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Old 07-29-2013, 04:03 PM   #71
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Ouch. Very tightly coiled, and the hottest part was the center of the coil, where the magnetic field would be the strongest.
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Old 07-29-2013, 04:23 PM   #72
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Quote:
Originally Posted by steveclv
Well, what do you think??
That was quick too!
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Old 07-29-2013, 06:07 PM   #73
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Originally Posted by Sky_Boss View Post
OK My Friend...

You got my attention.

I guess the question is has anyone else heard of this and are there others that follow the same practice?

I'm not doubting you but I am a tad surprised that the manufacturers, especially those that have hose reels, don't seem to talk about this at all. Is there some kind of safety label I have missed?

I have seen some reels labeled to tell you to fully extend the cord.. I forget where I first read about this, as I said I tested it back when I was still working and the warning is true, My 12ga cord got very hot for the current it was hauling,

As an electronics technician and again as a ham radio operator I understand why this is. (inductance) but explaining that. I do not wish to do.
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Old 07-29-2013, 06:34 PM   #74
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One more thought on this subject, When do any of us have our 50 amp. or 30 amp. cord maxed out even in hot weather? One would have to turn on everything electrical all at once that is supported by the Coach to even come close to heating the electrical cord up to a point of making heat, it might feel warm with both air's running with a bunch of other things. At any givem time that I have ever checked my amp draw even with both air's running, fridge,hot water and a couple of other thing that are on I have never seen much over 20 - 25 amps. on a leg of 50 amp. service with my Coach and the coiled cord never felt warm or hot. I am not saying that it can't happen but I would think that there would have to be a electrical problem of sorts to cause a 50 - 30 amp. cord to heat to the point of melting without tripping the breaker that is supplying the current to the electric cord.
Loose connections are a electric supply's worst enemy..........builds heat and this melting condition can happen more so that a coiled electrical sow cord. Again, I am not saying that a coiled cord does not build a bit of heat due to the coiled condition, but that is not enough to melt a cord of that size, 30 or 50 amp.
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Old 07-29-2013, 06:40 PM   #75
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Palehorse89, you are correct - the likelihood of it causing a problem is low especially on 50amp cables - but it's something to be aware of. The example I showed was a 100' cable tightly wound and pulling it's max amps - in other words it was a 'worst case scenario'. The problem is more likely to occur where someone has a 30amp cord that is tightly wound and pulling max load. 50amp cable is so thick it would be hard to wind it that tight.
But if you can figure 8 in the compartment then it's good practice - as is unreeling the cable on a winder.
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Old 07-29-2013, 07:02 PM   #76
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I am not an Electrical Engineer, just a lowly baggy assed mechanic but I can tell you that if it is getting hot, you have resistance and it Will cause a problem eventually.

Just as a matter of good practice, one should be checking the shore connectors each time before use. If they LOOK Bad, junk em and replace. Don't try and save money by making your own. This stuff is not really expensive. Try to look for the UL or CSA sticker that hopefully will tell you it is not some "Made in China Junk"
BTW, as stated by the experts, make all your connections Outside of the Electrical Bay and if there is a problem it won't burn your rig down.

Not Rocket Science, just "Good Old Common Sense"
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Old 07-29-2013, 07:39 PM   #77
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I am not an Electrical Engineer, just a lowly baggy assed mechanic but I can tell you that if it is getting hot, you have resistance and it Will cause a problem eventually.

Just as a matter of good practice, one should be checking the shore connectors each time before use. If they LOOK Bad, junk em and replace. Don't try and save money by making your own. This stuff is not really expensive. Try to look for the UL or CSA sticker that hopefully will tell you it is not some "Made in China Junk"
BTW, as stated by the experts, make all your connections Outside of the Electrical Bay and if there is a problem it won't burn your rig down.

Not Rocket Science, just "Good Old Common Sense"
P/S. Thank you for this post.
I hope it will open a lot of eyes and hopefully make folks think about their electrical equipment a little more seriously. Back in my former life I used to service a lot of 5 KW And under gensets and it always used to amaze me the lack of simple electrical knowledge most RVers have. "Why won't my 500 Watt generator work when I plug in my AC? It is 110 Volts!
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Old 07-29-2013, 08:21 PM   #78
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I have to take issue with this statement from a licensed contractor because I believe that you may be wrong.

