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Basic electricity for boat builders, boat repairers and owners. What you need to know about the electrical systems on your boat. Transformers, AC safety, Appliances, AC Connections and Connectors.

More Transformers

Another transformer used to isolate the AC System on the boat from the AC system ashore is  a Polarization transformer. Obviously, from the name it is intended to maintain polarity in the circuit.  Here is an article from Technical Information Exchange, Published by BOATUS, entitled Isolation or Polarization, Which is the Safest Transformer Installation?:  When reading this keep in mind that the author is stating his own beliefs, but I believe that both isolation and polarization transformers have advantages and disadvantages. Which you choose is up to you, but they both will give you a good level of safety. The big difference with a polarization transformer is the green wire on the boat is still connected to the green wire ashore. This article is pretty technical but it does have a good discussion of galvanic corrosion and the use of transformers to protect the boat. 
See Corrosion On Boats.

AC Safety

All this talk of corrosion aside, the number one consideration with AC is Safety! AC is downright deadly.  There are some basic safety rules that you must follow when dealing with AC circuits.

Never work on a live circuit! Sounds obvious, but people do it. Go turn the main breaker off and put a big red tag on it that says "DO NOT TURN ON. I AM WORKING ON THIS SYSTEM " Under that it should say, "Contact me before removing this tag", with your name. I know this sounds kind of odd if you are alone on the boat, but do it anyway. Stranger things have happened. Someone could come aboard and flip the breaker because the cabin lights aren't working. I have had people turn on a circuit while I was working on it even though it was tagged.

The ONLY exception to the above is when making measurements of amperage or voltage. Then you should keep one hand in your pocket to avoid accidentally touching anything that might be grounded and completing the circuit. Electricians and electronics technicians are taught this simple technique from day one. The basic rules is:

Turn off the equipment.

Connect the meter.

Turn on the equipment.

Take the measurement.

Turn off the equipment.

Disconnect the meter.

Never work on AC or DC when bare foot, wearing sandals, or any other shoe that doesn't have rubber soles. Wearing rubber soled shoes insulates you from the surface you are standing on, which may be metal, or wet. Again this sounds obvious but I have seen people do it, and in a magazine article about electrical circuit testing, the person in the photos was wearing sandals.  Even pros make this mistake.

Never work with wet hands, or when decks or electrical circuits are wet. Nuff said!

Unplug both ends of the shore power cord. When working on circuits it is good to unplug the shore power cord to kill the electricity, but always unplug both ends, because that cord is still live and presents a hazard to anyone on the dock or in the water around the dock. If the end of the cord falls into the water, the water is now hot. Unplug both ends.

Never work with frayed, old, corroded or cracked cords. If you are using a piece of equipment, check the power cord first. If it is faulty, don't use the equipment until the cord has been fixed, or replaced.

Never cut off the third prong on electrical cords.  I covered this before, but if you do this you could accidentally reverse the plug and get reversed polarity.

Always use Marine Grade Products.

Always maintain correct Polarity.

Always makes sure the boats system is connected to a good ground when working on the electrical system, even when the power is off.

See Basic Electrical Practices

AC Appliances:

Many household AC appliances have a bonding strap connecting the green grounding wire and the white neutral wire. On boats this strap should be removed.  The green grounding wire should be connected to the metal case of the appliance, but if the bonding strap is left in place, then you have the green grounding wire and the white neutral wire connected on board the boat. This will result in AC current in the green wire.

Connectors and Connections:

Terminals must be used.  Bare wire to stud connections with the wire wrapped around the connector are not allowed.  A page on the Friendship Sloop Society web site explains it well.

Terminals must be ring terminals or spade type terminals that do not depend on how tight the nut is to prevent them from being pulled off of the terminal bus bar.

Terminals should be crimp type and not depend only on solder to connect to the wire.  Solder creates a hard spot, the same as having a solid conductor, and is subject to breaking, and some solders are subject to corrosion. Some marine electricians use solder, but they use it in combination with the crimp type lugs. Solder is allowed but should be used carefully by a trained technician.

The other end of the terminal that surrounds the wire should be insulated and sealed against moisture using a good dielectric grease and heat shrink tubing.

Do not use wire nuts. Wire nuts, commonly used in homes and appliances, are not allowed in a boats wiring. They loosen easily and are subject to corrosion. Do not even use the ones that claim to be sealed to keep out moisture.  Many household AC appliances come with internal connections made with wire nuts. These do not have to be removed. You should not mess around with the internal wiring of appliances. (Yes, I have actually been asked by boat owners if they should do this.) The exception is the connection between the green and white wire as explained above.

Links to Offsite References:
Wiring Your Boat 2007 All rights reserved. revised 04/06/2021