What's the purpose for the reverse polarity indicator light on the 115V AC portion of the fuse panel? Is this to detect an issue (I didn't think AC mattered in terms of polarity) with the shore power supply??
Reverse polarity indicator
- Thread starter Cool_Change
- Start date
- Status
YES
Reverse polarity from shore power is not compatible with inverter/charger systems such as Hearst, etc and will make a bang, blacken the plug, and hopefully trip the breaker before damage is done.
Reverse polarity from shore power is not compatible with inverter/charger systems such as Hearst, etc and will make a bang, blacken the plug, and hopefully trip the breaker before damage is done.
polarity
On the AC side, there are three conductors: hot, neutral and ground. The RP indicator, when lit, indicates current between the common and ground or hot and ground; either condition can cause a dangerous problem and potential electrical fire if not corrected. There are a number of possibilities why it is happening, the easiest of which to check is the shore power system to eliminate that before tearing apart the boat.
On the AC side, there are three conductors: hot, neutral and ground. The RP indicator, when lit, indicates current between the common and ground or hot and ground; either condition can cause a dangerous problem and potential electrical fire if not corrected. There are a number of possibilities why it is happening, the easiest of which to check is the shore power system to eliminate that before tearing apart the boat.
Thanks!
Haven't had trouble, it trip or for that matter even light up but better to know beforehand than not! Scott
Haven't had trouble, it trip or for that matter even light up but better to know beforehand than not! Scott
More detail
Well Don had very much the right idea but left the explanation to a current flow that doesn’t always exist in a reverse polarity situation unless there is a short circuit of some kind on the shore power or potentially on your boat. You are correct AC doesn’t really have “Polarity” but as the term is used here it means that the hot and neutral wires have been switched. Let me explain. There are three leads for most AC systems. One is called the hot lead and is colored black. The other current carrying lead is the neutral and is colored white. The current in the white wire should equal the current in the black wire. The third wire is a non-current carrying ground lead and is bare copper on shore and green on the boat. Electrical appliances are designed to run with the black and white in specific places for SAFETY purposes. That’s why 2-prong plugs have one prong wider than the other so that the plug only goes in one way, hence always establishing the correct white-to-white and black-to-black connection for the appliance. The non-current carrying ground wire is designed not to carry any current. A GFI (Ground Fault Interrupter) outlet is designed to detect if any current that was meant for the white or black wire actually flows on the ground wire. If any ground current is detected by the GFI the outlet trips off. Now, with that primer, let me say that if the voltage between the white wire and the ground wire isn’t near zero then your reverse polarity will light will illuminate and your main bus breaker in your boat panel will trip. For example if the white and black wires were reversed then the voltage between the white wire (now connected to black) and ground is 120 volts, and not zero as it should be. This would be a rare occurrence, since electricians have codes to follow, but mistakes can happen. A much more common reason would be to have a loose ground or neutral connection somewhere on shore. This can then cause the white wire voltage to “float” away from ground potential. Again this would mean that the voltage between the white wire and ground is not zero but not as high as in the more rare case where the white and black were reversed. In this case your reverse polarity light would come on dim but the breaker should still trip. Mine does and it happened just last month when the marina had a problem with the sewer lift pump. Lucky for me I had a newer boat so when the other boats started receiving either too high a voltage (I measured 200v) or too low a voltage (I measured 40 volts) my reverse polarity light came on and my breaker tripped. I couldn’t get it to close until we disconnected the sewer lift pump. Repairs were later made and the pump was reenergized. I hope the detail helped as opposed to confuse.
Well Don had very much the right idea but left the explanation to a current flow that doesn’t always exist in a reverse polarity situation unless there is a short circuit of some kind on the shore power or potentially on your boat. You are correct AC doesn’t really have “Polarity” but as the term is used here it means that the hot and neutral wires have been switched. Let me explain. There are three leads for most AC systems. One is called the hot lead and is colored black. The other current carrying lead is the neutral and is colored white. The current in the white wire should equal the current in the black wire. The third wire is a non-current carrying ground lead and is bare copper on shore and green on the boat. Electrical appliances are designed to run with the black and white in specific places for SAFETY purposes. That’s why 2-prong plugs have one prong wider than the other so that the plug only goes in one way, hence always establishing the correct white-to-white and black-to-black connection for the appliance. The non-current carrying ground wire is designed not to carry any current. A GFI (Ground Fault Interrupter) outlet is designed to detect if any current that was meant for the white or black wire actually flows on the ground wire. If any ground current is detected by the GFI the outlet trips off. Now, with that primer, let me say that if the voltage between the white wire and the ground wire isn’t near zero then your reverse polarity will light will illuminate and your main bus breaker in your boat panel will trip. For example if the white and black wires were reversed then the voltage between the white wire (now connected to black) and ground is 120 volts, and not zero as it should be. This would be a rare occurrence, since electricians have codes to follow, but mistakes can happen. A much more common reason would be to have a loose ground or neutral connection somewhere on shore. This can then cause the white wire voltage to “float” away from ground potential. Again this would mean that the voltage between the white wire and ground is not zero but not as high as in the more rare case where the white and black were reversed. In this case your reverse polarity light would come on dim but the breaker should still trip. Mine does and it happened just last month when the marina had a problem with the sewer lift pump. Lucky for me I had a newer boat so when the other boats started receiving either too high a voltage (I measured 200v) or too low a voltage (I measured 40 volts) my reverse polarity light came on and my breaker tripped. I couldn’t get it to close until we disconnected the sewer lift pump. Repairs were later made and the pump was reenergized. I hope the detail helped as opposed to confuse.
Detail / GFI
Great additional detail...thanks. Does the panel on the boat incorporate a GFI then or should I be considering adding a GFI to the first outlet in the circuit as in kitchens etc at home? Scott
Great additional detail...thanks. Does the panel on the boat incorporate a GFI then or should I be considering adding a GFI to the first outlet in the circuit as in kitchens etc at home? Scott
A GFI protects...
only "downstream" of the interrupter, not "upstream." So a GFI outlet in the galley will only give protection for something plugged in at the galley, or wired to the interrupter. The hore power should be GFI protected upstream of the boat.
only "downstream" of the interrupter, not "upstream." So a GFI outlet in the galley will only give protection for something plugged in at the galley, or wired to the interrupter. The hore power should be GFI protected upstream of the boat.
- Status