The length of 30amp cable and any connectors between the Pedestal and the first 30amp circuit breaker in the RV are NOT protected by a suitable circuit breaker and that is in breach of code. A failure of the 30amp circuit breaker or a failure of the cable and connector between it and the pedestal are 'protected' by the 50amp breaker in the pedestal and that is not acceptable.

Please correct me if I am wrong but surely you must protect wiring and connections with a suitably sized breaker which is not happening in this case?
I agree. That is the "out of the ordinary" in my post, if the local or national buliding codes were applicable it would never be allowed for the exact reason you describe.
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Old 07-29-2013, 08:30 PM   #79
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I am not an Electrical Engineer, just a lowly baggy assed mechanic but I can tell you that if it is getting hot, you have resistance and it Will cause a problem eventually.

Just as a matter of good practice, one should be checking the shore connectors each time before use. If they LOOK Bad, junk em and replace. Don't try and save money by making your own. This stuff is not really expensive. Try to look for the UL or CSA sticker that hopefully will tell you it is not some "Made in China Junk"
BTW, as stated by the experts, make all your connections Outside of the Electrical Bay and if there is a problem it won't burn your rig down.

Not Rocket Science, just "Good Old Common Sense"

You said it right there! Soooo many people are suprised when these things happen (the fire) when the breakers don't trip. The electrical energy is converted to heat because of resistance. While these nasty brown and black connections are overheating the coach is likely pulling less and less current. More series resistance equals less current, not more. When I bought my last used rig, I inspected both supplied adapters and the cord. All three were corroded and several terminals were already melting the plastic near them. The whole mess had to be replaced.
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Old 07-29-2013, 08:54 PM   #80
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I think Adaycj was referring to some of my statements. I can assure you, Adaycj, that if you lose the neutral on your 50A RV service it WILL cost you bucks for a new inverter and other things. I know folks that have had this problem. The 'protective' ground plays into the circuit at that point. I am not trying to be rude or argumentative. I am simply speaking from experience at one of the volunteer projects. The guy who was working on the rig in question did not verify the neutral. The folks using the rig had major and expensive problems.

I saw a mention of 'sticky breakers'. I think Adaycj will agree here that this is a more common problem than realized. One of the recommendations and practices I have used is to manually exercise the breakers once a year. This is a good practice even in your fixed domicile.

I have not noticed mention of the power control center of RV's. I am unfamiliar with most brands so I can only talk from my experience. I have had 3 DPs and each has had a power control center. When plugged into a 50A service the panel indicator told me I was on 50A. On 30 or 20A service I had to select which I was using and the amperage I was drawing was indicated. I mention this because of the way some of the discussion have gone. I am guessing this is not so in all RVs?

The folks with the fire have certainly gotten the attention of a bunch of us! This is a great and lively conversation. Too bad it had to start at the expense of these folks. I hope we all come away wiser.

Rick
You are not being rude or argumemtative. I would suggest that the neutral is the return path for both 120v wires in an RV 50A plug. A poor connection on this wire could cause some or all of the 120V circuits to fail to function. Excessive resistance in some or all of the neutral portion of the circuit could also cause low voltage to those circuits using the defective circuit. This could cause the dreaded low voltage that can burn out some devices, and I'll bet some of them are awfully expensive. The two "hot" wires in a 50A plug have 240V of potential between them, so I suspect we agree on that fact. That 240V finding its way into 120V devices in an otherwise properly wired rig might be a point of debate.

