Electrical Conundrum - Fiberglass RV


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Old 06-24-2015, 03:43 PM   #1
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Name: David
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Electrical Conundrum

My build is nearly complete including the electrical system for my Travel trailer . Everything electrical is working as it should be except for one small issue. I have discovered that the trailer chassis has a 22 volt AC charge as measured with a volt meter from the chassis to a wire stuck into the soil next to the trailer. If I am bare foot and on damp soil I can feel the current slightly when I touch the trailer or aluminum skin . I checked the electrical components and wiring and found that if I disconnect the AC shore cord the 22 volt charge disappears , also I found that if I just disconnect the converter unit from the onboard 120v AC outlet, the chassis charge drops to 8 volts.. Im wondering if I've got my grounding wrong . As it is, Ive connected my 120v AC 30amp shore power cord to a main 30Amp onboard breaker and then to two 15 Amp branch circuits. The ground wire on the 120v shore power cord is connected to the chassis as is the 12v DC battery and fuse block. Does anyone know if the 120v shore power ground should be isolated from the trailer chassis ? There might be some other reason for this issue as well .. Thanks for any advice ..
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Old 06-24-2015, 04:05 PM   #2
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Electrical tingles can lead to electrocution. Please stay safe.

I've found this site to be a good reference for how to check ground.

RV Electrical Safety: Part IV – Hot Skin | No~Shock~Zone
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Old 06-24-2015, 04:08 PM   #3
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Once again if don't know what you're doing with electricity leave it to the professionals.

Do you know the difference between the AC ground and the AC neutral? The neutral is white and ground is green. The green wire should be connected to the trailer frame. IT"S CALL SAFETY GROUND. Key word SAFETY.

Take the trailer to a professional before somebody dies.
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Old 06-24-2015, 04:08 PM   #4
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Think of your trailer as an appliance when hooked to shore power. The ground should be returned to the source.
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Old 06-24-2015, 04:08 PM   #5
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I would also check from the ground of the 120 vac shore power circuit to ground without the trailer plugged in The problem could be coming from that side as well. You could troubleshoot until the cows come home if that is the cause.
If the service entrance is poorly grounded then there you go.
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Old 06-24-2015, 04:24 PM   #6
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I have never seen a 120v grounded to the frame , the trailer is sitting on rubber . The ground should be returned to the source which hopefully is properly connected to earth . The only time 12v is connected to the frame is to complete the 12v cicuit [not too useful on a fiberglass trailer] .
.
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Old 06-24-2015, 04:29 PM   #7
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Quote:
Originally Posted by Bob in Mb View Post
I have never seen a 120v grounded to the frame , the trailer is sitting on rubber . The ground should be returned to the source which hopefully is properly connected to earth . The only time 12v is connected to the frame is to complete the 12v cicuit [not too useful on a fiberglass trailer] .
.
ALL TRAILERS with 120 AC have a SAFETY GROUND connected to the frame. That's the third wire, it's green in color.
I think our friend has the neutral and the hot wire mixed in some places and NO SAFETY GROUND.

The frame of the trailer when the trailer is isolated from earth, the safety ground provides the ground to prevent shocks, killer shocks, from happening. Like I say if you don't understand this stuff leave it to the professionals, or possible die.
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Old 06-24-2015, 04:32 PM   #8
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Have seen this problem far to many times. Something is connected wrong.
I will repost a previous reply. Yoru really need to purchase one of the checkers that is In The post. Then, use the checker to test the shore power B 4 you connect the camper then immediately check all receptacles in the camper to insure it all tests OK. The 3 lights on the checker will point out the problem.

Should you still have the same problem after the checker states it is OK, then get an electrician to check things out.

AC Wiring: White to lite and green is ground the world around.

What this means is that the white wire is the return and attaches to the shinny silver colored screw and the Black is the HOT wire and attaches to the brass connection and the Green is ground and attaches to the green connection.

On my camper, the white is also attached to a bus that has a wire attached to the frame of the camper.

You will need one of these to test to make sure all is correct.
Electrical Receptacle Tester with GFCI Diagnosis

Use that device each and every time you connect to a power source. Check the power source B 4 you connect then once connected, go inside the camper and check to make sure it is OK.
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Old 06-24-2015, 05:47 PM   #9
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"You will need one of these to test to make sure all is correct.
Electrical Receptacle Tester with GFCI Diagnosis

Use that device each and every time you connect to a power source. Check the power source B 4 you connect then once connected, go inside the camper and check to make sure it is OK."

