more reverse polarity discussion
George Some info from archives YOUR GENERATOR PROBLEM: Just because the generator does not light the reverse polarity light does not prove that you do not have reverse polarity. It is hard to determine your problem without measuring voltages, but here are some possible causes: 1. Your generator has a reversed internal polarity. You need to measure the AC voltage between the neutral and ground pins on the generator output connector to verify this. On a "standard" (wall type) socket) the neutral is the wider flat slot and the ground is the round hole. If you get over 100 volts, the generator has reverse polarity. If you get a fluctuation in voltage, you probably have a floating ground. 2. Your generator has a floating ground (This can cause the reverse polarity light). If this is the case, you need to connect the neutral line to the ground (case) of the generator." "LOW GLOW OF REVERSE POLARITY LIGHT: A low-level reverse polarity light when there is heavy current draw (like a heater or air conditioner) is not unusual. The reason is as follows: 1. The reverse polarity light is connected between the AC neutral (white) and AC ground (green) wires inside the distribution panel. If there is a voltage between these two lines, the light lights in proportion to the voltage. 2. When using shore power, the neutral and ground wires are connected together somewhere on the shore at a power distribution box. Between that point and your boat load (heater) are many feet of wire. Normally the AC current flows through the hot (black) wire to the load (heater) and back through the neutral (white) wire to the aforementioned distribution box (of course the current also flows through the black and white wire back to the power generator, but that is not pertinent to this discussion). 3. When current flows through a wire, the small resistance of the wire causes a voltage drop which is proportional to the length of the wire and the resistance of the wire. You see this on your AC voltage meter when you turn on a high current load (heater). Depending on the load and the length of wire, this voltage drop is sometimes 10 or more volts. 4. The reverse polarity lamp is effectively measuring the voltage between the neutral and ground wires at the boat. Since the ground wire is not (normally) carrying any current, there is no voltage drop in this wire. The neutral wire however is carrying current and does have a voltage drop. This voltage drop in the neutral wire appears across the reverse polarity lamp, causing it to glow, the brightness depending on the actual voltage drop in the neutral wire. This glow is not an indication of reverse polarity, and will not normally cause a problem. BRIGHT GLOW OF REVERSE POLARITY LIGHT: When you have a bright glow in the reverse polarity here is what happens: 1. In order for the bright glow to happen, there must be a high (about 100+ volts) voltage difference between the neutral and ground wires in your boat. 2. When the polarity is reversed, the power source's hot (black) wire is connected to the boat's neutral distribution, and the white (neutral) wire is connected to the boat's black wire. This can cause electrolysis and lots of other problems as well as being very unsafe. NEVER IGNORE A BRIGHT REVERSE POLARITY LIGHT!
Im actually going to copy that and put it in my "why things work on a boat" section of the maintenance log. Would be an effective tool for troubleshooting the dreaded "reverse polarity" light. Merry Christmas to all
