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Old 05-25-2010, 08:44 PM   #1
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Question polarity light

When I plug my trailer into an ac outlet my polarity light comes on and my power light is not on, I was wondering if anyone might know what my problem is?
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Old 05-25-2010, 08:55 PM   #2
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If it does it regardless to the source you plug into, the positive and negative wires are crossed somewhere in your system- at the plug would be my first guess. It is, however, possible that the outlet that you are plugged into is the culprit. There are a bunch of posts on this.
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Old 05-25-2010, 09:40 PM   #3
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Scotty see here and here
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Old 05-25-2010, 11:54 PM   #4
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This is an indication that either the power source or the plug on your trailer is wired wrong. There is no polarity on AC current. What this indicates is that the "hot leg" and the "neutral" are not connected correctly. Depending on whether or not the neutral is grounded to your trailer frame, IT SHOULD NOT BE, you could have a serious shock hazard. There are plenty of threads here to guide you through the process of making sure that any power source you connect to is correctly wired. But your first step should be to make sure your trailer is wired correctly.
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Old 05-26-2010, 12:12 AM   #5
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It might not be wired backwards. If your neutral line is broken, it will show up the same way. The polarity light only shows that you don't have the same voltage on neutral and ground.
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Old 05-26-2010, 11:10 AM   #6
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The polarity light only shows that you don't have the same voltage on neutral and ground.
This topic has a lot of confusion that needs careful definition of words, I think.

For one, "ground" means chassis or frame or skin connection and not earth ground. The chassis ground should be connected to the green wire in a modern electrical system. There should be only one place where that green wire is connected to earth and that is at the service entrance that is usually also where the meter is.

Another is that the polarity light indicates a current path and not necessarily just voltage (a subtle but important point). The service manual schematics are not clear about the actual wiring but it does appear that the light indicates that there is a potential for current to run from the 'neutral' side of the electrical system to the chassis ground. The 'neutral' or black wire should be connected to the chassis ground or green wire at only one point and that is also at the service entrance with the meter. Having current able to flow between them indicates that not only are they not connected together, they are connected to other things that can provide a circuit for electricity.

Some folks measure voltage between the green and black wires but the impedance is so high that no current will flow. This can happen with small, plug-in, 120v gensets which do not have a 'neutral' by code definition and may keep the power leads isolated from chassis ground. That also confuses people because the grid centric indicators do not show a light between hot (white wire) and ground as you should get when connected to a grid. Only one light on these wiring fault indicators with portable gensets is OK.

There are three circumstances that are involved. One is grid power where ground, neutral, and earth are connected together upstream from the RV at the pedestal or park (or home) service entrance. A second is when you have your rig plugged into a portable 120v genset or inverter where the hot leads can be isolated from the ground and, properly speaking, there is no neutral. The third case is when you have a transfer switch with a larger genset or 240v split phase power where the proper connections should be handled by the transfer switch.

Take due care as even the so called 'experts' on some blogs and magazines have offered ignorant advice on this topic (see Watch out for supposed experts).
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Old 05-26-2010, 06:45 PM   #7
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I totally disagree with Bryan. The BLACK is not the neutral. The WHITE wire is the neutral. Every electrical panel I have seen is wired with the Black wires on the "HOT" side of the circuit. All Black wires are connected to the circuit breakers in a distribution panel. The WHITE wires are connected to the NEUTRAL buss (a multiple screw bar mounted on the panel surface. There may be a GROUND buss in these distribution panels for connecting the Bare or green wire. Depending on the panel location in the electrical distribution system the NEUTRAL may not be connected to the ground buss. Connecting the ground wire to the chassis of the trailer, as it should be, does not guarantee that you will have an EARTH ground. The only way to absolutely guarantee that your trailer is grounded is to drive a proper ground rod that is driven into the EARTH which is in turn connected to the trailer chassis..
Do not confuse the Ground wire (which is actually the COMMON wire) in a DC circuit with the GROUND wire in an AC Circuit. They are totally different animals.
Virtually every AC electrical device with a metal chassis is wired with a plug that can only be plugged into the receptacle one way. You will notice that if the plug has 2 blades, one of them is wider than the other, unless it is a 3 prong plug with a ground connection. This is to make certain that the device is correctly connected that the neutral and the hot leg of the electrical circuit.
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Old 05-26-2010, 07:21 PM   #8
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Originally Posted by bryanl View Post
... The 'neutral' or black wire should be connected to ...

...Take due care as even the so called 'experts' on some blogs and magazines have offered ignorant advice on this topic ...
Quote:
Originally Posted by TG twinkie
I totally disagree with Bryan. The BLACK is not the neutral. The WHITE wire is the neutral.
I agree.

Bryan posted badly.

Let's hope he follows up with a re-statement. The information he posted does confirm to commonly accepted electrical practice.

