Working on electricity, whether on board or at home, is a scary prospect for many of us. But those who work with this invisible stuff on a regular basis - the folks who can change a wall switch without killing the power in the house and having to reset every clock - don't understand why the rest of us are so mystified. The following are some demystifying electrical basics you'll need to know to properly install or repair electronic instruments and systems on your boat. This article is designed as an introduction to the topic, but should provide you with enough info to pursue the subject further.

BASIC KNOWLEDGE
Before beginning, it's a good idea to familiarize yourself with some terminology. AC/DC is not just an old heavy metal rock band. Your house electricity is AC (Alternating Current), and your 12-, 24-, etc., volt boat is DC (Direct Current). If you're plugged into dockside electricity, you're back on AC, which is why refrigerators are "AC/DC."

An ohm is a measure of resistance to the flow of electricity through a circuit (every individual system is a circuit). A volt is the amount of power causing the current to move against resistance. Current (amperes) is the movement of electrons in a single direction. These three items are the basis for everything you'll be doing with electrics, and they're interrelated (it's called Ohm's Law) - if you know two values, you can find out the third. It will also assist in determining the sizes of wire, connectors and fuses, among other things. Watts is a rating of power.

The three elements of Ohm's Law are expressed as R for Ohms (resistance), C for current and V for voltage. It's simple: Volts divided by ohms gives you current (V / R = C). Current times ohms gives you voltage (C x R = V). Voltage divided by current gives you resistance (V / C = R).

There's a power formula worth knowing as well and it, too, can be expressed as a triangle, with W representing watts (a measure of power), V for volts, and A for amperage. Again, it's simple: Watts equals volts times amps (W = V x A). Amps equals watts divided by volts (A = W / V); and volts equals watts divided by amps (V = W / A). This may also come into play when determining wire, connector and/or fuse size.

One other term you'll need to know is "parallel circuit." This describes a situation in which each appliance (for example, lights) is connected positive-to-positive and negative-to-negative through an entire system. Nearly every circuit you'll deal with is either a single circuit going to one appliance (which is still parallel, i.e., positive to positive and negative to negative) or a parallel circuit going to several items. The other type is called a "series circuit" - where the positive of one appliance is connected to the negative of another. The only time you should see a series circuit is when batteries are connected to make higher voltage systems; i.e., two 12-volt batteries connected in a series make 24 volts.

TOOLS
The primary three tools you'll need for wiring are ones you probably already have: a pair of wire strippers that have crimping jaws, a straight screwdriver and diagonal pliers. A minitorch for shrinkwrap coverings on connections is also nice to have. Pros use a double-crimp ratcheting crimp tool and a separate stripper tool.

However, the most important troubleshooting tool you'll need is a multimeter. This is named such because it can be used for a number of tests. Multimeters come in digital or analog versions (go for the digital), and auto-ranging and self-ranging (go for the auto-ranging). Ideally, you want a multimeter meant for working on DC systems rather than AC. Multimeters always work on both, but they tend to have more uses with one rather than the other (one purchased at Home Depot is probably more geared to AC current than one bought at an auto or boat shop). They run from around $40 up to the thousands. Keep yours dry, don't drop it, and pay attention when using it because you can burn it up if you use it incorrectly. One of the biggest problems you'll find when using one is that it sort of requires three hands - one for each lead, and one to hold the multimeter somewhere
you can read it while testing.

USING THE MULTIMETER
Measuring voltage is accomplished by ensuring the multimeter is on the "DC volts" setting. Touch the red lead (positive, +) to the positive side of the appliance and the black lead (negative, -) to the negative side. If your multimeter is self-ranging, set the control dial to a higher-than-expected voltage reading.

If nothing registers on the meter, you're either doing it wrong, the circuit is off, or the circuit has a fault in the switch, breaker or power line. Although multimeters can perform other tests, much of your troubleshooting can be done by measuring voltage.

To isolate a problem in a circuit, you need to measure voltage drop. ABYC allows a 10 percent drop for non-critical appliances (lights) and a 3 percent drop for critical ones (pumps). Turn off everything except the circuit you're testing. Check the voltage at the battery and write it down. Next, check and record the voltage at the appliance (if you're running through a breaker panel, check it and record it there as well). If everything registers essentially the same voltage (there's always some voltage drop in a circuit), it's a good circuit.

