Plugged into 50-amp & systems started frying

[AdvToaster]

If you look at the diagram below you’ll see how your trailer power is run. If the neutral is cut off then the path goes from a hit across your appliances ok one leg, through the neutral (in your trailer) to the appliances on the other leg and then through the other hot. This gives everything hooked up 240v. That would explain what happened.



The second small diagram shows what voltages should be read from different readings on the power pedestal. If they don’t match up then the pedestal is wired wrong. If they do match up then the issue is in your cable, the surge protector, or the wiring inside your trailer.

[BayouBiker]

Originally Posted by Mollysdad

I'm having trouble picturing it as you describe. I'm not a master electrician, but I am a master debater.
You're saying that every 50 amp trailer that for some reason loses the neutral is now sending 220 v from the pedestal to every 120 v. circuit?
There is another option, where there is no current flowing without a neutral.
Nowhere in the trailer is a circuit with both hots as a circuit.

I think Mike hit this one out of the park! Let me add some more detail to Mikes explanation.

With no neutral, and no bonded ground the only path back is the alternate hot lead as described. Here is the scenario: On one leg is the converter with continuity from Line1 through its transformer and electronics to trailer neutral but on the other leg nothing is currently connected so no continuity from neutral to Line2 and the converter remains off. Now you don't know neutral has no continuity back at the pedestal and you connect an appliance like turn on the water heater. Now you have a total of 220 V from L1 through the converter transformer to neutral then from neutral through the water heater element and control board to L2. The voltages, loads and impeadance are imbalanced and the water heater controller and element starts to fry. The converter spikes the DC bus and the Zip Dee board fries. The fantastic fan is also sensitive to voltage spikes so you may want to check it too. Plugging in the portable heater repeated the process described.

Edit: nice schematic you beat me to the explanation.

[JayOhBee]

Based on the above responses, it sounds like you lost neutral. It looks like your TT is a 2019, so this is not likely the source of your problem but I'll mention it anyway. On my 2012, the female end of the 50A power cord was compromised due to the way it hangs off the side of the AS. One of the hot lead wires had come out of its terminal leaving me with power in 1/2 the trailer. The neutral was also loose, so... fire waiting to happen.

[Mollysdad]

Originally Posted by BayouBiker

With no neutral, and no bonded ground the only path back is the alternate hot lead as described.

Why does there have to be a path back? I'm looking at an outlet with nothing plugged in. There's no path back, therefore, no current flows.

It seems to me, you're starting with an outcome and forcing a scenario where it makes sense. Let's say I disconnect the neutral at a pedestal. What do I have as far as current flowing? None. Did everything suddenly become 220? No everything is dead.
Show me in the AC breaker panel in the Airstream how that other leg suddenly jumps across to the opposite buss?

[AdvToaster]

Originally Posted by Mollysdad

Why does there have to be a path back? I'm looking at an outlet with nothing plugged in. There's no path back, therefore, no current flows.

It seems to me, you're starting with an outcome and forcing a scenario where it makes sense. Let's say I disconnect the neutral at a pedestal. What do I have as far as current flowing? None. Did everything suddenly become 220? No everything is dead.
Show me in the AC breaker panel in the Airstream how that other leg suddenly jumps across to the opposite buss?

If there are any devices connected (converter, AC units, fridge, microwave, water heater, etc.) they become that connection. If you unplugged and disconnected every AC device then you’re correct, there wouldn’t be any path to create the 240v.

[BayouBiker]

Originally Posted by Mollysdad

Why does there have to be a path back? I'm looking at an outlet with nothing plugged in. There's no path back, therefore, no current flows.

It seems to me, you're starting with an outcome and forcing a scenario where it makes sense. Let's say I disconnect the neutral at a pedestal. What do I have as far as current flowing? None. Did everything suddenly become 220? No everything is dead.
Show me in the AC breaker panel in the Airstream how that other leg suddenly jumps across to the opposite buss?

Elaborating further to AdvToaster's response, if you had nothing connected and you disconnected neutral, both before and after there would be no current flow. If you had something connected to the L1 branch only and you disconnected neutral, there would be no path back, current would stop flowing and the connected appliance would stop. But if you had something connected to each L1 and L2 and you disconnected neutral at the pedestal, then the appliances acting as if they were wired in series as the diagram shows would now in combination see 220 V. If the appliances had balanced impedance and were thus drawing the same current with the same phase shift, both would continue to function without any significant issue. Since in practice most appliances are very different, the one drawing less current would experience higher voltage until it was forced to draw the same current as the larger appliance. The smaller aplliance would thus fry.

