Proper Grounding of 120V input

[PhilMateo]

Folks,

Been troubleshooting problems with A/C, and noticed the 120V cable into the main electrical box in rear of trailer has both hot and neutral properly wired in braker box, but the green ground is cut off. The 120V outlets and appliances are grounded inside the box to a traler frame grounding wire. This doesn't seem safe.

Is there a reason whe the 120V input would be done this way? I would assume the appliance and outlets should be grounded all the way out of the trailer to my house/generator/park hookups. Am I wrong?

Phil

[WHR]

Hi phil - I am also curious about any response you will get. I have a 24 foot international caravelle and discovered my ground was disconnected from the frame. Will watch your responses. Wade

[steelbird312]

Phil, Are you saying your shore power cord does not have the ground wire grounded to the trailer anywhere, and that the trailer wiring is not connected to the trailer either?
If it were mine, it would be tomorrow! Since that is the way new ones are wired aas well as houses, etc I would want mine the safest it could be!
Some will reason that the jack as well as the stabilizers will effectively ground your unit but I'm skeptical about that.

[Over59]

Three wires come from the cameground hookup, hot, neutral, ground. They need to stay separate in the trailer. Disconnect the AC and look inside your AC fuse panel. Are the neutral and ground connections common, that is are they connected electrically? Is there a third wire in the outlets. If not, prehaps someone modified a two wire system by adding grounded receptacles and grounding directly to the trailer. If so and your trailer is not connected to the service ground when plugged in at the campground I would fix it before using it again, the trailer could become hot and you become the ground when you touch it. The additional problems is how the fuse panel is mounted. Is the neutral electically connected to the trailer shell via the mounting. The neutral and ground "float" in a trailer and only come together out in the service panel at the campground, not in the trailer.

[RoadKingMoe]

The purpose of a ground wire is to provide a low resistance path (i.e. a short) back to the breaker panel, where the ground is tied to the neutral (completing the circuit), in case the hot wire touches an appliance case, or in this situation the body of the Airstream. This will cause the cirucuit breaker to trip, removing power.

Without it, if the hot wire touches the Airstream body, you can be electrocuted if you walk up to the Airstream and touch it. It can even electrify the ground around the trailer enough to paralyze you even if you don't touch it.

Whoever disconnected your ground wire should be sent to jail. That they did may indicate your trailer has a problem with the hot wire touching the trailer somewhere and they did this to stop the breaker from kicking off.

Neutral and ground should NOT be bonded together in the trailer, only at the campground source.

[azflycaster]

Originally Posted by RoadKingMoe

Neutral and ground should NOT be bonded together in the trailer, only at the campground source.

Is that why I do not show a ground with my 3 LED indicator when I am hooked to my generator?

[Beginner]

House wiring (as it applies to our 120 volt trailers) goes like this:
BLACK WIRE: Goes to the Main Breaker. The Main Breaker supplies the Main Buss that the circuit breakers plug onto. Turn the Main Breaker off, the house is disconnected from the outside world.

WHITE WIRE: CIRCUIT GROUND. This provides the return path for the electricity supplied by the Black wire to return to the sourse to complete circuit.

GREEN WIRE: Safety Ground. This wire connects to all the round prongs of the 120 V plugs. It goes directly to the ground rods driven into the ground outside your house. Ther is supposed to be at least a number 6 size wire connecting the ground rods to the ground buss in the circuit breaker box. Why we don't connect to the water pipes is another story.
Note: If you measure the resistance between the ground buss and the white buss in the circuit breaker box it will be less than one ohm(for pratical purposes a dead short).

Our Trailers:
BLACK WIRE: On our shore power power cord connects to the Main Breaker. The Main Breaker likewise supplies the Main Buss inside the Circuit Breaker Box that the Circuit Breakers plug on to. Like the house, turn this Main Breaker to off and all 120 V power to the trailer is turned off.

