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Old 08-02-2013, 01:57 PM   #113
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Originally Posted by Libero
Here is a real zinger - "current flows in one direction in one wire and the oppoisite direction in the other direction" I almost fell off my chair laughing at that one. Really??? What a hoot.
One of the most basic of principles of electricity is that current flows in one direction on a conductor (single wire). Even though AC current ("alternating current") reverses direction on a 60 hertz (cycle) basis, it still flows in one direction at at given instant in time. That's what I was taught in 5 years of engineering school. Even Wikipedia would appear to have this correct: Electric current - Wikipedia, the free encyclopedia Try googling AC current flow and you will find lots of discussions on this subject.

[moderator edit]

It occurred to me after reading a magazine article on an RV fire is that the plug and connector may not have been fully pushed together. It is very important to ensure that a plug and connector or receptacle are fully engaged to minimize contact resistance.
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Old 08-02-2013, 02:21 PM   #114
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Thanks to everyone for all the posts on electrical theory, etc., possible theories on causing this fire.

If you look at the first picture I posted, you can zoom in. It clearly shows (to me at least) that the 30A male plug on the 30-50A adapter is cooked. And no, it's not modified.

My recommendations are made to help other MH owner's out there who hopefully will never find themselves in a similar situation.

1) Use the shortest length of shore cord possible to the power pedestal.

2) Keep the 30-50A adapter outside of your coach. If it does catch on fire, it won't burn your coach.

3) Watch all 30A male connections. They melt and fail. Get a new 30-50A adapter every several years.

Safe Motorhoming.
Thanks Pusherman .... your summary is what folks should pay attention to. In addition, when making connections, the engagement of the pedestal breaker should be the LAST step. This prevents arcing at the receptacle and plug. Arcing will eventually cause a high resistance connection. And, clean all of the male blade connectors on a regular basis.
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Old 08-02-2013, 03:31 PM   #115
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If it's a 30-amp coach, adapting to a 50A power-post receptacle won't result in the coach drawing any more current. At several CG's we've visited, they re-wired a few years back to handle the newer 50A coaches that were appearing on the market. In that upgrade, they took out the old 15A residential sockets and the 30-TT sockets so they just have 50 A pedestals.

I would expect any 30A coach to have a 30A main breaker. Mine does.
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Old 08-02-2013, 04:21 PM   #116
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One of the most basic of principles of electricity is that current flows in one direction on a conductor (single wire). Even though AC current ("alternating current") reverses direction on a 60 hertz (cycle) basis, it still flows in one direction at at given instant in time. That's what I was taught in 5 years of engineering school. Even Wikipedia would appear to have this correct: Electric current - Wikipedia, the free encyclopedia Try googling AC current flow and you will find lots of discussions on this subject.

[moderator edit]

It occurred to me after reading a magazine article on an RV fire is that the plug and connector may not have been fully pushed together. It is very important to ensure that a plug and connector or receptacle are fully engaged to minimize contact resistance.
Redracer:

Not certain why you commented about my post, but I agree, my memory banks need recharging at times but my comment was about a chuckle I had regarding a reference you gave in jest, I think, and I found it amusing, not that I thought you believed it, in fact I believe you said you did not believe it. The Quote below is from your post 07:70 30- 2013:

"in a 2 wire AC circuit, the current flows one direction in one wire and the opposite direction in the other" Your words - really, check it out.

Of course current only flows one way at a time in any circuit AC or DC, impossible to do otherwise. My chuckle related to your statement above referring to the to current in one wire being in one direction and the oppoosite direction on the other in a 2 wire circuit. Obviously in AC circuits current reverses per the frequency of the source voltage and is the same direction in both wires at the same time - it is treated as a closed loop. Who on earth would suggest otherwise. I certainly did not.

