AC voltage bleeding to DC

[sirfallsalot]

I have about 24V of AC bleeding into my DC system. If I'm plugged into shore power, any time I touch a metal part of my RV I get a light shock. Any idea where to start looking for the source?

[bigb]

Originally Posted by sirfallsalot

I have about 24V of AC bleeding into my DC system. If I'm plugged into shore power, any time I touch a metal part of my RV I get a light shock. Any idea where to start looking for the source?

Where did you measure between to get 24 VAC? Depending on the resistance of your return path used for the test you could actually have full line voltage on your RV. 24 VAC is usually not enough to feel which is why I suspect you really have a direct fault to 120 volts. Using Mother Earth for a return current test point will not allow the full voltage to flow. This can be deadly so proceed very carefully. First step is to switch breakers off 1 at a time to see which circuit it is. If it doesn't go away look to a short on the power cord or the Romex feeding your breaker panel. If your RV is energized there are 2 things wrong 1. you have a short to metal and 2. your grounding is not correct

[Ray,IN]

Originally Posted by sirfallsalot

I have about 24V of AC bleeding into my DC system. If I'm plugged into shore power, any time I touch a metal part of my RV I get a light shock. Any idea where to start looking for the source?

The most common cause is a bad/faulty 120VAC electric water heating element.

Hot Skin/Stray Voltage explained.

[sirfallsalot]

Thanks! I measured AC volts across the +/- terminals of the coach batteries. I turned off the main breaker on the panel & it's still there. I turned off all the breakers & it's still there. It seems that the only place where AC and DC should be near one another is in the converter. I'll start disconnecting AC from stuff & see if/when it stops. ZAP!

[sirfallsalot]

Not sure I have one of those. I think my water heater is propane (?).

[Morich]

Lots of weird ideas get passed around and this is one of them!
Stray voltage? Yes, or it could very well be called"poor grounding"!

When we think about the frame of the RV, we shoud know that frame is used as ground for almost all the DC and it is also grounded through the power cord! Our AC power is called Multi grounded neutral (MGN) and that means it is grounded at multiple spots throughout the system, at the power poles, at the place where it enters the line to the house, at the breaker box and even at the PED and RV!

Why do we have three wires and three lugs on the power cord when we only need two (neutral and hot) for service? Because the third one is an added ground for safety in case the hot begins to contact the metal of some item like the RV!
Same as we find on small metal items like a drill with a metal body?

When we are feeling a shock (small or large and fatal?) it is because we are a better ground than the item we touched! When there is contact from hot to grounded metal, that current should go directly to ground and we should feel nothing.

Two causes seem likely to me.
One is the outlet wiring is bad, not well grounded. Two the RV wiring and likely at the plugs is bad and the ground wire is bad! One place to look for this is where the power cord enters a metal box as that is also a place where damaged insulation can let the ground wire break and the hot wire let power go to the metal of the frame.
When the frame is not grounded, that box is not grounded and then doesn't run the current to ground!

Look for bad grounding but disconnect the cord until you find the fault.


Failure to disconnect first can kill you!

[bigb]

If you are measuring across the batteries with the meter set to AC there is nothing unusual about seeing 24 volts, especially with an inexpensive meter. It does not mean there is AC voltage present, it just means you have the meter on the wrong setting. If you are getting shocked, the tingly kind not the snap kind, there is AC voltage present on the RV not necessarily having anything to do with the DC.

[Morich]

Originally Posted by bigb

If you are measuring across the batteries with the meter set to AC there is nothing unusual about seeing 24 volts, especially with an inexpensive meter. It does not mean there is AC voltage present, it just means you have the meter on the wrong setting. If you are getting shocked, the tingly kind not the snap kind, there is AC voltage present on the RV not necessarily having anything to do with the DC.

Good info here and I agree that testing can get confused! But the shock is a pretty good indicator that there is voltage on the RV and that means the grounding is not good.
You can often test voltage on ground but it is not possible for it to actually be there, for our uses ---- if the ground is actually good.

