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Old 12-11-2012, 12:30 PM   #1
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Open Neutral in a Motorhome..

This issue came up whilst I was checking my generator, but I thiunk it needs a seperate thread, as I believe the issue is not connected(pun intended!)

I have an "Open Neutral" in my 120v system, according to my little tester on the left here...
I am told this is potentially dangerous!




Its not on one plug, its all of them, and not to do with the onboard genset, as I get it when running on my portable 3500w generator, yet its plugs test good.

Now, the only thing I have touched on the 120V system was the connections in the juction box under the rear bed, when I removed the cable reel for restoration, and I was careful and think I replaced it as it was... which does not mean it was right!!!


Yesterday, I took another look at what I had done, and all looked tight... then I spotted something...
Outside the junction box there is a stray black wire....
I am holding it in LH side of this pic...




I traced it back and it goes rearward and into the wall under the gas filler assembly with a bunch of other wires...




Electrics is not my strong suit...
Any opinions would be valued!
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Old 12-11-2012, 12:58 PM   #2
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It is always difficult and dangerous to diagnose electrical issues, especially 120 volt ones, from a distance. However, here are a few thoughts.

I doubt that the stranded black wire you have located is a 120 volt one. It looks more like a 12 volt type wire to me. In that case it has nothing to do with your issue.

The "junction box" you are referring to, and show in your photos is the automatic generator transfer switch. It has 3 wires going to it. One is the input from your shore power 30 amp cord (and cord reel). The second is the input from your generator set. The third is the output to the coach electrical panel.

The black thing in the center is a relay. Normally it is "open or off" and the power flows from the cord set through the relay contacts to the main power panel. When the generator is operating the little time delay device in the upper left corner gets power from the generator. After 30 seconds or so it provides power to the coil of the relay, which "closes it, or turns it on". When that happens the power is transferred from the generator to the power panel. The net result is that either the shore power or the generator power is connected to the panel, but never both at the same time. Shore is normal, when activated the relay switches to generator power.

Both the neutral and the hot lines are routed through the relay, both are switched by it.

If any connection on the neutral (white) side of the relay is incorrect, or is open or the relay contacts themselves are pitted, worn or damaged you may come up with an open neutral indication on your tester. If the neutral wire in your cord set, plug, or in your cord reel is damaged you will get the same open neutral indication.

If you are not comfortable with electrical work, it may be best to have some one who is skilled in the area work on the system, methodically checking the path of the neutral from the coach plug, through the cord reel, and to the transfer switch relay and on up to the main panel.

That is the only safe way to know what is happening and to locate the problem. It must be corrected, of course.
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Old 12-11-2012, 12:59 PM   #3
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Have you confirmed that you do not have an open neutral at the 30amp receptacle where you plugged in?
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Old 12-11-2012, 01:04 PM   #4
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BTW, my best guess is that you will find the open neutral in the power cord, plug, or cord reel, especially if you have worked on those parts recently.
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Old 12-11-2012, 01:21 PM   #5
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Good info Idroba!

You may be correct about that wire, but I have no idea!
I only had my phone camera with me, so it was tricky to get a good shot.
My first concern was had I missed a wire when I reconnected the reel, but it all looked good.
Bkahler just posted a good reply over on my main MH resto thread where I had posted the same question...

I think I will get my take my buddy up on his offer to take a look as he was an electrical contractor for quite a few years.
He will at least know more than me!

I am not planning use the 120v electrical system in the MH until this is cured, but I did plug the shore power into my portable genset to top up the charge in the house batteries via the onboard charger...
Should I avoid doing that until I have this fixed?
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Old 12-11-2012, 01:25 PM   #6
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Quote:
Originally Posted by idroba View Post
BTW, my best guess is that you will find the open neutral in the power cord, plug, or cord reel, especially if you have worked on those parts recently.

Am I correct in saying, that you think there may be a broken wire in the cord or maybe in the plug?

If so, I should be able to disconnect and test each wire for continuity?
If there is an issue with the cord wire, could I replace it with a 50a gauge cable so I am ready should I choose to go with an upgrade to a full 50a later?
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Old 12-11-2012, 01:43 PM   #7
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Steve,

Keep in mind you are NOT connected to shore power right now so your neutral wire should not show connected to ground unless the generator is running. If you were running your generator and your test device indicated that you had an "open neutral" then as idroba said the issue is probably in your transfer switch or somewhere on the generator side of the transfer switch.

I can't see where the shore power cord comes into play in this situation.

Now if you ARE connected to shore power then disregard what I just said.

Brad
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Old 12-11-2012, 01:45 PM   #8
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One other thing. As I stated in our other thread. On the generator side the neutral and ground should be bonded together. On the shore power side in your main breaker panel the neutral should be isolated from ground.