Actually I received my MEng in the late 60's, not the 70's, I taught budding engineers in the early 70's and was a practising PEng for many many years, with so many advanced training seminars and courses throught the years I lost count. And some things like basic electricity are difficult to forget, albeit anything is possible. Like I said, if you don't use it you lose it. Heck I was agreeing with you not believing that quoted statement. But many mid 70's brains that were exercised and continue to be exercised may be much better than some younger brains. Sometimes the saying "Wise Old Man" might just be true. Not certain if that applies to me or not, but I am still asked for technical advice in engineering circles, so perhaps I can still contribute in some ways. Experience does count. In fact I suggest I learned more from practical experience than from what I learned in school. Most people do. School just provided me with the basic tool kit. Life was the real teacher. Many very smart people figure things out by themselves without having formal training. I have also come across Engineers that I had to mentor, mostly young inexperienced ones, wherein some had trouble solving real time problems encountered in the field. In most cases the very experienced and well trained technicians had the answer before the guy with the degree got involved. Go figure.

By the way Redracer, the technical stuff in your posts was sound and I thought it fell within the good stuff category. And I also agree that the fault in RV AC plugs is most often caused by a poor connection. If an electrical connection is hot, check it out.

I have been RVing since the 60's, albeit a POPUP in those days, and have seen many RVers with AC issues. Putting the connection inside the RV as noted in the OP was not a wise thing to do, this was the message, watch how you connect the external power and keep cords and plugs in good condition.

No problem with your comments, I like to keep my mind stimulated, I need it more and more these days.

A bit of technical savvy and a huge amount of common sense really goes a long way to solve but more important avoid RV problems.
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Old 08-02-2013, 04:33 PM   #117
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If it's a 30-amp coach, adapting to a 50A power-post receptacle won't result in the coach drawing any more current.
If something goes wrong then it can certainly pull more than 30 amps and that's the point of a sizeable part of this thread. Under failure conditions, the 30amp components from the failed breaker in the coach to the pedestal are not adequately protected (30amp compnents connected to a 50amp breaker).
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Old 08-02-2013, 05:31 PM   #118
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For those of you that think that a 30-amp motor home is not sufficiently protected when connected to a 50-amp circuit, consider this:

Most household outlet circuits are 15 or 20 amps. Most items plugged into those circuits consume much less and are wired accordingly. If I plug a radio that draws an amp and used #18 gauge zip cord, is the circuit legal and adequately protected?

If it is, why is that different than a 30 amp motor home plugged into a 50 amp circuit? For me the only takeaway from this discussion is to not leave cords coiled up.
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Old 08-02-2013, 05:47 PM   #119
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For those of you that think that a 30-amp motor home is not sufficiently protected when connected to a 50-amp circuit, consider this:

Most household outlet circuits are 15 or 20 amps. Most items plugged into those circuits consume much less and are wired accordingly. If I plug a radio that draws an amp and used #18 gauge zip cord, is the circuit legal and adequately protected?

If it is, why is that different than a 30 amp motor home plugged into a 50 amp circuit? For me the only takeaway from this discussion is to not leave cords coiled up.
To take this analogy a step further, suppose something in that radio goes wrong, and all of a sudden it starts drawing 20A, what happens to the zip cord? Wouldn't it be a safer situation if there were a 1A breaker at the radio's service entrance? This is exactly the situation with RVs.

I think this is the point that is being made: In the (unlikely) event that the RV's main breaker is bad, AND there is greater demand by the coach systems then the service entrance cable can safely carry, the service entrance cable is at risk of overload and failure.

In the case of the OP, I suspect a bad dogbone caused the failure. Not coiled cables, not demand in excess of capacity, not bad breakers.

My takeaway from this thread is to locate the most likely points of failure (adapters, extensions, etc) as far from the coach as possible.
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Old 08-02-2013, 06:44 PM   #120
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I think the part that that statement is ignoring is: ok we plug a 30 amp plug into a 30 amp breaker. In your RV a 15 amp breaker hangs...... you are plugged in to 30 amps correct? At that point you are not protecting that wire due to the fact that is is wired for 15 amps and you have the capability of 2x the current. They do go bad, I have seen it, it was 1 on hundreds of breakers after 22 years.
How many check their breaker panel each year, besides their plugs? Loose wires,loose breakers. Check preventive maintenance for any equipment that shakes or vibrates and you will find that checking electric connections is on the list. Loose connections at those points will also cause a higher current draw at your plugs.
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Old 08-02-2013, 07:23 PM   #121
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To take this analogy a step further, suppose something in that radio goes wrong, and all of a sudden it starts drawing 20A, what happens to the zip cord? Wouldn't it be a safer situation if there were a 1A breaker at the radio's service entrance? This is exactly the situation with RVs.