[stevejones]

Originally Posted by map372

I have a Progressive Industries 50-amp surge protector and via this plugged my 50-amp cable to the Airstream. I went inside ...

Sorry this happened and hope you can debug your power problem.

What I do at a new site is plug in my Progressive Industries EMS, but not the trailer power cable, then flip the breaker. I let the EMS cycle through its data display to check the voltages and to make sure it says E0. If the voltages are ok and it says E0 then I flip the breaker off, plug in the power cable, and hook up the trailer. Then flip the breaker on again. I only hook up to the trailer if I get an E0 and the voltages are OK.

If I get something other than an E0 then I ask to move to another site.

At one site I had both 50 and 30 amp hookups. When I hooked up the EMS to the 50A I got an error message on the EMS and the data display reported that one side of the power was 120V and the other leg was like 90V or something. Way under voltage. I tried the 30A outlet with a dogbone and got an E0 with good voltage so I ran with 30A.

Steve

[gator.bigfoot]

See attached for explanation. Remember in a split phase system the 2 phases are 180 degrees out of phase. If neutral connected and it is a balanced system the neutral conductor will carry 0 amps. As soon as it is imbalanced it will will start to carry the sum of the loads that are imbalanced. So with a 50 amps system if only one side is connected the neutral can only carry up to 50 amps. Once you start to draw power from both phases then the current on the neutral will decrease (see Kirchoffs law) https://electrical-engineering-porta...irchhoffs-laws

[lsbrodsky]

From my own experience, about 10 years ago I had an open neutral at the pole at my house. I was sitting at my kitchen table, ceiling fan on, and recognized the symptoms. I ran to the breaker boxes to trip the main breakers. Everything electronic that was on and not on a surge protector fried. The refrigerator thermal cutout protected it. No other major appliances were energized. Blew some light bulbs; they do not like 240v. Oh, the utility paid for everything as, in a longer story, it was their fault.

Larry

[richard5933]

I wonder if something simple like a burned or damaged shore power cord plug could cause this. I've seen some cord plugs with pretty messed up prongs - some so dirty or arced that they would not make a good connection. I've also experienced the prongs on a power cord moving in or out, especially if the cord ever got too hot or was pulled on too hard.

What I'm thinking here is that if the prongs for L1 & L2 make contact before the neutral & ground when plugging into a hot outlet, it's possible for 240v to momentarily flow across them before the neutral and ground make contact.

If the neutral prong and/or ground prong is damaged, it may not ever make a good electrical connection, potentially sending more than 120v on one of the legs.

[Al and Missy]

Originally Posted by richard5933

I wonder if something simple like a burned or damaged shore power cord plug could cause this. I've seen some cord plugs with pretty messed up prongs - some so dirty or arced that they would not make a good connection. I've also experienced the prongs on a power cord moving in or out, especially if the cord ever got too hot or was pulled on too hard.

What I'm thinking here is that if the prongs for L1 & L2 make contact before the neutral & ground when plugging into a hot outlet, it's possible for 240v to momentarily flow across them before the neutral and ground make contact.

If the neutral prong and/or ground prong is damaged, it may not ever make a good electrical connection, potentially sending more than 120v on one of the legs.

You are correct. This is a very good reason why if one is investing in an EMS an internal system would be preferred. One would be assured that the power would be good past all the potential trouble points.

[gator.bigfoot]

This sort of condition (lost neutral) is only an issue with 50 amp units. And then only if your not using a dog bone connecter. If you're concerned with the dangers of plugging in and out then install a disconnect inline with your cord. Or disconnect the main power at the pedestal and if that's not an feasible then your main AC disconnect in the RV. It is a bad idea to plug in and out with any load attached (even if your on 30 amps). You will always get an ARC. That's why over here in the UK they have switches attached to every outlet. I kind of like this idea. Too bad this sort of design is not offered across the pond. But in reality if your concerned then take matters into your own hands. Measure before you plug in and install a disconnect. Not sure if they offer a nice compact AC disconnect that is IP67 rated. All I could find quickly is this:
https://www.alliedelec.com/product/r...6223/70822687/

But none of this will resolve a lost neutral if the condition is on the utility side of things. You can protect things on your end, but on the utility end it's out of your control. I suppose you could design a circuit to drop the entire feed if you lose your neutral, but there would a at least a 250 ms delay by the time you drop a contactor. It could be as simple as running a contactor between hot and neutral to energize the feed. If the neutral is lost the contactor would trip and de-energize the feed. You could go a step further and put in a sealing circuit to only seal in the contactor with the press of a button.