WHITE WIRE: CIRCUIT GROUND. Same as in your house. Connects to the White wire buss in the Circuit Breaker Box.

GREEN WIRE: Connects to the Ground Buss in the Circuit Breaker Box. This Ground Buss MUST be connected to the Frame/Skin of the trailer, if not, it is possible (probable), in the event of a short(black wire comes in contact with the skin or an appliance shorts out) that the skin of the trailer could have 120 V on it. In short (no pun intended) if you touch the trailer barefoot, you will get shocked.

GFI: GFI recptacles and GFCI Circuit Breakers compare the amount of electricity flowing toward the appliance on the Black Wire and with that current flowing back to the source on the White Wire. If the two amounts are not equal the Recptacle pops or the GFCI Breaker will trip. The only reason that the power flowing down the White Wire back to the sourse will be different is when there is a short and a portion of the power delivered to the appliance by the Black Wire is now flowing back down the Green(ground) wire. This is why it is so imporntant that the Ground wires(Green Wire or Bare Wires) only attach to the ground bus in the Circuit Breaker Box. If you have connected the White Wire to the Ground Wire(Green or Bare Wire) anywhere in the trailer or in the house at a recptacle, the return current will divide between the White Wire and the Ground Wire(Green of Bare wire) and the GFCI Breaker will trip because it sinces that only half the power is returning on the White wire and trips(does its job).
At least thats my take on it.
Beginner

[Chuck]

just to add, we had a scarey (and "shocking", literally, for some) experience at our recent rally, when it was discovered that there was a wiring fault in the campground's electrical system. Turned out to be a faulty ground at the transformer that supplied a large section of the campsites. All "new" stuff, too...a recent upgrade. It took the electrician a long time to figure it out, too, because everything "appeared" to be correct, was all new, had just been inspected by the PTB, etc, etc. and STILL, with all those safeguards, was not right.
Several campers got zapped by touching their trailers. turns out, we were all "HOT". (those of us on this particular branch). voltmeter testing from the shell of one trailer to a steel anchor in the ground showed 120vAC

so even if your trailer is "right"...you still need to be wary. I'd like to know if there is any reliable way to test for this condition before hooking up.

[Beginner]

If you have on of those little testers that you can plug into a recptacle and tell if it is properly grounded you can plug it into the circuit breaker box at the campground (the 120V house recptacles) and see if it gives you a good reading there. If not, have the campground people try and explain why your little tester is giving you a faulty indication( I can't think of any reason plausable). The best version is to get an adapter that will plug into the socket that your trailer will be pluging into to a common house recptacle then plug your tester into that for a good reading. You should get a good reading. Don't let them snow you.

[Chuck]

is there a test you can do with a common voltmeter?

[Beginner]

Theoretically (uh-oh) you should get 120V from one of the rectangular openings where the flat prong goes to the other rectangular openings. Then from one of the rectangular openings to the round opening you should get 0V. From the other rectangular opening(where the flat prong goes) to the round opening you should get 120V. Then from the round opening to the metal circuit breaker box you should get 0V.
I like using an incandesent light bulb/wocked and pigtails because the light bulb draws enough current to tell the truth. A meter draws so little current (micro amps) that in some instances it will lie to you. That 100 watt blub draws 1 amp and will force thd issue but not enough to cause injury. By the way, if the bulb flaches and goes out and so does its replacment, or if it pops(explodes), you probally have 220V where you should have 120V or you have just blown up a 12 volt light bulb.
Beginner

[RoadKingMoe]

Originally Posted by azflycaster

Is that why I do not show a ground with my 3 LED indicator when I am hooked to my generator?

That is correct. Small inverter type generators do not bond neutral with ground. They rely on a GFCI for protection.

[ibedonc]

the guy I got my 83 from had the white wire going to one side of the bus and the black to the other and not though a main break ( both sides should been jumped ) of course nothing worked I wired it like my house , so I need to move green to trailer ground

[Beginner]

That's Scary. That means that inorder to ensure safety when running your generator, you have to establish an eath ground system(#6 solid wire running to two 8 foot ground rods driven in the ground at least 8 to 16 feet apart).

