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Topic: Reverse Polarity on Outlets

Posted By: OldGrandad on 04/12/08 02:32pm

Since I know only enough about electricity to get the you-know-what shocked out of me, I thought I'd ask the experts. Today, while exercising the generator, I was bored and got out my circuit tester. It's that yellow one with the four lights on the end.

Well, much to my surprise, it indicated reverse polarity on every outlet in the motorhome.

The odd thing was that the two electric heaters that I plugged into those outlets worked fine.

Bad tester? Or am I missing someting...because I thought reverse polarity would pretty much destroy those electric heaters!


1983 Bluebird Wanderlodge PT40
2007 Coachmen Mirada 300QB
2001 Chevy Malibu toad



Posted By: 2oldman on 04/12/08 02:38pm

Testers don't work well on gens or inverters. Don't sweat it. And no, reverse polarity doesn't make a hoot of difference.

Remember the old days before wide bladed plugs?


Posted By: vermilye on 04/12/08 03:17pm

Although many things work fine with reversed polarity, I wouldn't agree that it "doesn't make a hoot of difference." If the polarity is reversed, a fault between hot (now the neutral or white wire) & ground will not trip a breaker since the breaker is not protecting the neutral. Another problem - a few electronic devices built during the 50's & 60's had the chassis tied to the neutral. Although the manufacturers went to a great deal of trouble to insulate the chassis from the outside world, consumers did a good job of defeating the insulation. End results - shocks to ground from the knobs & switches of appliances. Probably not too much of a problem now since most of those devices have come & gone, but of some concern. One last point - modern devices are often designed so that the parts that a consumer is most likely to touch are connected to the neutral (grounded) side. Example - a lamp socket. The shell is connected to the neutral & the button at the bottom is the hot. Reversing the polarity makes the shell hot to ground, increasing the chance of a shock if the consumer replaces a lamp with the device plugged in.

By the way, the older receptacles had narrow, not wide blades. The wide blade is the grounded conductor or neutral.

As to the circuit tester indicating a problem - it only works properly with systems that have the neutral tied to ground (usually at the service entrance). If an RV generator only produces 120V, there is no requirement that the neutral be connected to ground. Some manufacturers do tie the white wire to ground, others don't. If it is tied to ground, it must be untied when connected to shore power since the only place it is legal to tie the identified conductor or neutral to ground is at the campground's service entrance.


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Posted By: b_salgado on 04/12/08 03:28pm

I tested electrical systems in homes for 10 years with one of those circuit testers. If you were running off your generator and not off shore power this is your problem. It is not a reversed polarity. It is an open ground. Is your generator grounded? Is it built into your coach? If so, then the tires are preventing you from grounding. Take a wire, tie it to your grounding lug on the generator, stick the other end into the ground outside. It should read correctly. Hook to shore power to make sure your coach wiring is correct.Those testers lie when you have an "open" ground.

To the other poster about reverse polarity... yes it does make a huge difference. If it is reversed, you are essentially running power through you neutral circuit... this is backwards. If the panel is bonded (neutral and ground tied together) in the converter, you are essentially running current through the frame of the rig. This can cause a serious electrocution hazard.


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Posted By: wa8yxm on 04/12/08 03:30pm

Normal house wires have 3 wires.. HOT, Neutral and Ground

Now, there is a reason you need a ground.. I will try to explain it

Power comes into the house, there is a safety ground at the service entrance, There is also a ground "elsewhere" on the secondary side (Primary is the high tension wires, secondary is the drops to your house, and the neighbor's and the.. Well you get it.)

Now let's assume that something happened. You are using, oh, say an electric drill, and there is a hot-wire to case short..IF you have not tampered with the round pin on the plug, then the case is connected to ground, the fuse (or breaker) goes and ... Well, it may take you a while but you figure it out, toss the drill and buy a new one that works.

Now let's run that same drill WITHOUT the safety ground

now we get the hot-to-case short... There being no other path to ground... It grounds via you... Been nice knowing you. Pardon if I'm not at your funeral but my travel funds are limited just now.

Hence the safety ground.. The "Three Light Tester" has a light from HOT to Neutral, From HOT to Ground and from Neutral to Ground. Proper the H-N and H-G lights light

When you run on the Generator though things are different (normally) there is no safety ground. So in the case of the shorted drill mentioned above.. THE CURRENT CAN NOT RETURN THROUGH YOUR BODY as there is no ground path back to the generator. (Unless. of course they bond neutral to ground) thus. The "REVERSE" light will come on... So should the "Proper" light, You should see all three lights on a generator


Home is where I park it.
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Posted By: jerryspoolman on 04/12/08 03:28pm

My honda does not have polarity, it is a floating voltage. AC coming from the power company has the netural at ground potential. I have never checked the Inverter. The generator has a warning label the Inverter does not.


