Article by Capt. Steve Katz
Shore Power – Be Sure!
The dock supply of standard electrical power to boats has become very standard and necessary for boats of all sizes. Some boats use as much power as a single-family house!
Let’s review a few key features of dockside power supply:
Most boats have a reverse polarity indicator on the interior electrical panel. This is required by ABYC on all boats with shore power unless another type of power safety system is installed. The purpose of this indicator is to let the people on board the boat know there is a potentially unsafe condition aboard before you turn the power on. If the reverse polarity alarm lights, you should not switch on the electrical power breaker to the boat and should investigate the cause of the problem.
What exactly is reverse polarity? It is a condition where the alternating current power wires, the typically Black and White are “accidentally” backwards in the electrical system. Most modern electrical outlets have three different shaped holes to allow a plug to be inserted only one way. This assures appliances and devices operate safely and properly. If the polarity is reversed, the “hot” wire can contact the neutral or ground system, allowing electricity to flow into parts of an appliance or wiring system that you can easily touch, such as the case of a coffee maker or into the ships bonding system, “electrifying” metal hardware on the boat.
What is the “hot “wire? Many people refer to the black wire of traditional alternating current power systems “hot” or line wire and usually measures 120 volts when tested to the neutral and carries the incoming current. The white wire is the neutral wire, sometimes referred to a return wire. This white wire carries the return current back to the power station. The green wire is the safety ground, usually connected to the earth at or near the source of power. This green wire does not normally carry current – but can in the event in a malfunction. In a 240-volt dockside power systems, there is a fourth supply wire, often red in color, this wire us also “hot” providing 120 volts when tested to the neutral wire. When the Black and Red wire are tested against each other, they should show approximately 240 volts.
The purpose of the green ground wire is very critical to human and boat safety, it provides a safety path for electricity in the event of a circuit malfunction. If there was a problem with an appliance, wire or other electrical device, the green wire can safely carry the electricity away from the boat and or cause a circuit breaker to trip, reducing the risk of an electrical shock to people.
Many larger marine appliances and devices operate on 240 volts, such as water heaters, air conditioning, stoves, water makers and battery chargers. Supplying this type of power to your boat requires a 4-wire shore power cord, red, black, white and green. This is the standard set-up for the shore power cord, often referred to as 50A 125/250V. The 50A refers to 50 Amps of 125V power on each of the two hot wires. The 125/250V referees to the voltage across the wires, approximately 250 volts total or 125 volts for each of two “hot” wires. For comparison purposes to other power sources, the common 50-amp 120/240-volt service is can provide a maximum of 12,000 watts. Note: some boats may have a special isolator and or transformer that conditions the incoming power – many of these specialized system creates their own neutral (white) wire on-board the boat and therefore do not require a neutral wire in the power cord from the dockside pedestal.
Boats that do not require as much electricity as the above system may use a less common 50A 125V power cord that has three wires; this configuration is not very popular and found mostly on older boats. For mid-sized boats, the most popular configuration is the 30A 125V power cord. This 30 Amp power cord also has three wires and supplies a maximum of 30 amps of 120 volts power to the boat. Often a second 30 Amp power cord is added if additional power is needed.
There are two newer style shore power cords connection configurations that may be seen when walking the docks. The Easily Engaged Locking (EEL) System is made by Marinco. They have eliminated the threaded sealing ring and created a one-handed locking system to attach the cord to the boat or dock receptacle. This EEL has a better waterproof seal using their new jaw clamp, an integral LED light and an LED power indicator so you’ll know that power is flowing through your cord. This cord is compatible with existing power inlets.
The SmartPlug is an upgrade to the conventional shore power configuration, it has larger electrical connector pins, so it is less likely to overheat, and if it does, there is an internal thermostat that cuts power at the first sign of overheating. The SmartPlug also has triple weatherproof seals to keep the insides dry, a multi-point locking system for a solid, sealed connection, and stainless-steel external hardware. Its unique shape only allows you to insert it one way, so there’s no chance of misalignment. The boat side inlet mounts using the same four-hole pattern as the traditional shore power cord but is NOT compatible with traditional power inlets.
Now that we know how a shore power system works, we can review the maintenance of the shore power cord and connections. The most common problem is overheating of the connections, either the boat or dock connection points. Overheating generally results from a few common conditions: corrosion on the male metal blades or female contacts, loose connection between the plug/receptacle or loose wiring inside the plugs or receptacles. If the end of your cord gets dropped into salt water or even splashed with salt water and isn’t thoroughly cleaned and dried, the contacts can corrode, causing a poor electrical connection and overheating in the near future. Marinco recommends that a power coed dropped in salt water be rinsed with fresh water, allowed to dry and sprayed with a moisture displacement product/light lubricant.
A regular inspection and maintenance of your shore power cord and receptacles will help provide a long lasting and safe system.
Until next time... Stay Grounded!