[sirfallsalot]

Originally Posted by Morich

Good info here and I agree that testing can get confused! But the shock is a pretty good indicator that there is voltage on the RV and that means the grounding is not good.
You can often test voltage on ground but it is not possible for it to actually be there, for our uses ---- if the ground is actually good.

Will check grounding. Thanks!

[bigb]

In order to see how much actual voltage is on the RV plug an extension cord into a known grounded outlet, take the cord into the RV to where you got shocked and put one meter probe on the area that shocked you and the other probe in the ground hole on the extension cord. Be very careful not to contact the non-insulated parts of the probes during this test. Do it power up and disconnected. Use the AC setting on the meter. In order to get the probe to make contact in the extension cord you may need to lean it over or wiggle it around.

[Morich]

This is a bit of info on what to expect at the outlet and how to test between the three different points. It is NOT wired as we might expect a drier outlet with three points as we only want 120 not 220!



This shows that you will find 120 volts but it really is normal to find different voltages at any time of day, so general "range" of 108 to 130, more or less is good for this.

So if you go to the ground with one probe and then to the hot, expect to see "around" 110-120, then check the neutral by moving one probe from ground to neutral and expect the same reading pretty close.
Inside the box, the neutral and ground both go to a ground point and meet, so they should read the same, assuming both are good clean connections.

But if you find one reading way off from the other, you have found one is not making the good connection inside the box!

If this is what you find, then you can switch to reading ohms (resistance) and there should be very near zero resistance between neutral and ground as they are connected together very close to where you are testing!

If you are at a campsite, park,etc. they are semi-famous for having electrical wiring problems at peds!!
It's a rough place being outside in the weather and all kinds of folks banging around or driving over some of them!
It can be hard to keep track of who just drove off and tore the thing up??

[sirfallsalot]

Originally Posted by bigb

In order to see how much actual voltage is on the RV plug an extension cord into a known grounded outlet, take the cord into the RV to where you got shocked and put one meter probe on the area that shocked you and the other probe in the ground hole on the extension cord. Be very careful not to contact the non-insulated parts of the probes during this test. Do it power up and disconnected. Use the AC setting on the meter. In order to get the probe to make contact in the extension cord you may need to lean it over or wiggle it around.

I tried your extension cord idea, and found following. Pretty weird stuff & I'm pretty confused.

Unplugged:
RV unplugged from shore power, and all coach breakers off, no voltage between a bolt on the coach and the GND lead of the extension cord. Turn on all breakers & same results. As expected.

Shore Power:
Coach plugged into shore power, all breakers off: 4V to 5V AC measured from bolt to ext cord GND.
- No tingle when standing in bare feet on concrete, and touching bolt with wet finger. Touch the bolt with my tongue I get a light tingle.

Main breaker on: still 4-5V

Main + Breaker 1: 8V. No tingle with wet finger, light with tongue.
Main + B2: 8V. light tingle with tongue
Main + B3: 8.5V. light tingle with tongue
Main + B4: 18-19V. Light tingle with wet finger, not trying tongue ;-)
Main + B5: 5.6V. light tingle with tongue

Main+B4+B1 ON: 20.1V - significant tingle with wet finger.
B4+B2 ON: 20V - significant finger tingle
B4+B3 ON: 20.1V - significant finger tingle
B4+B5 ON: 17.6V - significant finger tingle

Trickle Charger on chassis (van) battery:
Unplugged from shore power. All breakers off: 18V AC from the bolt to extension cord ground. Significant tingle on wet finger.

Main breaker on: 18V
Main + B1: 18V
Main + B2: 18V
Main + B3: 18V
Main + B4: 18V
Main + B5: 18V
Main + all: 18V

How could a trickle charger feed 18VAC to chassis?

Shore power + trickle charger:
Breakers off: 6.5V.

