Open Neutral at 50 amp Pedestal Causes Damage

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Open Neutral at 50 amp Pedestal Causes Damage

Postby Randy & Nancy » Wed Sep 27, 2017 10:29 am

johnnyb440 wrote:Here is a link to a simple youtube video that will explain how this happens. I can assure you there was no bond between the ground and neutral. We were measuring 239 volts between the neutral and the hot in one of the outlets. Electricity will take the shortest path to ground if there is no ground. In this case, it was probably through another appliance plugged in possibly and was using the other hot leg from the 50 amp service for ground, which in effect doubled the normal voltage. I have seen this at my own home several years ago. We lost the power company neutral lead to the house because of a bad splice. All of a sudden, many appliances were smoking and most all in the home were damaged. The measured voltage would read 240 volts on one leg and about 20 volts on the other leg. This little video helps explain how this happens.

https://www.youtube.com/watch?v=O-Q0M32puGY


Hang on a minute. I am not in any way being critical of what Johnny and Richard did or disputing what they found. I agree that they did a good job of analyzing the apparent problem and getting Danny fixed. What I was attempting to point out is that the open neutral may not be the ONLY problem contributing to the issue and I would hope Danny would not just quit there. A bond anywhere between the neutral and safety or grounding wire gives yet another path for fault current to travel to the outlet neutral often making ALL outlets from both legs show a higher than normal voltage. It takes one fault to make the second apparent and if overlooked it can put us back into the same risk category.

Grounds or grounding in any electrical circuit can take a semester or more to teach. They can be extremely complex. Despite NEC directives, way too many campgrounds do not follow the rules and make their system bond at the power pedestal using only 3 wires back to the SEP (saves money on cable). But, this makes resistances between the neutral and grounding wire different which can cause ground loops and a number of other freakish power situations in the RV, especially when there is an open neutral in the power cord. Checking for a bond, either intentional or through a faulted appliance is always a good idea especially when an occurrence like Danny has happened.

Let's step back and look at what did happen and what cannot happen.

Look at figure 1

Image

This is an example of the normal current flow between two wired devices in your RV when both are turned on. As noted the neutral or center tap serves both L1 and L2 alternately as each leg has a 120 degree phase differential (but single phase power). In Figure 1 all is good inside the RV. You have 240 volts across L1 to L2 but have nothing in the RV that ties them into one independent circuit when plugged into a properly wired 50-50 amp power pedestal.


Let's scroll down to Figure 2

Image

Here we have an open neutral in the power cord (what Danny experienced) that gives a path for current from L1 and L2 to flow between two wired appliances. For this to happen both appliances need to be turned on (circuit closed) and the open neutral must come before the neutral bus (like in the power cord or pedestal). In this example current flows through the circuitry of the air conditioner back to the neutral bus and then into the circuitry of the converter/charger provided it is connected to a different leg of incoming power. Again, this is an example. Any two appliances or circuits on alternate bus’s can experience the same problem.

Keep in mind that if the total supplied voltage is 240 volts AC you cannot have 240 volts on one leg and 20 volts on the other. That adds up to 280 volts. While series connected voltages are summative, in a single phase circuit they cannot exceed the supplied EMF (ElectroMotive Force). You can only distribute the supplied voltage across the two resistances. You may want to look at this web page for a detailed explanation on how this works. http://www.solved-problems.com/. Depending on the internal resistance of each item in the current path it is likely that ONE of the two appliances will experience a voltage higher than 120 VAC. If the appliance is not designed to carry the extra amperage that results from the increased voltage it will be damaged - even get hot and smoke and could catch on fire. Ironically, the other appliance in the circuit will most likely escape damage unless the voltage is high enough to make the appliance try to operate but the load keeps it from turning on. In this case it can overheat and smoke if there is no internal safety thermal or overload device to open the circuit. In the YouTube video Johnny pointed to, one important piece of info was eliminated by the videographer – the two incandescent light bulbs are not the same wattage,, meaning the filament resistances were not equal. The bulb with the lower resistance will of course burn brighter than the one with higher resistance when placed in a series circuit.

CONTINUED IN NEXT POSTING SPACE
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Randy & Nancy » Wed Sep 27, 2017 11:32 am

CONTINUED FROM POSTING #1
All right - what happens to the 120 VAC duplex outlets in a situation such as noted in figure 3?