For troubleshooting an appliance that's not working, take readings wherever you can - switches, fuses, breakers, etc. If the voltage is fine at the battery connection and not at the breaker, you know your problem lies between the two. (If it's fine at the fuse or breaker, but not at the appliance, ditto.) You're looking for - in most cases - a lack of voltage rather than a drop in voltage (however, a big enough drop can cause the problem). The bottom line is that any drop should be minimal, and if it isn't, you want to isolate the section in which your problem lies.

In addition to following the tips listed here, it behooves you to read and follow the instructions that come with your specific multimeter.

 
STRIPPING AND CRIMPING
Know your wire size and match the stripper hole or cutting edge to the wire's size, since too small a hole will cut wire strands (even nicks are to be avoided), and too big a hole won't cut anything. Crimping, whether using a specific tool or not, is critical. For a good crimp, first slide a shrinkwrap sleeve down the wire. Strip the length of wire to match the length of the connector stem (use ring connectors wherever and whenever possible) and add another 1/16-inch. Crimp the end nearest the ring first then crimp the aft part (this provides pressure relief; a double-crimp tool will do both in one motion). Check the connection with a solid tug. Slide the shrinkwrap collar up to just cover the wire visible above the stem, and heat. Now you're done.

WIRE AND CONNECTORS
Wire and connectors both come in sizes that are determined (for our purposes) by the loads they have to carry. The only kind of wiring to use is stranded copper, and tinned stranded copper is even better. Use marine-specific wire whether tinned or un-tinned, period.

You want to see the letters AWG - American Wire Gauge - on all of the wire that you're going to use. This is a measurement standard. Ideally you'll want Type 3 (this has more strands than Type 2 and is more flexible) AWG tinned copper wire.

Wire rule one: The smaller the AWG number, the thicker the wire. Rule two: When measuring a circuit, it's the distance from source to appliance and back. If your radio is 15 feet from your battery, that's a 30-foot circuit. Rule three: When in doubt, go up a size.

There are two ways to find out the size of wire and connectors you'll need, the easy way and the hard way. For the easy way, go to the Ancor Products website (www.ancorproducts.com). They have a wire size calculator, lots of tables, etc., in their "Technical Information" section.

Failing that, you can calculate the size you'll need with the following formula: CM= K x I x L/E, in which CM is the circular mill area of the conductor (this is what you're trying to find); K is 10.75 (a resistance standard for copper wire); I is the current in amps; L is the conductor length (remember, there and back) and E is the voltage drop (E = K x I x L/CM). You'll end up with an answer that's between four and six digits long, which you still have to apply to a table to convert to AWG size.

Match your fuses - everything runs through a fuse or circuit breaker - to your appliance's amperes. In a system with several different appliances on it, base the fuse on the smallest drawing appliance.

Fuses (the new auto-style blade fuses), connectors and wire all have ABYC standardized colors for size and/or use. In wiring, navigation lights and tachs will be grey; accessory feeds, orange; fuel gauge, pink; ignition and instrument panel feed, purple; bilge blowers, brown with a yellow stripe; and tilt systems, blue with a stripe. There are lots more - for that and other color-coding, visit the Ancor website.

Quick Tips 

- In places where wire runs through a panel or bulkhead, either wrap a considerable amount of tape where the wire passes through, or use rubber grommets or some sort of protection to avoid chafing.
- If you're replacing a run of wire and have connected the new wire to the old and are pulling it through, make hooks in both wires' ends, then wrap each wire around itself (like the wrap on a hangman's noose), then tape completely so that there are no catch points.   
- Feeding wire or cable through a blind section is best accomplished using a fishtape or feed rod - a thin, jointed, stiff rod that can push or pull wire through tight, unseen space. An amazing variety of these can be found in electrician supply shops. For short runs, a straightened coat hanger with a hook on the end (wrapped and taped as above) can be used. Remember: Ideally, you want to be able to inspect as much of the circuit as possible.

ADDITIONAL READING
If you're looking to delve a little deeper into the world of electrical work, you should definitely check out the book Understanding Boat Wiring by John C. Payne (Sheridan House, $13.95). Payne has also written Motorboat Electrical and Electronics Manual (Sheridan House, $55), which should be on your shelf as well. Another good book that's aimed at electric simpletons is The 12 Volt Doctor's Practical Handbook by Edgar J. Beyn (Weems & Plath, fifth edition, $27). The troubleshooting section in this book is pretty good. Get one of the books mentioned above if you plan on installing or repairing your boat's electronic systems. - G.J.