Main Breaker on: 6.5V

Main + B1: 10V
Main + B2: 10V
Main + B3: 10V
Main + B4: 18V
Main + B5: 7V

Main + 4 + 1: 22V
Main + 4 + 2: 21V
Main + 4 + 3: 22V
Main + 4 + 5: 19V

Main + all: 29V

[Morich]

Testing voltage with your tongue?
Have you considered what happens if the wiring changes just a little bit due to something as simple as wind blowing the cord a bit, so that the voltage jumps to 110?

People often get killed after storms when they go out to pick up the "dead" wires because they don't want to drive over them!

I'm out of this one!

[powercat_ras]

This is discussing the statements that there is voltage between grounded places and AC neutral measurable in the RV. The maximum one should be able to measure when plugged into shore power or when running off a generator is 2 volts AC.

The "tongue" or "wet finger" measuring method is DANGEROUS and can hurt you or at worst kill you. DON'T DO IT.

= = = = =

AC Neutral and Ground are not connected together anywhere in the RV (if properly wired) and the only place they are connected together is at the main electrical service panel with main breaker in the source of power. They are also connected together on the generator side of the transfer switch if you have a RV mounted generator.

It is not unusual to be able to measure a small voltage between neutral and ground in a RV, if this voltage is higher than 2 volts, there is a reason and something can be done to reduce it.

The reason there can be a voltage to ground on neutrals in RV outets is that there is always resistance in the neutral wiring that causes a AC voltage that forms across the neutral wiring between where the mesurement is being taking at and the point where the Neutral and Ground are connected together. The ground wiring has almost zero current so there is no voltage forming across it. Thus there is a difference.

This voltage is developed because current is flowing thru the neutral side. The current flowing back thru the neutral side, if the power is being fed from a panel without main disconnect breaker, or a sub-panel is coming from all branches fed from that panel, not just from the RV. So you can see a voltage sometimes even with NOTHING powered in the RV generating current.

The AC voltage measured between neutral and ground measured at any outlet should be 2 volts or less. If more than that then there is something causing more voltage to develop across the neutral current path between the point where neutral and ground is bonded together and the point the measurement is being taken. This can be a poor connection in the neutral path or a under-sized wire in the path.

[sirfallsalot]

Originally Posted by powercat_ras

This is discussing the statements that there is voltage between grounded places and AC neutral measurable in the RV. The maximum one should be able to measure when plugged into shore power or when running off a generator is 2 volts AC.

The "tongue" or "wet finger" measuring method is DANGEROUS and can hurt you or at worst kill you. DON'T DO IT.

= = = = =

AC Neutral and Ground are not connected together anywhere in the RV (if properly wired) and the only place they are connected together is at the main electrical service panel with main breaker in the source of power. They are also connected together on the generator side of the transfer switch if you have a RV mounted generator.

It is not unusual to be able to measure a small voltage between neutral and ground in a RV, if this voltage is higher than 2 volts, there is a reason and something can be done to reduce it.

The reason there can be a voltage to ground on neutrals in RV outets is that there is always resistance in the neutral wiring that causes a AC voltage that forms across the neutral wiring between where the mesurement is being taking at and the point where the Neutral and Ground are connected together. The ground wiring has almost zero current so there is no voltage forming across it. Thus there is a difference.

This voltage is developed because current is flowing thru the neutral side. The current flowing back thru the neutral side, if the power is being fed from a panel without main disconnect breaker, or a sub-panel is coming from all branches fed from that panel, not just from the RV. So you can see a voltage sometimes even with NOTHING powered in the RV generating current.

The AC voltage measured between neutral and ground measured at any outlet should be 2 volts or less. If more than that then there is something causing more voltage to develop across the neutral current path between the point where neutral and ground is bonded together and the point the measurement is being taken. This can be a poor connection in the neutral path or a under-sized wire in the path.

Always tested with meter first. Anyway, I'm not measuring/seeing voltage between GND and Neutral. I'm seeing it between any bolt on the chassis (i.e. Chassis GND), and Earth GND. Somewhere I have a high impedance short that is feeding AC voltage to the chassis.