Image

If we only have an open neutral in the power cord without the inclusion of wired appliances or multiple plug-in items across opposing power legs nothing will happen – that is unless the appliances are on. Since many electronic devices like TV’s, microwave ovens, coffee pots, electric clocks and computer switching supplies are on and are completing the circuit even if the power switch is off damage can occur. This is just one reason we are told to unplug devices in a thunder storm or when we are away/not in use as a precaution against damage or fire.

Now we can move to Figure 4. This where a whole bunch of stuff in the trailer can get fried.

Image

Without the benefit of a connected neutral to the outside power supply the voltage (and resultant current) that appears on the common neutral bus will appear at the neutral slot (long one) on the duplex outlet. If the phase differential of the voltage on the neutral bus going to a particular outlet is different than the supply from either L1 or L2, and if something is plugged in that is completing the circuit then that item may also go up in smoke. This would explain how (Richard?) measured 239 volts across a duplex outlet.

As previously noted a power management device that plugs in at the pedestal will protect from situations that occur before the power cord but typically provide no protection down line other than a ground fault. If the management system is installed at or in the trailer you will have protection from cord malfunctions.

Another device that can help is to have surge protectors plugged into duplex outlets inside the trailer. These are often inexpensive devices available at Wal-Mart or home stores for around $10. Inside you will find one or more MOVs (Metal Oxide Varistor) that shunt voltages over a specified level – usually 135 volts on residential 120 volt branch circuits. Most are designed so that when the MOV shunts enough voltage and current to literally explode then a fuse or relay in the surge protector opens the circuit. All of this happens in a matter of milliseconds. Having the surge protector between the appliance and power if you want to protect it from an overvoltage condition as noted above is the best method. But, protection from momentary transients or surges is provided to all items on a branch circuit with a single surge protector.

Next question. Why did only the neutral connection in Danny's power cord burn open? Why didn't L1 and/or L2 also burn open?
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby johnnyb440 » Wed Sep 27, 2017 11:52 am

It took a little bit for me to get my head around this when it happened at our home. The only way I believe this can happen is indeed if there are appliances plugged into both circuits. The ground comes from the appliances, which is on one leg or the other. Since Danny's appliances were blowing slowly and we did not catch the high voltage fast enough is why the difference in voltage between the two legs and ground. When we first checked the voltage it was reading 123 volts on each leg. But that was to ground. It took about 5 minutes for us to realize that the voltage between the neutral and each leg was indeed a problem. In this case, if there had been a bond between the neutral and the ground, nothing would have been damaged and you probably may not have known about this for some time. If there were no appliances (loads) on each circuit, nothing would have happened except you would have noticed no power to anything. Since we did not take the time to trace out the breakers on each leg, we have no way of knowing what appliances were plugged in where. What Danny first experienced was the satellite quit, then the tv in the living room. Then a couple of minutes later, smoke. The convertor was on fire. Well, smoking anyway. When we were checking voltages and had not measured to neutral yet, the microwave started smoking. That is when we discovered from each leg to neutral there was a real problem. After that, did not take much troubleshooting to determine where the problem was. Our initial thought was the convertor was just bad since we had 123 volts to ground. This only took maybe 5 minutes for figure out, but by that time more damage was done.

Now, on another thought, if the EMS would have been hard mounted in the trailer and not at the campground pedestal and the neutral broke in the cord, it would have also caught the problem I believe. These cords are in use everyday you camp and take a lot of abuse, so it makes sense that they can fail first. If the cord fails and the EMS is at the pedestal, you are on your own.

It's rather hard to most of us to grasp that the other things plugged into the trailer was supplying the ground to system. That is why in the video posted, one light dimmed and one got very bright. The dimmed light was supplying the ground, but that caused the high voltage on the other light.

I think I understand this, but it's pretty confusing at first thought.
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby BandJCarm » Wed Sep 27, 2017 12:20 pm

I have a minor in Physics.

I don't remember a single piece of information from it! LOL

This is all interesting. But I can't decipher and sift out the wheat from the chaff. Sorry, my misgivings, not y'all's.

