December 16, 2014

Shore-power Lost; AC connections at fault

[Updated: 22-Jan-2015; 1-Oct-2016]

Murphy struck while we were away from the boat.  [6-10 flying hours away...]

The other day our remote vessel monitoring system sent an SMS to our cell phones notifying us that shore-power to the boat was off. [Several times within a 3 hour period.] 

We immediately contacted our diligent caretaker who quickly confirmed that power was indeed on in the marina, but found that the 50 amp AC connection between the shore-power cord and boat had failed.  

Receptacle on boat. (That is the Neutral post that was affected.)



Output (Boat) end of shore power cord

Something caused poor connectivity/conductivity of the neutral terminal.

Typical causes include:
  • electrical connectors [mating tangs] were no longer tight, or the connection worked loose [rotated to the unlock position of the twist-lock] 
    • [Yes, the power cord was secured to the receptacle with the threaded lock cap- which was reported as still tight. And when the new plug was put on the cord, the wires showed no sign of shorting or overheating. I'll see what the wires on the boat receptacle look like when I replace it this spring... Update 22-Jan-2015, below; the wires were fine...
  • water ingress 
    • [Our caretaker reported the socket was dry, but the heat generated by the resistance of the bad connection could have cooked off any moisture...] 
  • corrosion [most likely...?]
  • or were just worn out
    • [The previous owner completely revamped the AC system in 1999-2000, so these components may be that old...]
What about too much current you ask? 

Well, that 50 A female connector is actually part of an 30 A to 50 A adapter [pigtail]. I had the 30 A (10 Gauge) cord running to the 30 A 115 VAC dock power and connected to the boat 50 A inlet through the adapter. [The boat has two 50 A 125/250 VAC input receptacles.] Therefore, even if we were drawing a maximum of 30 amps the 50 A adapter cord and receptacle should not have been overloaded.  [The most I measured (before I left the boat) with everything running was 18 A... The dock breaker will trip when it hits 30+ Amps; something we have inadvertently demonstrated on several occasions...]

Since we needed AC power to keep the batteries charged, and for the dehumidifier and modicum of heat we left on to prevent mildew, the quickest resolution [predicated by what parts could be obtained locally...] was to replace the damaged socket on the shore power cord and plug it into the 2nd power inlet on the boat. [We have one on both port and starboard sides for convenience.] 

We left the fried receptacle as it was for the time being. [Since the two power inlets have separate breakers on the boat AC panel, and since only one can be switched on at a time due to a physical lock-out mechanism, I deemed this a safe approach, although a temporary one...]

This met our need for continued AC shore power for the time being...

But what to do for the long term to reduce the possibilities of this occurring again in the future? 

One approach is to replace the damaged input receptacle with the same set-up. [We have these heavy-duty stainless receptacles on the boat...]

Another is to eliminate the receptacle all together and just hardwire the shore power cord in place. [Like may RVs and campers do...] There are cord reels made for this type of install, but since we have two inlets (port and starboard for convenience) I decided not to take up space in 2 lazarettes with 2 cords and 2 reels.

Therefore it was time to research replacing the input receptacles on the boat with something better. [Since it looks like we will be stuck with the current twist-lock standard on North American docks for the foreseeable future, why not limit the issues to that end of the shore power connection?]

I've know about the SmartPlug alternative for some time, and did a bit more research now that I was contemplating a change. 

This is not an uncommon problem with the old style connectors, and things could have been much worse if it weren't for our extremely reliable and capable caretaker. [Thank you, Kim!] 

It seems to me like the SmartPlug is the way to go for all the reasons given on the manufacturer's web site as well as 3rd party information I read online. [Search the internet for SmartPlug and you will find plenty to read...] 

Where to buy? We ordered ours from Amazon at very competitive pricing and free shipping. 


Want to learn more?

Update 26-Dec-2014: We ordered a new Smartplug 50Amp inlet and cord end (per photos above). We will order another set (remember the boat has 2 inlets...) if it works out as expected when we install it this coming spring...

Update 22-Jan-2015: I had a chance to stop by the boat as part of a trip to Seattle, so I took the opportunity to install the new SmartPlug 50A inlet between rain squalls while I was there. 

It easily fit into the hole for the socket being replaced, and wiring was easy- especially since the manufacturer uses stainless steel socket head set screws instead of the usual slotted set screw.

The only minor modification I had to make was to drill the mounting screw holes slightly larger since oversize screws had been used to mount the legacy outlet. I also increased the tapered countersink to accommodate the larger flathead screws I had to use. Five minutes freehand work with the drill, including clean-up. [The body is stainless steel, so use sharp bits, and do this before installing if warranted...] 

Before securing the socket, I wrapped a couple of layers of self-amalgamating silicone tape around the area where the set screw heads are accessed as an extra precaution.  [Even though they are slightly recessed as you can see in the next photo. (Sorry. I didn't think to take a photo after installing the tape...)]

Update: 1-Oct-2016: We have not had a single issue with shore power connections on the boat since converting both of our AC inlets to 50A SmartPlugs. 

I have even tested the limits by running all 3 air conditioners and some portable electric heaters to put maximum load [~48 amps] on the 50A dock service, and the SmartPlug hardware never even got warm to the touch...

The following photos are of the first SmartPlug inlet replacement on our boat. It shows a 50A inlet, and a 50A plug on our 30A [10 AWG] shore power cord. [Which is smaller in diameter than the 6 AWG 50A cord, so I had to fill the black rubber strain relief on the 50A SmartPlug cord fitting with silicone to make up the difference in size and get it to seal around the smaller, 30A cord...]

We now have both SmartPlug receptacles installed on the boat, and the 50A shore power cord has the 50A connector on it as well. 

Would I do it this way again? Without hesitation; this is the next best thing to hard wiring the cords to the boat. 


















































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