Important - check this every time you set up |
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
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Topic: Important - check this every time you set up Posted: 27 May 2014 at 10:17pm |
A NCVT such as a Fluke VoltAlert gets its ground reference by coupling through your feet to the ground, which is why you need to grip the tester in your hand. For a voltmeter test, a screwdriver in the ground will suffice for earth reference. If you're in dry soil, dump a gallon of water on the dirt first to improve conductivity. Please note that this is NOT a true ground rod and won't protect you from a hot-skin current leakage. It's a high-impedance earth reference at best, but should give you an accurate earth potential measurement using a modern digital voltmeter. Don't use a solenoid tester for this measurement as it has too low of an impedance for this type of quickie earth ground. |
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mike@noshockzone.org
www.noshockzone.org |
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Kermit
Newbie Joined: 16 Mar 2014 Location: SC Online Status: Offline Posts: 17 |
Post Options Quote Reply Posted: 28 May 2014 at 12:05am |
Ok, thanks.
I have a no touch cheap tester that seems to work well for testing the power outlets. I thought i had a hot skin condition this past weekend on our trip. The 30 amp outlet at the power post had proper polarity however I was getting a positive test with my no touch tester around the steps,door frame, and frame behind the steps. I had to touch the tip of the tester to the surfaces for it go off though.(My power distribution panel for the rv is directly next to the door just inside within 8 inches.). I switched over to the 20 amp outlet on the post and at first my tester was positive at the steps but neg on the door frame. I double checked the polarity of the 20 amp outlet and it was correct. Afterwards I could not get a positive signal again at the steps or anywhere else. (I know my tester was working bc I check the breakers in my distribution panel and it worked). I never switched back to the 30 amp outlet and tested the camper again hooked to 30 amps. At home in the driveway I have a 30 amp outlet and I do not get a positive result. I have not checked with my multimeter yet as I wasn't quit sure how to reach a ground for my meter.
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'14 182g
Towed by various Jeeps |
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
Post Options Quote Reply Posted: 28 May 2014 at 4:26am |
Everyone should be aware that reversed Hot-Neutral polarity by itself WILL NOT cause a hot skin condition of any kind. It will, however, endanger the life of any technician working inside an open electrical panel that's powered up. Also, it's important that your NCVT is calibrated against some known standard. Some of them have higher sensitivity than others and thus there's no easy way to predict the actual voltage they'll trigger on with various energized surface areas. Even with a common NCVT, there will be a lot of trigger voltage variance depending on how large of a surface area is energized. If you get ANY NCVT beep/flash touching the tester tip to ANY part of your RV, then I would suspect you have at least 40-volts hot-skin. Usually, beeping at 4 inches away from an RV chassis suggests around 60 volts, 8 inches away suggests 80 volts, and 1 to 2 feet away suggests 120-volts. Of course, an RV with a totally metal skin will offer a much larger energized surface than a fiberglass RV. So an Airstream with an aluminum body at 120-volt hot-skin will light up a tester from 2 feet away, but your R-pod with 120-volts might only do it from 1 ft away. However, the only way to know for sure is to do exactly what you propose... measure between earth ground and the RV chassis with an actual voltmeter. Remember that you'll need to poke through any paint or rust on the RV to get an accurate reading, so I've found that the lug-nuts on the wheels to be a good spot to poke a meter probe that won't damage any cosmetics. No need to try this at multiple spots on your RV. If it tests high at one spot, then it will be everywhere. Measuring any more than 2 or 3 volts from the RV chassis to an earth ground rod reference is suspicious and needs to be looked at much closer. As an example, here's a video of me testing a 40-ft RV for various hot-skin voltages using a Fluke VoltAlert. http://www.youtube.com/watch?v=Y8h64X33aKg Kids, don't try this at home as it's a VERY dangerous experiment to do. However, I do perform this demonstration in my NO~Shock~Zone clinics using various RVs at hand. It's a real crowd pleaser... |
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mike@noshockzone.org
www.noshockzone.org |
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techntrek
Admin Group - pHp Joined: 29 Jul 2009 Location: MD Online Status: Offline Posts: 9059 |
Post Options Quote Reply Posted: 28 May 2014 at 8:32am |
Kermit, one possible ground connection, if you are testing with a voltmeter, would be an extension cord plugged into the 20 amp outlet. Just make sure you are hitting the ground pin and not the hot leg or you could get a false positive.
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Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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fwunder
Senior Member Joined: 04 Oct 2013 Location: New Jersey Online Status: Offline Posts: 1676 |
Post Options Quote Reply Posted: 28 May 2014 at 1:29pm |
This was definitely a wake up, slap in the face revelation for me after finding I had a hot skin situation in my driveway just because I was trying to save a few dollars with my extension cord. Really pretty stupid considering I just ordered a 25 foot proper extension for $36.00.