When the dust settles (smoke clears???) someone tell me what to buy to make sure this doesn't happen to me, and tell me who's gonna install it and when!! LOL

Thanks

Danny.......you are way more laid back than I'll ever be!!!
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Danny & Cheryl » Wed Sep 27, 2017 3:19 pm

I am Recovering from a near Break Down in Kansas, I have the Ref fixed now ,replaced the Elect Heating element, got Cheryl a new Keuring Coffee maker, she is happy now. ordered new 30 amp ends for my cords for use here at home. Got an Electrician coming to check and Verify my 50 amp plugs here before plugging into them. Still need a new TV and Microwave but that can wait a while. It is 5 o'clock somewhere. Bill dont you have the PE PT-50 EMS like i do. I think we should have gotten the HW version. But this will never happen again to anyone. I Hope
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby BandJCarm » Wed Sep 27, 2017 3:43 pm

Yes I do.

The idea of putting the EMS between cord and camper instead of between cord and pedestal, sounds good. Might be the answer. Not sure how to convert the portable to put it inside, but I'm all ears. But not sure that's the answer yet. Still listening to those who know; waiting on their idea to fix.

In the meantime, I'm cogitating.... I just bought a 10' 50-amp cord. I THOUGHT it was a replacement for the OEM cord (meaning it had a 4-prong end and a 3-hole female end), but it isn't........it's just a short extension cord. So I can't use it without the OEM cord, because I need the 3-hole female end. So I guess I'll buy ANOTHER device.......the 18" 50 amp short plug (CAMCO part 55562), and use that with the short 10 foot cord. That will work I think. But now I have two new power cords and I have to assume they are good!! Which takes me back to a hardwired EMS (and figuring out how to install it). I guess I could just buy one and sell the portable...........

Sigh.

This stinking rolling money pit is gonna break me. Someday I guess I can just camp at home.........
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Randy & Nancy » Wed Sep 27, 2017 6:16 pm

Bill, you could use the portable inside. The easiest, and possibly the best, approach would be to cut the #6-4 supply wire just before the double pole 50 amp circuit breaker. You would then install a female outlet on the supply wire and a male plug on the circuit breaker wire. If you did this you could plug your device inside the camper but you would not be able to see the display. If you wanted to take it out you could and just plug the two cords together inside the camper. If this is a priority, my advice is to have a licensed electrician familiar with RV wiring install a hard wired device with a remote info/control panel inside the camper where you can see the readings or fault codes. I am sure you can sell your present device. I don't know if you looked at my system or not but it is hardwired with a rather comprehensive display panel inside. George at Cedar Creek kids me about it being a flux capacitor.

Keep in mind that it is not normal for the neutral wire to burn open in the power supply cord. It happened, but it was an unusual occurrence. The likelihood of this happening to you is probably pretty slim. Depending on your feelings about risk assessment what you have now is good protection from the most likely fault source.
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Danny & Cheryl » Wed Sep 27, 2017 7:06 pm

Randy I have two 50 amp receptacles in my shop. When I checked them today with my EMS it showed both have open grounds. After what happened in Kasas I am scared to plug the camper into them. I have an Electrician coming tomorrow to inspect and repair them. More to follow after the repair.
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Randy & Nancy » Thu Sep 28, 2017 10:10 am

Danny & Cheryl wrote:Randy I have two 50 amp receptacles in my shop. When I checked them today with my EMS it showed both have open grounds. After what happened in Kasas I am scared to plug the camper into them. I have an Electrician coming tomorrow to inspect and repair them. More to follow after the repair.


Wise decision.
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Danny & Cheryl » Thu Sep 28, 2017 2:13 pm

My electrician checked everything from the meter loop all the way into both receptacles and found that all is ok. I plugged in and everything is working, No Smoke. I put a single outlet surge protector on the ref outlet and will add more as I replace other components .
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Chuck & Sue » Fri Sep 29, 2017 7:41 am

Danny, where did you get the single outlet surge protector? I want to get some for our microwave, fridge, etc.
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Danny & Cheryl » Fri Sep 29, 2017 9:08 am

WalMart, i think it was $9 in their hardware Elect section. I am going to get another one for the Microwave when I get it replaced.
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Re: Open Neutral at 50 amp Pedestal Causes Damage

Postby Randy & Nancy » Fri Sep 29, 2017 5:53 pm

Back in 2009 we had a pretty good Q&A on surge guards, voltage transients and protection modes. If you care to review the thread you can find it by clicking here http://www.cedarcreekrvownersclub.com/phpBB3/viewtopic.php?f=6&t=1241
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