[uncle_bob]

Originally Posted by Mollysdad

Why does there have to be a path back? I'm looking at an outlet with nothing plugged in. There's no path back, therefore, no current flows.

It seems to me, you're starting with an outcome and forcing a scenario where it makes sense. Let's say I disconnect the neutral at a pedestal. What do I have as far as current flowing? None. Did everything suddenly become 220? No everything is dead.
Show me in the AC breaker panel in the Airstream how that other leg suddenly jumps across to the opposite buss?

Hi

Ok, with no neutral on a 240V plug, you have a *very* normal 240V connection. Indeed no current flows to the neutral (it's not there anymore). All the current flows between the two 240V "hot" leads. Why are they *both* hot? They each are 120V to ground. It's not like a 120V circuit where one is a zero volts and the other is at 120V.

A "normal" 240V plug is often how your dryer (or other large appliances) get hooked up. It's a three prong plug with two hots and a safety ground. It's the sort of plug you very much do *not* want to hook your AS up to.

What happens in this case is that the loads try to "balance out" the voltage. If you have exactly the same loads on both sides, you still would have 120V on each set of loads. Since this never happens, instead you get a lot of voltage on the *smaller* load side and not much voltage on the *larger* load side.

When you put all the voltage on the smallest load you get snap crackle pop in whatever device that happens to be. It's running way over voltage and usually isn't very happy doing so. (yes, some things are OK with 240V on the 120V input. That's not true of what gets hard wired into an AS).

Yes there's more to it than just load power. This is AC and power factor (angle between the current and voltage) gets into the act. Yes, that's getting complicated, welcome to electricity ..... (and some non trivial part of what you learn when you get an EE degree).

Bob

[AdvToaster]

Originally Posted by gator.bigfoot

This sort of condition (lost neutral) is only an issue with 50 amp units. And then only if your not using a dog bone connecter. If you're concerned with the dangers of plugging in and out then install a disconnect inline with your cord. Or disconnect the main power at the pedestal and if that's not an feasible then your main AC disconnect in the RV. It is a bad idea to plug in and out with any load attached (even if your on 30 amps). You will always get an ARC. That's why over here in the UK they have switches attached to every outlet. I kind of like this idea. Too bad this sort of design is not offered across the pond. But in reality if your concerned then take matters into your own hands. Measure before you plug in and install a disconnect. Not sure if they offer a nice compact AC disconnect that is IP67 rated. All I could find quickly is this:
https://www.alliedelec.com/product/r...6223/70822687/

But none of this will resolve a lost neutral if the condition is on the utility side of things. You can protect things on your end, but on the utility end it's out of your control. I suppose you could design a circuit to drop the entire feed if you lose your neutral, but there would a at least a 250 ms delay by the time you drop a contactor. It could be as simple as running a contactor between hot and neutral to energize the feed. If the neutral is lost the contactor would trip and de-energize the feed. You could go a step further and put in a sealing circuit to only seal in the contactor with the press of a button.

Power pedestals (at least every one I’ve seen) always have a breaker on them. You should never plug or unplug the RV power cable without shutting the breaker off. You could also (if you were worried) shut off the feed breakers inside the trailer.

As far as dropping power if there’s a lost neutral, that’s exactly what the Progressive hardwire EMS does. When you apply power it tests everything before connecting the contractors. If it detects any wire faults or over or under voltage it won’t connect and the trailer never sees power. If it detects a fault while already running it will drop the power.

Someone else above commented on the possibility of the shore power cable or its prongs being damaged. This is actually pretty common. If a power pedestal is wired up so both hits are actually attached to the same line then you can easily over power the neutral (you could pull up to 100A across a wire and contact designed for 50). This can cause the wire or contact to burn up. If that happens then the next time you plug that cable into a correctly wired socket you might have an open neutral.

Situations like the above are reasons why you should always look closely at a power socket before plugging in. If there are any scorch marks or damage then don’t plug in until you’ve verified that it’s wired properly!

