Electrical problem at Tank Probes

[Scout1457]

I was working under my 5th wheel today and my sewage tank was exposed. There is one probe by itself with a white wire and on the other side there are three probes with different coloured wires. When my forearm touched the white wire on the tank probe I got a shock. I unplugged the trailer from 110V and no longer got a shock. When I plugged it back in I again received a shock. Any Idea what could be causing this? The tank is clean and my monitors are working

[wa8yxm]

j-d wrote:

wa8yxm wrote:
That 60 volts (RMS) comes from a voltage divider made up of two capacitors.. The capacitor is two metal pieces with insulation between them

The neutral wire and the safety ground in a piece of ROMEX = Capacitor
The HOT wire and the safety ground = The other capacitor.

Since all 3 wires are the same length that makes a 1/2 voltage divider.

Current limit is kind of tiny though.

So does this mean many or most rigs WILL tingle, even if wiring is OK on an Outlet Tester?

NOT at all... If all is proper the chassis is tied to shore ground.
This can only happen if the shore ground is OPEN. And that is a "Fault" condition.

[enblethen]

j-d that is not correct. There will be a slight capacitance on the ungrounded conductor.

[j-d]

wa8yxm wrote:
That 60 volts (RMS) comes from a voltage divider made up of two capacitors.. The capacitor is two metal pieces with insulation between them

The neutral wire and the safety ground in a piece of ROMEX = Capacitor
The HOT wire and the safety ground = The other capacitor.

Since all 3 wires are the same length that makes a 1/2 voltage divider.

Current limit is kind of tiny though.

So does this mean many or most rigs WILL tingle, even if wiring is OK on an Outlet Tester?

[wa8yxm]

Open ground on the shore cord or outlet.. The "Probe by itself" is a chassis ground. or basically a chassis ground. It has no connection to the 120 volt systems but.. If the shore ground is open there may be 60 volts on this wire relative to earth ground This is NORMAL under the conditions, but the conditions (open shore ground) are NOT normal. The Shore ground has two jobs.. ONE of them is to take that 60 volts and short it out (make is zero).

Page 2 That 60 volts (RMS) comes from a voltage divider made up of two capacitors.. The capacitor is two metal pieces with insulation between them

The neutral wire and the safety ground in a piece of ROMEX = Capacitor
The HOT wire and the safety ground = The other capacitor.

Since all 3 wirs are the same length that makes a 1/2 voltage divider.

Current limit is kind of tiny though.

but the problem is an open ground between RV and Shore.. Where it is I can not tell without testing.

The good news: Current kills. and as I said, this low-value voltage divider can not provide much of that.

[time2roll]

What did the outlet tester say?

[tenbear]

I suspect there is a problem with the 120v power ground, a poor extension cord or something like that.

Unplugging the RV would not change the voltage in the tank level monitoring system, but it would change the voltage between the RV ground and the true ground.

[GMandJM]

Were you touching exposed wire, insulated wire or the outside of the probe itself?

There's supposed to be electrical current running between the single probe and the other three. That's how your tank levels are measured.

[myredracer]

First, turn off the power so that nobody gets a shock or electrocuted and don't use the FW again until the problem is diagnosed and fixed.

You could try a non-contact voltage tester (NCVT) but it sounds like there is a "hot skin" condition.

Below is a wiring diagram for the monitor panel and level sensors that are commonly used that have button sensors/probes. The monitor and sensors operate on 12VDC so there isn't 120VAC introduced through that. The lowest sensor is grounded though so would be at the same potential as the frame and anything else that is connected to ground.

If at home, likely a faulty extension cord or shore power cord. There are other possibilities. As mentioned, google "RV hot skin". Good thing that you inadvertently discovered this as a hot skin is dangerous.

[enblethen]

Check your ground in the shore power cord and inspect and test your adapter if one is being used.

[YC_1]

Do a search for "Hot Skin". The white wire is likely the ground for the tank probes and any ground on the rv was or is probably hot in reference to earth. This is a very common but serious issue. You can actually measure the voltage by putting a voltmeter probe on the earth ground where you were standing and then place the other probe on the contact where you felt the shock.

Were you using an extension cord? Did you have an air conditioner running? Heavy loads and poor extension cords can compound the issue.

[dave17352]

Because there is electricity flowing through that wire. I would imagine you were touching some part of the frame when you touched that wire and zap. Probably 12 volt coming from your converter. JMHO