I keep burning out 30A plugs...

Hi all,

    I've been going through a lot of plugs lately, the male ones at the end of my 30A shore power cord.  One about every three months or so.  The plug gets hot and internal damage is done until the wire end and the prong/tab fries and my power goes out.  When this happens no breakers inside the rig trip, but the one on the pedestal does.  In the summer I'm running one AC (front AC during the day, rear AC at night), a desktop computer, TV, and the fridge.  In the winter I'm running the front overhead heat strip (usually just at night), desktop computer, TV, and fridge.

I'm been at the same park for over a year and this has happened in three different spaces.  Three times this has happened while plugged into a 30A outlet on a pedestal (one time the female outlet on the pedestal was burnt as well and the park replaced it).  The last time this happened, just a couple of weeks ago, I was plugged into a 50A outlet on a pedestal (I was using a 30A female to 50A male adaptor (both the male 30A plug on my shore power cord and the 30A female end of the adaptor were burnt.

The guy that does the maintenance at the park says I'm drawing too much power, but I'm not tripping an internal breaker.  I'm trying to watch my power usage but I have to wonder if the problem is simply running the AC 24/7. 

Can anybody tell me what's going on?

Thanks in advance.

Luca1369 said:

Can anybody tell me what's going on?

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I don't think so. At least not without real data.

A seven day recording ammeter will tell the tale.
Even several of them on different legs of the distribution system
(which assumes that the system has accurate as built's)

(I'm also assuming the problem isn't poor assembly of the cord caps...
as with all the practice you are getting you could probably give lessons... but it should be considered too)

My best guess is that you are drawing more than 30 amps and your main breaker isn't tripping because it is defective. A 30 amp breaker is not that expensive nor too hard to replace so you might want to start there.

First off, the problem is not in the wiring of the plugs, they're fairly simple, black/white/green.

As for the main breaker, that's a good point, but it did trip earlier this year, when I tried to run the microwave along with everything else and found out I cannot do that...

Luca1369 said:

First off, the problem is not in the wiring of the plugs, they're fairly simple, black/white/green.

As for the main breaker, that's a good point, but it did trip earlier this year, when I tried to run the microwave along with everything else and found out I cannot do that...

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It sounds like it is not tripping at 30 amps. AC computer tv and fridge sound like more than 30 amps.

Steve; I've seen this happen with low voltage at the pedestal. Since it is at the same park but different spaces it would make one wonder about the park voltage. Just a thought............  Let us know what you find...                Jim

It is not unusual for the 30A plugs and outlets to get hot if run continuously at a 30A load. The wire in your shore cord is probably 10 ga, which is maxed out at 30A, and if the connections at the plug are not perfect, the heat will get intense there. Ditto on the outlet side.  When you replace the plug, make sure the ends of the wire are clean and bright, and that they are well clamped into the plugs connector. Tinning the wires may help get a better connection too.

The rating assumption is that the max amps are not continuous - the 24/7 load is considered to be 80% of peak. If you indeed are hitting a continuous 30A, you really are stretching the rated limits of those devices. The a/c alone won't do that, however. It draws about 14A. But with the fridge and water heater??? Maybe you need to put them on propane for those very hot days.

I've also found that the typical RV 30A adapter can't handle a sustained 25+ amp load without getting so hot that things start to melt.  Clearly the ratings are marginal.

Now that I have had time to wake up and think this problem over I will tell you what I would do. First off P=I*E which means that power (watts) is always equal to the amperage (I) times the voltage (E). Since the wattage of all your electrical appliances are constant then if the voltage is low the amperage goes up. In your case you are running near max amperage so if the voltage drops your amperage gets dangerously close to 30 amps. Not enough to trip the breaker but certainly enough to heat the wires up. But I am skeptical about it melting the plugs just because of a low voltage. You will need something else going on to melt the plug.

