When I called SmartPlug, during the research phase of this article, I spend many hours or sometimes weeks researching before I delve into a detailed article, I asked about independent testing and temp scanning.


They told me that Cascade Thermal Imaging, Inc. of Redmond Washington had in fact conducted some independent, third part thermal imaging tests on the Smart Plug.


I was then able to convinced them to send me this thermal image of two BRAND NEW plugs & inlets, both 30A. One is the circa 1938 NEMA L5-30 twist-lock standard, most boaters are using today, and the other is a Smart Plug.


These plugs and inlets were both 30A versions run at 28A or 93% of the face value rating. They were loaded to 28A for 1.5 hours at an ambient room temp of 72F..


I think the image speaks for itself and represents pretty much what I see in the real world. When you look at the temp spread you can see a 23F rise in temperature, from the ambient air temp, on the circa 1938 NEMA L5-30 plug standard. Loaded identically, the SmartPlug yields just a 4F rise from ambient room temp.


I am playing devils advocate here, but there may be differences in the plug casings and how they transmit heat? My gut instinct is that I suspect 1.5 hours should be sufficient to get any heating at the plug/socket juncture to the surface of the plug.


Keep in mind that a 30A NEMA L5-30 circuit should never be loaded to this level for long durations. This was 28A in a controlled testing environment with BRAND NEW specimens. Even at this 93% of rating level the Smart Plug handles the current in a far better manner. I suspect if the NEMA L5-30 standard were tested today, to today's standards, it would have never gained approvals.


I regularly measure plug temps with my infrared thermometer, wish I had a Flir, and also see this in the real world. Here in Maine we do have a fair number of boats that winter over many of which use electric heat.


I will say it again, portable electric heaters can be VERY, VERY dangerous even on well maintained cord sets and inlets because they draw immense current. Please be CAREFUL!


The max level at which you want to load these circuits is 80%. Keep in mind this is when NEW with CLEAN tight connections. As the connections age corrosion can set in and this can create high resistance, especially with the 1938 twist-lock standard.


I generally don't recommend loading a NEMA L5-30 30A circuit to more than 70% of its face value rating, especially in the MARINE environment. This means approx 21A on a 30A circuit. If you want to push it to 80%, and feel safe about that, the number is 24A. As a marine electrician I DO NOT feel safe about that with the 1938 NEMA L5-30 plug standard..