Pin and sleeve connectors for 30a shore power

[Dockhead]

Originally Posted by thinwater

. . . Is the problem the twist lock, or that they are 20-30 years old and poorly maintained?

No, the problem is the design, which has far too little contact area, and which allows the contacts to not fully engage.

[Dockhead]

Originally Posted by wholybee

. . . But I think the failure rate of a newer, properly installed and maintained twist lock is actually rather low. Just my gut without any real data.

This is not exactly data ("the plural of anecdote is not data" ), but for whatever it's worth, based on a lot of observations over decades since the early 90's -- anyone using shore power for any kind of serious load (aircon, electric heating) burns the twist connector in short order, even new ones, even fastidious owners. I used to keep a spare one on board at all times and replaced them every two years, and even then I often got burned contacts. In my experience, they are simply unfit for purpose. After switching to Smartplug, not the slightest hint of any scorch -- it's a great relief not to be worrying about that all the time.

Originally Posted by wholybee

.. . One interesting anecdote. The Marin County fireboat at my marina uses a smartplug.

Indeed!

[rslifkin]

Originally Posted by Dockhead

This is not exactly data ("the plural of anecdote is not data" ), but for whatever it's worth, based on a lot of observations over decades since the early 90's -- anyone using shore power for any kind of serious load (aircon, electric heating) burns the twist connector in short order, even new ones, even fastidious owners. I used to keep a spare one on board at all times and replaced them every two years, and even then I often got burned contacts. In my experience, they are simply unfit for purpose. After switching to Smartplug, not the slightest hint of any scorch -- it's a great relief not to be worrying about that all the time.

That seems common on the 30A twist locks, but I can't say I've ever seen burned contact on the 50A ones unless they were suffering from significant corrosion. They do have much stronger springs in the female connectors than the 30A ones do, judging by the dramatically higher insertion force.

[Dockhead]

Originally Posted by Jammer

. . . My interest in pin-and-sleeve is based on the fact that they are already widely used outdoors including in marine environments, and seem to enjoy a good reputation. The only problems with them are that they are big and expensive.

The IEC pin-and-sleeve connectors are not that big, and not expensive at all. This is a vastly better design than the Hubbell/Marinco ones -- much cheaper to make, much simpler and more reliable. The more common type is not really waterproof, however, and the shape of the male part is awkward for the boat side connection. I used one of these for a year after trashing the last Marinco plug and it worked fine; you can get them made for this purpose in Europe.


IEC connectors are almost universal on pedestals in Europe, commonly blue 16a single phase ones in leisure boat harbours, and several different red three-phase ones in commercial harbours. In Northern Europe you sometimes see household 10a Shucko sockets. We carry a large bag full of different adapters and components.


On the East Coast of Iceland, there are no leisure harbours at all, and the only power available is from three phase red sockets. We were glad to have the adapters (as it was cold and we wanted the electric heat).

Originally Posted by Jammer

As a separate thought experiment, I've considered adding a temperature sensor to the shore power connection (with any type of connector) with an Arduino or something to indicate when heating is occurring and open a remotely located contactor to disconect the load when it is excessive. I believe SmartPlug tried something like this for a while but was trying to fit it all inside the inlet, which left them with an auto-reset thermal breaker that did not pass regulatory muster. (Because auto-reset breakers pose a number of safety problems of their own, including surprise energizing of circuits posing a hazard to electricians)

It's a shame that Smartplug abandoned this. Why couldn't they just use a non-auto-reset breaker?

[Dockhead]

Originally Posted by rslifkin

That seems common on the 30A twist locks, but I can't say I've ever seen burned contact on the 50A ones unless they were suffering from significant corrosion. They do have much stronger springs in the female connectors than the 30A ones do, judging by the dramatically higher insertion force.

Good point. I always had only the 30a ones, so I can't speak to the 50a ones at all.

[Jammer]

For 10 years I had an Airstream trailer that used the 50a twist-lock connector. Most frequently I used it with a shore power cord that had the 50a twist-lock connector on the trailer end and the 30a twist-lock connector on the pedestal end, because the 50a cordset is heavy and unmanageable, we rarely had 50a at the pedestal, and didn't need 50a unless running the heat or air conditioning.


It worked fine. Problems with shore power connectors burning up do occur in the RV community but not with the frequency they occur in marine applications. I am not sure that it is a materially better connector. It still has a weak locking mechanism compared to the force exerted by the cord.