Next will be a proper 30 amp receptacle for home. fred
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2014 RPod 178 => MyMods and Buying Habits
2008 4Runner Limited 4.0-liter V6 Yes, those are wild ponies dining on grass while dumping tanks! |
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Kermit
Newbie Joined: 16 Mar 2014 Location: SC Online Status: Offline Posts: 17 |
Post Options Quote Reply Posted: 28 May 2014 at 2:52pm |
At the site I was at this past weekend, if both the 30 amp outlet and the 20 amp had proper polarity, would the possible hot skin reading I was getting caused by a faulty ground on the power post. What is the correct procedure to verify the ground on the outlets?
I will be using this same camping spot in the future as my in laws have a permanent site there and the site I used is the only tent site that they allow small campers/pop ups to use. Thanks Joe |
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'14 182g
Towed by various Jeeps |
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techntrek
Admin Group - pHp Joined: 29 Jul 2009 Location: MD Online Status: Offline Posts: 9059 |
Post Options Quote Reply Posted: 28 May 2014 at 3:06pm |
Assuming the outlets are wired correctly, then a broken ground is likely the only problem. This is the situation I encountered at home last summer. The best way to test for this is with a voltmeter - testing for continuity between a known good ground connection (another outlet or the enclosure) and the ground in question. Or testing for continuity with the neutral. Or, testing for voltage between the hot leg and the ground pin. A plug-in tester would also identify a broken ground, probably doing the same thing as the last test I mentioned.
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Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual
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jmsokol
Groupie Joined: 21 May 2014 Location: Maryland Online Status: Offline Posts: 89 |
Post Options Quote Reply Posted: 29 May 2014 at 7:38am |
One thing I do as a quickie alert is to leave a basic 3-light cube tester plugged into an RV outlet that's visible. If you do have a ground open up on an extension cord, you'll see the light pattern change. It's not a definitive test for every problem, but it will tell you if there's a lost ground. And yes, using the ground of a second extension cord to test for hot-skin voltage is valid, but only if it's correctly wired with solid continuity. Also, while a surge protector won't alert or protect you from an open ground or hot-skin condition, a surge/voltage protector from a company like Progressive Industries will disconnect your RV from the hot/neutral lines if it detects an incoming open ground. That should protect you from 99% of outlet failures, but WILL NOT detect or protect you from an RPBG hot-ground. I think the $300 cost of a voltage/surge protector is pretty cheap insurance considering the investment you have in your RV. |
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mike@noshockzone.org
www.noshockzone.org |
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fwunder
Senior Member Joined: 04 Oct 2013 Location: New Jersey Online Status: Offline Posts: 1676 |
Post Options Quote Reply Posted: 29 May 2014 at 8:30am |
Mike,
I've been doing quite a bit of reading since my chassis lit up from an open ground extension cord. My understanding now is that the open ground itself could not be causing the hot-skin. There must be a circuit leak somewhere else causing current to the chassis. Is this correct? If so, how would I check the rPod appliances and circuitry to expose the leak? Thanks for the info! fred Edited to add: My garage is the only part of my home that was not rebuilt a few years ago and has miles of wiring and it's own panel. Could there be a "short" upstream of the pod causing a leak? |
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2014 RPod 178 => MyMods and Buying Habits
2008 4Runner Limited 4.0-liter V6 Yes, those are wild ponies dining on grass while dumping tanks! |
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Old Dingo&Mrs.Dingo
Senior Member Joined: 07 Jul 2012 Location: Tarentum, PA Online Status: Offline Posts: 138 |
Post Options Quote Reply Posted: 29 May 2014 at 9:09am |
I've been following this thread with great interest, and I will be the first to admit, I know very little about electricity, except the more I learn about it, the less I seem to know.
If we keep the safety chains and tongue jack on the ground, without an insulating wheel or plate, how can the "hot skin" be a danger? (assuming the chains and jack are resting directly on the earth or grass, and not on a concrete pad) The human body isn't as good a conductor as the steel jack or the safety chains. Electricity chooses the most direct (easiest) path to ground, and we are using the same "ground" in both cases. What about a external ground strap from the chassis to a conductive "pin" in the ground, installed before the unit is connected to the "power supply"? Maybe a plastic mat in front of the step? (I use one anyway to limit the dirt tracked into the 'pod) Shouldn't we be advocating these steps, as well as testing, as part of a safe "power post connection procedure", knowing that everything can change the minute someone backs into a power post??
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Old Dingo and/or Mrs. Dingo
181G 2013 Jeep Grand Cherokee |
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