Open Ground Hunt

[Stilwellian]

Three of the 120 receptacles in my '68 Tradewind are not working. I have replaced the 2 circuit breakers in the trailer so I was working with new units. By testing all 6 outlets in the 3 receptacles I see each has power coming through the hot (black) wire. Each outlet shows it is grounded by inserting the probes in the hot inlet and the ground inlet. Each electrical box shows grounding contact by inserting one probe in the outlet and touching the other probe to the center screw. However no voltage registers in any of the outlets. The plug tester shows the problem is an "open ground." All other receptacles throughout the trailer work fine and show appropriate voltage. I believe the 3 that are not working are daisy chained together ( all located on the same side of the trailer and in close proximity with 2 receptacles in the rear bath and the 3rd on the same wall in the rear bedroom) so locating the point causing the "open ground" reading should close the circuit and return voltage to all 3 receptacles.

Does my summary of an open ground seem like a reasonable diagnosis?

And if it does, how do I systematically locate the problem so I can remedy this situation?

Trying to get our baby ready to roll and this one has me stumped at the moment.....

[uncle_bob]

Hi

If you are using a multimeter as your "probes" then you are testing with a high impedance tester. Simply put, it pulls no current. A high resistance ground (or high resistance neutral) will show "ok" in this sort of test but fail when you put a load on the circuit. The "easy" answer is to grab a good old incandescent light bulb (like a 100W version). Plug it in to the various sockets and see what the voltages read. (or just see if the bulb lights ....).

Indeed this does not do much for the ground lead. A load does not put any current onto that line to the receptacle. The procedure above simply tells you that both the hot and neutral are "ok".

To check the ground, you kill the power and switch your multimeter to the "ohms" function. You should read under an ohm between ground and neutral on each of the sockets. If you are reading over 10 ohms, there is indeed a problem with the ground wire. Somewhere along the line, it has gone open ....

Bob

[Wolfe]

sounds like the wight (working ground) has gone open start at the ground buss at the braker box as the daisy chain starts there, its more mechanical prob than elect pull testing

[Mollysdad]

Originally Posted by Stilwellian

Does my summary of an open ground seem like a reasonable diagnosis?

No.
The ground is not needed to make a outlet "work". One could plug in a 120vac appliance and never know it didn't have a ground.
Open Neutral?
Using your multi meter do you see a reading between neutral and ground? Or neutral and the gas screw? Or does it show open?

[rickst29]

"Open Ground Hunt" was an unclear title, this is actually a "Hunt For Broken Current-Carrying Neutral" (AKA "Wight"). Wolf and MollysDad pointed out this stuff, but let me clarify a bit more:

1. 120v "hot" black wires should only be connected to other 120v "hot" black wires, on their way back to a circuit breaker. (This part seems OK.)
2. Current-Carrying "neutral" white wires should only be connected to other 120v "neutral" wires, on their way back to a shared "neutral" bus. This Bus connects the RV power cord "neutral". It does not connect to the "grounding" wires, or the frame, anywhere inside the Trailer.
3. Green or bare "grounding" wires for 120v may be connected to each other, and also the the TraiIer frame, on their way back to a shared "grounding bus". The grounding bus connects to the green safety "grounding wire" on the RV power cord.

When outlets and appliances are operating correctly, The trailer frame and green wires should never carry current. (They carry current, and hopefully reduce all the Voltage, when appliances develop a "fault".) From the RV power cord, the "green" grounding wires should not be joined with "white" current carrying wires until they reach the Service Panel. (Green wires should also have a genuine "earth" grounding pole installed there.)

Your "broken path" for Current-Carrying Neutral might show a Voltage differential from the 120VAC hot lead (based on impedance), but can't carry current back to the Utility Service Panel.

- - - -
On NEMA 5-15R Receptacles, the narrow vertical is 120VAC "hot". The tall vertical is Current Carrying "Neutral". The "U"-shaped socket in the bottom middle is the safety "Grounding" terminal.

If you use a voltmeter to test this string of sockets, you should first test for Resistance - without plugging the Trailer Power Cord into electrical Service. In order to do this, you will need a long piece of flexible, stranded wire.

