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Old 10-25-2009, 02:35 PM   #15
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I think I understand - but?

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Originally Posted by wmarsha View Post
Okay, look at the electrical system in its totality for a moment. each circuit in the AS is protected by a circuit breaker-if any individual load begins to draw more than the circuit breaker's rating-it will trip. Now, looking at the coach as a whole-it should never exceed 30 amps, right? well, no. If each of the individual circuits in your AS are drawing say 10 amps each, then if you have four circuits, you actually are drawing 40 amps. Now, knowing that is possible, if your umbilical is plugged into a 30 amp breaker, either in your surge protector, or in the circuit from home or rv camp or wherever then that breaker should operate. Now, you didn't say any circuit breaker operated-meaning the current flow through this umbilical never exceeded 30 amps. So what gives? Okay there is a mechanical connection that has begun to fail. that connection is/are the spades of the plug/receptacle. Those spades have introduced a resistance into the circuit and the result (energy usage) of that resistance is heat.

Okay, what is causing the resistance? Well, the physical connecting action of the plug/receptacle is supposed to "clean" the spades when inserted. However, the female receptacle's spring action of its contacts can become weakened over time, not cleaning the male spade's surface area, causing resistance. If the female end is "loose" (no offense intended), then it, too introduces resistance. Once the joint begins to heat, it becomes a heat sink, causing more and more heat until something oxidizes (burns) causing more resistance, and hence more heat.

Cure? keep contacts (male spades) clean, lubricate the receptacle with dielectric compound, insert the male plug straight into the female receptacle with as little side-to-side motion as is possible. Once a male end is heated like the one you have-time to cut it off and wire up a new one. When purchasing a new plug or receptacle, look at the construction of the piece-check out the "robustness" of the copper contacts-compare less expensive ones to more expensive ones-size does matter, here. a larger surface area (within the specifications of the plug/receptacle design) is better. Twist locks are probably better because of the physical twisting action of the contact connection. Plugs with the handle at the back may be better because they allow for straight pull apart action (no side-to-side). Once again, lubricate with dielectric compound.
Great explanation! But what about the Surge Guard? Shouldn't it have cut the power before melting? Or was it possibly malfunctioning.

Carol
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Old 10-25-2009, 02:55 PM   #16
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You don't need to have 30a to melt the plug. You only need a little resistance across a poorly made connection to generate 50 or 100 watts of power. More than enough power to start a fire inside the plug. I think most of the previous posters are right, it's a shoddy internal connection in the plug.
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Old 10-25-2009, 04:24 PM   #17
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surge guard cutting power before melting?

Carol's question is an excellent one. As long as the current flow through the surge guard does not exceed its capacity, then, no it will not cut the power. The "heating" of the mechanical connection looks just like an appliance to the surge guard-the heating is a relatively slow process, so there is no surge; and until the resistance reaches a point where it causes more current to flow than the surge guard will allow-the surge guard is happily doing its job-passing a maximum amount of current and not allowing any voltage spikes (surges). The "bad" mechanical connection looks just like a heater unit to the surge protector.

By the way, as long as we've reached this point let's talk about another interesting possibility: 1)Assume the RV park has 240VAC at 50 amps service for each camping spot. 2) we have the correct adapter to convert this to a 120VAC 30 amp female receptacle so that we can plug our AS umbilical into the RV park's power pedestal. In this scene, the adapter's connections can draw 50 amps of power before operating a breaker. The male end of your umbilical cord, if acting as a resistive fault (bad mechanical connection), can "see" 50 amps of 120VAC causing it to melt and possibly burn right at the connection-it would only pass as much current as your AS asked for (less than 30 amps, usually) but it could use the extra 20+amps right at the connection to cause it to melt into the adapter. So, using a device such as the surge guard when adapting from one type of AC service to another is always a good idea.

Upsizing the umbilical cord can carry the 50 amps further towards the AS, too, so make sure the 50 to 30 amp "adaptation" is outside of the coach-preferably in open air.

In a perfect world, there would be no need for adapters. But...
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Old 10-25-2009, 05:26 PM   #18
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Here's another way to overload things: our trailer has 3 or 4 120 v. breakers—you could have the heat pump, a microwave and a toaster on separate circuits and that would add up to more than 30 amps. If there are 4 circuits, an electric heater can replace the heat pump in the overload situation. And you might be able to do it with two appliances if they each have more than 15 amps. I don't think there is main breaker to prevent that. If the surge protector isn't working, or it only prevents surges and not overamping, melting time has arrived.

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Old 10-25-2009, 05:39 PM   #19
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Gene,

If you don't have a 30a main breaker you should probably add one. You need one if you have more than two circuits.
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Old 10-25-2009, 07:47 PM   #20
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I got down on the floor and actually looked at it. There are 4 20 amp breakers, one a GFCI. One is dedicated to the A/C, the others are branch circuits although one is labeled as a "microwave". It may not go anywhere. There is a 30 amp main breaker. Being used to household wiring, 4 20 amp circuits with a 30 amp main is strange to me although I did know this trailer's limit was 30 amps.

