I am having an intermittent electrical problem with one set of plugs in our motorhome. Plug happens to be on an inverter circuit although inverter is off and we are on shore power. Sometimes, when I plug in the computer charger I get a notice that the computer does not recognize the voltage and it reverts to battery - most of the time if I unplug and reinsert all is ok. I have an oxygen concentrator that will not run at all on this plug.Voltage measures 113 - 117 at this outlet(various times) when I check it. Three prong tester says it is wired correctly (right lights come on) - items that do not work at this outlet work in all others.My electrical skills are rank amateur so I am seeking guidance on where to start looking for the problem - I am thinking maybe replacing the outlet first. Any other thoughts?

I suspect that the problem is that you do not have a "true sign wave" inverter. Most inverters actually produce a voltage that takes a series of steps up in voltage and then back down to 0V, then reverses direction and goes back through the same steps. It results in a voltage pattern that looks rather like the teeth of a saw, rather than in a nice sign wave pattern that rises smoothly from 0V to +120V and back to 0V followed by a smooth increase to -120V and back to 0V.

There are many electronic items that do not like the step pattern and do not recognize it as AC current, which it really isn't. There are inverters which come very close to the actual sign wave of real AC power but they also usually cost more.

Kirk,thank you for the quick response. I thought about the sine wave thing, but would that be an issue with the inverter off?Also,the equipment works intermittently.Last week of June while hooked to 50m Amp service had problems with this plug, then seemed to correct itself until yesterday. We are now on 30 Amp service. Does not seem to be a problem,either,plugging the equipment into other plugs labeled inverter. I have not looked at electrical schematics yet so I do not know if all the inverter plugs are on one circuit or more.

If this is happening when the inverter is turned off and you are running on shore power, the problem can't be the inverter. The symptoms sure sound like it though.

If this is the only outlet in the whole rig that has this problem, I would be tempted to replace the outlet. Any chance it is a GFI outlet?

When you get readings of low voltage at the offending plug, have you checked any other outlets, or park power?

Whatever voltage I read at the problem plug is the same voltage at every other outlet in the coach.I will try replacing the plug if I can get one tomorrow.Thanks for all the thoughts.

...what makes a receptical[F] go bad?.....vibration and bad contact between the plug [M]and the receptical.[F]...enough said?....geofkaye

Up to now, I thought that my electrical skills ranked up pretty well, but what you tell me really puzzles me? I see nothing wrong with trying a new outlet to see if that helps as that don't cost much, but if it does that will really give me food for thought.

It could be some weird internal problem in the outlet as such things can happen and every experienced tech. has had problems that were repaired by replacing something that made no sense and this could be one of those.

One thing about reading voltages is that unless they are under load they will nearly always read the same throughout the circuit. But if you were to have a high resistance of some kind inside of that outlet, voltage would read whatever the source is, until you began to draw power for some appliance. A poor connection is a good example of this kind of issue. With no current flow through the bad connection, the voltage seen beyond it will be normal. But when you begin to operate something from that circuit, there will then be a voltage drop across the bad connection that will lower the voltage to the load by however much is lost across the connection. That connection then acts like a resistor in series with the load.

If you do find something, by all means do let us know what solves the problem.

Unlike Kirk my electrical skills are abysmal. And I don't do inverters or gensets or solar never have. But I have had two similar problems without any of those. In fact almost had two fires because of them.

Humor me. Wherever your converter, not inverter, converter is, if it also has 110 breakers, pull the cover off and check the condition of your neutral wires in back for signs of heat or looseness. If an inverter has a panel check those too, as well as the main breaker panel.

I would also check the romex from the breaker to the plug, with a meter after it has heated up and check for an ARC fault.

Since it is only one plug, unless it is an isolated circuit like the microwave or water heater, it has to be the plug, or the romex with an arc inside between it and where it joins the circuit.

Remember, I said I am not an electrical guru.

Derek is correct that any loose connection is a bad thing and will cause a heat build-up if power still passes through it. It is a good practice to check all power connections for tightness on a regular basis. I do so annually. Be sure to remove all power sources before you attempt to do this.

I think Kirk and RV might be onto your problem. Plug a toaster or something else that draws a lot of power into one side of the plug while you read the voltage in the other side. If the voltage drops off under load then check for loose or broken wires, a bad neutral or a bad plug. Like RV says, this is a potentially dangerous situation. Bad connections = heat = fire.

Another thought. You said this is an inverter circuit but the inverter is off. In that case there must be a circuit in the inverter that passes park voltage through to the plug when the inverter is turned off. That could be the problem as well. Make sure the connection into and out of the inverter is good.

Is the voltage at the plug good when the inverter is turned on?

Just one more thought from the peanut gallery.

An ARC fault is when the insulation on the wires inside the romex are passing some electricity between them causing heat, but not enough to cause a direct short to trip a breaker. Arc faults can be from defective insulation from the factory, but more often from staples or handling that do not cause visible defects on the romex outside skin, with damage to the insulation on the individual wires inside.

My electrical knowledge/guesses are now exhausted, or exposed for lack of. Hope ya find it.

Refer to Gurus above.

quote:

Originally posted by JoeZ:
I am having an intermittent electrical problem with one set of plugs in our motorhome. Plug happens to be on an inverter circuit although inverter is off and we are on shore power.

If the outlet in question is on the output of your inverter, it has to be somehow switched from shore power to inverter power when you are off the AC mains. This is usually accomplished by a relay built into the inverter itself.
Are there other outlets on the same circuit and do they have the same symptoms?
You can locate these by turning the associated breaker for outlet in question off then determining what other outlets, appliances etc go off at the same time.
If other outlets exibit same symptome, the problem is likely in the inverter. If other outlets on the same inverter output circuit function OK, it is likely this outlet or the cable feeding it.
In this case, I would examine the wiring connections on the outlet in question closely for blackened areas that indicates arcing due to loose connections. It is usually advisable to replace an outlet with arcing damage since it is extremely hard to clean it enough to insure that it won't continue and it is a fire hazard.
Second look at the cable. A number of outlets, or other appliances, are typically paralleled on one run of cable from a breaker, or inverter and it could be a cable run between outlets but is more likely a wiring connection on the back of one of the outlets.

Derek - An arcing fault (breaker now required by the NEC for bedroom outlets in houses) has to do with a loose connection. It is less than a short (trip breaker) (between hot and neutral, although that may appear to happen do to the scorching heat from the loose connection). This loose connection will create a 'signature' waveform that is recognizable by an arc fault (microprocessor) breaker and trip it.

This arcing fault may be from the loose wire or loose plug that the power supply is seeing. Or loose wires in the transfer switch or breaker panel (see Kirk's post) or anywhere along the path of power to the receptacle.