First test, without the long cord: Within each outlet, verify that Resistance between of the 3 terminals is infinity. (This probably passes, and it's not related to the situation you describe.)

Second test, with the long cord: Connect one end of the long cord to the GROUNDING Bus (the one with green and/or naked wires attached). Verify that each of the "U"-shaped grounding terminals has ZERO resistance to the Bus. (This probably passes too, and it's not related to the problem you describe.)

But if you are checking these terminals, you might also want to verify that the frame has ZERO resistance to the Grounding Bus. There should be a big wire from a firmly connected frame lug into the Bus.

Third test, with the long cord: Remove the end of the long cord from the GROUNDING Bus, and connect it to the Current-Carrying "NEUTRAL" Bus instead. Verify that the tall terminal on each socket, has ZERO resistance back to the Current Carrying Neutral Bus. (At one outlet or another, this test probably fails. The box for the first failed outlet contains your broken wire path.)

If all tests pass, then the problem is not within the Trailer Body. Test the Power Cord.

Third Test, through the power cord: Pull the end of the main Trailer Power Cord inside the Trailer, and set it down next to the power distribution panel. Check that all 3 plug ends (or, in the case of 50A service, all 4) have ZERO Resistance through the cable, and into their corresponding Distribution Panel Bus Bars.

For you, pay special attention to the Current-Carrying Neutral. If Resistance is not ZERO, then a wire is broken within the cable. (Replace the whole cable, do not try to repair it.)
- - - -
If all these tests pass, the the problem exists within your Service Outlet, and not within the Trailer at all.

[Stilwellian]

Interesting afternoon of detective work checking continuity in all wiring and outlets in the 4 outlets operating on one of the two circuit breakers in my trailer. I have discovered the sequence of the outlets in the daisy chain from first to the end of the run. It is th exact opposite of what my first guess was with the outlet closest to the breaker box actually being the end of the run and the farthest one from the breaker being the first outlet in the chain which was the only one working btw. I was checking all the connections in the breaker box determining which cable out powers the 4 receptacles with the problem and which cable out powers all the other receptacles working correctly. Good information to know. As I followed the three wires from the shore power cable into the box, I could see where the hot (black) wire was connected and the neutral (white) wire connection. As I followed the ground (green) wire trying to see where it connected I gently touched and pulled the slack in the wire since it had a loop that made it hard to see ....lo and behold it was not connected to any of the terminals in the bus bar. I am hoping by connecting the ground (green) wire to the bus bar the outlet problem will be solved.

I do not know “the” correct or “a”correct location on the bus bar ( if more than one is possible) to connect this ground wire coming in from the shore power cord. I am a bit puzzled that only the outlets on one breaker were impacted by the loose or disconnected ground wire. Could it be that even though not secured by a mounting screw on the bus bar the wire was grounding enough to let all the outlets on one circuit operate while causing the problem with outlets on the other circuit?

If it would help to post a picture of my breaker box wiring I can do that. I could not find anything in my manual wiring diagrams or on any threads here in the forum clarifying where the ground ( green) wire needs to be connected.

Suggestions?

[uncle_bob]

Originally Posted by Stilwellian

Interesting afternoon of detective work checking continuity in all wiring and outlets in the 4 outlets operating on one of the two circuit breakers in my trailer. I have discovered the sequence of the outlets in the daisy chain from first to the end of the run. It is th exact opposite of what my first guess was with the outlet closest to the breaker box actually being the end of the run and the farthest one from the breaker being the first outlet in the chain which was the only one working btw. I was checking all the connections in the breaker box determining which cable out powers the 4 receptacles with the problem and which cable out powers all the other receptacles working correctly. Good information to know. As I followed the three wires from the shore power cable into the box, I could see where the hot (black) wire was connected and the neutral (white) wire connection. As I followed the ground (green) wire trying to see where it connected I gently touched and pulled the slack in the wire since it had a loop that made it hard to see ....lo and behold it was not connected to any of the terminals in the bus bar. I am hoping by connecting the ground (green) wire to the bus bar the outlet problem will be solved.

