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Old 11-20-2013, 09:59 AM   #71
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Re: RV Electrical Safety

Hey Mike,
Super great information! I have a short story about a hot skin condition I personally experianced.

I was working on a boxcar years ago that had been converted to a rolling railroad office. I ran new wiring in conduit to a fan and light in the ceiling. I turned the light switch on and hooked up the power cable. The fan and light came on and worked fine. When I turned off the switch, the fan continued to turn and the lights were very dim. For a puzzled moment I just stared at it, then realized I must have a ground somewhere and it was backfeeding through the fan and through the skin of the boxcar to the rails to power the fan! I yelled at everyone working with me not to touch anything and got a fella on the ground to go kill the breaker. Sure enough after tearing down what I had just pulled up I had nicked the hot wire in a bend of conduit.

We were lucky!

I do have a question though. I have a grounding rod from an old military generator that I kept because I tend to keep everything. It has a slide hammer already installed. Do you think it would be a practical idea to pound that baby in everytime I get to a new campsite and connect it well to the chassis and hence the 120vac ground? Seems like that might trip the breaker on a RPBG outlet if I happened to connect to one. What are you thoughts and why or why not would this be worth doing? Thanks!
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Old 11-20-2013, 12:37 PM   #72
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Re: RV Electrical Safety

Quote:
Originally Posted by ferroequinologist
Hey Mike,
I do have a question though. I have a grounding rod from an old military generator that I kept because I tend to keep everything. It has a slide hammer already installed. Do you think it would be a practical idea to pound that baby in everytime I get to a new campsite and connect it well to the chassis and hence the 120vac ground? Seems like that might trip the breaker on a RPBG outlet if I happened to connect to one. What are you thoughts and why or why not would this be worth doing? Thanks!
While at first blush this seems like a good idea, in actuality it will only help ground out any low-current (high resistance) hot-skin leakages. That's because a ground rod driven 8-ft into the dirt could easily have 100-ohms resistance to earth and still be code compliant. So let's assume you have a dead short between a wire with the insulation pinched and making contact with a screw or conduit (as in your example). Since Ohm's law states that voltage divided by resistance equals current (E/R=I) then 120-volts on the frame of your bus will only send 1.2 amps of fault current through your local ground rod (120 volts /100 ohms = 1.2 amperes). Since 1.2 amps will not trip a 20-amp breaker, you'll be lulled into a false sense of security with your local ground rod.

However, a ground rod WILL short out low-current (high resistance) hot-skin currents that are caused by normal hot-to-chassis leakages in all appliances with a grounded power plug. The NEC and UL allow up to 3.5 mA (milliamps) of leakage current from small grounded appliances such as your microwave, computer, television, etc... So these low-current leakages, while generally not dangerous as a shock hazard, would be shunted to earth by your local ground rod, could easily turn into high-current leakages in a heartbeat, which your local ground rod with 100-ohms earth resistance could do nothing to stop, or warn you about. A high-current hot-skin is certainly lethal if you're standing on the wet ground and touch your bus's metal door frame or steps at the same time.

So in short, a local ground rod won't do anything to trip your circuit breaker if plugged into an RPBG outlet.

Mike Sokol
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Old 11-21-2013, 11:13 AM   #73
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Re: RV Electrical Safety

Thanks for your response and after doing the math I agree it would have little benefit.

I will just make sure I do the test for an RPBG outlet everytime I get to a new location.
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Old 11-21-2013, 01:00 PM   #74
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Re: RV Electrical Safety

Quote:
Originally Posted by ferroequinologist
Thanks for your response and after doing the math I agree it would have little benefit. I will just make sure I do the test for an RPBG outlet everytime I get to a new location.
Excellent. Please post a picture of you testing for an RPBG outlet with your bus in the background whenever you get the chance.

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Old 11-22-2013, 09:49 AM   #75
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Re: RV Electrical Safety

Quote:
Originally Posted by jmsokol
Quote:
Originally Posted by ferroequinologist
Thanks for your response and after doing the math I agree it would have little benefit. I will just make sure I do the test for an RPBG outlet everytime I get to a new location.
Excellent. Please post a picture of you testing for an RPBG outlet with your bus in the background whenever you get the chance.

Mike Sokol
Hey Mike,

I have three temp electical box installed in my bus. They are the steel one that I have screwed to the support to the bus. It looks like the outlets connect the ground to the bottom screw I attached the outlet to the box. So for now I have the ground wire conected to the steel of my bus. I do plan to change this.

My question is I test the ground of my outdoor outlet using my DVM. The red wire to the ground plug and the black I stick into the ground. I get about 3 VAC. Is this a good way to test? I get about the same on the bus.
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Old 11-22-2013, 08:37 PM   #76
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Re: RV Electrical Safety

Quote:
Originally Posted by wmkbailey
My question is I test the ground of my outdoor outlet using my DVM. The red wire to the ground plug and the black I stick into the ground. I get about 3 VAC. Is this a good way to test? I get about the same on the bus.
That small voltage difference between the frame of your "grounded" bus and the earth is perfectly normal and expected. In fact, if you were to lengthen the leads of your meter to 100 ft and poke them into the earth that far apart, you would likely find several volts difference, especially if you're close to industrial buildings with lots of electrical machinery. That's because as I often say, the earth is a pretty poor ground. But if you find that your RV's chassis/skin is more than 5 volts above earth potential, then there's a very good chance that your RV's safety ground wire is disconnected from the electrical service box's Ground-Neutral-Earth bonding point which forms what I think of as a "ground plane".

So not to fear. Measuring 3 volts between the frame of your bus and something like a screwdriver stuck in the dirt is quite normal.

Mike Sokol
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Old 12-21-2013, 09:33 PM   #77
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Re: RV Electrical Safety

Something else the moderator may want to move up to the top page of this thread. I've just written an article defining both low-current and high-current hot-skin conditions, along with an explanation of what causes each to occur. It's in the December 2013 issue of RV University e-zine. Here's a link to a free copy: http://www.rvuniversity.com/article.php ... 3015512298

As always, contact me directly if you have any RV electrical safety questions.

Mike Sokol
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Old 12-22-2013, 02:38 PM   #78
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Re: RV Electrical Safety

Mike
As always thank you!
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Old 12-22-2013, 03:22 PM   #79
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Re: RV Electrical Safety

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Originally Posted by bansil
Mike
As always thank you!
You're most welcome.

Just to keep you all in the loop, I'm working on a grant that will allow me to produce a series of electrical training and safety videos/articles for the pro-sound and theater lighting industries (my real gig). Unfortunately, I've come up with zero support for the more RV electrical safety articles. That's a pity since there's a lot more RV owners then there are pro-sound engineers. I consider this to be a consumer health and safety issue, so I'll continue looking for a government or foundation grant. If anyone here knows of any such grants, please let me know.

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Old 06-12-2014, 08:08 PM   #80
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Re: RV Electrical Safety

Please post the following to any forums you belong to.

Mike Sokol from The No~Shock~Zone will appear live on the RVtravel webinar on Saturday, June 21 at noon EST. He'll be discussing RV electrical safety as well as announcing his upcoming eBook on Amazon titled "No~Shock~Zone - RV Electrical Safety". Here’s the link to the webinar: https://www.youtube.com/user/RVtravel

Email your RV electrical questions in advance to mike@noshockzone.org

Thanks... Mike Sokol (jmsokol)
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