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Old 02-15-2010, 10:14 PM   #1
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What's this?

On the back of my '76 Tradewind is a small 1/2" glass bubble. Does anyone know what it is for? It is in the attached picture just to the left of the license plate.

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Old 02-15-2010, 10:16 PM   #2
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On the back of my '76 Tradewind is a small 1/2" glass bubble. Does anyone know what it is for? It is in the attached picture just to the left of the license plate.

Attachment 96300
That's the lens for the "reverse polarity" light.

Andy
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Old 02-15-2010, 10:19 PM   #3
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On the back of my '76 Tradewind is a small 1/2" glass bubble. Does anyone know what it is for? It is in the attached picture just to the left of the license plate.

Attachment 96300
A polarity light, it illuminates when the polarity is reversed on your shore power connection.

Bill
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Old 02-15-2010, 10:48 PM   #4
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Thanks Bill. I think it would be pretty difficult to reverse the polarity on a three pronged plug.
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Old 02-15-2010, 10:59 PM   #5
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Thanks Bill. I think it would be pretty difficult to reverse the polarity on a three pronged plug.
It's not the polarity on your plug, its the polarity on the utility pedestal which would be reversed.

Bill
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Old 02-16-2010, 02:08 AM   #6
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If the RV park is wired backwards AND their ground is bad at your receptacle, the reverse polarity light will energize your shell and give you a nasty shock if you step onto wet ground while holding onto any part of the shell. Check out your wiring schematic and you'll see how that can happen.

Low probability, yes. Has it happened? Yes, at least a couple members have posted about this. The real probability is unknown, but if the person who wired the hot/neutral backwards was that inept, then not having a good ground is more likely, which makes this more like a single failure than a dual failure. By the way, when the ground is bad, the light doesn't come on, it just waits quietly to shock you.

I've advocated disconnecting the light. Although the polarity light may have some use today, it's really a holdover from the days when some appliances, like [believe it or not] table-top tube radios, had the 115V "neutral" wired directly to the chasis. If you reversed the old two-prong plugs on those suckers and then touched the chasis, it knocked you on your keester.

Disconnect the light and get a 3-prong polarity tester at HF for $4.

Zep
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Old 02-16-2010, 10:17 AM   #7
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Since you don't know if the source (the outlet you plug in to) or the trailer has a grounded neutral or not, the light is pretty much useless. Especially if there is not a real good ground at the source. I haven't looked into the one on my trailer, but I am assuming the light is wired between the neutral and the ground, which under normal circumstances would be at the same potential (0 volts) or close to that. Then the light should not come on. If someone has wired the source or the trailer the wrong way then the neutral in your trailer will be the hot leg and therefore if you have a good ground it will lite the light since there is a potential (voltage) difference of what could be as much as 120 volts and a serious shock hazard if the neutral of the trailer is in contact with any part of the metal. The ground in the trailer should NOT be connected to the neutral. If you truly want a light to indicate if the trailer power is wired correctly, where you won't get shocked when you are standing on the ground and touch the metal part of the trailer. That is a light that is wired to the metal part of the trailer and to a metal (preferably copper) stake driven into the ground.
Alternating Current, called AC is the power typically used in the home or business. AC power has no polarity, so it is incorrect to call it a "Polarity" light.
Just because the outlet that you plug the trailer in to has three prongs doesn't mean that a ground is present. The safest way would be to have a ground rod ( which is driven into the ground) connected to the trailer via a wire.
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