I think this is the point that is being made: In the (unlikely) event that the RV's main breaker is bad, AND there is greater demand by the coach systems then the service entrance cable can safely carry, the service entrance cable is at risk of overload and failure.

In the case of the OP, I suspect a bad dogbone caused the failure. Not coiled cables, not demand in excess of capacity, not bad breakers.

My takeaway from this thread is to locate the most likely points of failure (adapters, extensions, etc) as far from the coach as possible.
I'm rather ignorant about electrical theory, so I have a question. Isn't a house with a 200A panel wired to the much higher amperage capacity utility service line also in danger? I think your house and mine, well-everyone's is wired that way. Would that not be the same as mrschwartz' scenario?
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Old 08-02-2013, 08:33 PM   #122
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I'm rather ignorant about electrical theory, so I have a question. Isn't a house with a 200A panel wired to the much higher amperage capacity utility service line also in danger? I think your house and mine, well-everyone's is wired that way. Would that not be the same as mrschwartz' scenario?
It's exactly the same, to my understanding. The service entrance cable that connects your home panel to the utility service is at risk of overload if your main breaker is faulty AND you demand more than 200A in your house, AND there is no other protection farther upstream (like oversized service entrance cable, for instance).

I'm interested to know from one of our licensed electricians if this is on target.
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Old 08-02-2013, 10:09 PM   #123
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I'm rather ignorant about electrical theory, so I have a question. Isn't a house with a 200A panel wired to the much higher amperage capacity utility service line also in danger? I think your house and mine, well-everyone's is wired that way. Would that not be the same as mrschwartz' scenario?
I could be wrong but I believe there are fuses on the transformer that feeds power to the house.
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Old 08-02-2013, 10:17 PM   #124
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Actually I think I am the one that is guilty of muddying the water...

I am confusing the code for permanent wiring installation with the extension cable analogy which I guess is what an RV could be considered as using - I mean it would be better to use the correct connections if possible but as it is a temporary installation it is probably accepted practice.
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Old 08-03-2013, 06:25 AM   #125
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Here is a thought. There is only one wire used in any circuit. One portion of the wire is connected to the power source and the "hot" side of the load. The other portion is connected to "neutral" side of the load and finds its way to ground by design, the same ground as the source (hot) uses. One wire per circuit. Load in the path.

Water flows down hill. The sun and wind pick it up and dump it back up to the pond to start the process all over again. Not much different in principle than electrical current flow.

Too much of a good thing makes for failure. Controlled heat is a good thing. Uncontrolled, no matter the source, it can cause man many problems. RV fires for instance.
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Old 08-03-2013, 10:15 AM   #126
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Here is a thought. There is only one wire used in any circuit. One portion of the wire is connected to the power source and the "hot" side of the load. The other portion is connected to "neutral" side of the load and finds its way to ground by design, the same ground as the source (hot) uses. One wire per circuit. Load in the path.

Water flows down hill. The sun and wind pick it up and dump it back up to the pond to start the process all over again. Not much different in principle than electrical current flow.

Too much of a good thing makes for failure. Controlled heat is a good thing. Uncontrolled, no matter the source, it can cause man many problems. RV fires for instance.
So if I cut the Neutral wire in my RV's shore power cord, everything will work O.K. since: "There is only one wire used in any circuit. One portion of the wire is connected to the power source and the "hot" side of the load. The other portion is connected to "neutral" side of the load and finds its way to ground by design, the same ground as the source (hot) uses. One wire per circuit. Load in the path."

WRONG!!! If that were true GFI protectors wouldn't work since they detect the balance of current in the hot and neutral wires, and trip when there is an imbalance (current leaking to ground - assumed to be through a human body). You COULD make stuff work the way you describe, but it is a violation of electrical code. The ground wiring is an "Electrical Safety Ground" and not intended to routinely carry load current. It is designed to carry load current when there is a hot-ground short, and trip the circuit breaker protection to shut off the current.
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