is such an issue that many marinas in Europe do not allow boats to remain connected to shore power when nobody is onboard.

I will also likely use a SmartPlug again but you can be certain that I will enclose the receptacle in a stainless steel junction box that will have its own thermal breaker inside AND I will remove it for inspection EVERY YEAR!

Four lousy screws and 15 minutes for peace of mind.

[noelex 77]

Originally Posted by bobatkins

You can't solve a high resistance connection by de-rating it.

This is not correct. You just need to de-rate the capacity sufficiently.

The problem is shore power connections are specified for as new conditions with no corrosion. This is not realistic.

[Jammer]

Originally Posted by bobatkins

You could de-rate a bad connection to 100W and still easily generate enough heat to start a fire.

There is a continuum. With a 100 watt load the most heat a high-resistance connection can produce is 50 watts. In a properly designed connector that shouldn't lead to a fire. Ordinarily the housing of a connector assembly (one designed for power rather than data etc) is flame retardant. While it may be possible to heat it to the point where it melts or deteriorates, it should not burn.

Most of the literature on arc faults (i.e. series high resistance) says that you have to be passing around 500 watts through a circuit for them to be a significant hazard. This matches my experience. I've never seen a flaky connection overheat at these lower power levels, they just become unreliable. On the other hand run a couple thousand watts and you can burn things up.

[Jammer]

Originally Posted by bobatkins

While the pin and sleeve connectors appear to be more durable for solving the connect/disconnect wear problem - the same issue being solved by the SmartPlug. They also have the same dissimilar metal issues:

Pins & Sleeves: Nickel Plated Brass
Sleeve Force Ring: Zinc Plated Steel
Terminal Screws: Nickel Plated Steel

Copper wire being held in place against Nickel Plated Brass with Nickel Plated Steel screws will eventually result in galvanic corrosion and a high resistance connection.

The standard Marinco receptacles and plugs are all copper lugs and screws. There is no possibility of galvanic corrosion between the inside copper wire and the pins/lugs/screws of the receptacle. I so wish I had thought about this before I lost my boat.

Well, the terminal screw doesn't carry current to any significant degree, doesn't matter if they rust. The sleeve force ring doesn't carry current. They use that to improve the wiping properties of the sleeve, so that corrosion and foreign materials on the pin and the sleeve tend to be removed during the connect/disconnect cycle.



The Marinco connectors use brass contacts (not copper) and these are the current carrying components that attach to the wires. The negative one is plated with nickel or something for identification. Which is fine. You can still get corrosion but it is ordinarily not serious. I've taken apart electrical components in barns where ammonia vapor makes for a highly corrosive atmosphere, and brass terminals copper wires and steel screws make for reliable connections.



There is more to reliable connector design than materials selection for the contacts although that is certainly one aspect of it. It's not a thought exercise. The best designs are tested in a salt spray environment in the lab and then proven through extensive use in the field.

The problem of fires being started by shore power is such an issue that many marinas in Europe do not allow boats to remain connected to shore power when nobody is onboard.

I will also likely use a SmartPlug again but you can be certain that I will enclose the receptacle in a stainless steel junction box that will have its own thermal breaker inside AND I will remove it for inspection EVERY YEAR!

Four lousy screws and 15 minutes for peace of mind.

Be careful not to fight the last war


There are plenty of places where fires can start. The shore power inlet is but one, and should not be a focus of attention to the exclusion of other important areas.

[Jammer]

Originally Posted by bobatkins

Galvanic corrosion will happen between ANY dissimilar metals over time - especially in a humid marine environment whether using clamped, super high quality ferrules or not.

A properly crimped ferrule is supposed to be gas tight.

[boat driver]

Originally Posted by bobatkins

I ended up regretting the above post in a major way. On Feb 15th, 2020 I lost my boat to an electrical fire. I had personally installed the Smartplug on my boat about 6.5 years earlier and the receptacle externally showed absolutely no signs of degradation. The image below of the receptacle was AFTER the fire and even though there was a conflagration behind it - whatever they made the middle part from didn't show any signs of distress - essentially fire proof. Yes, the dockside shore power breaker blew. Yes, it was the latest GFI protection on new docks. But overload breakers don't protect against heat caused by a high resistance connection - they only blow when the circuit load exceeds the breaker's load limit. GFI breakers only work to protect against live to ground current leakage. Only a thermal breaker at the point of the heat source will protect against a high resistance connection and this was one of the primary reasons that 6.5 years earlier, I purchased the SmartPlug to replace my old 30A Marinco receptacle that had started showing signs of thermal damage.

