An electrical troubleshooting question regarding my camping trailer. Thoughts?

[Kevin in Keswick]

Hello everyone. Last year while camping I came across an issue with my camping trailer that resulted in me receiving a very small electrical shock. I will try to explain and hopefully some of you can possibly help me out.

-Trailer is plugged into the parks electrical service.
-everything working fine

During the evening as the ground and grassy area in front of my trailer entrance became damp I stepped up to trailer to enter in my bare feet in the grass. As I put my hand on the aluminum frame of the entrance i received a small jolt. When I say small I mean I wasn't even sure if it was an electrical shock and so I touched the frame again and sure enough received the shock again. It was so minor that it almost felt like static or something. Here is what I was able to determine.

-When I received the shock I was standing in BARE feet on damp ground and the light in trailer was ON.
-Standing in BARE feet on damp ground with light in trailer OFF= NO SHOCK
-Standing on damp ground with shoes on with light on or off = NO SHOCK
-Standing in trailer with bare feet or shoes and with light on or off=NO SHOCK

Trailer was hooked up to 120v.

The issue is obviously something to do with the light and specifically when it is turned on. In my mind I think I am acting as some sort of ground when standing in bare feet on damp ground.

The trailer is an old lionel lpl110 from 1972. I bought it from my uncle who only used it for one week a year and then stored it in his garage. They had no kids so it has been very well taken care of. Basically when it is opened up it is pretty much perfect and the canvas were replaced about 10 years ago so they are in fantastic shape as well. Being that it is quite old I am not going to get to fancy with it and try to rewire or something like that but I would like to try and fix this issue if fairly reasonable.

Thanks for reading and I appreciate you offering your knowledge.

[binders]

more than likly that is only 12 volt exterior light try puting a ground from the hitch to the earth small wire and rod into the earth try on pavement to see if you still get shock, use a volt meter from trailer hitch to the damp earth to see if you get a reading ,maybe the safty chain from the tongue to ground will do it ,check ground wiring from the inverter charge to the frame

[willr]

Is it a three wire circuit? Is the ground connected to the frame? Are you using an adapter to defeat the grounding?

I presume that the AC is wired throughout the trailer and that the light you are turning on is indeed AC -- or is the AC for recharging (floating) a battery?

As stated -- you can hook it up at home and test for the presence of AC between the frame and the earth if you have a decent voltmeter.

If you detect a voltage then you can use the Ohmeter portion to look for the connection between the hot lead (black/small) and the frame from your sockets inside. With the AC input disconnected of course...

[Bill R.]

In older trailers it was common for exterior lights to be grounded to the aluminum shell. If you could connect a good ground from the shell to the trailer frame this may do the trick and save having to run a ground from the light to the frame.

Bill R

[billh]

Yes, you were acting as a ground and it very likely means that the ground for the trailer (the third pin on the plug) is open or the outlet it was plugged into had no working ground or you used, as mentioned above, a 2 pin to 3 pin cheater.

What makes slightly less sense to me is how the inverter comes into the equation assuming the lights are 12V and only run off 120V via the inverter. 12V should not give you a shock.

You didn't mention how bad the shock was, if it was just a bit of a tingle you may just have some insulation leakage. If the trailer was grounded you wouldn't notice it because the trailer frame should be grounded. I have an old refrigerator that I would get a tingle from if I touched it and the stove. I measured about 50V between it and the grounded stove. (With an analog meter, reducing the voltage range will cause the apparent voltage to drop because the impedence of the meter is reduced, this won't work with a digital meter.) The refrigerator only had a 2 pin plug so addng a ground wire fixed the problem and that was 40 years ago.

If the light is 12V powered by the inverter then it seems the inverter is only powered up if a light/load is turned on.

Check the ground first. If there is a hard short from the inverter to the frame and you fix the ground it will likely blow the fuse or something!!! This makes me wonder if maybe there is a short and it blew open the ground wire/connection at some point.

The worst shock I ever got was standing on a basement floor in my socks and touching a 120V source. be careful.

billh

[jim in Halifax]

Personally I would get a licenced electrican to check it out...A minor shock could develope into something serious!!!!! Looks like a ground problem...An electrican will "megger" the grd circuit...J

[Kevin in Keswick]

Hey guys,

Thanks for your input. Jim, I actually already have contacted a friend / contractor that I know and he has agrred to come over tomorrow and check it out at noon. There was a lot of thoughts in the posts above which led me to believ that it may not be that simple to determine.

I will post an update tomorrow evening. Like I said. I am not going to get alll that fancy with it because I can just run an extension cord from the camground power source and bring a lamp instead for lighting.

Kevin

[Mike in Waubaushene]

Good idea. I had a 73 model Starcraft pop up. The only things in there that were110volts was the receptacles. The lights were 12 volt thru an inverter. I could see you having a leakage from your 110 circuit after in ran thru inverter to the receptacles. 12 volt won't even give you a tingle. The 110 volt line on my trailer came out of inverter to the exposed underside of trailer and ran thru holes in the steel frame. If yours is similar, there could be abrasion at one of those holes. 40 years of aging will make wiring coverings brittle.

