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Old 01-12-2022, 01:17 PM   #1
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Electrical Confusion... Who has the problem?

Hello,

We are a long time Boondockers Welcome Host site. So we get a lot of different rigs staying at our place. I have a 15 amp circuit available for guests to plug in to. Over the past few years we have had on several occasions people that use the in-line surge protectors/circuit tester gadget. Several have commented on the fact that their tester is showing that the hot and neutral wire are reversed. Which would not be good.. However, I personally know the electrician that put that circuit in, ME. I also know it is wired correctly...yet this strange anomaly manifest itself.

Last week a guest reported the same problem and was confident it was wired incorrectly. He asked if he could swap the wires in my 12 gauge extension cord I have available with a gang plug on the business end. I finally just told him sure. He reversed the hot and neutral and guess what... It still showed the two wires were reversed. He swapped them back and the reading was the same. In the meantime I did put a meter on the outlet to ensure, once again, that the hot and neutral were wired correctly. Anyway...He just said...I give up and I guess well just be careful with the camper.

Later he realized that his camper was still plugged into his truck. He unplugged it and then noticed the gadget was reading correctly. He plugged it back into his truck and it once again showed swapped hot and neutral. He brought that to my attention... Well...that's something new...

Since this problem has occurred a few times I am wondering if being plugged into the truck somehow messes with the gadget and causes it read incorrectly. Has anyone else ran across this?
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Old 01-12-2022, 01:25 PM   #2
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You are talking about a regular 110V 15A receptacle ?
Go down to Home Depot or whatever is nearby and grab a plug in type circuit tester that has all of the different scenarios that light up. Test the circuit by plugging that into the receptacle and only that should be plugged in. Go by those results.
Once again... do not have anything else plugged in except for the tester.
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Old 01-12-2022, 01:58 PM   #3
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Plugging in a 7 pin tow connector should not change the "reversed" 120 volt diagnosis. The highest voltage on the 7 pin is 12 volts DC.

The only possibility is the device is using the ground wire and some odd electrical characteristic to arrive at a diagnosis. It may be getting a ripple signal from the tow vehicle electrical system.

Plug the device directly into the 120 volt shore power outlet. Do not plug it into an RV outlet or guests power cord.

There is no telling what is inside that RV. Lots of them have system grounding issues. Some of them have 12 volt ground ripple from their battery charger that may trip an overly sensitive detector.

Verify the detection device as you have done.
  1. Measure the outlet small blade to large blade. You should get 120 volts.
  2. Measure the small blade to ground pin. You should again get 120 volts.
  3. Measure the large blade to the ground pin. You should get 0 volts.

If the detection device reports a "reverse" error, it is defective.

I am an electronics technician. I learned my trade in 1969. There was no such thing as a plug in circuit tester back then.

Over the years various little black boxes have been introduced. I ignored them for a while, then bought one. I tried it out in various places. I got lots of strange error indications. I discarded the device.

I wired many of those circuits. I know they were wired correctly. Others were wired by someone else, but it is not magic to test them using a multi-meter.

There is no telling what the device is measuring and it is not worth finding out. If you can't trust a measuring device, there is no point in using it.

The advertising and low price gives people a false sense that the device is infallible.
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Old 01-12-2022, 02:21 PM   #4
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Quote:
Originally Posted by Persistent View Post
I am an electronics technician. I learned my trade in 1969. There was no such thing as a plug in circuit tester back then.
I was born in 1969.
Seguin high school Electrical Trades 1988.
Texas State Technical School, Waco - Electrical Power Technology 1990.
Wired dozens of new construction and rehabs over the years.
Been in the electrical utility field since 1991.
SCADA systems operator since 1991... Administrator since 2012.

Now that we have that out of the way...
The electrical testers such as the type that I recommend to the OP actually function very well for the purpose of verifying proper polarity and ground.
The reason for my recommendation is to keep it simple for the OP.
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Old 01-12-2022, 02:30 PM   #5
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In a standard 15 amp outlet:

Short straight= hot
Long straight= neutral
Round= ground
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Old 01-12-2022, 02:52 PM   #6
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Quote:
Originally Posted by 77Travco View Post
You are talking about a regular 110V 15A receptacle ?
Go down to Home Depot or whatever is nearby and grab a plug in type circuit tester that has all of the different scenarios that light up. Test the circuit by plugging that into the receptacle and only that should be plugged in. Go by those results.
Once again... do not have anything else plugged in except for the tester.
Perfect little tool to have and use. I have a couple around my shop and house, and I keep one plugged into an outlet on my MH kitchen counter. Easy to see at a glance if I am hooked up to a properly wired post at a CG.