Tom
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Old 05-26-2010, 09:57 PM   #9
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The info posted by Bryan appears to be refering to Generators. They call them generators, but they are really alternators, which produce AC current. The inverter type generate DC and it is converted thru the INVERTER to resemble AC. In these type of power sources both wires of the Genset are floating above ground. If you had a high impedance voltmeter you may be able to read a potential difference (voltage) between the output wires and earth ground.
If one of the conductors comes in contact with the EARTH thru moisture or mechanical damage and the other conductor comes in contact with the chassis of the trailer. You could get a shock if you're standing on the ground and touch bare metal on the trailer. This is where grounding the trailer with a ground rod would make sense. The current would then pass thru the ground wire and not you. It will take the path of least resistance, that could be you if the system is not safe..
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Old 05-27-2010, 09:10 AM   #10
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The BLACK is not the neutral. The WHITE wire is the neutral. Every electrical panel I have seen is wired with the Black wires on the "HOT" side of the circuit. ... Bryan posted badly.
yep, thanks for the correction. good catch.

re: "The info posted by Bryan appears to be refering to Generators. They call them generators, but they are really alternators, which produce AC current." --
Sorry. The Honda 2000, for example, is referred to as a generator or perhaps genset. I do not know of any such devices being called alternators.

re: "If one of the conductors comes in contact with the EARTH" --
If there is only a single fault, you won't get a shock hazard. With an isolated system that would take two faults.

There is no need or reason in any practical power terms to go around putting an earth ground in for your trailer at campsites. Nor is there any need or reason to override the manufacturer and connect the 'neutral' to the chassis ground in a small portable plug in type genset.

The electrical code has evolved of the years and has much experience within it. It should not be set aside without very good reason supported by equivalent theory and practice.
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Old 05-27-2010, 09:44 AM   #11
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interesting phenomena here -- worth thinking about IMHO.

The color swap error is a good one to catch but all it should need is a simple correction. Important, but no biggee as the principles described were not impacted.

But why the "totally disagree," the alternator idea, or the request for a 're-statement' ??

"totally" is a strong word. The alternator thing goes back to when alternators replaced generators for engines many years ago. There is no need to restate a mistatement where a simple correction is provided that doesn't change the underlying principles.

It seems something else is going on here. It's like I provided a threat or something. Now, why could a simple rundown of modern electrical code do that? What is it that actually bothers people enough to come in with such strong words?

I do know that this particular topic does seem to get some people going. The earth and faults and GFI topics, especially, seem to really stimulate blind advocacy to near fanatical levels. Why?
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Old 05-28-2010, 12:17 AM   #12
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Hey Bryan. Nothing personal at all. I just didn't want someone thinking that the white wire was the problem because it wasn't the hot wire.
I don't understand why the generator-alternator thing is such a touchy issue. Even the manufacturers still call them generators. I was only trying to point out to the novice (and I don't mean you) that there is a difference. Just like there is in Converters and Inverters.
I get concerned when there is incorrect information put out. Some ones life could be at risk. It's merely a safety issue from my point of view.
I didn't say the neutral should be connected to the chassis. In fact I said just the opposite. It is my opinion that only the ground wire should be connected to the chassis. The reason being, now I'm not talking about portable power here, I'm talking about drawing power from the grid. Here is my reasoning. In the case where you draw power from the grid, there is a true neutral and a true hot wire, white and black respectively. If the plug on the trailer or the receptacle at the power source is wired incorrectly, meaning the neutral and hot have been reversed where the white wire (neutral) is now the hot wire and it is attached to the chassis, then the skin of the trailer is hot. This creates a shock hazard. If the neutral wire is not connected to the chassis then there is no hazard either way.
You are correct that if everything is wired to code it should be safe. But when you pull into some mom and pop RV park. How do you know that they have a properly wired and grounded system? You can carry a plug in device that will help you determine that, but not all people do. I'm also not advocating that you need to drive a ground rod every time you camp, but it is the safest solution.
I apologize if I hit a nerve here. I think we should keep discussions like this going. Everyone learns from them. And by all means if you think that I am wrong about the neutral not being tied to the chassis, please give me your input.
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Old 05-28-2010, 05:24 AM   #13
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For Scotty if the polarity light comes on you most likely have a reversed hot / neutral wire either at your plug end or where you are plugged into.

The plug should wired black to the copper screw, white to the silver screw and bare or green to the green screw.

For Twinkie;

Do "not" bond the ground (bare or green wire) to the trailer chassis, the RV is considered a sub panel and should be wired as such.

As bryanl said neutral and ground are "only" bonded at the service panel (CG main breaker box) and not in the camper breaker box.
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Old 05-28-2010, 09:02 AM   #14
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Every outlet receptacle I have ever seen the ground terminal is connected to the metal frame of the receptacle and that is the mounting flange which is screwed to the receptacle box. The box is fastened to the metal skin of the trailer thus grounding the skin of the trailer. Unless it is a non conductive box. Lots of light fixtures also have the ground wire fastened to the frame of the fixture which may touch the aluminum inner skin of the trailer, thus making the skin both common and ground. If the white and ground are fastened to a common buss in the entry box then the trailer skin becomes the same as the common and ground. Which if the common and hot wires are switched at a campground service creates a shock hazard from the trailer skin.
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