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Topic: Check your shore power cable every now and again (Read 801 times) previous topic - next topic

Check your shore power cable every now and again

I just thought I'd put this out here in case anyone else is in the same boat with an older coach.  I recently "got" to get the radiator re-cored, and did the R & R in my driveway. I noticed, as I was doing this oh so fun job, that every now and again I'd feel a pinprick sometimes, like there was something sharp on my creeper that was poking at me. I never did find anything though. Then, getting ready for our most recent trip, whilst checking the undercarriage and looking for any leaks and doing the general preflight inspection, once in a while well there it is again.. What the heck? Was that a bee sting, or a.... jolt? Naw. Couldn't be. Everything in the rig is fine, nothing wrong showing on the power meter, my little polarity/short checker tool that you plug into a socket said all clear no troubles here, boss. Well, I may be slow on the uptake, but I have a jaundiced and suspicious nature when it comes to electricity. So out comes the multimeter and I intermittently  measured about 40v AC between a wheel and the ground when plugged into shore power. During those fun occasions my little socket tester no longer said "all AOK"...My, how alarming. I have to wonder, given how galvanic corrosion can work, how much this ground short had to do with needing to re-core the radiator in the first place. Anyway, I figured I'd start by checking the shore cable front to back and quickly diagnosed a fault in the plug at the shore end. New plug at camping world, cut off old plug and install the new one, complete with a nice layer of solder on the joints just to be certain. I think, I hope, i dodged a bullet. This much power to ground could be a real horror show for things like wheel bearings, and, well, everything electrical. From here on out I'm going to use my outlet tester every time I plug into shore power.
Jay
1989 U280 SE, 36', 3208T Cat, build 3292

Re: Check your shore power cable every now and again

Reply #1 –
Quote from: twobus –
...intermittently  measured about 40v AC between a wheel and the ground...
Thanks for sharing.  Glad you found this without more that a minor jolt!

Wondering, is this condition one that would be detected by a Progressive EMS unit?
Mark Duckworth
2003 U320 4220
Build 6199, Motorcade 17971

Re: Check your shore power cable every now and again

Reply #2 –
Quote from: twobus –
So out comes the multimeter and I intermittently  measured about 40v AC between a wheel and the ground when plugged into shore power. During those fun occasions my little socket tester no longer said "all AOK"...My, how alarming. I have to wonder, given how galvanic corrosion can work, how much this ground short had to do with needing to re-core the radiator in the first place. Anyway, I figured I'd start by checking the shore cable front to back and quickly diagnosed a fault in the plug at the shore end. New plug at camping world, cut off old plug and install the new one, complete with a nice layer of solder on the joints just to be certain. I think, I hope, i dodged a bullet. This much power to ground could be a real horror show for things like wheel bearings, and, well, everything electrical. From here on out I'm going to use my outlet tester every time I plug into shore power.

Jay, I could be wrong, but I believe that's what's known as "hot skin" in the RV world and is dangerous to more than just electronics.  If it *is* the same as "hot skin" it can kill, so very good that you found the problem and fixed it!

Michelle
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Check your shore power cable every now and again

Reply #3 –
If I ever had to change my cord and or plug I would go with the orange aftermarket brand,can research here on the forum plenty of info.
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: Check your shore power cable every now and again

Reply #4 –
Chuck - the link came up as a "404 - not found" for me.

ETA - I looked at the "RV Safety" on that site and see both "Hot Skin", one of the oldest articles, and "Are Little Shocks Normal/OK" (or something like that) as one of the newest articles.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Check your shore power cable every now and again

Reply #5 –
No~Shock~Zone ยป August 2013
Then click on 24 comments.
JohnH
Coachless, now use aircraft. 2003 Ford Travelair TC280 class C. Super shape. Just for 1 yr .
1994 Ford E350 ClassC,total renovation inside and out. Now sold.
2000 U295  36' Cummins 350 c/w Banks Stinger, Resonator upgrade,Solar, LED lites.Residential fridge with slide out pantry. Build 5674. Sold
ex 92 GV 022C ored Cummins. Sold
ex 95 GV240 cat 3116. Sold
2017 Mini cooper s & 2016 land Rover LR2 HSE  LUX.
jhaygarth@aol.com    SKP #130098
treat everyone as you would like to be.