I do not know “the” correct or “a”correct location on the bus bar ( if more than one is possible) to connect this ground wire coming in from the shore power cord. I am a bit puzzled that only the outlets on one breaker were impacted by the loose or disconnected ground wire. Could it be that even though not secured by a mounting screw on the bus bar the wire was grounding enough to let all the outlets on one circuit operate while causing the problem with outlets on the other circuit?

If it would help to post a picture of my breaker box wiring I can do that. I could not find anything in my manual wiring diagrams or on any threads here in the forum clarifying where the ground ( green) wire needs to be connected.

Suggestions?

Hi

Your trailer has serious wiring issues. Find a pro and let them dive into it. Doing it this way is dangerous. You may or may not spot things that are significant if you are not familiar with how things should be done. Trying to do it from pictures is equally dangerous, they often do not show the whole picture.

As noted above, ground has absolutely nothing at all in any way to do with an outlet working or not. Zero impact. For a lot of years, outlets did not have grounds on them and we happily plugged stuff into them. It all worked fine. Ground is there as a *safety* feature.

Bob

[rickst29]

White "Current Carrying Neutral" wires are mis-connected or un-connected (all of them, or 3 of them as a string). You didn't find this. Maybe you didn't even look for this. You found a second wiring problem.

But your newest post still shows confusion about the role of white wires. That's OK... after all, there are a lot of things in my own house and car which I can't fix for myself. You should not try further attempts to "fix" the 120V system on your own. Get a Pro.

[Stilwellian]

Thanks for all the tips and suggestions. I reconnected the disconnected ground wire from the power cord to the ground bus bar along with all the other ground wires connected there. None of the neutral wires (all on the opposite bus bar btw) are disconnected. All have continuity and proper resistance readings. The outlets all test out correctly. The culprit is a damaged hot (black) wire with no continuity in that wire between two of the outlets creating an open circuit. A new hot (black) wire replacing the damaged one and the remaining outlets in the chain work fine and give proper voltage readings. I consulted an electrician about this issue and how to troubleshoot to locate the problem (as well as following the steps recommended above using a long wire and multi tester). I am scheduling an appointment with my RV repair shop to explain the problem, the troubleshooting and the solution to make sure everything is copasetic to be on the safe side. I apologize if my asking to post a picture of the breaker box to see if there were any other suggestions gave any of you anxiety. Didn't mean to shock you(figuratively)...nor myself (literally). For now the circuit is closed and hopefully the case is too. I will let you know if there are any changes. Thanks again for all the input.

[Stilwellian]

I may not have communicated this clearly, but none of the neutral wires were disconnected either at the box or anywhere along the string. I did check each one individually between each connection. Only one wire was not connecting between two of the outlets in the chain which was a hot (black wire) leaving the circuit open. A new hot wire replacing the broken one closed the circuit and all 4 outlets are functioning properly now.

[GCinSC2]

Originally Posted by rickst29

"Open Ground Hunt" was an unclear title, this is actually a "Hunt For Broken Current-Carrying Neutral" (AKA "Wight"). Wolf and MollysDad pointed out this stuff, but let me clarify a bit more:
[LIST=1][*]120v "hot" black wires should only be connected to other 120v "hot" black wires, on their way back to a circuit breaker. (This part seems OK.)

.........................

For you, pay special attention to the Current-Carrying Neutral. If Resistance is not ZERO, then a wire is broken within the cable. (Replace the whole cable, do not try to repair it.)
- - - -
If all these tests pass, the the problem exists within your Service Outlet, and not within the Trailer at all.

Quite a bit of effort went into this post.

Gary

[Stilwellian]

I find most issues with a 1968 model require quite a bit of effort. This is our alpha and omega trailer so everything I tackle yields lots of new learnings. I have completely removed the rear bedroom/bath to replace rotted subfloor. I tore out all the old copper water lines and replumbed it with pex. Installed new refrigerator, oven/stove and a new tankless water heater. It pulls great and has worked like a champ on several trips in Kansas, Missouri, Colorado, New Mexico and Oklahoma....so far. This electrical issue just surfaced so I was reaching out to the aluminum hive mind. I appreciate the efforts to respond to my questions. Helpful web site for sure.