Unfortunately the back of the SmartPlug receptacle is made from material that can and did melt. That flaming melted goo went down the AC wire and stopped at the PVC conduit carrying the DC wires and set it on fire - all buried inside the back of my boat behind the engine panel and the rest as they say was history... Right before the start of the pandemic lockdown I lost the boat I had since new, had maintained like my aircraft and dearly loved.

The pictures and the fire investigation clearly show that the fire started behind the Smartplug. As an engineer I wanted to know how a fire could start behind what was supposed to be a thermally protected receptacle! You be the judge of the X-ray images.

Here are the pictures:



This is what the receptacle looked like Post fire!



Here are the X-ray images of the burned receptacle:





This is the receptacle from another boat that almost caught fire!!



You can clearly see that the X-rays show that there is a direct connection between the inside wires and the lugs on the Smartplug that go directly through the housing.

The last picture is that of another Smartplug (also about 6 years in service) from another boat where the owner happened to be on board when he smelt electrical smoke and disconnected the shore power before an inferno started. You can clearly see where the problem started.

Why, after about 6+ years did this happen?

Well - first of all it is clear that the thermal protection advertised for this receptacle failed to do its job.

But why the melted wire - as shown in the last picture? Because the Smartplug receptacle has nickel plated steel lugs/pins, unlike the typical Marinco (round 30/50A) receptacles that use copper lugs/pins. The AC wire inside the boat is copper. Need I say more? In a marine environment, the dissimilar metals between the nickel plated steel and the copper wire setup galvanic corrosion whereas this won't happen with the typical copper lug/pin Marinco receptacles.

Unlike the Marinco which shows evidence of failure/overheating in the form of externally visible discoloration of the plastic in the receptacle - giving warning of failure, the Smartplug conceals such failure from view - behind it and out of sight! For some reason the materials used on the backside of the receptacle are nowhere near as fireproof as the middle of it!

For the last year+ I have been so angry. I have blamed myself for not being able to put out the fire - I was nearby when it started but it was already too far along by the time I got to the boat. My attempt to put it out by fighting it down below landed me in the ER. Thankfully the fireboat arrived quickly and prevented the boat from burning to the waterline which also preserved the evidence of how the fire started. Total time of the fire was about 10-15 minutes and the boat was totalled - burned inside from stern to bow!

I never in a million years thought that I would need to remove the 4 screws that secured the receptacle to the boat to look behind it to check for any potential issues!!

4 f***ing screws and I would still have my boat... :-(

But I am seriously pissed off at SmartPlug because they set me up for a total false sense of security - the very reason that I installed their f***ing receptacle in the first place - to protect against the possibility of exactly what happened - a shore fire induced electrical fire!!

Everyone one of these receptacles are ticking timebombs - they are ALL suffering galvanic corrosion and likely most, if not all of them have no internal thermal protection as advertised. Who knows how many boats have been lost already!

I hope one day to find another boat and I will no longer take any chances - I plan to install a stainless steel junction box behind the AC receptacle into which I will also install a real thermal breaker with visible external status/reset. If it ever goes - it will not reset automatically. I will carry the internal main copper AC wires inside a stainless flex conduit to the main AC breaker which I will also enclose in a stainless steel junction box with its own thermal breaker. Exposed AC wire and connections are not allowed in any building. Commercial buildings require steel junction boxes and conduit for all AC wires! Why is this same standard not applied to boats???

And I will make a point of inspecting the back side of the shore power receptacle annually for any signs of failure.