Brad
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Old 12-11-2012, 02:12 PM   #9
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If your tester shows an "open neutral" you should not be able to get 120 volt power in your coach at all (assuming you are plugged into shore power). That is nothing should be working, on the 120 volt side, including the battery charger.

If 120 volts is working there must be some issue with either the tester itself, or your return power is going back via the ground wire, which is a dangerous situation.

In any event, I don't think you should use the system at all until it is straightened out. There are too many potential dangers here.
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Old 12-11-2012, 02:15 PM   #10
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idroba,

I believe Steve's coach is parked at a storage facility and the only "shore" power has is when he uses his small portable generator and plugs the coach into it. He normally uses his on board Kohler generator when he is working on his coach.

What I'm not sure based on his posts is whether he found the open neutral while using the small portable generator or while he was using the on board Kohler generator. Knowing that bit of information would help pin point where the problem might be.

Brad
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Old 12-11-2012, 02:28 PM   #11
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Quote:
Originally Posted by idroba View Post
If your tester shows an "open neutral" you should not be able to get 120 volt power in your coach at all (assuming you are plugged into shore power). That is nothing should be working, on the 120 volt side, including the battery charger.

If 120 volts is working there must be some issue with either the tester itself, or your return power is going back via the ground wire, which is a dangerous situation.

In any event, I don't think you should use the system at all until it is straightened out. There are too many potential dangers here.
Ok, good info.
I have no shore power at the storage, so its the onboard genset... which is not working at the moment, or my little portable unit.
I have power at all my recepticles... but all of them are showing Open Neutral... Testing the recepticle on the genset whilst running shows good.
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Old 12-11-2012, 02:38 PM   #12
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Ok, good info.
I have no shore power at the storage, so its the onboard genset... which is not working at the moment, or my little portable unit.
I have power at all my recepticles... but all of them are showing Open Neutral... Testing the recepticle on the genset whilst running shows good.
So you're running on your portable genset plugged into your shore power cable.

The open neutral indication is telling me that your portable generator is not bonding the neutral to the ground wire at the generator. Remember, the little portable generator is mimicking the connection to shore power. With a shore power connection the neutral and ground are bonded at the main breaker panel where power is coming from, say your house, or some camp ground.

I think you might be able to test this by turning the generator off and measuring resistance between the neutral and ground connections on the generator. If no reading then there is your problem. If there is a reading then I guess I'm confused!

I can't see where the problem would be in the cable or the power real because the coach itself does not have the neutral and ground bonded together so that would automatically be an "open neutral" condition. Bonding takes place at the power source so check your portable generator.

Brad
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Old 12-11-2012, 02:38 PM   #13
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We crossed over there Brad, but you were correct.

I had not noticed any power issues when using the genset when it was running, but the last time I tried to run both AC units, the front would not work... and it had done before...

The thing that got me into finding this open neutral issue was that I felt my Buffer lacked torque when I was using it at the MH off the onboard genset, and I wanted to check the Voltage.
The genset refused to start(fuel pump issue) as a pure coincidence, so I was forced to use the portable.

I went around the whole MH testing the outlets with the orange tester... all showed an open neutral. I unplugged the shore power cable from the portable genset and ran it, and plugged in the tester and it read perfect.
I adjusted its running speed as it was only showing 112v and 60hz, up to 118v and still 60hz. I then plugged in the MH shore power and tested the outlets inside and was getting 117v... so a 1v drop.
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Old 12-11-2012, 02:59 PM   #14
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We crossed over there Brad, but you were correct.

I had not noticed any power issues when using the genset when it was running, but the last time I tried to run both AC units, the front would not work... and it had done before...

The thing that got me into finding this open neutral issue was that I felt my Buffer lacked torque when I was using it at the MH off the onboard genset, and I wanted to check the Voltage.
The genset refused to start(fuel pump issue) as a pure coincidence, so I was forced to use the portable.

I went around the whole MH testing the outlets with the orange tester... all showed an open neutral. I unplugged the shore power cable from the portable genset and ran it, and plugged in the tester and it read perfect.
Interesting. I think I missed something in my previous response. If your portable generator is correctly bonded at the generator and you show an open neutral in the coach then it goes back to what idroba said about the problem being at the cable real or power cord itself.

Quote:
I adjusted its running speed as it was only showing 112v and 60hz, up to 118v and still 60hz. I then plugged in the MH shore power and tested the outlets inside and was getting 117v... so a 1v drop.
Do you still have the open neutral showing in the motorhome outlets? Or did the problem go away?

Also, you could probably use a 50 amp 4-wire cord to replace the existing cord but I don't think it will work with the power reel so you would have to eliminate the power real and connect directly into the transfer box. I also think you would need the appropriate adapter at the shore power pole.

I doubt that the entire 30 amp shore power cord is bad. Most likely the problem is at the plug end or else where the connections are made in side.

Brad
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