RV Electricity – Just Ask Mike (J.A.M.): Why does my 30-amp plug overheat?

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By Mike Sokol

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.


Dear Mike,

I’ve had my 30-amp plug burn up a few times in the last couple of seasons. Is it something I’m doing wrong, or something the campground is doing wrong? —Burt

Dear Burt,

Well, as I like to tell my engineering students, “It depends.” Anytime a power connection begins to heat up there’s something wrong.

If the outlet on the pedestal has been overheated before, then its own contacts can overheat your perfectly good 30-amp plug. Or if your 30-amp plug is damaged or corroded, it can damage a perfectly good campsite outlet.

There’s also the possibility that either the shore power plug or outlet was built in a foreign factory that doesn’t comply with all NEMA dimensional and material standards for those connectors. I just don’t know enough to venture a definitive opinion yet.

But all is not lost as Mike Zimmerman and I (over on the RVelectricity Facebook group) are taking on the challenge of trying to determine why this problem seems to happen on a lot of 30-amp shore power connectors, and why it appears that the neutral contacts overheat much more frequently than the hot contacts. It’s a riddle, wrapped in a mystery, inside an enigma.

But not to worry, as I’m designing a high-current testing device that can overload any RV connector with up to 180 amperes of current for hours at a time, all without driving up my electric bill too much. It’s just one more piece of test gear I need to build that just doesn’t exist outside of a large test lab, but which can help answer these seemingly simple but rather deep questions. Please Stand By for more science.

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
Join Mike’s popular and informative Facebook group.
And you don’t want to miss Mike’s webcasts on his YouTube channel.

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29 Comments
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chris p hemstead
20 days ago

I didn’t read all the replies, so I hope this isn’t a repeat answer. I searched for “loose” and didn’t find what I’m adding…..

My, and I assume “all”, 30a plugs have screw connectors. Over time, IF they work loose, that will definitely start to make a lot of heat.

Joe
27 days ago

I would suggest using a well used green colored Scotchbrite pad to clean the blades on the male plug rather than using emery cloth or a wire brush. Overtime the emery cloth will wear away the blade thickness and the wire brush will score the softer metal of the blade. Also as I have posted before a very light coating of electrical dielectric grease will help make the plug slide in easier and help improve connection, just remember that it will attract dirt and must be kept clean!

Wolfe
27 days ago

What would be a good temperature at which to warn the user? This stuff goes clear at 88F (so, paint the plug bright red and this over it — looks black normaly so if it’s red again, it’s too hot):

https://www.amazon.com/PRESTIGE-THERMOCHROMIC-TRANSPARENT-Temperature-Transparent/dp/B07D1S2MSJ

Slightly more techie, a thermal alarm (open thermal reed switch on a piezo) would be very easy to make, although if readers try it, should NOT be built inside the plug housing.

wanderer
27 days ago
Reply to  Wolfe

Clever idea, but good luck with that in Texas in the summer where 88 can be the low for the day.

mike henrich
27 days ago

I’ve had 1 case that I still don’t understand. We were at a campground that was laid out kind of weird. Hookups far away from the site. The campground gave us an extension cord to use. Brand new, 30 amp. The plug on my RV was pretty new, on it’s 3rd use. We only ran the AC for a short time on 1 day during the 4 days we were there. This was before I started metering everything every time we went somewhere. When we went to leave, the brand new extension cord ans my almost brand new plug end were melted together. We used 2 screw drivers to pry them apart. Even with the 60′ of voltage drop, considering the AC only ran for a short time, and nothing tripped that weekend, I never fully understood why the cords melted. Connections were clean and tight.

Joe
1 month ago

I have built an RV park from scratch. You either have a 50 Amp or 30 Amp hookups for an RV. Now, a 50A will have 2 hots , 1 neutral, and 1 ground. A 30A will have 2 hots and 1 ground. No neutral. So whatever 30A outlet that you are hooking up to should have no neutral in it. To do any testing, make sure you got that part right first… Now that being said, you need to consider the fact that you tend to plug in more devices in an RV such as laptops , phones , etc. The more devices you plug in , the more likely you will destroy your RV plug overloading it. The RV park will only give you a 50A or 30A only. Be safe .
.

Karl Eby
1 month ago
Reply to  Joe

You need to check your information on the RV 30 amp outlet.
It’s one hot, one neutral and one ground for 110 volts.
Two hots will give you 220 volts.

brian
17 days ago
Reply to  Joe

No offence but you “built an RV park from scratch” and you’re saying a 30 amp hookup is 240 volts with no neutral?? That’s just plain wrong, and scary.
Also note that “phones and laptops” draw very, very tiny amounts of current and will have a barely discernible effect on the total draw of power when plugged in. When it comes to big current users it is always things that make heat, things that make cold, and things that have motors.

Wolfe
1 month ago

I think the 30A melting down more than 50A is a simple electrical vs. social engineering problem:

When a 30A Camper pulls in, he turns on the 13A A/C and the 9A hot water. His wife starts cooking with a 10A microwave, 8A crock pot, and maybe a 9A griddle because they want bacon on their burgers. Their teen’s hair got messed up by the open window while driving, so she takes a shower and blowdries her hair (13A…). Of course, on 30A they have hopefully blown the breaker many times, but ultimately all those draws are going to get their turn even with some power management — but the plug is kept NEAR 30A for hours, when most code (I think) I expects 80% duty at worst. Folks are just too used to unlimited power. He pulls out again in the morning, giving the pedestal 300-some connection cycles a year…

Mr. 50A Bus pulls in, and has 12KW available to handle the same loads, less urgently. He moves monthly, giving the pedestal only 10 cycles a year.