I have seen a breaker fail and stick. It most often happens when the breaker is repeatedly and quickly reset after an overload. More correctly the breaker thermally failed, and then failed to properly function from a mechanical sense. It does make you wonder about decades old pedestals in some campgrounds.
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Old 07-30-2013, 09:01 AM   #81
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Been following this thread and all of the commentaries. Nobody has addressed the failure point. If you look carefully at the 1st picture, the failure occurred at the 50A male to the 30A female adaptor. You can see the yellow female plug with the 4 connection points. The part that failed seems to be the 50A male plug. If the plug had a damaged neutral or a damaged Hot blade, a high resistance connection could have been the initial problem. With a 30A to 50A adaptor, 30A could be going to either Hot leg but always through the neutral. Coiling or not coiling would make any diffenece in this case. JM2...
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Old 07-30-2013, 10:02 AM   #82
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On the inductance "theory" - I just don't believe this one. In a 2-wire AC circuit, the current flows in one direction in one wire and in the opposite direction in the other. The magnetic field created by each wire will be in the opposite direction and will be cancelled out. Thus there will be no magnetic field created by a coil of 2-wire cable (or "3-wire" if you include the ground wire). If the wire was a single conductor and coiled up, that would be a different matter, but won't happen with any power circuits in an RV. The 120 volt circuits are always 2-wire. Same thing with a 3-wire 50 amp cable. The magnetic fields cancel out.

If the magnetic fields did not cancel out, the cable would be attracted to any steel object or structure and that doesn't happen. Without a magnetic field, there can't be any inductance. A transformer works on inductance, but only one circuit conductor is wound around the metallic core.

A GFCI receptacle works by having a little sensing coil around the hot and neutral wires together. If there is an unbalanced current caused by leakage through the ground wire, then the GFCI trips. As long as the hot and neutral have the same current flow, which they would under normal circumstances, there is no magnetic field induced into the sensing coil.

So my previous comments on overheating of the cable is my belief why coiled cords overheat. That's my opinion and I am sticking to it....

An EMS will not "protect" you if plugging into shore power live. The only way to prevent this is to either shut off the pedestal breaker or the main breaker inside the RV. The pedestal breaker is obviously more accessible. You'll often find that the pedestal breakers seem kind of beat up and tired. That's because the get turned on and off a lot.

Never forget that you also have the main breaker in the panel inside the RV for protection. You've always got two breakers in series for overcurrent/overload protection so under normal circumstances you are well protected. As long as you have a 30 amp breaker in your RV panel and have a 30 amp cord and plug, it is safe to plug into anything higher than 30 amps at the pedestal. The 30 amp breaker in the panel is there to protect the cable and there is no way to overload it to the point of being unsafe. Same thing applies in building construction.

Bundling wires or cables together in any situation is not a good idea unless the current rating is reduced. In building wiring, they will be de-rated to 80% or 65% for example.

I think the temperature rating of the power cord is important to recognise. If you have a cord that is listed and carries a rating on the jacket of 60 degrees centigrade, or 140 degrees F, that's not really that high. I heard recently that there is supposed to be a record temperature somewhere in the US this summer of 140 degrees F. Imagine how hot a cord can get inside the confined space of an RV compartment. When you consider the ambient air temp., the effect of direct sunlight on a enclosed compartment and the heat created from the current flowing in the wires, you can see how it would not be hard to exceed the 140 deg. F rating. Do it long and/or often enough and the cord will fail.

You could easily calculate the heat given off by your power cord. All you need to do is measure the current flow. You'll need a clip-on ammeter. Available at Harbor Freight for eg. Then measure the voltage at one end of the cord and the other. The heat given off would be the voltage difference times the current. Whatever that happens to be gets trapped inside a tightly coiled cord because the insulation jacket also traps heat inside and it can't easily escape. A smaller gauge cord, like say a #16 gauge 15 amp one is going to have much higher resistance than a 30 or 50 amp one so if it is tightly coiled is going to heat up more easily even if the current is less.

I think the answer to preventing cord damage is to not use them when coiled up. Especially if in an enclosed compartment, on warm/hot days and when putting a high load through the cords. I would periodically inspect the cables. If you have a choice, get a cord with a higher temp. rating. As I mentioned previously, Marinco and Conntek have different ratings. I think another type of jacket is used on some cables other than STW which may have a higher temp. rating. One thing to watch on jacket type is when it gets colder out, the cord can get pretty stiff. You should be able to see the tech. specs. of your 30 or 50 amp cord throughout the entire length of the exterior.