Just Jerry and Vangie


Posted By: Pete D on 04/12/08 04:13pm

I believe that lack of green ground is why the Honda inverter generators built for the CA market can't be paralleled. Apparently US codes allow it for small generators but CA codes don't.


1998 Ranger 4.0 4x4
1991 Scamp 13'


Posted By: BFL13 on 04/12/08 05:17pm

Who could resist checking that out? [emoticon]

So on shore power using the three light tester, I get "correct" two yellow lights on the shore power outlet and at all outlets in the trailer.

Eliminator 400w inverter clamped to the battery lugs I get all three lights at the inverter AC outlets, which is not a choice on the tester's diagram, so it must be impossible [emoticon]

Honda 3000 says it has a floating neutral. The tester shows only one yellow light in the middle indicating an "open ground". When shore power cable is plugged into the gen, all trailer outlets also indicate this same condition of Open Ground.

There is a grounding method for the Honda using its frame but I don't bother with that. I work it from the bed of the truck (on tires) to the trailer (on tires) and so far we are still alive.

IMO if the OP has a red light indicating reverse polarity in his rig's outlets this is bad news, and the problem should be corrected.


1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
See Profile for House electronics set-up.


Posted By: Wayne Dohnal on 04/12/08 05:38pm

It would be helpful to know two more things:

(1)Does the outlet tester read correctly when plugged into shore power? and (2) Is this a built-in or portable generator.

If the reading is ok on shore power and it's a built-in generator, I believe the only answer is that the generator is wired incorrectly to the RV. The electrical devices usually don't care at all if the polarity is reversed. It's a personal safety issue.


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Posted By: CA Traveler on 04/12/08 06:02pm

Wayne Dohnal wrote:

It would be helpful to know two more things:

(1)Does the outlet tester read correctly when plugged into shore power? and (2) Is this a built-in or portable generator.

If the reading is ok on shore power and it's a built-in generator, I believe the only answer is that the generator is wired incorrectly to the RV. The electrical devices usually don't care at all if the polarity is reversed. It's a personal safety issue.
Best post so far.


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Bob



Posted By: wa8yxm on 04/12/08 06:51pm

I should have included that "Open ground" is also an option... It may depend (in part) on the size of the rig. I won't go into all the details here but what can happen is that enough current to light the indicator can be coupled to the ground wires IN SOME CASES. Plus there are different types of generators


Posted By: MELM on 04/12/08 09:16pm

The Coachman Mirada should have an Onan genset, and the neutral is connected to ground in the genset. I am assuming that you are exercising that genset.

The tester should function normally on this installed unit.

There is almost nothing that won't work normally with reversal of the hot and neutral. vermilye's post is correct.

Following Wayne's post...

Test the tester in several household outlets and see if it works correctly (some have found incorrectly wired outlets in their homes when they tried out the tester). Check one where you can plug in the MH to be sure it is wired correctly, then check the outlets in the MH.

Let us know what you find with those tests.


Mel & Mary Ann; Mo'Be (More Behave...) and Bella
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90 Champion LaSalle MH 29 ft P30 (89 Chassis)

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Posted By: Retired_nuke_ET on 07/18/08 02:24pm

Ok this post seems to have died but I'll resurrect it since I don't see a definite answer and I seem to have the exact same issue.While I'm sure things are OK, I'd like someone with a true knowledge of RV electrical to agree or provide guidance.

Just completed the PDI and picked up the RV mere hours ago. During the PDI it was hooked to shore power and I tested every outlet with a tester and got two yellow/amber indicators (good). Came home and plugged into my portable Honda 6500 generator I use as back up for the house. Connecter through a homemade twistlock to 30A pigtail. Plug tester in to 5er outlet just to verify first time on generator is good and I get Red and Center Amber lights (Hot and Neutral switched). Disconnect everything and continuity test the pigtail again, it's good. Fire up the generator and plug the tester into the generator and it reads Center Amber only (open ground) hummmmm. Without digging out the manual and schematic of the generator I seem to recall the neutral and ground are separate and without sitting down and drawing out a simplified circuit to nuke it out, that seems like it would be the cause. log in to the forum and do a search and viola seems like I'm not the only one.

