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50 amp electrical issue.


TXiceman

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I have a strange issue going on with the power. I have a 50 amp RV with a Progressive Industries EMS and also a Hughes Auto Transformer when needed.

 

As long as the campground does not have many campers (this is on the 30 amp loop, but we have "50 amp" service), we do OK to a point and I have to use the Auto Transformer so that we can run the heat pumps or A/C. We are southwest of Houston, so we get really mixed weather.

 

Now the problem. Without the Auto Transformer, L1 will drop voltage as low as 104 volts which shuts down the EMS. When L1 leg goes low, L2 goes high to about 127 volts with no or a very small load on L2. The EMS drops the trailer off line with L1 low voltage.

 

If I put the Auto Transformer on line, L1 will drop with a 20 amp load and it will boost the voltage on L1 to keep the voltage up. Then L2 will go high and the EMS will take the trailer off line on high voltage on L2.

 

With no or 3 or 4 amp load, both legs will read 121 volts. Add some load and the voltage drops like a rock. I had the park check the pedestal and everything is OK there. I checked all of the connections in the RV and all is tight.

 

The park flooded twice last year and the electrical was under water for 2 or 3 weeks. They closed the park and pulled the guts in all of the panels and replaced them after the water went down.

 

I am at a loss to solve the problem and the park is no help. We are hosting here until the end of March but maybe forced to leave early if they can not get us dependable power. The trailer has a 22 cubic foot residential refrigerator, washer drier, dishwasher and two heat pumps. All appliances are pulling normal amps when at voltage.

 

Any ideas to pass along would be appreciated.

 

Ken

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When you say all appliances are pulling normal amps, how many amps is that. If you are on a 30 amp loop in the campground, you only have 30 amps available for L1 and L2 in your 50 amp rig (not 30 + 30, but 30 total). Running heat pumps, a refrigerator, entertainment center, battery charger/converter and maybe some other miscellaneous 110v loads, I would say you are at or near your total available 30 amps. As you try to draw high amps across a 30 amp circuit, the voltage will begin to drop causing your EMS to kick in and cut power.

 

What type of battery charger do you have in your coach. Is it an inverter/charger or a standard converter. If it is an inverter/charger like a Magnum 2012/2812/3012 the charger side is between 100 amp and 150 amp and can draw a lot of power while charging the batteries. These type of chargers can be manually set to use less power when you are on a limited power supply like a 30 amp pedestal. When running the heat pumps, turn off or down all other non essential loads and see if the problem continues. Try with just one heat pump instead of two, etc. There is only so much power available on a 30 amp circuit.

 

Even your autoformer can't make something out of nothing and it in fact could be exacerbating the problem. As the voltage drops, the autoformer will pull higher amps and convert that to voltage to try to keep the voltage up - again using up your precious 30 amp supply.

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What you are describing is a loose or broken neutral cable or connection. With you connected to a 30 amp service, you are only working with one hot leg, so this condition which is referred to as a high-low condition in the electric utility business, is most likely on your side of the pedestal, where you are working with two hot legs, even though they are coming from the same hot leg in the pedestal. You have a bad neutral cable, or a bad or loose neutral connection. When you apply load to one hot leg, that leg will drop voltage and the other leg will rise in voltage. If you reverse the load to the other leg, the reverse will happen. Your hot legs are OK, but your neutral is open somewhere. It could also be in the 50 amp to 30 amp adapter.

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Chad, the two host sites are supposed to be 50 amps, but I suspect they have 30 amp wiring pulled from the distribution panel. The panel has a typical 50 amp double breaker. The site is supposed to be directly from the distribution panel. I am not using any adapters and the only plug in the pedestal is a 50 amp, 4 pin plug.

 

The Progressive Ind EMS is supposed to check for neutral and ground issues. But if it is a weak neutral, it may be OK until you apply much load.

 

The invert/ charger is a Magnum 2800 Watt and I have it set on a reduced charge rate. The solar panels keep the batteries topped off.

 

What is so confusing is the fact that the L1 leg drops in voltage with a load and the voltage on the L2 leg goes up with no load or a load load on it. The lower the voltage drops on L1, the higher the voltage on L2.

 

The running amps on the AC/heat pumps are with in the ratings on the units.

 

I am beginning to think they have a neutral problem on the wiring to the site. Right now we are operating on one heat pump and minimizing any other loads.