Re: Check your shore power cable every now and again

Reply #6 –
Quote from: Mark Duckworth –
...........................Wondering, is this condition one that would be detected by a Progressive EMS unit?....................
Mark,

Yes.  If a "hot skin" condition exists,  Progressive Industries EMS devices will detect reverse polarity and prevent energizing the coach (downstream of the EMS) from a faulty (reverse polarity) source of power.  Once energized through the EMS, a "Hot Skin" coach fault downstream of the EMS will also cause it to trip.  "Hot Skin" is reverse polarity.  In other words, if either neutral or ground becomes "higher" than the other, detected by the neutral not being within some small electrical potential from the ground wiring - anything more than a few volts, the EMS will not connect to the power source or will trip it if connected.  Side note trivia:  Yamaha and Honda generators have "floating" Ground and Neutral wiring and because EMS is looking for near zero volts difference between G and N, a PI EMS (or TRC) will not connect to a Yamaha or Honda Generator.

By National Electrical Code (NEC), any system (eg - home or commercial building) is allowed to connect ground (a long copper rod driven into the ground) to neutral in only one place - ONLY within the power entrance panel to that home or business.  RVIA code says that the ground and the neutral must be separated from one another everywhere (floating) throughout the RV and its extension cording.  This is for the purpose of preserving the NEC and also for not allowing cross currents between the neutral and ground conductors, anywhere except back at the home or business incoming power source panel connections.  There will be wiring resistance between the breaker panel and the EMS and that resistance will develop some voltage difference between neutral and ground, but when it reaches a few volts (3 or so), the EMS will no longer connect or stay connected, because it believes there is a reverse polarity.

Now when a true reverse polarity condition occurs on a coach, through whatever wire or component fault, the ground or "skin" of the coach can become "elevated" to a dangerous voltage.  What is that dangerous voltage number, for an unsuspecting person?  Well it depends upon the fault and how much current that fault can supply, but in general, if it's 30 volts or more, it can, at worst, stop you heart in an instant.  Especially if the current runs, for example, from your left hand to your right foot (which happens to be on the ground) through your heart.  Strong heart and good luck - you live.  Poor luck and no help - a slight tingle can start atrial fibrillation that will be the death of you.

Two reasonably inexpensive  devices will protect you from these undetectable (invisible) and unanticipated conditions (that all too often occurs in the many, many different places that you happen to plug into).  Your coach, after all, is not like your house where you wire it once, test it once and it is good forever after.

    • Progressive Industries EMS (there may be equal or better, but I haven't found it)
    • Always use a shore power tester, that you test the power pedestal with, before you plug in.  I built mine for less than $50 or so.  I've offered plans before. There's a picture below.
    [/list]

    Some logical ways to protect your on board systems from the power surge insults and challenges, that will eventually damage them, is to treat every opportunity to be conservative with power source changes as an opportunity to preserve the longevity of your coach. 
    For example:
      • Always Open the shore power breaker (or pull the shore power plug) before starting your generator. 
      • Always test unknown shore power before plugging into it, even if you have an automatic Electrical Monitoring System (EMS) or equivalent.
      • If you don't have one, invest in a good EMS.  It has saved us numerous times in totally unpredictable, unanticipated ways.
      • Wire your EMS to protect your own generated power as well as incoming shore power faults.  I've had generator output problems that would have caused very expensive damage long before I ever knew I had a problem. 
      • Always Stop your generator before plugging into shore power.
      • Always unload all of your large loads (AC's, microwave, hair dryer, toaster, resistive heaters, etc.) before you stop a running generator or open the shore power breaker.
      • Always open the shore power breaker before plugging into the shore power receptacle or unplugging from it. 
      • Always keep your shore power plug blades clean and lightly coated w/dielectric grease and don't drop the plug in the dirt or grass.
      • Some people even turn off their inverter before starting/stopping their generator or before bringing shore power on/off the coach.  I don't because the inverter sensing circuitry is specifically designed to seamlessly handle these transitions and I'm lazy (as in I don't like reprogramming clocks that don't have memory backup), but it would be ultra conservative to follow their example.
      • Etc., add your own.