So this thread didn't seem to come to a conclusion but correct me if I'm wrong:

Since the generator does not bond ground and neutral together, the handheld circuit tester may not give a correct reading since it assumes the ground and neutral will be bonded together?

As long as the tester showed correct readings on shore power, the trailer wiring is correct? (since shore power does bond GND and NEU)

There is nothing we can or should do when running on generator power to correct this?


Posted By: b_salgado on 07/18/08 04:56pm

Retired,
You answered your own question. It is not the fact that Neut and ground aren't bonded, Its the fact that the gen is not grounded. If you take a section of wire and hook it to the ground lug on the generator ans stick it in the ground you will see the mis wire condition go away.


Posted By: Wayne Dohnal on 07/18/08 05:42pm

Quote:


There is nothing we can or should do when running on generator power to correct this?
I'm responding with the assumption that the genset is an eu6500is. As noted in the "System Ground" section of the Owner's Manual, a receptacle tester "will not show the same ground circuit condition as for a home receptacle." Could you do something to correct this? Yes, you could connect one of the AC output lines to the generator case ground to create a grounded conductor, commonly called a bonded neutral. Being a 120/240 volt genset complicates doing this. Should you do something to correct this? IMO, no. There's a valid safety argument either way. I'd personally leave it the way it is. If you want to verify that the ground wire is properly connected, connect the genset to the RV as you normally do, then use a meter to verify that there is a very low resistance (a few ohms max) between the genset case and the RV frame (or a ground connector in one of the outlets). A connection to earth ground has nothing whatsoever to do with the indication you're seeing.


Posted By: PatJ on 07/18/08 06:40pm

b_salgado wrote:

Retired,
You answered your own question. It is not the fact that Neut and ground aren't bonded, Its the fact that the gen is not grounded. If you take a section of wire and hook it to the ground lug on the generator ans stick it in the ground you will see the mis wire condition go away.


That little plug-in circuit tester doesn't care one bit what the voltage is relative to earth ground and that is not what it is testing. The plug-in tester is simply looking to see if the neutral line is connected to the trailer's electrical ground at some point. The whole mess could be 600 volts above the earth and the little tester wouldn't know the difference.

Retired Nuke, your gen and wiring are fine. Your conclusions are correct. If you really wanted to, you could tie the neutral and ground together somewhere on the generator side of your transfer switch, but the only thing you would gain is that your plug in tester would read correctly.


Patrick


Posted By: Retired_nuke_ET on 07/18/08 07:41pm

Thanks Bryan, Wayne, Pat!

It's an older ES6500 that carried us through Isabelle without breaking a sweat. The only reason I plugged in the outlet tester while on the generator was strictly to make sure the pigtail I wired was correct. When the tester said it wasn't right but when I checked it over and it everything was connected right, I figured something strange was going on. Again thanks guys.


Posted By: b_salgado on 07/18/08 08:08pm

PatJ wrote:

b_salgado wrote:

Retired,
You answered your own question. It is not the fact that Neut and ground aren't bonded, Its the fact that the gen is not grounded. If you take a section of wire and hook it to the ground lug on the generator ans stick it in the ground you will see the mis wire condition go away.


That little plug-in circuit tester doesn't care one bit what the voltage is relative to earth ground and that is not what it is testing. The plug-in tester is simply looking to see if the neutral line is connected to the trailer's electrical ground at some point. The whole mess could be 600 volts above the earth and the little tester wouldn't know the difference.

Retired Nuke, your gen and wiring are fine. Your conclusions are correct. If you really wanted to, you could tie the neutral and ground together somewhere on the generator side of your transfer switch, but the only thing you would gain is that your plug in tester would read correctly.
That's where your not entirely correct. Most gens run with a floating ground. Unless it's a sine wave converter, this could result in damage to electronics. Almost every generator made has a ground lug on it for this purpose. That little plug in tester will sense any combination of circuit fault, including, but not limited to, Open ground, open neutral, open hot, reverse polarity, hot and ground reversed, neutral and ground reversed, ect. I was a diagnostic troubleshooter for more than 12 years on home and generator circuits. Once you learn how to "read" the lights on the tester, you can also tell if you have a loose connection or nicked wire just by how bright the lights are. I can do the same thing with a stick type tester or a continuity tester. I can trace down shorts and other mind boggling electrical issues usually in less than 30 mins that would take the normal person with logical reasoning hours. I did it day in and day out. That little tester will lie to you in a heartbeat also. It will tell you that you have a reverse polarity issue or open neutral(I have seen it both ways) when in fact, you will only have an open ground. This is where the stick tester come in. Here is a quick check for you. Take your generator and plug in your TT. Take your rec tester and go in the TT and plug it in. See what the lights say. Then take your stick tester and test the rec. Touch the pin on the left (hot) to the pin on the right (neutral) you should get a light from your tester. Then take the probe out of the neutral and go to ground. If it is "open", you will have no light. Now, step 2.... go and ground your generator like I mentioned above or you can tie a ground to the neutral via a jumper wire in the rec. It will make the lights read correctly. The 2 outside lights should light orange. None of the others should be lit. We had a home that actually energized the sheet rock walls because of an open ground. You could get 50V by touching wet painted walls on 2 different circuits... IE: bathroom wall and hallway walls. It blew everyone's minds until I plugged in my little rec tester and I tested the ground. This is your electrical lesson for Friday night.[emoticon]