 

Ken

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Anytime I hear "the RV park checked the pedestal and all was fine" red flags rise to the top lol. That's because if ??????? all they do is measure the unloaded voltage that doesn't tell the full story. What yields additional information is if you placed an actual load on the pedestal and checked the voltage under load !!!!!!!!!!!! If there happens to be a loose or burned or resistive connection ITS ONLY WHEN CURRENT FLOWS YOU GET THE V = I X R VOLTAGE DROP. Also as far as loaded or unloaded voltage measurements are concerned, if you're measuring Line to Line Neutral isn't in the equation but either L1 or L 2 to Neutral of course it is.

 

When we had problems at our Naval industrial complex it was often caused by a loose or burned or resistive connection be it in the Line or Neutral.

 

Of course a 30 amp "loop" (whatever that means) only supplies one leg L1 or L2 but I'm sure you're well aware of all those issues. I cant say from here if you have a full true 50 amp RV 120/240 service which has both legs available or not??? Is there 240 from L1 to L2 ???

 

Just too many unknowns to tell the problem sitting here.

 

John T Long retired power distribution design engineer and rusty so no warrant on anything above lol

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You have a bad neutral cable, or a bad or loose neutral connection. When you apply load to one hot leg, that leg will drop voltage and the other leg will rise in voltage. If you reverse the load to the other leg, the reverse will happen. Your hot legs are OK, but your neutral is open somewhere. It could also be in the 50 amp to 30 amp adapter.

This is it. Classic description of what happens when there is a bad neutral on that circuit.
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If the pedestal was wired by a licensed electrician, it is pretty safe to say that it has proper power supply wiring. Since we know that the park was flooded, it is quite possible that there are connection problems in the existing circuitry, but that could be difficult to pin down. A good friend of ours recently experienced a situation where one leg would drop in voltage but the other held up just as it should. Eventually the house electrician found that there was a bad connection between the problem leg and the buss bar of the distribution panel. This sort of problem will impact one leg with the other acting normally.

What is so confusing is the fact that the L1 leg drops in voltage with a load and the voltage on the L2 leg goes up with no load or a load load on it. The lower the voltage drops on L1, the higher the voltage on L2.

This symptom is exactly what is meant by the term "floating ground." In a 50a system if the loads are exactly matched with the identical load (current draw or amps) on each leg, there is no current flow through the neutral wire. If you were to open, or remove the neutral wire and then apply a load to only one leg, the entire voltage between the two legs, 240V, would then be applied to the load on that one leg. With a "floating ground" the neutral leg is there but it has some unintended extra resistance in that leg. The result is that when one leg has a load that is higher than the other, that resistance in the neutral leg will in effect move that neutral leg from centered between the two legs and cause an unequal application of the total voltage. The result is that the total voltage between the two legs is still 240V but it no longer applies 120V of that to each leg, but rather splits it unequally, depending upon the load on each leg.

 

This happens because your power actually comes from a transformer that has 240V across the secondary winding with L1 attached at one end and L2 attached to the other. The neutral wire then connects to the center between the two, which gives each one half of that 240V, as long as the neutral remains where it should be, or if each leg has the exact same load. The resistance in the neutral lead has the effect of moving the neutral leg away from the leg with high voltage and toward the one with low voltage. For that reason we call it a floating ground. Just how much voltage each leg actually sees in this situation is dependent upon the ratio of loading between the two legs.

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TXiceman, on 10 Feb 2017 - 12:45 PM, said:

 

 

 

Thanks for the replies. Pretty much as I suspected on the neutral problem. Now to get the park maintenance folks to open up the distribution panel and check connections there.

 

Ken

 

You could always use this as a good excuse to trade. :ph34r:

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TX, as most suspected a loose/resistive connection may well be the problem HOWEVER as I alluded to before a simple UNLOADED voltage check doesn't fully address a potential problem. Also sometimes a visual inspection alone may not indicate a loose connection. Often there are signs of burning heat and carbon but I have seen some connections that appeared fine but still were loose and resistive. At our facility I instructed our electricians to insure proper torque at connections as part of routine maintenance.

 

Unlike some smaller generators were talking about having a BONDED versus a FLOATING Neutral in this situation. Neutral Ground BONDING is NOT the same thing as Earth Grounding of the Neutral for lightning and surge suppression and keeping the grid at a common low voltage reference. WE always earth grounded the Neutrals at the service transformers and again at the customer's service entrance (weatherhead drop or meter base or main panel) and BONDED the Neutral Buss to the Equipment Ground Buss in the Main distribution panel (but NEVER at downstream sub panels). You often see Grounding and Bonding confused INCLUDING BY ME AS IM TOO LONG RETIRED AND RUSTY AT POWER DISTRIBUTION GRRRRRRRRRRRR. A problem is if the Neutral was completely open there would be ZERO VOLTS from L1 or L2 to a wire that wasn't (due to open connection) connected to anything. Of course, you would get 240 volts from L1 to L2 with no Neutral even connected.