[sirfallsalot]

Originally Posted by sirfallsalot

I tried your extension cord idea, and found following. Pretty weird stuff & I'm pretty confused.

Unplugged:
RV unplugged from shore power, and all coach breakers off, no voltage between a bolt on the coach and the GND lead of the extension cord. Turn on all breakers & same results. As expected.

Shore Power:
Coach plugged into shore power, all breakers off: 4V to 5V AC measured from bolt to ext cord GND.
- No tingle when standing in bare feet on concrete, and touching bolt with wet finger. Touch the bolt with my tongue I get a light tingle.

Main breaker on: still 4-5V

Main + Breaker 1: 8V. No tingle with wet finger, light with tongue.
Main + B2: 8V. light tingle with tongue
Main + B3: 8.5V. light tingle with tongue
Main + B4: 18-19V. Light tingle with wet finger, not trying tongue ;-)
Main + B5: 5.6V. light tingle with tongue

Main+B4+B1 ON: 20.1V - significant tingle with wet finger.
B4+B2 ON: 20V - significant finger tingle
B4+B3 ON: 20.1V - significant finger tingle
B4+B5 ON: 17.6V - significant finger tingle

Trickle Charger on chassis (van) battery:
Unplugged from shore power. All breakers off: 18V AC from the bolt to extension cord ground. Significant tingle on wet finger.

Main breaker on: 18V
Main + B1: 18V
Main + B2: 18V
Main + B3: 18V
Main + B4: 18V
Main + B5: 18V
Main + all: 18V

How could a trickle charger feed 18VAC to chassis?

Shore power + trickle charger:
Breakers off: 6.5V.

Main Breaker on: 6.5V

Main + B1: 10V
Main + B2: 10V
Main + B3: 10V
Main + B4: 18V
Main + B5: 7V

Main + 4 + 1: 22V
Main + 4 + 2: 21V
Main + 4 + 3: 22V
Main + 4 + 5: 19V

Main + all: 29V

And it gets weirder. Connect ONLY the GND terminal of trickle charger to van battery GND, leaving positive terminal of charger unconnected, and I still get 18VAC from the bolt to earth GND (i.e. wet finger tingle). WTH?

[bigb]

Not too long ago Mike Sokul had an article that showed certain battery chargers that would induce a measurable AC voltage onto the RV. I had one of the chargers he mentioned so I hooked it up and sure enough I got AC voltage on my RV measured with both a DVM and a non-contact stick, but with an old Simpson 260 analog meter I didn't read any voltage and concluded that it was a phantom voltage.
As far as voltage on your RV while plugged in I think powercat_ras is on the right track, you may have a poor connection to neutral somewhere including the shore panel which can cause voltage to back up on the grounding conductor thru the neutral/ground bond. When we look for current or voltage on a ground wire we disconnect it, if it is connected the potential will be closer to ground but once open one end will rise to line voltage. If you do this be aware that the disconnected ground could rise to full line voltage. One of the things we always do when separating ground wires in a device box is sniff them all once disconnected, many times one will be live from someone cheating and connecting a neutral load upstream but it will not be at full potential till disconnected. We also find where people used the ground wire on a wall timer or illuminated switch as the return because the switch box didn't have a neutral, this can get you as well even if your circuit is switched off. My point is that a compromised return path can cause the issues you are seeing.

[Ray,IN]

What is Hot Skin, stray voltage

[jerichorick]

Originally Posted by sirfallsalot

I have about 24V of AC bleeding into my DC system. If I'm plugged into shore power, any time I touch a metal part of my RV I get a light shock. Any idea where to start looking for the source?

My first thought is the ground to the pedestal. Does the pedestal have a breaker associated with the outlet? If yes then the ground should be at the pedestal. If the ground is from the feeding service panel it may be so far away it is not grounding correctly... too much resistance.


My next guess would be the ATS if you have one. Make certain all the connections are tight and none at burned in this device.


Hope you find your problem soon.

[ldfeat]

Try disconnecting from shore power then run the generator AC current and see if it does the same thing... Larry, 2014 Reyo P.