If the main is slow blow, you could use 2 high amp appliances with 17 or 18 amps and it might take a few minutes before the main flipped. I don't think that would be enough to melt anything the first time, but if you do it a lot, maybe so. But don't listen to me—I could have looked before, but didn't want to get on the floor.

Interestingly enough, I'm at the Terraport and hooked up to the 50 amp receptacle because it was the only one available. Maybe I'll see just what I can melt.

I think it wouldn't be too hard to upgrade the breaker panel with heavier wire for a 50 amp main and add a 50 amp plug on the exterior. Maybe two parallel mains, 30 and 50, with a switch, meters, lights, and I better stop coming up with fantasies.

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Old 10-26-2009, 12:51 AM   #21
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It's very common with molded plug heads. Thats the weak link. Just cut it off and replace it, should be fine.

Al
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Old 10-26-2009, 01:10 AM   #22
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Hi, melted connectors and/or plugs are caused by a loose/poor connection. A larger load will just make it happen quicker. An overload with proper connections will trip the circuit breaker, either in your trailer or at the power source. I have been to camp grounds where the plug slips in real easy; This is not good. I have not done this to my trailer and I hope I never have to, but you can bend your contact blades into a slight arch and this will make a tight fit in a loose receptical.
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Old 10-26-2009, 08:32 AM   #23
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I looked at the 50-to-30 adapters. The wire size is small.
When they rate them at 30 amps...that is MAX amp draw
for a short "Duty Cycle". The modern Air Coditioner - by itself -
can strain(heat) the OEM 30 amp cord. Any added adapters
can make it worse because they are often of smaller wire size.
If a person wants to use All of the MAX 30 amps....then it seems
a larger supply cord(one that is capable of >30 amps) continuous
duty would work fine. I suggest an outdoor cable that is sunlight
and water resistant 6/3 with ground the entire distance. It seems
better to "over supply and under-use" than to "under supply and over-use".
These melted cords are evidence of "under supply and over-use".
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Old 03-13-2010, 11:00 PM   #24
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Incineration???

I just had a handyman electrician install a 30 amp and a couple 15 amp outlets in a box outside my barn....making available power to any visiting Airstreamer.....and me when parked out under the trees. BUT, before I go any further with it...even test it...I have a nagging recollection that somewhere here in the Forum...a mention was made about being sure that the electrician knew that this was to be power for an RV...not a residence. 220 volts/240 volts something like that. I know nothing about it and and need to be sure about this....any input out there?
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Old 03-13-2010, 11:21 PM   #25
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Quote:
Originally Posted by CanoeStream View Post
Chuck has found a 20 amp outlet can be used if you aren't trying to run any other high-demand appliances on house current (eg, no microwave, put fridge on propane, etc) -- but most people don't even have 20 amp outlets in their home.
Hi, electrical code for my Lakewood house has 15 amp circuits for all ceiling lamps/porch lamps and wall mounted light switches; All recepticals are 20 amp. I would think that should be national standard, but maybe not. This may be a code upgrade from adding on and running new systems for remodeling our home. Our original wall plugs were two prong/non-grounded.
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Old 03-14-2010, 12:19 PM   #26
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Quote:
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Chuck has found a 20 amp outlet can be used if you aren't trying to run any other high-demand appliances on house current (eg, no microwave, put fridge on propane, etc) -- but most people don't even have 20 amp outlets in their home.
Depends on the age of your house. My house is full of 20A circuits. The addition in the 1990s has 15A outlets.
I added a 30A RV outlet by the street plus a 20A and an temp switched 15A. Total draw for all three is 40A.
I will be installing a 30A RV outlet where I park my trailer in the back yard. Just have to wait for the ground to thaw.

Both of the eletricians I have dealt with in Missoula will only install 12ga wire. Keeps problems to a minimum.
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Old 03-14-2010, 12:29 PM   #27
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this might help
http://www.airforums.com/forums/f37/...ram-25523.html

Quote:
Originally Posted by Melody Ranch View Post
I just had a handyman electrician install a 30 amp and a couple 15 amp outlets in a box outside my barn....making available power to any visiting Airstreamer.....and me when parked out under the trees. BUT, before I go any further with it...even test it...I have a nagging recollection that somewhere here in the Forum...a mention was made about being sure that the electrician knew that this was to be power for an RV...not a residence. 220 volts/240 volts something like that. I know nothing about it and and need to be sure about this....any input out there?
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Old 03-14-2010, 12:31 PM   #28
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Quote:
Originally Posted by Melody Ranch View Post
I just had a handyman electrician install a 30 amp and a couple 15 amp outlets in a box outside my barn....making available power to any visiting Airstreamer.....and me when parked out under the trees. BUT, before I go any further with it...even test it...I have a nagging recollection that somewhere here in the Forum...a mention was made about being sure that the electrician knew that this was to be power for an RV...not a residence. 220 volts/240 volts something like that. I know nothing about it and and need to be sure about this....any input out there?
Find someone who has a multimeter and can test it to see what voltage is on it. Also call the installer and ask him what he did. But, as you mentioned, until you know, don't plug anything into it.

Regards,
Ken
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