The first thing I would check would be the connections inside the pedestal. I know you have hooked up to three different pedestals, but there is the slim possibility that the same electrician wired them all up and he was a wimp. Or they could all be old and have loosed up due to earthquake activity (I don't know where you are located, I am just exploring all possibilities). So if you can get the power to your pedestal shut off then you should make sure the wires to the breaker and the outlet are really really tight.

Next I would suspect the 30 amp plug that is installed on the end of the cord. If should have very shiny contacts and they should be very tight.

Then comes the cord itself. How long is it? Over 25 feet would be bad news, shorten it. You will also need to check the size of the wires. They need to be 10 gauge minimum. If you don't know what 10 gauge looks like you could go to Home Depot and buy a foot of number 10 stranded wire to compare. Personally, if it were my RV and this were happening to me I would not put a new plug on the cord when it melted, I would have replaced the entire cord with a molded plug on the end.

Next is your 30 amp main breaker. If it is defective it might not trip at 30 amps, it might take 35 to trip it.

Last would be the connections in the main panel of your motorhome. The three wires should be very tight.

It has to be one of the above. Good luck.

RV Roamer said:

But with the fridge and water heater???

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Only the fridge is run on AC, the water heater works better on propane, I never run it on AC.

seilerbird said:

The first thing I would check would be the connections inside the pedestal. I know you have hooked up to three different pedestals, but there is the slim possibility that the same electrician wired them all up and he was a wimp.

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Tom,

    The pedestals are all old, and like I said, one had to be replaced at the same time as my plug.  The connections on my plugs, when I install them, are as good as I can get them, tight, with shiny wires, I usually cut off several inches of wire to get to shiny stuff. 

    A guy in another gig also thought it might be my power cord, he suggested going up a size.  The cord is probably 25' from cord end to circuit panel, 10 gauge, and the breaker connections are tight, all looks good there.

    I've gotten to the point that I keep an extra pair of male plus to replace the burnt ones.  There's a guy on eBay who's getting rich selling me 30A male plugs.

Since you had the problem even when connected to a 50A outlet, it's certainly that you're drawing too much current.  Try setting the refrigerator to gas when running the A/C.

Well, much folklore in this thread along with a few useful observations.

Here are some facts to consider.

1) Overheating like this is almost always caused by resistance between the plug blade and the metal portion of the socket that clamps it.  This is most frequently caused by three things: a) A loss of clamping pressure as a result of metal fatigue in the socket, b ) Oxidation on the metal surfaces, either the plug blade or the metal portion of the socket that clamps the blade, and c) Badly designed sockets that don't have enough contact area or clamping pressure.

2) Less frequently overheating can be caused by poor contact between the conductors in the shore power cable and the plug, or the conductors between the receptacle and the pedestal breaker.

3) The actual ampacity of 10 gauge wire is somewhat higher than 30 amps but the electrical code limits it to the lower figure because smaller gauge wires are often sloppily installed.  This is done with 12 and 14 gauge wires, too, which is why there's such a jump in official published ampacity from 10 to 8 gauge.

4) If the pedestal breaker isn't tripping and the RV breaker isn't tripping then the obvious conclusion is that the power being drawn isn't over 30 amps.

Now, what to do.

A) Keep the plug contacts clean and shiny using steel wool or fine sandpaper or emery cloth.

B) Seat and remove the plug in the receptacle several times.  The wiping action will help remove corrosion from the receptacle contacts.

C) Use a good quality antioxidant electrical grease, sparingly, on the plug contacts.  The product sold for use with aluminum wire in home centers works well for this and is readily available.  There are industrial products sold specifically for high-amp connectors but they are very similar in composition and are not readily available in retail stores.

D) When installing a new plug work some of the same grease into the strands of the wire before you screw it down.  I know your cord doesn't use aluminum wire.  Do it anyway.

E) Screw connections between the wire and the plug should be TIGHT.  As tight as you can get them without breaking stuff.  Any time there is a problem, you should consider taking the cover off the plug and retightening them.

