This is 220 volts AC?
Some time ago member
Gord May wrote this:-
Reverse Polarity (AC)
This common problem is one that should be thoroughly understood by all boaters. Reversed polarity can exist on the dock
or within your own boat, which should be equipped with a Reverse Polarity Indicator (RPI) on your main AC electric
panel. Regardless of whether the reversing point is on the dock or in you own boat, this is going to energize the neutral ground and create an electrical
shock hazard. It should not find its way into your bonding system because these circuits should never be joined.
Keeping track of which wire is the Neutral (white) is necessary in order to prevent potentially dangerous voltage differences from existing between one boat and another, connected to the same or separated shore-power systems. In a properly wired AC system, there should be no significant voltage difference between the white Neutral wire and the green safety
Ground wire. Therefore, an incorrect connection may be detected by sensing a current
flow between the neutral wire from the shore power
system and the electrical
Upon detection of a reverse-polarity indication on any boat the shore power
should be immediately disconnected and the shore-power system wiring
on the dock inspected. It may be that the polarity of the shore power is reversed from the normal or the neutral is "floating" and not properly referenced to ground. It is also possible that the shore power safety ground wire (the green wire) may not be connected to proper earth ground. Connecting to an improperly wired shore-power system can create potentially harmful conditions for personnel as well as damaging galvanic currents.
Perhaps the easiest way to visualize the working of a Reverse Polarity Indicator (RPI) is to first visualize the relationship of the Safety Ground and Neutral wires. In a normal marine installation
, when connected to shore power, these two wires are are not connected on the boat, but are connected together on shore at the system grounding point.
The job of the RPI is to determine if there is voltage potential between Safety Ground and Neutral. The Safety Ground and Neutral are effectively two ends of the same wire and therefore should have the same voltage potential and not be capable of lighting
One further ABYC requirement for RPI's is that they contain a minimum 25,000 Ohm Resistor. A full treatment of the reason for this is beyond the scope
of this article. It is sufficient, however, to say that because the Safety Green wire is connected to devices aboard the boat that may contain stray currents, the link created by an RPI could provide a path for stray currents via the grounded Neutral wire. (See also Note 3)
It is possible for such a circuit to faintly illuminate the Reverse Polarity light even though the circuit is properly wired. It is useful for boaters to understand how this can occur.
Because voltage is always consumed pushing amperage through a resistance (wire), the voltage is different at points A and B on the Neutral wire when there is current
flowing through it. This is called “voltage drop”. When high amperage loads are operated in the circuit, enough voltage drop in the length of the Neutral wire can be created to overcome the resistance in the 25K resistor required by ABYC that sufficient current is driven through the LED to cause faint illumination. This situation is not inherently dangerous, however, it can indicate undersized wiring in the dock, shorepower cord or ship’s wiring portion of the AC circuit.
From ABYC E-8.10 SHORE POWER POLARITY DEVICES
E-8.10.1 Reverse polarity indicating devices providing a continuous visible or audible signal shall be installed in 120 V AC shore power systems and must respond to the reversal of the ungrounded (black) and the grounded (white) conductors (See E-8.23.1, Diagram 3,)
E-18.104.22.168 the polarity of the system must be maintained for the proper operation of the electrical devices in the system,
E-22.214.171.124 a branch circuit is provided with overcurrent protection in only the ungrounded current-carrying conductors per ABYC E-126.96.36.199
E-8.10.2 Reverse polarity indicating devices are not required in systems employing polarization or isolation transformers that establish the polarity on the boat.
E-8.10.3 The total impedance of polarity indicating and protection devices connected between normal current carrying conductors (grounded [white] conductor and ungrounded [black] conductor) and the grounding conductor shall not be less than 25,000 ohms at 120 volts, 60 hertz at all times.
1. Reverse polarity indicating devices respond to the reversal of an ungrounded conductor and the grounded (white) conductor only when there is continuity of the grounding (green) conductor to shore.
2. Reverse polarity indicating devices might not respond to reversals of an ungrounded conductor and the grounding (green) conductor, the grounded (white) conductor and the grounding (green) conductor, or three phase conductors.
3. Another strategy (NOT recognized by the ABYC) is to install a Momentary “Push to Test” Pushbutton in series with the RPI. The has the effect of entirely disconnecting the RPI from the circuit, until you test for polarity (by pushing button when you first connect to shore power).
4. I highly recommend the use of an AC Receptacle Tester* (circuit analizer), which will also indicate reversed Neutral & Ground, and open grounds etc. Test the Marina’s Shore Power System prior to (immediately upon) connecting your shore power cable.
A few examples:
*GB Electrical GFI-501A (And GB #GRT-800) Ground Fault Receptacle Tester & Circuit Analyzer - Tests for seven conditions: GFI interruption, open ground, open neutral, open hot, hot/ground reverse, hot/neutral reverse, and correct wiring.
*Ideal Model 61-035 tests for open ground, reverse polarity, open hot, open neutral, hot and ground reversed, hot on neutral, and hot open.
Ideal Model 61-051 also checks GFI-protected outlets against trip at minimal leakage current of 2mA, and tests their mechanical operation (with the push of a button) by intentionally overloading the GFI breaker with a 6.8mA current through the ground blade.