[RoadKingMoe]

The output of a small inverter-type generator is like the 240/120VAC split single-phase power coming into your house. Instead of neutral being bonded to ground and being 0 volts, neutral is at 60VAC with respect to ground and hot is at 60VAC with respect to ground. Just as the two legs of residential power have 240VAC between them, the generator hot and neutral have 120 volts between them. The difference is that the center tap of the 240/120VAC split single-phase is neutral to get 120VAC off of each of the two legs, while on the generator, the center tap is just chassis ground.

If either the hot or neutral wire in the trailer touch the trailer chassis, or if either the hot or neutral in an appliance or tool touches a grounded case, and the trailer chassis is connected to the generator chassis, as it should be through the power cable ground wire, current in that side of the generator will increase, causing an imbalance in the GFCI output, activating its protection. Note that neither the trailer nor the generator has to be earth-grounded for this to happen.

[Beginner]

No wonder theplug in cable is reffered to as "Shore Power". The Generator is hooked up like the NAVYships that I am familiar with(split 120VAC).

[herrgirdner]

Let me see if I got this straight. Looking at the 120 VAC plug, there is a round hole and two rectanglar slots. The left slot is connected to the white wire and is longer than the right one which is hooked to the black wire. The round hole is green-wire (safety) ground, the long left-hand slot is neutral, and the short right-hand slot is hot.
OK, so I plug my light bulb into the left hand slot and the right hand slot, and it lights. If there is a GFI protecting this connector, and I plug my light bulb into the right-hand slot and the round hole, would the GFI sense an imbalance and shut down? What if I had plugged the light bulb into the right-hand slot and the round hole first?

[Over59]

Originally Posted by Beginner

House wiring (as it applies to our 120 volt trailers) goes like this:

GREEN WIRE: Connects to the Ground Buss in the Circuit Breaker Box. This Ground Buss MUST be connected to the Frame/Skin of the trailer, if not, it is possible (probable), in the event of a short(black wire comes in contact with the skin or an appliance shorts out) that the skin of the trailer could have 120 V on it. In short (no pun intended) if you touch the trailer barefoot, you will get shocked.

So I should run a separate ground from my shell to the internal system ground, ie the marine panel ground or an outlet's ground? Wait a minute. I do think my Marinco power recepticle has this covered, have to check.

[RoadKingMoe]

Originally Posted by herrgirdner

Let me see if I got this straight. Looking at the 120 VAC plug, there is a round hole and two rectanglar slots. The left slot is connected to the white wire and is longer than the right one which is hooked to the black wire. The round hole is green-wire (safety) ground, the long left-hand slot is neutral, and the short right-hand slot is hot.
OK, so I plug my light bulb into the left hand slot and the right hand slot, and it lights. If there is a GFI protecting this connector, and I plug my light bulb into the right-hand slot and the round hole, would the GFI sense an imbalance and shut down? What if I had plugged the light bulb into the right-hand slot and the round hole first?

The answer is, "it depends." I have a neon 90-300V test light that doesn't draw enough current to trip a GFCI. With one of these, you should see light between hot (right) and neutral (left), and hot and ground (round), but NOT between neutral and ground.

But yes, if you put a typical incandescent light between hot and ground, it should trip the GFCI regardless of when you do it.

[herrgirdner]

Got it.
So, I am going to Lowes and get one of those little plug-in gizmos that tell if the 120 outlet is wired up correctly.

But that brings up another thought, how do you make sure that 30 amp outlet is wired correctly? Is it good enough to use the tester in your camper once you have connected to shore power, or is there something better to do before making that connection?
I wonder if they sell one of those gadgets that tests the 30 amp outlet, or do you have to use a voltmeter?
regards