Hope this helps.  With today's higher temperature plastics you should be able to run way more than 30 amps through a 30 amp plug without damage (not that I'm recommending this, switch to a 50a plug if you're going to do that) so if you're having problems they're with your setup not with the current draw.

Jammer said:

...so if you're having problems they're with your setup not with the current draw.

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So you can absolutely guarantee that the breakers work perfectly?

seilerbird said:

So you can absolutely guarantee that the breakers work perfectly?

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Of course not, but like I said, it tripped earlier this year.  This last time that my plug burnt, a couple of weeks ago, it was the 30A contacts between my shore power cord and the 30A/50A adaptor that went, the outlet on the pedestal and the 50A side of the adatpor were not affected.

I don't believe I'm running over 30 amps.  Like I said, one AC, Norcold fridge, desktop computer, 12" TV.  To me that appears less than 30 amps, not much less however.  I've taken to running the AC on medium instead of high (this also due to the fact that the other day when it was 97 the AC breaker, 20A, tripped one time but the other breakers, including the main 30A breaker, did not).

I didn't address the comment to you Steve, it was addressed to Jammer, who seems to think everyone else's advice is folklore. I think his reply was folklore.

Luca1369 said:

I don't believe I'm running over 30 amps.  Like I said, one AC, Norcold fridge, desktop computer, 12" TV.  To me that appears less than 30 amps, not much less however. 

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http://www.2rvguys.com/breaker.html
Using this web sites figures you have an A/C drawing 15-17 amps, a fridge drawing 5.7 amps, a TV drawing 2 amps and a computer drawing 2-3 amps. That makes it between 25 and 28 amps. And that doesn't take into account for all the smaller draws you have, like your battery charger, clocks, LP detectors, etc. 80% of 30 amps is 24 amps, which is the most you should be drawing to be safe. You are way over the limit. You should run your fridge on propane to solve your problem, like Ned said. Otherwise you might come home some day to a smoldering pile of ashes that at one time used to be your motorhome. Overheated wires are extremely dangerous.

>With today's higher temperature plastics you should be able to run way more than 30 amps through a 30 amp plug without damage...

That is just not true.

Just a little thought.  (Burned 30a male plugs)

Every time you change one, make sure that the new wires are (pure copper); that means you may have to cut the insulation back to where the wire is clean copper. An oxidized/burned wire bundle will continue to present a poor connection and will heat up. 

  Make sure that all the strands of wire are all solidly connected to the crews...no short cut

Sounds like your plug connection is the weak link.

carson

Heat is caused by resistance, resistance is usually caused by a bas/loose connection. Yes the breakers should be checked/tested/replaced, as well as the line voltage on the park's female receptacle.

Im thinking that the shore line wire is to blame. What do the wires look like when you have to replace the plug? Any bubbleing of the copper wire on the ends?

Either way, I'd replace my shore line with larger wire, too small of wire, over a long run, will cause tremendous resistance ie. HEAT.

while everything is running, check voltage and amp draw at the female park plug and then at the trailer, in your box and see how much of a drop there is. Big drop. big heat.

Just so everybody is clear on this...when I replace the plug I always strip the wire back to clean, shiny wire.  The wires are twisted good and tight, and the screw clamps are clamped down HARD!

Thanks Tom for your insight, I am running a bit much here, but I hate running the fridge on propane since it doesn't stay as cold and it's a bit costly if I'm sitting still.  Guess I'll turn some other things off and turn the fridge down. 

Thanks all!

Luca1369 said:

Just so everybody is clear on this...when I replace the plug I always strip the wire back to clean, shiny wire.  The wires are twisted good and tight, and the screw clamps are clamped down HARD!

Thanks Tom for your insight, I am running a bit much here, but I hate running the fridge on propane since it doesn't stay as cold and it's a bit costly if I'm sitting still.  Guess I'll turn some other things off and turn the fridge down. 

Thanks all!

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All the refers I have had stayed just as cold on ac as on propane. You should have your refer checked out. Rather than turn the refer down, try propane instead, same difference.