[Kevin in Keswick]

Well here is the update. Met with electrician and it turns out that the problem was caused by the campground power source. My electrican confirmed that everything was grounding properly and said that it had to be coming from the source of power i was using which obviously was at the campground.

Question though if someone hopefully doesn't mind explaining for me. First of all, can someone please explain this to me in an easy to understand way and why would it be sending a small shock when the light only when the light was on and not off?

Thanks for your help

[willr]

Well here is the update. Met with electrician and it turns out that the problem was caused by the campground power source. My electrican confirmed that everything was grounding properly and said that it had to be coming from the source of power i was using which obviously was at the campground.

Question though if someone hopefully doesn't mind explaining for me. First of all, can someone please explain this to me in an easy to understand way and why would it be sending a small shock when the light only when the light was on and not off?

Thanks for your help

A faulty ground is the most likely. But who knows????

Buy a circuit tester that lights up to show if plug wiring is faulty and test before you use campground power.
http://en.wikipedia.org/wiki/Receptacle_tester

There are many types.
http://www.myrv.us/electric/Pg/testing.htm

It could be worth your life...

[Rod Sheridan]

Well here is the update. Met with electrician and it turns out that the problem was caused by the campground power source. My electrican confirmed that everything was grounding properly and said that it had to be coming from the source of power i was using which obviously was at the campground.

Question though if someone hopefully doesn't mind explaining for me. First of all, can someone please explain this to me in an easy to understand way and why would it be sending a small shock when the light only when the light was on and not off?

Thanks for your help

Hi, all electrical devices have a very small amount of current that "leaks" to ground either through the insulation or capacitive coupling.

If your trailer isn't properly grounded, this small leakage current will flow through you to ground if you're not wearing a good set of foot wear.

In a properly grounded system this current will flow to ground via the ground conductor.

The current will be small, maybe 5 to 10 milli-amperes ( a 60 watt lamp would use 500 milli-amperes).

If the current exceeds about 75 to 100 milli-amperes, ventricular fibrilation will take place.

At about 10 to 15 milli-amperes your muscles cannot release and you will not be able to let go of the trailer door handle.

At this point the amount of current that would run acouple night lights has resulted in a fatality................Grounding is the only wire in the electrical system that has to work perfectly............Rod.

[Pete in Milton]

I don't know if this would work but I'd wire in a GFCI just after the trailer to park plug in , that way everything "downstream" should be protected.

[willr]

I don't know if this would work but I'd wire in a GFCI just after the trailer to park plug in , that way everything "downstream" should be protected.

It certainly would work -- unless it were a defective ground or mis-wiring of hot and neutral -- and that would be likely for what is described. He has to deal with the problem "at source". After he checks that the camp wiring is correct -- then a ground to the trailer should suffice -- although a GFCI would be nice insurance. So the GFCI will only do it's job if the wiring is correct to begin with.

[kerfin]

Would a polarity check light at the trailer input help? Check that for reverse polarity before switching on 120V in the trailer?

[Kevin in Keswick]

It certainly would work -- unless it were a defective ground or mis-wiring of hot and neutral -- and that would be likely for what is described. He has to deal with the problem "at source". After he checks that the camp wiring is correct -- then a ground to the trailer should suffice -- although a GFCI would be nice insurance. So the GFCI will only do it's job if the wiring is correct to begin with.

WILLR, it is interesting that you said what you did about the reverse polarity. My electrican did confirm that one (only one) of the 4 receptacles inside the trailer has reverse polarity and I am going to fix that when I get a chance over the next few days. This receptacle was not in use when the shock happened. I also suggested that I pick up a GFCI Power Bar to him and he said that would be fine but that it may cause problems if the supply from the campground that I am using is a GFCI itself.

Would this be the case and would a gfci power bar have solved the original shock incident that began this thread?

I am sorry for the questions but I REALLY APPRECIATE the help.

[Kevin in Keswick]

Canadian Tire has this

http://www.canadiantire.ca/AST/brows...=en#product_aa

It is a gfci power bar. That should work shouldn't it?

[billh]

Well here is the update. Met with electrician and it turns out that the problem was caused by the campground power source. My electrican confirmed that everything was grounding properly and said that it had to be coming from the source of power i was using which obviously was at the campground.

Question though if someone hopefully doesn't mind explaining for me. First of all, can someone please explain this to me in an easy to understand way and why would it be sending a small shock when the light only when the light was on and not off?

Thanks for your help

The problem is I don't think we know exactly how the circuit is wired. Is the light the only thing that is on the circuit? If so, then the problem could be a little leakage from the device powering the light. For example, if the lamp is 12V and is powered by a 120V to 12V transformer when the trailer is plugged in and the switch applies power to the transformer the leakage in the transformer could be the problem. In any case the presence of a good ground on the trailer frame would eliminate the problem since the leakage current would be drained to ground an no voltage would be developed at the trailer frame.