I also have a voltmeter to keep an eye on CG voltage. Cheap and easy to set my mind at rest. One like this........


https://m.media-amazon.com/images/I/...AC_SL1001_.jpg

https://m.media-amazon.com/images/I/...5TERL._AC_.jpg
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Old 01-13-2022, 06:47 AM   #7
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Let's try to stay out of left field....

Yes, it is a 15 amp circuit (as stated in my OP),
Yes, it is wired correctly (as stated in my OP),
I don't need a plug in gadget to tell me if something is wire correctly...my expensive Fluke multimeter does fine...

MY QUESTION WAS... Has anyone come across a situation like this where the trailer being plugged into the the tow vehicle causes the in-line tester to read a hot/neutral reverse?

I don't have a clue what would cause this anomaly. But over the past few years we have had 3 or 4 guests that said their gadget was showing a wiring reverse. It must have something to do with the ground to the truck...but I still have no idea what would trigger this. I KNOW it is NOT my wiring! It is just weird.

More-so...if your gadget is showing something strange, try unplugging your tow vehicle and see if it changes. After our guest discovered this, we plugged and unplugged several times and each time the truck was plugged into the camper his gadget would show the hot/neutral reverse warning.
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Old 01-13-2022, 07:42 AM   #8
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An Unreliable Detector is Pointless

"I was born in 1969."

So was one of my children...

"The electrical testers such as the type that I recommend to the OP actually function very well for the purpose of verifying proper polarity and ground.
The reason for my recommendation is to keep it simple for the OP.

The OP already said she knew how to check it the old fashioned way. In fact she said she had wired the circuit herself.

Obviously the little black boxes frequently did not work. Using an unreliable detector is still pointless.
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Old 01-13-2022, 07:50 AM   #9
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Quote:
Originally Posted by Persistent View Post
"I was born in 1969."

So was one of my children...

The OP already said she knew how to check it the old fashioned way. In fact she said she had wired the circuit herself.

Obviously the little black boxes frequently did not work. Using an unreliable detector is still pointless.
Well, aren't you just a box of roses this morning

To answer the OP's question... Probably a diode is the issue.
The charger/converter is probably feeding the 12volt in a way that it's creating a backfeed situation that is throwing an error to the sensitive testers/monitors. Not that those tester thingies are reliable.
In other words, I believe the issues that you have seen are to do with the battery chargers of the RV's in question.
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Old 01-13-2022, 12:31 PM   #10
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These testers are reliable for what they indicate

The plug-in style of testers while simple are not really a black box with any logic built in and are actually very good for testing what they test. I suspect for most people may not have a good grasp of what is actually inside the plug-in tester.

What is inside is simply 3 neon bulbs (with resistors) that are connected to each terminal as I have listed B1, B2, B3, (click on the image to see it bigger) which corresponds to the Klein tester in the image for Bulb 1,2 and 3 (other testers are similar but the bulb positions can be different).

You could use a simple single bulb neon voltage tester and receive the same results as the plug in tester indicates (the neon tester with two probes that looks similar to a 12v test light) by connecting it to the three locations as listed for B1,B2,B3 and observing the results and matching the results up with the chart on the plug-in tester.

However, what a simple neon bulb tester (plug-in 3 neon bulb tester or simple neon probe test light) cannot do is tell you the resistance values or the voltage and it is important to note that a neon bulb requires extremely low current and will light even with a low voltage (lower than 120v that is, perhaps as low as half that depending on the bulb and it's resistor value).

So, how does this play into the OP's question? The answer is that from the testers location (wherever it is plugged in at) that there is voltage across B1 (Neutral to Ground)which should never be (notice on the tester legend that anytime B1 is lit there is an issue). Also consider that the tester doesn't indicate the reverse condition when the RV is not connected to the tow vehicle. What does it this mean?

What this means from the standpoint of the neon bulb test is that there is not a good connection (high resistance) between the ground and neutral connections from the neon tester's location back to where the ground and neutral connections are bonded (which should be only at the breaker panel) that feeds the plug that the extension cord is plugged into and there is voltage between the neutral and ground. The reason being for this understanding is that both the neutral and ground connections "should" have very low resistance (almost zero resistance) between the ground and neutral because they are supposed to be electrically bonded together at the origin (house breaker box). In this case this is not occurring and neon light testers cannot tell you why. I also suspect that the B1 and B3 lights on the tester are not all that bright (hard to tell with these testers) and in a very dark environment you may find that both are glowing a little with the RV connected or not.