[s/v Jedi]

50A twist lock: it’s okay

30A twist lock: horror

[OS2Dude]

We have two 30A smart plug inlets on our boat. Not to mention superior safety, they are also much easier to use. When we had twist connectors, it was hard to get them lined up correctly, and difficult to twist completely since the inlets are on the outside of the coaming and we weren't. Smart plugs can only go in one way, you can do it in the dark. They also have multiple locking mechanisms to hold the plug into the socket. I am still amazed by the number of people using cordage to try to keep their older style connectors in place, both on the boat and at the pedestal. Yes, that is a sure sign the connector and/or cord needs to be replaced, but so few seem to do it.

[Lancerbye]

As a retired ABYC certified electrician, I have seen a lot of burnt twistlock plugs and receptacles. Most of them were homemade. The problem that most people don't seem to realize is that the screw type connectors in the plugs and receptacles become loose over time increasing the contact resistance and thus creating more heat and eventually a burn out. As the current is run close to max, the wires warm up and expand, this forces movement at the screw connections allowing them to loosen a bit. This increases the resistance and the cycle continues until a fire results. I found most burnt plug cases not to be the fault of the plug, but rather the fault of the owner and how he used or abused it.

[intervivos]

While I agree that the plug design is not that great, I think to create a good one would be complex. From what I have seen, most of the issues come from user error. Keep the contacts clean [both the socket and cord] and use anti-corrosion spray. Make sure the power is off at the pedestal, connect the cord with a twist and actually secure the locking ring- nice and tight. Make sure the cord is plenty long enough so the cord and connections will never get stressed.

From what I have seen, it is when the boat moves a lot and the plug becomes loose that the problems start to occur. Thing start to arc and then tolerances degrade. That turns to heat, which turns to fire. I don't think any static plug will fix the issue, the only way to really fix it is to have a prongs that extend and retract based upon the proper connection. If the connection starts to loosen the the prongs fully retract fast to prevent an arc. When plugging in, the prongs extend fast to make the connection. Since this would be complicated it has the potential to get fowled up, and we are back to the beginning. Or develop some type of wireless charging [like you have for cell phones] that can handle the currents needs without a physical connection. Again, complex with its own set of problems I am sure.

[s/v Jedi]

I see all the factory attached plugs burn up (and there’s no access to the insides, they are molded) and the user attached plugs last longer because they are obviously better.

Also, the dock pedestals have nothing to screw the locking rings to. Use the 50A outlets instead!

[rslifkin]

Originally Posted by s/v Jedi

I see all the factory attached plugs burn up (and there’s no access to the insides, they are molded) and the user attached plugs last longer because they are obviously better.

Also, the dock pedestals have nothing to screw the locking rings to. Use the 50A outlets instead!

On the dock pedestals (for both 30A and 50A connections) I make a point to run the cable up over the top of the pedestal to minimize the weight hanging on the connector (as there's no locking ring attachment). The pedestals at our home marina have a large hook on them to loop a cable over for this purpose.

[thinwater]

Originally Posted by rslifkin

On the dock pedestals (for both 30A and 50A connections) I make a point to run the cable up over the top of the pedestal to minimize the weight hanging on the connector (as there's no locking ring attachment). The pedestals at our home marina have a large hook on them to loop a cable over for this purpose.

No locking ring is a code violation; advise the marina they are obligated to fix it. And obviously, the with any cord, the user is responsible for strain relief, not just let it hang over to the boat. And for cleaning and greasing the contacts (male part) periodically; it is a saltwater environment.

[rslifkin]

Originally Posted by thinwater

No locking ring is a code violation; advise the marina they are obligated to fix it. And obviously, the with any cord, the user is responsible for strain relief, not just let it hang over to the boat. And for cleaning and greasing the contacts (male part) periodically; it is a saltwater environment.

Are you sure code requires them to have a component for the lock ring to screw onto after the twist-lock is inserted? I've never seen the screw on part on any marina pedestal anywhere we've been (including brand new power installations). I've only ever seen it on adapters and boat side connectors.

[Jammer]

Originally Posted by thinwater

No locking ring is a code violation; advise the marina they are obligated to fix it.

Perhaps that's true, but I've been in many marinas where there were no locking rings on the 30A outlets. I believe they were all on pedestals that downward-facing outlets that were covered by "in use covers," that is, raintight covers that have a slot at the bottom for egress for the cord.


I believe that the NEC allows indoor outlets (i.e. without the locking ring) to be installed behind an in-use cover.