Is that running 110 or 220v?
I have fixed a significant number of problems with shore connections overheating. A number of discoveries:
1) As mentioned, corrosion over time creates high amperage and heat. Looking at your plug, I would suggest the thermal switch would not have helped if the "failure " was fast enough to create spontaneous ignition and thereby fire.
2) the load being drawn is important. Check and be sure both the load is balanced (220v) and if 110 then is it adequate. If a 30 amp 110v cord is drawing 27 amps constantly, little room is permitted for corrosion or bad/loose connections.
3) keep the connections dry- and this is paramount on shore connections that are mounted in the cabin top and have a slight top back flush mount. Over time they will leak water into the connection and it simply sits in the back of the smart plug.
4) put dielectric grease on the connectors. That will both ensure a smooth and clean contact, significantly reducing corrosion.
5) put the plug connector inside or under a dry weather protected location. I have corrected more problems by wiring a pigtail inside instead of solid bulkhead mount outside- so the cord passes though the porthole or other location.

[wholybee]

Most boats have an A/C volt meter on board. When you turn on a large load, the voltage will sag. The amount the voltage sags is the voltage drop through resistance in the connection. Multiply that by the current, and you know the wattage of heat that is being dissipated.

You don't know _where_ that heat is located, some will be along the length of the shore power cord, some in the internal boat wiring and connections. Some will be along the wire run down the dock.

But it is important to watch how much the voltage drops. As a shore power connection ages, that voltage drop will increase, and you can do the math to determine how much more power is being converted to heat. If the the voltage drop is suddenly larger than normal, you need to investigate it. It's a good early warning that a connector needs maintenance. And one I think too few people know to look for.

[wholybee]

Originally Posted by bobatkins

I ended up regretting the above post in a major way. On Feb 15th, 2020 I lost my boat to an electrical fire. ...

<snip>

I am sorry for your loss, thank you for sharing. This is one of my fears of boat ownership, and I don't have many.

[bobatkins]

Originally Posted by wholybee

Most boats have an A/C volt meter on board. When you turn on a large load, the voltage will sag. The amount the voltage sags is the voltage drop through resistance in the connection. Multiply that by the current, and you know the wattage of heat that is being dissipated.

You don't know _where_ that heat is located, some will be along the length of the shore power cord, some in the internal boat wiring and connections. Some will be along the wire run down the dock.

But it is important to watch how much the voltage drops. As a shore power connection ages, that voltage drop will increase, and you can do the math to determine how much more power is being converted to heat. If the the voltage drop is suddenly larger than normal, you need to investigate it. It's a good early warning that a connector needs maintenance. And one I think too few people know to look for.

Yes, and mine had an AC meter as well. With a 50ft extension cable and general +/- 5V of nominal AC voltage being an acceptable tolerance, especially on a boat dock, a high resistance connection would not result in enough of a voltage drop to be noticeable within normal AC line voltage variations.

I did (as I always) in fact check my AC meter in the boat after connecting shore power and before leaving it. It was reading around 115V - quite normal. Believe me if I saw an unusually low voltage (~100-105V) that would have gotten my immediate attention.

Everyone is giving me their good intentions. Some just want to de-rate a 30A service from 3300W to 100W which would be ridiculous. I was pulling 58% of rated capacity - barely more than half and I still suffered a fire as a direct result of a hidden high resistance connection.

The fire took about 20-25 minutes to start - so any properly implemented thermal protection device would have had plenty of time to shut down power since most would trigger at not much more than 150-180F. Such a device is supposed to be inside the SmartPlug receptacle and would have been very close to the heat source (wire to terminal) and where the plastic started to melt which requires >200F and should have shut off well before the plastic started to melt let alone catch fire (>400F). How do I know? I'm also in the plastics business so I know the melting points and flame temps of most plastics.

I agree that well crimped ferrules should be gas tight but - those ferrules then connect to the receptacle - and that's where dissimilar metal corrosion leading to a high resistance connection can occur.

High resistance within a properly spec'd wire is extremely rare. Connection points are the most likely points of high resistance in any electrical circuit.

Take my experience for whatever you want - it's free.

I wouldn't wish a boat fire on anyone - its was my worst nightmare. All the noxious fumes, progresses at an unbelievable rate and makes you realize how powerless you are if you don't do everything exactly right in the first few moments.