    HTH, let me know if you want plans for my Shore Power Tester!

    Neal
    The selected media item is not currently available.
    Neal (& Brenda) Pillsbury
    '02 U320 SPEC, 4200, DGFE, Build #5984
    '04 Gold Wing
    '07 Featherlite 24'
    '14 Jeep Grand Cherokee Summit
    MC #14494
    Exeter, NH & LaBelle FL
    Quality makes the Heart Soar long after Price is Forgotten

    Re: Check your shore power cable every now and again

    Reply #7 –
    Quote from: Neal Pillsbury –
    Mark,

    Yes.  If a "hot skin" condition exists,  Progressive Industries EMS devices will detect reverse polarity and prevent energizing the coach (downstream of the EMS) from a faulty (reverse polarity) source of power.  Once energized through the EMS, a "Hot Skin" coach fault downstream of the EMS will also cause it to trip.  "Hot Skin" is reverse polarity.  r.

    By National Electrical Code (NEC), any system (eg - home or commercial building) is allowed to connect ground (a long copper rod driven into the ground) to neutral in only one place - ONLY within the power entrance panel to that home or business.  RVIA code says that the ground and the neutral must be separated from one another everywhere (floating) throughout the RV and its extension cording. .

    Another scenario that the EMS may not pick up (I'm not sure on all the features), but a GFCI will prevent is this:  Broken ground wire between RV and power pole, and then a hot wire that is touching the frame or something metal in the RV. This could cause the "hot skin".

    Reverse polarity is not necessarily dangerous if all the wiring is correct and up to snuff. But it CAN become dangerous under certain circumstances.

    PS: I love my EMS hard wired 50amp with remote display. I'm installing one on my boat too!
    1998 U270 34'

    Re: Check your shore power cable every now and again

    Reply #8 –
    Quote from: Neal Pillsbury –
    Mark,

    Yes.  If a "hot skin" condition exists,  Progressive Industries EMS devices will detect reverse polarity and prevent energizing the coach (downstream of the EMS) from a faulty (reverse polarity) source of power. 

    In this case, wasn't the issue the OP's shore power cord plug end?  A hard-wired EMS would pick this up, but a portable plug-in at the power source would not, since the problem would be between the EMS and the coach, not coming into the EMS.
    Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

    2000 U320 36' non-slide / WildEBeest Rescue
    2003 U320

    Re: Check your shore power cable every now and again

    Reply #9 –
    Remember the static discharge straps on trucks years ago? Would something like that protect us from a hot skin contrition?
    John Duld
    1995 U320C SE 40'

    Re: Check your shore power cable every now and again

    Reply #10 –
    Quote from: Michelle –
    In this case, wasn't the issue the OP's shore power cord plug end?  A hard-wired EMS would pick this up, but a portable plug-in at the power source would not, since the problem would be between the EMS and the coach, not coming into the EMS.

    Michelle beat me to it. After a "near melt-down" we not only got a EMS pedestal-mount, but replaced the cord ends, AND the connection in the wet bay!  ^.^d  A quick aside: after we bought this coach, I had always noticed a rubber tube scraping the ground, figured it was a "discharge strap". Finally tracked it down, it was the "slobber tube" that had come loose!
    1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
    Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                          Build # 4297
                                          PNW natives
                          Home base:  'Cactus Hug' (Ajo, Arizona)
                            DW Judy & Chet the wonder dog
                            Full-Timers 'Sailing the asphalt sea'