The leakage current could be very small and still give you a tingle (not an eye-watering shock). If you assume your dry skin has a resistance of 200K ohms and the device has a resistance to its frame which normally would be grounded of 200K ohms then when you touch the ungrounded leaky device you will have 200K/400K x 120V across you to ground. This is a potential of 60Vand you would definitely feel a good tingle. Note that the current in this case is only 300 microamps or 0.300 milliamps and would not trip a GFI. Normally device insulation is measured in hundreds or even thousands of megohms so leakage current is virtually zero. Insulation breakdown will cause leakage currents in the microamps that don't cause the device to fail.

Moisture can easily cause leakage in the microamp or higher range.

If your trailer grounding is in good condition then the trailer park outlet is suspect. You should be able to measure 120V between the hot and the neutral obviously and you should also be able to measure 120V between the hot and the ground if the ground is in good condition. If you aren't comfortable using a meter then a plug checker gizmo will do the job. It should detect an open ground if it is present and will also indicate reversed polarity. Maintaining proper "polarity" is the correct thing to do, but it should not cause the trouble you are encountering

billh

[willr]

WILLR, it is interesting that you said what you did about the reverse polarity. My electrican did confirm that one (only one) of the 4 receptacles inside the trailer has reverse polarity and I am going to fix that when I get a chance over the next few days. This receptacle was not in use when the shock happened. I also suggested that I pick up a GFCI Power Bar to him and he said that would be fine but that it may cause problems if the supply from the campground that I am using is a GFCI itself.

If the reversed outlet was not in use it is a non-issue. (But do correct it.)

If the camp power was GFCI protected -- then it should have tripped upon your mild shock. So it does not seem likely that you were protected.

Would this be the case and would a gfci power bar have solved the original shock incident that began this thread?

I am sorry for the questions but I REALLY APPRECIATE the help.

Not if the Ground were not connected between the trailer and the campground power. Without knowing whether the power wiring was correct -- then who knows?

The GFCI will only be effective if the power wiring is correct at the insertion point.

So -- one of the test units, or better a voltmeter check is the right way to do it. Get a voltmeter, then the article on how to check the power with a voltmeter would be the best bet by far.

Once you know the power connection is correct you can even run a ground wire from the trailer frame/shell to a copper pipe you pound into the ground -- then you should never get a shock in the future.

Until you check (at every hookup time) the power connections, and know that the connection is correct you will never know if any protection method will be effective.

See the technical explanation here:
http://en.wikipedia.org/wiki/Residual-current_device

A residual current circuit breaker cannot remove all risk of electric shock or fire. In particular, an RCD alone will not detect overload conditions, phase to neutral short circuits or phase-to-phase short circuits (see three phase electric power). Over-current protection (fuses or circuit breakers) must be provided. Circuit breakers that combine the functions of an RCD with overcurrent protection respond to both types of fault. These are known as RCBOs, and are available in 1, 2, 3 and 4 pole configurations. RCBOs will typically have separate circuits for detecting current imbalance and for overload current but will have a common interrupting mechanism.


An RCD will help to protect against electric shock where current flows through a person from a phase (live / line / hot) to earth. It cannot protect against electric shock where current flows through a person from phase to neutral or phase to phase, for example where a finger touches both live and neutral contacts in a light fitting; a device can not differentiate between current flow through an intended load from flow through a person.

It's correct even if it is written in English english...

See here as well:
http://www.thecircuitdetective.com/gfis.htm
hth

[billh]

Regarding GFI protection.
A ground does not have to be present for a GFI to work. It senses the current that does down the hot and back the neutral. If they are balanced within around 5-10mA typically then the GFI considers the current is not being misdirected such as through you to ground. You can get the feeling of a shock with less than 5mA of current and the GFI will not trip.

It also means if you touch the hot wire on the circuit and also touch the neutral for the same circuit, the GFI will not trip because all the current that went down the hot also went back on the neutral. This is why it is a Ground Fault Interrupter - it detects currents that flow to ground rather than back on the neutral.

Anything other than finding the leakage/lack of ground is treating the symptom and not the cause.

billh

[willr]

Regarding GFI protection.
A ground does not have to be present for a GFI to work. It senses the current that does down the hot and back the neutral. If they are balanced within around 5-10mA typically then the GFI considers the current is not being misdirected such as through you to ground. You can get the feeling of a shock with less than 5mA of current and the GFI will not trip.

It also means if you touch the hot wire on the circuit and also touch the neutral for the same circuit, the GFI will not trip because all the current that went down the hot also went back on the neutral. This is why it is a Ground Fault Interrupter - it detects currents that flow to ground rather than back on the neutral.

Anything other than finding the leakage/lack of ground is treating the symptom and not the cause.

billh

Bill:

I think we agree with everything except the point underlined. Clearly the ground has to be there to unbalance the circuit -- even if it is through you...

But it is a good paraphrase of the last paragraph I quoted -- but it's the last time I copy a quote written in received English.