[GreenWave]

Originally Posted by flightlead404

hmmmmm.....I've been drinking strictly RO water for over 20 years. No problems.

I use RO water ice spheres in my cocktails too.

I make my coffee with RO water (and then add back in just the right level of carbonate and non-carbonate hardness, yes I'm a coffee nerd).

Hasn't killed me yet.

RO water (from most systems) is not Distilled water. DW is much purer so to speak. So you will live another 20 years I am sure!

[Bill Seal]

How about checking for hot spots with an IR thermometer?

[wholybee]

Originally Posted by bobatkins

Yes, and mine had an AC meter as well. With a 50ft extension cable and general +/- 5V of nominal AC voltage being an acceptable tolerance, especially on a boat dock, a high resistance connection would not result in enough of a voltage drop to be noticeable within normal AC line voltage variations.

I did (as I always) in fact check my AC meter in the boat after connecting shore power and before leaving it. It was reading around 115V - quite normal. Believe me if I saw an unusually low voltage (~100-105V) that would have gotten my immediate attention.

Everyone is giving me their good intentions. Some just want to de-rate a 30A service from 3300W to 100W which would be ridiculous. I was pulling 58% of rated capacity - barely more than half and I still suffered a fire as a direct result of a hidden high resistance connection.

The fire took about 20-25 minutes to start - so any properly implemented thermal protection device would have had plenty of time to shut down power since most would trigger at not much more than 150-180F. Such a device is supposed to be inside the SmartPlug receptacle and would have been very close to the heat source (wire to terminal) and where the plastic started to melt which requires >200F and should have shut off well before the plastic started to melt let alone catch fire (>400F). How do I know? I'm also in the plastics business so I know the melting points and flame temps of most plastics.

I agree that well crimped ferrules should be gas tight but - those ferrules then connect to the receptacle - and that's where dissimilar metal corrosion leading to a high resistance connection can occur.

High resistance within a properly spec'd wire is extremely rare. Connection points are the most likely points of high resistance in any electrical circuit.

Take my experience for whatever you want - it's free.

I wouldn't wish a boat fire on anyone - its was my worst nightmare. All the noxious fumes, progresses at an unbelievable rate and makes you realize how powerless you are if you don't do everything exactly right in the first few moments.

It must be terrible dealing with your loss. I don't blame anything you did or did not do. You invested in what was supposed to prevent this, and it wasn't terribly old. And it supposedly had a thermal device. As angry and upset as you must be, don't blame yourself.

I don't feel derating the service is necessary, but am offering my 2 cents experience to others. A 5V voltage drop when you turn on a load is not ok. With a 20A load (not even the full rating of the circuit) that would be 100W of power tuned into heat. That is easily enough to start a fire *if* it were a bad connection at the shore power cord. A voltage drop of only 1 or 2 volts is enough to start a fire. But you need to get a baseline, because as I mentioned you don't know where the drop is, or how much is normal in the run down the dock, etc. If the run down the dock is a smaller gauge wire, you could have a significant voltage drop, but no fire risk. So you need to get a baseline voltage drop when you know everything is good, and watch for changes.

But a change over time, even of only 1 volt, is significant. That one volt might be the connector starting to degrade, and it could escalate very quickly once it starts to heat.

My service is 120V with everything off. If I ever saw it drop to 115V when I turned on a load I would turn it off and disconnect my shore power until I could track it down.

My personal experience with this, I replaced my shore power cord last year. Normally, when I run my AC or heater (depending on season) I have a voltage drop of 1 or 2 volts. When it was consistently 2 volts, and sometimes 3, I investigated, and found that the connector on my shore power cord had begun to discolor. Time to replace, and the voltage drop returned to normal 1-2 volts.

[wholybee]

Originally Posted by Bill Seal

How about checking for hot spots with an IR thermometer?

If you have access to an IR camera that is a reasonable thing to do. We have some very high current equipment at work, and do thermal imaging every year. We often find a terminal on a circuit breaker that needs re-torqued.

Which brings up another point of failure, the terminals the wires connect to in the back of the connector, and the terminals on the main breaker on the boat. If those work loose, even a tiny bit, they will get hot.