    Re: Check your shore power cable every now and again

    Reply #11 –
    Quote from: Michelle –
    ..............A hard-wired EMS would pick this up, but a portable plug-in at the power source would not, since the problem would be between the EMS and the coach, not coming into the EMS.....................
    Michelle,
    Good catch. 
    The safe answer is yes (an HW EMS would catch it and a Portable would "maybe" not), because we don't know exactly what the OP found wrong with the cord and what else is "broken" on the coach that is causing one or both of the Lines (Line 1 or Line 2) to "leak" to ground (the coach frame)
    If it was just an open ground or an intermittently open ground conductor in the shore cable, the Portable EMS would not recognize the condition, whereas the Hardwired EMS would see the condition instantly upon open (fault) occurrence.

    The "maybe" (which I was thinking, but not getting wordy about when I posted) comes in where the OP's coach has a double fault (actually a more common occurrence) where some failed component on the coach is allowing the ground (frame) to become partially elevated in electrical potential and the intermittent open ground doesn't provide a continuous drain for that potential.  I was trying to read too much into the OP's intermittent condition, the 40 VAC measurement and some sort of plug end problem.  If there were a strong connection from Line to Ground, the coach frame would have been reading a full 110 VAC to ground whenever the ground conductor was "open".  If it was a failed component, like an air conditioner or refrigerator, that is not on a GFCI circuit, and the fault was a weak fault, then either a hardwired or portable EMS would see the intermittent open ground in the shore power cable when the ground and neutral conductors became mismatched by greater than 3 VAC or so.  In that condition, either one (HW or PT) would trip to shut off incoming shore power. 

    Double faults are more common because the ground wiring masks weak faults to ground by continuously draining away the elevated potential.  Then it takes an interruption of the ground path (fault #2) to make fault conditions obvious.  We have a lot of non-GFCI protected loads on a coach, where weak faults to ground can occur.  Once the condition becomes obvious (elevated frame potential), I would be shutting off all AC breakers and watching the frame voltage as I reenergized the components, one by one, trying to find the component that has the "leak" to ground.  Then I would have both a faulty component AND the shore power cable to fix.  But that's just me.

    Quote from: John Duld –
    Remember the static discharge straps on trucks years ago? Would something like that protect us from a hot skin contrition?
    John,
    "Hot Skin" condition is just a surplus of electrons accumulated where they should not be (in the frame), so anything that will FULLY drain the electrons back to ground potential will remove the condition.  Ground straps on trucks were meant to discharge the electrons accumulated by the vehicle moving through air and over ground, picking up loose (weakly bonded) electrons and creating a static charge buildup on the truck. Touch a grounded gas nozzle to the metal of the fuel nozzle and fuel vapors from the open tank go into riot mode.  Gas pump design has considerably relieved that nowadays. 
    A loose ground strap on a coach (from frame to earth) would be less certain to have good contact with the earth (ground) than a four wire shore power cord and an EMS that was monitoring the G and N for abnormal electrical potential between the Ground and Neutral conductors in that power cord.
    HTH,
    Neal
    The selected media item is not currently available.
    Neal (& Brenda) Pillsbury
    '02 U320 SPEC, 4200, DGFE, Build #5984
    '04 Gold Wing
    '07 Featherlite 24'
    '14 Jeep Grand Cherokee Summit
    MC #14494
    Exeter, NH & LaBelle FL
    Quality makes the Heart Soar long after Price is Forgotten
     

    Re: Check your shore power cable every now and again

    Reply #12 –
    The other item to check on your power cord at the point where it plugs into the shore power socket, is how dirty are the contact pins.
    I regularly sand with 600 grit to keep them a shiny brass colour.
    I have seen plugs where the plastic housing has been melted because it got hot due to dirty contacts or weak contact pressure in the shore power receptacle.
    I will also check the temperature of the plug after using it a couple hours, if you cannot hold on to it because it is hot, look for the problem.
    Wyatt
    96 U320 40 WTFE, build 4943
    84 Toyota Supra towd
    2015 Jeep Wrangler towd
    Victoria, BC, Canada