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Old 10-24-2009, 10:13 PM   #1
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shore power plug melted

Well DH returned with a problem, the shore power plug of the AS melted into the plug of the surge protector using the heat pump presumably.

Previously on a different AS the shore power plug melted into the heavy duty RV extension using the AC at home.

Is this an issue of available current or poor connections or what? Thanks in advance.
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Old 10-24-2009, 10:19 PM   #2
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We've heard of this melting problem while trying to use the AC if one uses a 15 amp adapter on the male end of the 30 amp power cord. The heat pump still uses the AC compressor IIRC.

Same as the air conditioner -- ya need more available amps. The appliance (AC in this case) will try to pull the higher amperage thru an inadequate outlet & adapter.

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.
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Old 10-24-2009, 10:48 PM   #3
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A poor connection at the plug, or within the plug, can cause heat when a draw is applied to the circuit. If there is a big draw, the weakest part of that circuit, perhaps where cords are plugged together, can get very hot.

All electric devices contain smoke. They will quit working if you let the smoke out.
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Old 10-24-2009, 11:42 PM   #4
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I did a quick search. Some links within these threads are useful. Jim, there are even a couple mentions of smoke.

http://www.airforums.com/forums/f37/...ord-42108.html
http://www.airforums.com/forums/f37/...rds-43494.html

Just Jim - nobody else - http://www.airforums.com/forums/f7/s...tml#post145580
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Old 10-24-2009, 11:58 PM   #5
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I willing to bet that's it's the guage of wire used in more cases than not.

Ever notice how heavy the good ones are? That's not by accident. Skinny wire's resistance produces heat. Heat will eventually produce smoke, and in extreme cases, even fire.

Like in most things, you'll never hear anybody complain that the cables they bought were too heavy-duty.

Think of it like plumbing: you want to move a lot of water, you need a fatter pipe.
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Old 10-25-2009, 12:21 AM   #6
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Guage is very important.
When I was a Snap-On dealer we sold a set of very good jumper cables made from heavy welding cable and heavy duty clamps. Some would pass on them because of their hefty, nearly $50.00 price tag, and get the $7.95 junk from some other place.

After all, "I'm not going to use them every day, I only want them for an emergency."

Go figure.
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Old 10-25-2009, 08:19 AM   #7
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Quote:
Originally Posted by wheel interested View Post
Well DH returned with a problem, the shore power plug of the AS melted into the plug of the surge protector using the heat pump presumably.

Previously on a different AS the shore power plug melted into the heavy duty RV extension using the AC at home.

Is this an issue of available current or poor connections or what? Thanks in advance.
Carol,
Could be both. Dirty (not shinny) contact cause resistance which will raise the power (current) draw. Low voltage will raise the power (current) draw.
Too small a wire will raise power draw. Too much use will fray the wires at the end of the wire, this will cause an incrase in power draw. I had this happen and cut off the end of the trailer cable and put on a new 30A plug.
Problem solved.
I have been told by a good AS tech that if you do not twist lock and screw the collar down this can cause the receptical and plug in the AS to fuse together. An expensive fix.

Replace the cable and use 30A extension cables and a 30A outlet. I know you were doing this for you AS but with two do you have two 30A outlets on seperate circuits?
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Old 10-25-2009, 08:52 AM   #8
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The shore power line should be capable of running what ever is in the unit. More than likely there is a poor connection inside the shore power plug so you're not getting the full use of the heavy gage wire. Is the surge protector rated for 30a ?
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Old 10-25-2009, 09:07 AM   #9
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We had a similar problem with Lucy's 30 amp OEM shore power cord earlier this year. In May, we were camped at Quartzsite, Arizona. The daytime temperatures were spiking near 110 degrees. Lucy's air conditioner was running pretty much steadily during the day. Lucy was plugged into a 50 amp outlet using a 30 to 50 pigtail. Lucy's electric service continued to work for a couple of days. As we were braking camp, I noticed that the male end of Lucy's power cord was very hot as was the female end of the 50amp/30amo adapter. They had melted together.

I unplugged from the campground power outlet. The male end of the adapter was not warm at all. I was able to separate the pigtail adapter using a sharp knife. I was able to continue Lucy's long western trip using the same semi-melted power cord without any further problems. When we returned home two months later, I did replace the male end of Lucy's shore power cord. I have also replaced the 50 to 30 adapter.

I have assumed that the problem was with the adapter.

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Old 10-25-2009, 09:37 AM   #10
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Can't say for sure what caused this. A/C full blast. A/S shipped me a new one... hasn't happened since.
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Old 10-25-2009, 10:20 AM   #11
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Besides cleaning the prongs how can we make better connections?

Here is the surge guard and it's rated for 30 amp.

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We have one dedicated 30 amp connection run separate and directly from the main electrical box to the exterior covered garage wall plug at home and we only plug in one AS at a time.

Our extension cord is heavy duty 30 amp cord, same thickness as the shore power cord it looks like to me. We bought it from the AS factory. We have two extensions Michelle. Brad has bought a plastic covered connector box(?) and plugs the AS cord and extension cord into that, at home, since the melting eposode. It seems the plastic in between the rubber plugs makes a better seal or does not allow the rubber ends to melt together.

Brian, Brad will try his Exacto blade to separate the cords. For the time being they are still together. I may also pm you and Michelle about replacing the plug. He wants to replace the entire cord rather than mess with replacement.

All this troubleshooting is invaluable to us. I am appreciating everyone's input.

I wonder if the current going to the makeshift campsite where he seasoned was suspect, yet the Surge Guard would have kicked the electric off, I would have thought, before it would melt. How do you check the connection inside the shore power plug, or does he already know this? I am just the mediator and running between the trailer (it's a beautiful day here in Michigan) and the computer...I know he's got guages or meters.
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Old 10-25-2009, 11:43 AM   #12
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protected, but still warmed up

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.
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Old 10-25-2009, 11:50 AM   #13
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The shore power plug in the picture looks to be molded whi ch means it cannot be checked . It can be cut off and a replacement put on , any RV dealer has them. With a bad connection at the plug I would think there would be a voltage drop between the house and trailer.
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Old 10-25-2009, 12:14 PM   #14
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My A/S came with a somewhat-melted plug. It "appeared" that there was a high current-draw event of some sort that caused this (probably a poor internal connection, but it too was a molded plug that could not be checked) ... I cut it off and replaced it the week I got it, making sure all wires had a good connection. No problems since.

Glad you got your DH back!
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Old 10-25-2009, 02:35 PM   #15
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I think I understand - but?

Quote:
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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