Re: stray current
Yes and yes. If you could give me a brief explanation how the reverse polarity feature in my boat works, how much voltage it takes to trigger it and how it shuts my boat down without tripping any breakers on my boat I would appreciate it. Thanks Mike
Those questions are excellent and are the reason I sound dumbfounded.
This is going to be a long read, but worth the effort if your inquiring mind needs to know!
First understand that the Common(White) and the Ground(Green) wires are connected together at the ground point of the power panel. In your case this is likely a few hundred feet away in a large Circuit Breaker Panel inside of the Marina and completely out of sight, and also out of your reach.
In theory the White and Ground will both be at Zero Volts ground potential. No difference between them.
The Hot(Black) wire carries the Current out the the boat and the Common(White) returns the current to the Panel.
In reality there is always some voltage dropped on these wire because although they are good conductors, they are not perfect conductors.
You will notice that when a large load like an air-conditioner turns ON, that the lights in the area commonly dim slightly.
This is due to the voltage drop across the power (Blk+Wht) wires.
If you measured the AC Voltage on the boat you may find that the 120 volts now read 116 volt. Normal and not a big deal.
Where did the other 4 volts go? 2 volts were lost/dropped on each of the power(Blk/Wht) wires.
If measured from the Ground(Grn) wire you would find the Black Wire now at 118(120-2) Volts and the White wire at 2(0+2) Volts. The difference between the Black(118) and the White(2) is the 118-2=116 volts that the devices on the boat now see.
Notice that the Common(Wht) wire now shows an actual voltage relative to the Ground(Grn) wire. Completely Normal.
When your electrician stated that the Ground on the boat had 1/2 volt, the next question to ask would have been, "1/2 volt Relative to What?"
I told you all that so I could tell you this.....
Normally the Common(Wht) and the Ground(Grn) wire are at, or very near, the same voltage (Zero).
The Reverse Polarity Indicator(RPI) Lamp is connected between these two wires in your power panel on the boat, and normally will see a difference of Zero to a few volts at the most. the RPI will not illuminate under most normal conditions. If it is an LED type Lamp you might see it glowing very dimly under very dark conditions if you are using a lot of power. Again Normal.
Now something Stupid happens.
The Connectors on the Power Pedestals get corroded and the Marina tells their local handyman to replace the Bad ones. He messes up and gets his wire crossed. Now the Common(White) Wire on your boat gets supplied with the 120 volts and your Hot(Blk) wire becomes the Zero Volt Return wire to the panel.
Surprisingly, nothing dramatic happens. The lights and air conditioning keep working as usual and no one complains much.
HOWEVER... The White wire with the 120 volts now supplies full voltage to that RPI lamp and it glows at full brightness warning of the Reverse Polarity Condition. Ground is still at Zero.
The Danger now is that the Breakers are all in the Hot(Blk) Wires, But now the power is in the Formerly Common Wires. Normally shorting a Common wire out to ground has little effect, But now you will have a full power short to ground. A Big fireball ensues and because the breakers are not seeing the over-current, the short continues until the wires melt and everything else catches fire. A very bad day follows!
Notice that nothing in all of this reverse polarity condition did anything to shut down anything on the boat or anywhere else.
There is No Reverse Polarity Switch that shuts off the power, Only a light that warns of the problem.
This is the part that is so confusing!!!