Posted By: PatJ on 07/18/08 09:48pm

b_salgado wrote:

Here is a quick check for you. Take your generator and plug in your TT. Take your rec tester and go in the TT and plug it in. See what the lights say. Then take your stick tester and test the rec. Touch the pin on the left (hot) to the pin on the right (neutral) you should get a light from your tester. Then take the probe out of the neutral and go to ground. If it is "open", you will have no light. Now, step 2.... go and ground your generator like I mentioned above....It will make the lights read correctly.


So are you telling me that if I have an RV plugged in to a normal portable generator, and I ground the chassis of the portable generator, the test lights will read "correctly" in the RV? When I say "correctly" I mean a ~120v potential difference between the ground prong and the hot prong in my RV's receptacle. Is that what you are saying? Regardless of the fact that no where in this system would the neutral and ground be bonded?

b_salgado wrote:

Take a wire, tie it to your grounding lug on the generator, stick the other end into the ground outside. It should read correctly.


Is that what this means? Where is the complete circuit? How would grounding the generator's chassis tie neutral and ground together?


Posted By: PatJ on 07/18/08 10:02pm

Please forgive the crude drawing, but you are telling me that in this situation, the stick-type test light will illuminate?

This is even giving the benefit of the doubt to the ground prong on the generator actually being tied to the generator's chassis, which in the case of my Honda I do not believe is true.

[image]


Posted By: b_salgado on 07/19/08 02:22pm

You got it. The easiest way to tell if your ground is tied to the frame is to take a continuity tester or ohm meter and touch the frame of the gen to the ground pin on the gen rec. If it lights, then it is grounded to the frame. Then you can find the ground lug (it should be a green terminal with a set screw on it) stick a short length of heavy copper ground wire into the ground and then terminate it on the lug. Start your gen. and test the rec again. It should light the way I told you. Hot to neutral and hot to ground. Then, plug in your rig and go inside and do the same thing. It should read correctly. The reading you are getting, has nothing to do with the rigs wiring. You have the correct idea. Now it's going to be time to find the ground lug and try it out. My generator does the same thing. It is not a Honda


Posted By: ve7prt on 07/20/08 08:13pm

Um, for those of you who think that a portable generator's neutral and ground wires are bonded, think again. They are NOT. I have 2 generators, and neither of them have the neutral and ground bonded together. In fact, my older one has a sticker on it stating that the neutral is floating. My new one came with a wiring schematic, and if you follow it, you can see that at no time is the ground wire connected to the neutral. In fact, on this genset, you cannot bond the two - its very design precludes that option. Heck, the 15/20Amp connector is a GFCI outlet! That should tell you something.

So, pounding in a ground rod and strapping it to the generator's chassis ground lug would do absolutely nothing at all for safety. That is why the GFCI outlet is there. It will provide far more protection in this case than a ground stake would.

And as for the tester showing an open Hot->Ground, that is correct on a portable generator. In this case, nothing is wrong with the RV or genset, it is a normal condition, so long as the RV tests normal when connected to shorepower. If it doesn't, then you have a problem.

Cheers!
Mike


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Posted By: b_salgado on 07/20/08 08:24pm

My generator does not have a GFCI outlet. It does read incorrectly when the tester is plugged in. It does correct when I ground it. I don't pound a ground rod in every time I use it. I simply drive a metal tent stake into the ground and tie a wire to it with a clamp. When I use the generator at the house, I use the ground rod that is driven into the ground for the service entrance. It works great. We were without power for well over 2 weeks about 6 years back and I ran almost the entire house off the gen. I did not have the TT then, or I would have moved into that. We still had no heat in the house (electric heat pump) and had to use propane heaters. It was a long 2 weeks.


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