# Checking Polarity



## GoVols (Oct 7, 2005)

One of the RV electrical 101 items is to check the polarity of the campground's power pedestal before hooking up your RV. If it is wired incorrectly you can be in for a nasty shock or damaged equipment. Here's my problem/question: you can find circuit testers all day that fit a normal 15 amp plug, but I'm wondering how you check polarity on the 30 amp plug? I'm not an EE, but I would think checking the 15 amp plug with your $10 circuit tester does NOTHING for determining whether or not the 30 amp is OK.

Am I missing something? How do you check polarity/correct wiring on the 30 amp plug?


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## GoVols (Oct 7, 2005)

I am going to answer my own question! WHEW! Glad I thought of this before someone else pointed out my stupidity:









Use your 30 to 15 amp converter plug, stupid! Plug the 15 amp circuit tester into the converter plug, then the converter plug into the 30 amp socket.


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## biga (Apr 17, 2006)

I think you can determine it using a volt meter. I have a buddy that is an electrician, and I have seen him do it, but I don't remember exactly what it should look like. I think you should have 110v from one prong to the ground, and 0v from the other prong to ground, but I'm not shure which would be which.


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## GoVols (Oct 7, 2005)

biga said:


> . . . , but I'm not shure which would be which.
> [snapback]111940[/snapback]​


Me neither; that's why I will use one of those plug-in testers. I do use my multimeter to keep abreast of voltage though.


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## CamperAndy (Aug 26, 2004)

You have a 30 to 15 amp adapter? Not too much call for that kind is there? I have a 15 to 30 amp adapter which will not help too much. Below is a picture of a plug and the identification of the holes so you can check with a VOM.


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## biga (Apr 17, 2006)

I talked to my buddy, and on a 15A plug, the short slot is the hot. You should see full voltage from the hot to the ground and from the hot to the common (or neutral). Ideally, you should see no voltage from the common to the ground, but sometimes you will see a few volts.

Given the picture Andy posted, you would check the 30A the same way.


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## Katrina (Dec 16, 2004)

CamperAndy said:


> You have a 30 to 15 amp adapter?
> [snapback]111947[/snapback]​


Don't you?









I bought one just to keep a polarity tester plugged into for checking CG power.
Easier for me than dragging out the volt meter.
3 bucks for the polarity tester and 3 bucks for the adapter.
Easy to use.


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## GoVols (Oct 7, 2005)

Katrina said:


> CamperAndy said:
> 
> 
> > You have a 30 to 15 amp adapter?
> ...


Yes, yes, you know what I mean . . . that do-witchy thang that lets you step down your 30A RV male plug into a 15A socket so you can overload the circuit and throw the breaker!









The REAL question is, "how many of you check polarity before hooking up?"


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## hatcityhosehauler (Feb 13, 2004)

I never have, but I guess I will start now. To be honest, I'll have to claim some ignorance here. I never realized polarity mattered much with AC current, as I always understood it as constantly alternating....hence the name. I see that I am wrong.

Tim


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## GoVols (Oct 7, 2005)

I would expect with the popularity of camping, and the limited number of campgrounds, that any polarity problems out there have been found by an unfortunate few -- then corrected. I would expect the greater danger would be within the RVs themselves, whenever Gilligan is running wire at the plant that day!


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## s'more (Jun 8, 2005)

While at home, with the TT plugged into an extension cord, parked in the driveway and installing a license plate frame on the new TT, I thought that I was feeling a bit of a tickle in my arm that was resting on the rear aluminum bumper. After feeling this a few times, I wondered if I was actually feeling electricity. Got out my ohm meter, stuck one lead into the earth, and the other on the bumper ..... 49 volts.

After first mentally assigning some new colorful expletive names to "Gilligan," I wondered how this could happen. Then realized the problem may not be in the TT. Checked the outlet that I was plugged into, = reversed polarity.

Apparently reversed polarity can energize the metal frame of the TT because the hot (source) is going to the TT neutral or common, which is probably tied to the ground (I haven't actually looked yet).

The safety hazard then, would be if you were to grab the metal handrail outside the entry door, while standing on bare ground, especially if you were barefoot, and double especially if it were raining or wet, then you would be completing the circuit between the TT and ground ..... ouch.
Or possibly one bare foot on the metal step, and one bare foot on wet earth ..... ouch again.

One bright note about having reversed polarity though, ....... at least the bathroom exhaust fan would be spinning the right way







.


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## Huskytracks (Apr 18, 2005)

Do the tester/ adapter thingy. Thats how I checked the line out in my garden.


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## shaela21 (Aug 16, 2005)

The Surge Guard 30 amp surge protector checks the polarity before you plug into the pedestal. Before this I would check the power supply and I never did find any polarity problems, but I did find a low voltage outlet once. We ended up dry camping that weekend







.


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## outbackgeorgia (Jan 28, 2004)

The "polarity" referred to here is the "HOT" and "Ground" polarity, not the polarity of the electricity which is indeed alternating.
The issue is safety, so a third safety ground wire is separately run in case the palarity is reversed.
s'more, you should check the wiring, as even if the "polarity" is reversed, you should NOT get a "tickle" from the metal as the "safety ground" should prevent this. This is the third "round" pin and green wiring throughout the trailer. Neutran and Ground should be securly bonded together at a single point in the trailer.
There have been several cases if loose setscrews in the wiring systems, easily fixed.
This indicates less than a perfect ground somewhere in your trailer frame system.

Outbackgeorgia, BSEE


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