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Reverse Polarity

August 08, 2010, 05:49:40 pm

Reverse polarity is now a days a brain f@#t on an electrician's part.  In modern electrical installations the hot (usually black or red) 110v wire is supposed to be fixed to the 110v outlet "brass" colored terminal and the white common wire to the silver colored terminal of the outlet.  Most 110v outlets today have green tinted screw terminal to wire the third uninsulated wire otherwise known as "ground".  Reverse polarity is the result of reversing the hot & common wires at the outlet installation.
 
If you own an appliance which has only two prongs for insertion to the outlet, reverse polarity does not affect the appliance performance.  If the appliance has a third prong, it's because polarity matters to the appliance's performance.
 
Here's a story of how I learned this lesson.  About 4 years ago I was visiting with friends in Arkansas and they invited me to park the coach out back by the barn.  The weather was cool so I really did not need to be plugged-in to shore power as my stay was for only two days.  My friend insisted that I plug-in at the barn outlet.  It was a 110v 15 amp outlet.  So as not to be a PITA, I said "Okay, I'll plug 'er-in".  Then I noticed the reverse polarity in the coach's panel glowing red for the first and only time ever.
 
I told my friend about the reverse polarity issue and he said "No problem, I can fix that in 2 seconds."  I was lucky that my 30 amp to 20 amp addapter plug has only two prongs instead of three (as most of them do).  All he did was umplug the addapter and give it a 180 degree turn and re-pluggd back in.  Reverse polarity issue solved.

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Re: Reverse Polarity

Reply #1 – August 08, 2010, 06:55:55 pm

But, (read that a BIG BUT), that means you had no ground connection (since there were only two prongs-- hence "reversible" and no ground prong)!

Not a good idea.

Brett Wolfe

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Re: Reverse Polarity

Reply #2 – August 08, 2010, 07:06:59 pm

Aha...I was lucky and uninformed (read that stupid).  Glad to say that today I'm better informed thanks to this group.  I still read the posts and understand how to apply a lot of the knowledge transfered here...but not all.  Sometimes I'm embarassed to ask seemingly simple questions (read that Stupid as well). 

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Re: Reverse Polarity

Reply #3 – August 08, 2010, 07:14:33 pm

If an appliance has a third wire, it is probably not for performance.  It usually grounds the casing (of a drill, etc), the cabinet (washer, etc) so you do not get electrocuted!
It is there for safety.  Electrons are lazy.  They want to take the shortest path or the path of least resistance.  If there is a hot bare wire touching a handle or housing, the electricity would go through you to get to ground if it were easier than going all of the way back to the wall and then to a ground in the system.  The third wire "helps" the electrons go the right way and not through you, the "short"est way. 

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Reply #4 – August 08, 2010, 08:57:53 pm

I love a hornets nest of ideas. 
We understand the 120 VAC plugs etc.  There are many versions, and now you know why the GFI came about.  Everyone had their own idea of correct wiring and people died from some examples,  at least shocked silly.
I just never saw a indicator in a panel in a RV showing the polarity.
Must admitt that it is a real good idea for a lot of folks.
FWIW
Dave

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Re: Reverse Polarity

Reply #5 – August 08, 2010, 09:17:11 pm

Dave, here's the U270's monitor panel showing the reverse polarity indicator:
http://foreforums.com/index.php?action=media;sa=media;in=1023;preview

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Reply #6 – August 08, 2010, 09:59:20 pm

Our 1976 Airstream trailer had a reverse polarity indicator on the outside of the trailer near the electric cable. There was no voltage meter, but there was warning in case of reserved polarity.

There was a series of articles on RV wiring in recent Family Motor Coaching magazines. I found it very informative regarding polarity and safety issues associated with wiring in recreational vehicles.

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Re: Reverse Polarity

Reply #7 – August 08, 2010, 10:05:05 pm

Hi Dave,
Everyone beat me to this and I posted my reply to the wrong topic!  So I'll try again.
In Peter's PowerWatch photo, the AC Polarity Lights (Normal = Green "ON" and Reversed = Red "ON") are part of the standard PowerWatch Panel that came with our coach. 

The PowerWatch meter above the lights shows the incoming voltage value from either shore power or from the Gen Set. 

A lit Green "Normal Polarity" just means that the 120VAC lines of the incoming line voltages are properly connected to the Hot side (Black) wiring legs throughout the coach. 

If the Red "Reversed Polarity" is lit, either brightly or dimly, it means that the 120VAC incoming voltage has somehow become improperly connected to the NEUTRAL (White) wiring in the coach (i.e.. It is "Reversed"). 

Reversed polarity ALSO means that those highly energetic, but lazy, electrons are just waiting for you to touch the frame (or any other ungrounded coach component (ungrounded by the third Green wire)) and Mother Earth simultaneously and they are going to try to go through you to Mother Earth Ground.  It may be much easier for them to go through you than through some higher resistance load like a light or a motor or any other electrical load on the coach.  It can be a very dangerous situation depending on the various resistances to current flow that are involved (how much current flows through you) and what your muscles do in reaction to the voltage shock (clench and you can't let go). 

There are a lot of ways that polarity can become reversed and, therefore, become highly dangerous:
The power source may be wired wrong (reversed).  Not likely in an RV park but entirely possible in a limited use area, like a service facility or someone's home outlet.  I had this happen at TN RV just this spring.  It had been that way for quite some time and before I noticed it, they were previously unaware of the issue.

The Shore Power receptacle may be improperly wired: i.e., 120 VAC and Neutral reversed

The extension cord may be internally reversed or partially or fully shorted.

120VAC may be partially or fully shorted to neutral somewhere (anywhere) on the coach., like a staple through a Hot wire or a Hot wire partially or fully shorted to the framed or a wire run cover somewhere  Etc.

Anyway, probably much more than you wanted to know, but valuable for us all to keep in mind because we generally came from stable, stick built homes and we are especially prone to wiring anomalies, sitting on our rubber tires, insulated from Mother Earth Ground and routinely plugging into all sorts of power sources, wired by others, with varying degrees of understanding of proper RV wiring and how critical AC polarity is to our personal safety.
Thanks for asking,
Neal

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Reply #8 – August 08, 2010, 11:27:24 pm

Our coaches have a good power management system in them. I was at a campground and plugged in and saw that I had an open ground. The guy putting the wires in the box hadnskinned one and the whole box was hot as were the plugs you plugged into it.  Ouch. The power mananagement system did not let the power into the coach but I got a shock up plugging and then went and found the own and told him he had a huge problem.

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