AC Electrical Query
Dear RV Doctor:
I have a quick electrical question. My friend was cleaning his motorhome, and when he touched the rims, he received a slight tingling sensation or shock. When I came over, we first checked the shore power outlet at his house and it was fine. But where the cord plugged into the adapter at the motorhome, we found that the ground prong was broken off. We hooked the coach up to a new extension cord with the proper ground prongs, and that solved the motorhome’s hot skin issue. Why would there be stray voltage or leakage at all, given that the electrical system should be in working order? Should my friend be concerned that there is a screw nicking a hot wire, etc., or do you think everything is okay?
Michael
Under no circumstances should you ever feel a tingle or any type of shock when touching a metallic portion of an RV. A hot skin condition exists only when something is wrong with the electrical source, a pigtail adapter, a shoreline cord, an extension cord, or some other device in the source circuitry. In rare cases, something could be amiss inside the motorhome. Having an open ground connection is indicative of a dangerous situation and should be investigated and fixed.
Since the connection is coming from the house outlet, you should check the outlet for proper polarity. The short and straight slot is hot; the long and straight slot is neutral; and the round is ground. So connecting short to long or ground should register 120 volts. Connecting long to round should register 0 volts.
Most 120-volt-AC components connected in the motorhome and its outlets will have a small amount of current leakage to chassis ground. Moisture in the wiring, worn insulation, a loose or corroded ground connection, an aging transformer in the converter/charger, or a failed component in any other device can cause this leakage to ground, provided there is a good safety ground throughout the circuitry. Typically, low voltages — 30 volts or so — are current-limited and have only a few milliamps running through them. If there’s a tear in the insulation of a conductor or a loose connection, etc., the voltage can go much higher and the current might soar to 20 milliamps or more.
With dry hands, 30 volts might result in a slight tingle, but if the ground is wet or your hands are damp, that same low voltage might produce upward of 30 milliamps of current. Receiving a 20-milliamp shock is significant enough to lock up muscles, and 30 milliamps can cause a heart attack.
Using an ungrounded extension cord or pigtail adapter is what my friend, Mike Sokol, who answers electrical questions at www.noschockzone.org, calls an electrical version of Russian roulette. The bottom line is to never use an ungrounded extension cord, shore power cord, or receptacle to power the motorhome. In my seminars, I teach folks to always measure for the proper voltage AND test the voltage for the proper polarity before plugging in to any voltage source. An inexpensive non-contact proximity tester is a must-have device for all motorhome owners. The tester is used to verify the source voltage polarity after measuring just how much voltage is present at the receptacle. Check out this video (www.youtube.com/watch?v=gc65hEmeyPE) that was shot during FMCA’s Family Reunion and Motorhome Showcase in Gillette, Wyoming. It demonstrates how to perform these tests.
The coach itself can be tested using a ground loop impedance tester to determine whether anything is amiss. A simple digital meter can be used to verify that the motorhome is void of any remnant electricity that could lead to a hot skin condition.
I would highly recommend that your friend have his motorhome thoroughly tested to be certain that the missing ground pin on the adapter was the cause of the shock. This is one area where redundant testing is encouraged. Using a non-contact proximity tester is the best way to determine polarity; to make sure that each of the contact points in any source receptacle is correct; and to ensure that hot is where it should be, neutral is where it should be, and that there is a secure safety ground, bonded to the frame of the motorhome and consistent all the way through the circuitry.
Oops! Gray Tank Damage
Dear RV Doctor:
I have a problem with the gray water tank on our 2007 Pleasure-Way Plateau Type B motorhome. The motorhome high-centered (the bottom scraped across the ground), and the connection to the drainpipe was damaged. The spin fitting cracked, and there is a fine crack approximately 1.25 inches into the gray tank at the opening to the drainpipe. The spin fitting has been removed (kind of chiseled off). My question is, can a new spin fitting repair be done? Is it worth trying, or do we need to replace the tank?
Shelley Drogin
Kirkland, Washington
In many instances, plastic holding tanks can be permanently repaired through plastic welding. In some cases, though, it might be better to replace the tank altogether. If the crack extends into the actual drain opening of the tank, I’d probably lean toward replacing the entire tank. Plastic welding requires a special plastic welding machine and specific training; not all RV service centers are so equipped. I would recommend careful analysis and inspection by a pro technician before condemning the tank. If the drainpipe or dump valves put just a little bit of undue stress on the tank outlet, even plastic welding the crack may not suffice. I’m not aware of any RV service centers in the Seattle area that can perform professional plastic welding, but it would be worth the time to call a few.
Alarm Problem
Dear RV Doctor:
Following the “Ask the Experts” panel discussion that was held during FMCA’s Family Reunion and Motorhome Showcase in Gillette, Wyoming, I spoke with Walter Cannon, executive director of the Recreation Vehicle Safety & Education Foundation, about what might be causing carbon monoxide/propane alarm failures in my motorhome. I just put in the fourth unit since the coach was built in January 2012. He feels strongly that the problem must be power-related but suggested that you were better qualified to address this. The Atwood LP/CO alarm has both power (red) wires connected to 12+ and the black return to a white wire (ground?). I think the failures have occurred when parked and connected to shore power. The converter/charger is a Xantrex XADC P50. Do you have any ideas as to what is going on? I think it might be switching pulses, so I’d like to add a ferrite choke on the 12+ at the alarm to see whether that might help.
Dick Reid, F403470
Boynton Beach, Florida
The only thing that immediately comes to mind is that the sensitivity of the combination CO/LP alarm might be such that it requires filtered voltage instead of converter output voltage, which at times can produce “dirty” electric, oftentimes with AC voltage residue. I’ve not heard of any issue with the Atwood alarm. Before adding any electrical components to the circuit — I’m always hesitant to modify such equipment unless necessary — I’d first temporarily wire a conductor directly to the positive post on the battery bank rather than tapping in at the existing location. A bank of batteries is the ultimate filter, and having that provide the voltage, rather than a connection at the converter, should do the trick. If that method sufficiently satisfies the sensitivity of the alarm, then route a permanent wire directly to the battery bank, protected by a fuse, of course.
By the way, isn’t it great that FMCA schedules that “Ask the Experts” seminar? Being on that panel over the years has been a joy, and the level of technical understanding among the attendees and other panelists always impresses me.