One major thing that helps to minimize a cord's plug and connector from overheating is simply to turn off the power at the pedestal and shut off before pulling the plug out. That's so easy to do and it should become part of your ritual when setting up and breaking camp.

On the cause of the failure in the photo by the OP, is is really not possible to conclude what the cause of the failure was without being there. I highly suspect though that the reason is that the cord was plugged in all the time when it was live eventually resulting in pitting and resistance high enough to generate localized heat high enough to melt the plug and/or connector enough to cause a short circuit. It may have also reached a point where there was an arcing fault causing even more heat before there was an eventual full short circuit. Using a shorter cord is not a solution. Keeping the plug blades clean will help but you cannot get inside the cord's connector to inspect or clean. In the OPs info., the owner of the MH with the fire had two cords plugged in together in series. Thus there could very have well been a high resistance connection between the 50 &30 amp plug and connector. The overall length of the cords could not have been a contributing factor IMO. If a short occurred at the connection between the two cords, the damage to the 30 amp cord would have been more severe which is exactly what you see in the photo. But did they have the 30 amp cord adapted back to 50 amps at the pedestal? If so, then of course the 30 amp cord could get fried.... If they did that, then that is plain dumb. Therein lies the inherent potential danger of using up and down adapters without knowing or thinking about what you are doing.

To reiterate, it's my opinion that the only cause of overheating and failing cords is due to several possible temperature causes and nothing to do with inductance. I hope this helps.
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Old 07-30-2013, 11:12 AM   #83
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Palehorse89, you are correct - the likelihood of it causing a problem is low especially on 50amp cables - but it's something to be aware of. The example I showed was a 100' cable tightly wound and pulling it's max amps - in other words it was a 'worst case scenario'. The problem is more likely to occur where someone has a 30amp cord that is tightly wound and pulling max load. 50amp cable is so thick it would be hard to wind it that tight.
But if you can figure 8 in the compartment then it's good practice - as is unreeling the cable on a winder.

Steve, about a year ago, I traveled down south in 110 degree heat with the generator running, both house airs, etc. I have 30 amp service/cord. When I got to the park in Bandera, the shore cord plug and the cord itself were very warm, almost HOT. The Cord WAS also coiled. I could not find any reason, other than the extremely high (110+) temperatures and the A/C demand. I checked the blades, checked the outlet, etc. Nothing. Couldn't figure it out.

Now I know, I know that shore cord was at max and being tightly coiled up in that portion of the bay (probably about a 15" coil) is the answer to that question.

Then I plugged into the pedestal, (30 amp) and it popped breakers about 5 minutes later, and continued a second and 3rd time. Called the CG, they came, told me the pedestal outlet plug was damaged and the breaker, so they replaced both of them. The pedestal breakers no longer popped after he replaced the outlet and breaker, but the EMS cut the power off of the coach when it dropped below its threshold minimum (I think 104 or 103 volts). So I put up with that another time or two, then went back out, unplugged from the pedestal, plugged back in to the genny outlet, and fired up the generator, and had no more problems that afternoon. Later in the evening, around 7 or 8, I shut the genny down and plugged back into the park pedestal, and had no issues from then on out. The park power was at its tolerance, and low voltage is a prevalant issue in older parks especially with the 30 amp service in high heat/high A/C usage.

One thing I have done since then and never had an issue so far is I plug into 50 amp service with my 30 to 50 adapter and have not had any low voltage issues in high heat since.....

Anyway, thanks for the info! I am glad to have that question explained....!!
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Old 07-30-2013, 12:43 PM   #84
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On the inductance "theory" - I just don't believe this one. In a 2-wire AC circuit, the current flows in one direction in one wire and in the opposite direction in the other. The magnetic field created by each wire will be in the opposite direction and will be cancelled out. Thus there will be no magnetic field created by a coil of 2-wire cable (or "3-wire" if you include the ground wire). If the wire was a single conductor and coiled up, that would be a different matter, but won't happen with any power circuits in an RV. The 120 volt circuits are always 2-wire. Same thing with a 3-wire 50 amp cable. The magnetic fields cancel out.
All I can do is point you to a Tutorial on AC Inductance and Inductive Reactance HERE

There will be a test when you have read it
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