Never considered this, but it seems a prudent thing to do.
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Old 06-24-2015, 08:18 PM   #10
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Having worked in the CATV (cable) industry for about 20 years, I learned to fear outages in mobile home parks. More often than not they were caused by improperly grounded electric services but not always. Once a defective clock on a kitchen stove was returning 120 VAC to the frame of the mobile home as confirmed by sticking one probe of a voltmeter in the dirt and touching the other probe to any part of the mobile home - frame, siding, door, you name it. Our company's policy was to cut the drop (service wire) to the mobile home with insulated cutters and to not restore service until the the service had been repaired and certified safe by a licensed electrician.
This is nothing to fool with. Bring in the professionals before someone is seriously hurt or dies. I had a friend die working on the water well system of a mobile home. He was lying on damp ground and touched the frame of the the mobile home. Left a wife and two kids. 'Nuff said!
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Old 06-24-2015, 10:48 PM   #11
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White and green wires

The National Electrical Code calls for the White wire to be terminated back at the breaker box and is to be considered a "CURRENT CARRYING CONDUCTOR"

The green conductor as someone has said is the ground.

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Old 06-25-2015, 12:40 AM   #12
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Many Thanks

Many thanks for the concern and advice from the FG RV community , I especially want to thank Red Barron for leading me to the source of this problem. I double checked my AC wiring and found that the on board neutrals and grounds were separate, (and yes I do know the difference between the two) I also verified that I had a safety ground (green wire from shore cable to chassis ground block . Lastly I inspected my shore cable and discovered that the ground terminal (green) wire had become detached inside the plug. Once repaired, the chassis voltage to ground dropped to near zero. Problem solved.
Thanks again , it is much appreciated.!! I do plan on purchasing the electrical checker as it is cheap insurance in the event that a camp ground hook up is damaged or defective. Id rather buy a checker than risk toasting a laptop , converter box or worse.
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Old 06-25-2015, 08:59 AM   #13
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Originally Posted by frankcfx View Post
The National Electrical Code calls for the White wire to be terminated back at the breaker box and is to be considered a "CURRENT CARRYING CONDUCTOR"

The green conductor as someone has said is the ground.

I agree the 120 VAC grounded conductor
(neutral ) (white) is connected to the neutral buss in your converter which is electrically isolated.
The green wire in your 120 VAC feed is the grounding wire ( equipment ground ) and is connected to the grouding buss and the frame . The two wires are electrically isolated except at the service entrance. Connecting the white wire (neutral) of your AC system to the frame is not only illegal but unsafe. If you connect the neutral to the frame of your trailer and you loose the neutral in your trailers service cord
the frame of the trailer will become hot and you will get 120VAC. from the frame to ground.
Reading voltage from your trailer frame to earth ground can be caused by several reasons . If the ground at your trailer is a lower resistance ground than at your service entrance then you wil get a voltage reading from frame to ground
Example. If you take a 120 VAC drill with a 3 wire cord and attempt to drill a hole into structural steel ,you will get a spark off the end of the drill bit when you touch the bit to the steel. I have seen voltage readings from the drill case to structural steel as high as 50 volts. This is caused by the fact that the structural metal is a better path to ground than the ground rod at the service entrance,
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Old 06-25-2015, 10:06 AM   #14
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I'm Mike Sokol from the No~Shock~Zone. Thanks for linking to my electrical safety articles above. Note that if your RV chassis measures any more than a few volts (perhaps 3 to 5 volts) above earth ground, that's an indication that your RV has a compromised EGC (Equipment Grounding Conductor) commonly referred to as a safety ground. And as you discovered, it can occur internally in your RV's panel, in any of your extension cords or dog-bone adapters, and even in the power pedestal or home outlet you plug into. This creates what's commonly referred to as a hot-skin condition which can be very dangerous under the right conditions of damp earth and two points of contact by a person or pet.

If you want to see something really interesting, here's a video where I create a hot-skin condtion using a 40 ft RV, then show how to test for it with a basic Non Contact Voltage Tester (NCVT).
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