 

HOWEVER if there was a loose resistive connection (NOT total open) in any of the line or neutral connections yet no load was applied (RV owner sticks a meter on the pedestal and says all is well lol) you would still read full voltage from line to Neutral. BUT if you apply a load and current flows through that loose/resistive connection you get an I X R Voltage drop so while you may have 120 volts at the source you only drop 110 across your load and 10 across the loose resistive connection.

 

I would start checking and tightening ALL connections at the pedestal then apply 120 volt loads on each leg and see what happens??? If alls NOT well there move back to the parks distribution panel and do the same thing as the loose/resistive connection may be other then the pedestal. When I observed good 240 volts under load but imbalances in the 120 I checked and tightened all connections of course, but most important and suspect were the Neutral connections.......OPEN OR LOOSE/RESISTIVE Neutrals are NOT a good thing

 

Best wishes let us know if and where a loose connection appears????????/

 

John T Too long retired EE and rusty so no warranty and this may be total wrong as rain grrrrrrrrrrrrrrrrrrr

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It could also be in your rv.

I don't see how that could be true because the Auto Transformer & the EMS should both be between the RV distribution box and the park power pedestal. Even if both are installed internal to the RV, the only thing belonging to the RV that could cause this would be the RV power cord.

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The PI EMS is mounted internally. The Auto Transformer is connected at the pedestal. The pedestal has been checked and all connections are tight. I have checked and made sure all trailer connections are tight. So the problem is external to the trailer.

 

As with all state parks, they are operating on limited funding and limited staff. I am fully capable of opening the distribution panel, but as a host, we are not allowed to perform such work. So I have to wait until they can get around to looking to the external sources.

 

In the mean time we are watching what we operate and what the electrical load is.

 

Ken

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An Autotransformer with it's single winding won't isolate current flow from a defective neutral. For that you need a full transformer with the primary connected for 240 volts input (from the two hot legs) and the secondary connected to provide 240 volts or 120 volts from each hot leg to the transformer's center tap.

 

At that point the park's neutral becomes a non-current carrying ground reference.

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The PI EMS is mounted internally. The Auto Transformer is connected at the pedestal. The pedestal has been checked and all connections are tight. I have checked and made sure all trailer connections are tight. So the problem is external to the trailer.

 

As with all state parks, they are operating on limited funding and limited staff. I am fully capable of opening the distribution panel, but as a host, we are not allowed to perform such work. So I have to wait until they can get around to looking to the external sources.

 

In the mean time we are watching what we operate and what the electrical load is.

 

Ken

 

Ken, for sure if its NOT the pedestal and NOT internal, there's a good chance you will find that loose/resistive connection in the distribution panel (or upstream from there). If they can just get an electrician in there checking and tightening and/or repairing connections will be an easy job.

 

Best wishes

 

John T

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An Autotransformer with it's single winding won't isolate current flow from a defective neutral. For that you need a full transformer with the primary connected for 240 volts input (from the two hot legs) and the secondary connected to provide 240 volts or 120 volts from each hot leg to the transformer's center tap.

 

At that point the park's neutral becomes a non-current carrying ground reference.

 

True, the autotransformer may not isolate the neutral, but it does pass it through with at least connections at the input and output that could be failure points. It's simple enough to test it...

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An "Autotransformer" isn't necessarily the same as a true "isolation transformer". An "isolation" transformer could have a two wire L1 & L2 240 VAC INPUT that didn't use or rely on or draw current or have any connection whatsoever to the parks Neutral with a total isolated no common connection 120/240 VAC OUTPUT. The output could have 240 VAC LIne to LIne with a center tap similar to a utility pole residential transformer so L1 or L2 is 120 VAC line to Neutral. I would suggest it should be wired and configured as a "Separately Derived Source" with the Neutral bonded to a Grounding Electrode just like if it were the utility. Then you get into the whole subject of Single point grounding and Neutral Ground Bonding recalling the RV panel has separate isolated Neutral and Ground Busses unlike in your home. Not sure how the park would react (likely has no idea lol) and I prefer a grounded versus a floating system.

 

John T

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It couldn't hurt to do as Dutch suggests and take your Autoformer out of the circuit just to see if anything changes. I'm doubting that it will prove to be the cause, but removing it would insure that to be the case. Clearly it isn't solving any problems at present so the test won't hurt anything.

 

 

EDIT: I always believe in doing the easiest checks first.

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