Logical?

Wolfe
1 month ago

I make a habit of checking my plug by feel every few minutes after initial connection (when all the draws are “recovering”), and periodically thereafter. I also don’t slam everything on all at once — usually AC to cool from the drive; when that settles, 120V hot water; and when that settles, everything else. I’ve melted my plug myself (dirty deformed contacts?), but I think a lot of the 30A overheats are just because people “land” and turn everything on at once, while 30A is about 1/2 of what most trailers WANT to draw with everything on.

There are paints that change color based on temperature — totally passive and unpowered. It would be pretty easy to paint your 30A plug(s) and at least have an easy visual indicator for as often as you happen to look at it.

Larry & Bev Lee
1 month ago

Good article, But i have another question, I have a new 2020 Forrest River TT. It has a 13,500. A/C unit. My generator( Champion 3600w dual fuel) worked on our last unit with the same size A/C unit. Now I do only use the gas side for this operation, not propane. This A/c unit knox the heck out of it and over loads it every time. I’m thinking of purchasing that new soft switch for the A/C unit? Any suggestions??

Daryl Deranleau
1 month ago

My gosh people, use your maintenance skills, esp when it comes time to use your RV plugs. The constant using and reusing of a cord connection, esp when it’s been overheated, is sinful. When you take a 50 amp, 240 volt plug, and use only half of the voltage applied, ( Hench the 30 amp, to 110 voltage adapter) what do you think is going to happen.
I’m going to assume your wire is sized correctly, probably not, but that’s another topic. If your plug in is getting warm, to hot, take the damn plug apart, and re tighten the screws, back on wire. Make sure you cut the burned off part of the damaged wire before re-attaching to the screws.
Wake up RV owners, we can do this.
Thanks.

John C Jackson
1 month ago

I use emery cloth to clean the contacts on the 30 amp plug and then spray with Deoxit Shield; do this at least twice a year. Helps reduce the corrosion and makes a better contact with less heat. 50 amp plug does not need it as often because the prongs are much larger.

Tommy Molnar
27 days ago
Reply to  John C Jackson

I bought a cheapo cordless Dremmel-like tool from Wally and use it with a wire brush attachment to clean off my plug. Then a bit of sanding and a blast of contact cleaner. I do this every so often and it seems to help in the hot plug situation.

Snayte
1 month ago

That is because the production of substandard products is not limited to China. In fact there has been a trend in the last few years for Chinese companies to offshore some of their production to countries where the labor is even cheaper.

David Ozanne
1 month ago

I had this problem and found it was because I was not turning the power off when connecting and disconnecting.

Mike Sokol
1 month ago
Reply to  David Ozanne

Yes, that’s likely another factor. I see this a lot as well. And it damages the pedestal outlet which can overheat a brand new shore power plug. This creates a vicious cycle of failure.

James S.
1 month ago

Ralph Williamson,
Will you please be kind enough to explain exactly how you “. . . almost always caught it before it did permanent damage?” I’ve had the burned-up plug problem several times and I want to avoid a recurrence. Thanks for anything you can offer.

WEB
1 month ago
Reply to  James S.

The simplest way is to go to the pedestal and feel the cord plug. If it is warm to the touch on the rubber outside, you can be sure it is warmer on the inside where the contact is being made. If it is a cheap cable, the internal connection of the male plug (inside the rubber) could also be at fault.
Remember that if you are running at full load i.e. two A/Cs on a 30 amp cable, then it could be naturally warm, not much you can do then except monitor it.

James S.
1 month ago

Mike, I’ve had the same problem as Burt with my 30 amp plug burning up several times.

You commented that it “. . . seems to happen on a lot of 30-amp shore power connectors, and why it appears that the neutral contacts overheat much more frequently than the hot contacts.”

Then, Ralph Williamson posted he has been successful using a 50 amp to 30 amp dogbone.

Is it safer, possibly, to use the 50 amp to 30 amp dogbone for a campground 30 amp power connection?

I thought you might want to address this in you follow-up after your testing.

Thanks for everything you do.

Ralph Williamson
1 month ago

I don’t see how an EMS would help unless it monitored the temperature of the contacts. I can confidently say that 99% of the time, this is caused by a worn out jack. It’s happened to me several times, but I almost always caught it before it did permanent damage. I’d then switch to a 50A to 30A adapter and have no issues. Therefore if my 50A to 30A jack and plug never had a problem, then it must have been the pedestal jack at issue each time. I think when they get worn out or overheated, the wiping action of the contacts is insufficient to make a good contact.

Mike Sokol
1 month ago

That’s the main suspect, but there’s also a few other possibilities. We test because we care….

Irv
1 month ago
Reply to  Mike Sokol

Assuming Ralph is correct.

Might it help to spray my male plug and/or the pedestal female with contact cleaner and remove/insert several times? (At least not hurt anything.)

I suspect a major part of the problem is people not turning off the pedestal breaker before plugging/unplugging. About 80% of the time I find the breaker already on when I arrive.

I guess I’ll start checking my male plug after an hour or so.

My male plug happens to be an expensive surge protector. I’m going to start using my 50A to 30A adapter to protect the EMS.

Mike Sokol
1 month ago

That’s true, but there’s a few EMS/Advanced surge protectors that include a thermistor on their female outlets to monitor contact temperature. But I don’t know of any that monitor the temp of their male plugs.

Notfunny
1 month ago

Mike:
Reading your response on this 30 Amp question: Would a EMS surge protector help in this case or not?