No smoking — shore power connections

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By Chris Dougherty
Chris Dougherty is a certified RV technician. Here is a letter he received from a reader while he was serving as RVtravel.com’s technical editor.

Dear Chris,
A couple weekends ago, we were using close to the rated 30 amp draw on our trailer with fridge, water heater, periodic microwave, HVAC, etc., when my son suddenly told me that the power plug outside was smoking slightly. When I looked, sure enough it was melting in the socket!


I actually had three ammeters running at the moment (genny output, AC input, and an experimental graphing smart monitor) and they all agreed we were at about 27 amps for the last few minutes before meltdown. Yes, close to maximum but not quite over. Just to check for a defective main breaker, after replacing the plug, I intentionally put 32A draw on for a few seconds, and the breaker popped immediately. How normal is it for slightly less than 30A to still dangerously overheat the shore cord?

I would have expected a margin of safety that apparently doesn’t exist here. Is there anything else I should check? If this IS normal for borderline draws, perhaps the newsletter should warn folks to stay further below the max draw? —Wolfe

Dear Wolfe,
This is a great point, and it’s not just because of the amp draw. This is likely the result of resistive heating. Resistive heating occurs in an electrical connection where power can’t flow freely, usually because of a poor or dirty connection.

Let’s look at a hose. Water is measured in pressure (psi) and flow (gpm or gallons per minute.) Firefighters use different size hoses for different water flows. Would you see a firefighter go into a fire with a garden hose? No, because it can’t flow enough water. On the same note, a firefighter is in a fire and he loses pressure on his line, only to find that it got caught under a door which restricted the flow.

The same thing happens with electrical conductors. If the contact in a plug doesn’t connect firmly due to age, heating, corrosion and/or being bent, then as it tries to pass the electrical energy it starts to have arcing at the contact, which heats the metal, it expands, and the problem worsens. Over time, with repeated heating, this will get worse.

Campground plugs/receptacles are continuously connected and disconnected, and abused in other ways. So, if the terminals on either side were bent and/or corroded, this would lead to exactly what you experienced. The plug and receptacle assembly normally can pass this amperage without an issue. Unfortunately the contacts do wear on both sides which can lead to this condition.

You will have to replace the plug on your shore power cord. Unfortunately, because of maintenance and wear issues on the campground side, you probably can’t prevent this from happening. Many RVers never experience it, but those that do, including me, just have to make the repairs.

#RVDT1227

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TravelingMan

Electrical Connector Bodies should be checked regularly as part of the electrical maintenance program (in addition to the electrical panel, electrical receptacles, light switches and battery connections).

We have found that if you use a 50A electric cord with a straight connector, it places a lot of tension and stress on the connector body prongs. To prevent this, use the 50A 90 degree adapter. You will remove the stress on the connector and get a better connection point.

We also find that over time, the terminations on the back of the connector body tend to loose tightness. This requires pulling the plug out of the RV (usually by removing the 4 screws).

Regarding the light switches, I have pulled numerous switches out to find that the wires are loose in the wire nut or crimp nut. This causes heat to build while the lights are on (just like at the main 50A connector). This can also result in a fire or at least melting of the light switch.

Electrical receptacles can also also come loose.

And connections should be checked in the electrical panel.

Be sure to de-energize the RV from all potential electrical sources prior to performing these checks (both 12V and 120V).

Gary Reed

The same thing happened to our travel trailer in Nevada where temps ran in the 100 + for days. The white ground plug receptacle terminal on the trailer and the connecting terminal on the shore power cord was welded to the trailer connection. Had replace both connections to correct the damage. Now when I run the ac I do not use the electric on the hot water heater. We use the propane on the water heater.

Fred

Carry some electronics contact cleaner spray with you & spray both the park receptacle & your plug before inserting. This is not a cure all for a really bad plug, but it does help with light to medium corrosion. Also spray all the plugs & receptacles in your rv occasionally

Tony King

When going to hook up to power to my RV I shut off breaker and plug in my Electrical tester and switch back on to view test and make sure receptacle wiring is correct. If all is good I shut off breaker remove tester and plug in my RV power cord and switch breaker back on. This reduces arcing/sparking that occurs each time you plug in with power making connection. It sounds like a hassle but once you make it routine it only takes a minute to complete the whole process. It makes your plugs/devices last.

Richard Smith

Putting a dab of Camco 55013 PowerGrip Electrical Protectant and Lube onto the plug before plugging into the shore power connection will also help with improving your connectivity.