While the entire understanding of what is occurring cannot be absolutely determined by using only a simple neon bulb style tester (other than that there is enough voltage across the neutral and ground to light a neon bulb), if more testing occurred with the Fluke digital voltage meter (between the Hot, Neutral, and Ground) then for sure the reason for what is occurring could be better determined. What I suspect is that when the RV is connected to the Tow Vehicle is that the resistance changes slightly on the ground circuit which is just enough to light B1.

Points to consider that do not change. There should never be any voltage when measured between the neutral and ground. Any voltage reading indicates a poor connection back to where the two are bonded (or a reverse condition that would never change based on if the tow vehicle is connected or not). In this case, my best thoughts are that the neutral has higher resistance back to the breaker panel where the neutral and ground are bonded and that there is slightly lower resistance to the ground when the tow vehicle is connected.

What to do? Power off the breaker that feeds this circuit, check the resistance between the neutral and ground at the end of the cord (should be 1~2 ohms max, maybe an ohm higher with more cable length), then check the resistance at the plug the cord is connected to and then back to the bond for the two at the breaker panel for this circuit (you may find the issue before checking the breaker panel if what you read is different at the plug than the end of the extension cord). Each point along the way check, tighten, and clean both the ground and neutral line (may as well check the hot as well). I would normally start at the breaker panel, but since this is occurring at the end of an extension cord I would likely start there. If that doesn't reveal an issue, then the next time this occurs, check the voltages while the issue is occurring using your Fluke voltage meter. If B1 is lit then you will find voltage between the neutral and ground, and less voltage between the neutral and ground when the RV is not connected to the tow vehicle (just enough to make the difference for a neon bulb). I suspect that you will still read some voltage (tow vehicle connected or not) and again, there should not be any voltage ever between the neutral and ground as any voltage there (other than a outlet wired wrong) indicates a high resistance connection and in this case most likely on the neutral side.

Also to note, the issue could be with the RV itself, I suspect that is less likely as you have seen multiple RV's report the same issue and those RV'rs likely would know if they see the same issue at other campgrounds or wherever the plug in at, so I highly suspect the issue is on the OP's end and not with the RV. But, it could be anywhere between the tester and the originating breaker panel.

~CA
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Old 01-13-2022, 01:23 PM   #11
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craigav

Very well stated! Thanks for posting
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Old 01-13-2022, 02:27 PM   #12
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Quote:
Originally Posted by FlyboyTR View Post

MY QUESTION WAS... Has anyone come across a situation like this where the trailer being plugged into the the tow vehicle causes the in-line tester to read a hot/neutral reverse?

Yes. There's a couple of reasons why that may be that have nothing to do with your plug and a couple that do. What do the people whose testers show reverse polarity have in common? Is it always GM tow vehicles, for example? Is it always the same brand of tester? Do the trailers all have electric brakes? LED lights? Same brand of charger?



If there is any voltage detected on either neutral or ground pins a tester will indicate reverse polarity. There are a bunch of reasons why a tester might show that, even if the outlet is wired correctly. Without some more information though, it will be hard to pin down. You already know that it only happens when they're using a tester that's connected to their trailer and the trailer is connected to the tow vehicle. You know that there's voltage to the ground or neutral. See if there's another thing that these instances have in common. That will help point you in the right direction. You might also check for a high resistance short in the receptacle. They aren't common and can be hard to detect. It could be that you have a problem on your end that you just haven't detected yet and only some testers are sensitive enough to catch it. Some tow vehicles allow voltage back into them through the trailer wiring harness, and some have isolators. You might find that there's voltage in the ground or neutral only when the right combination of circumstances exist or maybe it's only detectable when the right circumstances exist. Good luck.
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Old 01-16-2022, 08:13 AM   #13
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Thank you CraigAV for a well written explanation.
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Old 01-16-2022, 09:11 PM   #14
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The reason for having the tester is simple, Any RV'er who shows up and says that there is a problem will understand when you show them that the two lights are illuminated and one is out and that shows as CORRECT on the tester. Its real simple, they can understand that. Sure, the voltmeter does the job, everyone who owns and RV should be carrying one, but few people understand them. If you show them with the meter that it is wired correctly, and then begin to explain that this and that is 120v and this and that is zero volts, etc, their eyes are going to glaze over, and they are still not going to be trusting of what you tell them. The tester makes it fool proof simple to show someone its connected properly.

I carry a 15 amp to 30a puck adapter with me and have a cheap harbor freight tester stuck in it. I use it to verify the campground pedestal first. If it looks OK, then I plug my Hughes Power Watchdog into the pedestal, hook up my shore cord and continue to set up.

Charles
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