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Old 04-17-2016, 09:38 AM   #1
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Inlet 110vac Twist Lock Power Connector.

This winter I had a 1,200 watt space heater and the 700 watt water heater turned on to keep the Van above freezing. Total 1900 watts. The breaker on the source end was 20 amps and didn't trip. I don't think there was ever more than 20 amps being drawn thru the twist lock plug on the side of the van.

Although this connector is rated at 30 amps here is a picture of the melted connector. It was not possable to get them appart after they melted together.



Sure glad there was no fire.

I replaced the connector with a "SmartPlug".

30 Amp Inlet and Connector | Shore Power SmartPlug

Best keep your eye on your outside 110ac plug to make sure it is not getting hot.
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Old 04-17-2016, 10:21 AM   #2
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Originally Posted by DCHitt View Post
20 amps and didn't trip. I don't think there was ever more than 20 amps being drawn thru the twist lock plug on the side of the van.

Although this connector is rated at 30 amps here is a picture of the melted connector. It was not possible to get them apart after they melted together.
Totally reminds of an experience when I was sailing across the Atlantic. Mid-Atlantic, sitting at the Nav station at midnight after coming off my watch, I hear a buzzing sound coming from the electrical panel. The sailboat had a 220V big generator running at the time. I opened the panel and could hear the arcing in the barrel switch used for selecting Shore/Generator. Immediately shut down the genny and told the next watch person to not use the generator and I would deal with it when I woke up.

Next morning I dissected the barrel switch, found terminals that were pretty smoked and went hunting for a spare. This 80 ft. boat had spares for everything - except a barrel switch! Took the whole thing apart and found contacts that head become high resistance points due to age and the arcing. The worst contacts were unusable, so I cleaned up what I could and reassembled so it would work with genny power, since the shore power cord was not 1500 miles long to reach land . Interesting experience!

Had something similar to your situation happen with our power boat. Shore power was 2 x 30 Amp sockets and I found one that looked like yours. The wire connections to the terminals showed signs of corrosion/oxidation. It was a salt environment, similar to what an SMB might see on wet salted winter roads. That moisture getting into the shore power connector housing is going to do some damage to the copper and metal which is going to result in resistance and heat well away from the breakers as it is mid connection. It would likely not be until the wires crossed that the breaker would trip. In the meantime the plastic may have reached a smoldering state.

Definitely worth an inspection as part of a Spring Check Out of the systems. One way would be with an Ohm meter. There should be very little resistance on a large gauge wire used for shore power. With shore power disconnected, Inverter/transfer switch OFF - check ohms from each of the male plug terminals on the outside the van to a the corresponding wire end where the wire connects inside of the van. Make sure to do the visual inspection on the back of the connector, as well. And while you are at it, check your shore power cord, too!

Glad you caught this before a fire occurred. Scary!
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Old 04-17-2016, 11:48 AM   #3
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1der: Doing an internet search, I find many cases of boat fires starting do to these connectors. You seem to have had similar problems. Time for a better connector.....
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Old 04-17-2016, 12:10 PM   #4
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This is a very common problem with 30a twist lock plugs. That design was first introduced in the 40s and never improved until recently. I installed a smart plug on our boat that solved the problem. Heaters are the most common cause of melted plugs as they cause a continous high amp load that runs for long periods. Once some corrosion starts, the resistance in the contacts goes up causing heating. That heating causes the temper in the contacts to be lost which reduces the spring tension required to maintain good contact. After that, the contact can arc but still be well below the full current rating of the circuit breaker. Once it begins to arc, melting doesn't take long. Another quick check is to use an infared heat gun to measure the temp of the plug while it has been under full load for a while. On my van, I simply hard wired the cord to eliminate the plug, and the cord stores inside a small access door. The photo of the melted plug shows two very small wires attached to the plug. I would be concerned about that due to the 30 amp potential being applied to wires probably good for about 10a. What ever they power probably draws little current, but if they ever short, the copper will melt before the breaker trips.
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Old 04-17-2016, 12:21 PM   #5
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arctictraveller: The small wires are for a light that is in the cover. It comes on when there is power at the connector.
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Old 04-17-2016, 02:03 PM   #6
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I plug in every time I return to home so it gets a lot of use. I don't have a corrosion issue but the contacts are getting used a lot and I suspect in time I'll have to replace mine due to wear alone. I just rarely use that high of amperage. One of the things SMB warned me about was plugging in under a load and what it can do to contacts.
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Old 04-17-2016, 03:49 PM   #7
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More Pictures

Just for fun here is some additional pictures. The "Hot" pin is the one that is welded in the socket. I bent it trying to get it out.



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Old 04-17-2016, 04:19 PM   #8
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How about a pic of the improved replacement?
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Old 04-17-2016, 04:26 PM   #9
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I didn't get it from this site but this is the replacement connector.
Not cheap. But it seems strong. Also I have heard it has a built in thermal.

Click on this....
30 Amp Inlet and Connector | Shore Power SmartPlug
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Old 04-18-2016, 03:12 PM   #10
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New "SmartPlug" on my Sportsmobile

I put the new plug on my old cord so it had an RV standard plug on the other end. I don't know if you can find a cord with RV on one end and SmartPlug on the other....

This is my installation.

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