[map372]

Thanks for all the replies, below is an update:

After speaking with several Airstream technicians the consensus is that I fried the converter and it will definitely need a replacement. Luckily, we were able to test everything else with a safe 120V connection and I did not fry anything else except for maybe the refrigerator circuit board since I can’t get that to operate on 120V only on propane (water heater, furnace, TVs, microwave, ACs are okay).

Oddly, now when I turn on the furnace the heat pump on the zone 2 AC unit kicks on too, I’ve had to turn off the breaker for now. The awning is also still dead, which based on looking into circuit replacement parts (yep, the green lights) looks like it may end up being the most expensive repair if it doesn’t resolve with a new converter. I wish the awning were manual, I’ve had several other problems with that, it just seems overly complicated and problematic.

I worked with the park engineers and we tested everything starting at the pedestal then through the SP then the 50-amp cable, it was 118V for the first two components and only 107V coming out of the cable. It seems like the cable is probably damaged and I’m not surprised now that I think about it. I’ve been storing the cable tightly wrapped into the storage in the back bumper meaning there are many very tight bends in the cable, this can’t be good for it, I would not be surprised if there is a short or broken wire or some problem with the cable. The park had a spare 50-amp cable and we tested that one and it was 118V out of the cable, I did all the subsequent testing with that cable with no problems. I will definitely not be storing a new cable in that back bumper! One of the Airstream technicians also believes it was the cable.

I’m full time in this AS and so now the only challenge I’m facing until I get this repaired is that the AC & DC systems cannot talk to each other so I’m completely dependent on the solar panels to keep my battery charged to run all the DC since the AC connection will not charge the batteries without the converter. I went to an auto parts store and bought a car battery charger and will use that from the pedestal if necessary.

[BayouBiker]

The zip dee does not depend on the converter, it just needs 12-14.6 volts from the battery. I suspect your suspicions are correct. Glad to hear only the refrigerator and converter (makes sense as they are on opposing circuits) and zip dee are bad. Good luck and let's hope you don't have a repeat.

[guskmg]

In my case the converter must have gotten to 220c and doubled the 12v output momentarily. Some of my DC stuff like the water pump was toasted. My converter and GFIC breaker were burned up and had to be replaced. My insurance Company paid for the damage.
guskmg

[uncle_bob]

Originally Posted by map372

.... I’ve been storing the cable tightly wrapped into the storage in the back bumper meaning there are many very tight bends in the cable, this can’t be good for it, I would not be surprised if there is a short or broken wire or some problem with the cable. ......

Hi

The bends aren't the only issue in the back bumper. That spot gets a *lot* of road dirt blown up into it. Dirt / salt /grime /crud / water is a combo pretty much guaranteed to damage things like connectors.

===========

That said, you *should* be able to work out what went wrong. This isn't rocket science. The point that things broke at likely had some significant arcing and heat associated with it. You should be able to *smell* it If it was the cable, there should be a *lot* of evidence at the point of failure.

Not real surprised about the converter going. That's what the same issue did to me back a couple of years ago ...

Bob

[Jtom]

I had a very similar issue with my 2019 Flying Cloud...I guess I was lucky, just lost the microwave. We were using a PI EMS_PT50X....i could only run one AC unit with it or it would throw the breaker.....got back from our 2 month trip and took it in to our AS dealer....they plugged in the trailer without the PI EMS and everything worked fine....they plugged in with the PI EMS 50 and the microwave blew the microwave. I called PI and they are sending a new EMS PT50X....but now I’m afraid to use their product, after reading your post. I’m sending them back the old one to have it tested to determine exactly what the issue is. Good luck

[ITSNO60]

The majority of failed plug and cord connections happen at the ends, usually the plug end from the repeated movement over time. Even the molded plugs ends deteriorate over time as the fine strands break one at a time till the connection becomes so poor it overheats and finishes the connection off.
Open neutrals on a 240/120 system spell disaster, you no longer have any LINE TO NEUTRAL loads, they all become LINE TO LINE loads in a SERIES circuit and each load will see different current amounts relative to it's resistance. The sensitive loads that see more than 120 volts will suffer.
I have seen two major house fires caused by open neutrals. The TV set will commonly catch fire in this situation. Often the fire investigators don't understand how this works and they will cite the cause as "faulty wiring" or "faulty appliance".