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Check the Wires

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Dick Johnson
1st Mate

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USA
40 Posts

Initially Posted - 05/14/2004 : 06:57:56

I have a 1987 SK and have moved from Ohio to NC on salt water. This week the motor refused to start. Searching for the problem, I discovered that the wires going to and from the battery had corroded inside the insulation. It seems that the installer of the motor, a marina, used house wiring and not marine.

Dick Johnson,
Langiappe #5512
Havelock, NC

Richard Johnson

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 05/14/2004 : 22:36:12

Guess the word "Marine" can be significant, even if it means "3-1/2 times the price at Home Dopey."

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OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 05/15/2004 : 08:33:48

For the technical people out there . . . I understand that electricity travels on the surface of copper wire. Does one assume that stranded wire will carry <i>more</i> (term?) electricity than solid core wire like Romex?

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 05/15/2004 : 09:38:49

There is less resistance on the surface, but electrons pass charge and exist to do that on all of the atoms of the conductor. Stranded wire has more surface and hence less resistance than solid wire of the same gauge. Mostly at the voltage and amperages we use the value of the stranded wire is its flexibility. Here is a somewhat whacked out fellow's explanation which explains it to a degree. (He revels in obfuscation.)

<i>ELECTRIC CHARGES ONLY FLOW ON THE SURFACES OF WIRES? Wrong.
During a Direct Current in a simple circuit, the flow of charges takes place throughout the whole wire. The flow is not just on the surface. If the level of current is very high, then the wire will become hot, and the current will heat up the inside of the wire as well as its surface. Thin hollow pipes make poor conductors; their electrical resistance is too high. To avoid overheating the metal we should use thick solid bars instead.

There is a persistent 'rumor' that electric current exists only on the surface of metals. This mistaken idea probably comes about through a misunderstanding of the nature of electric charge. After all, when electric charge is deposited onto a metal object, it distributes itself over the surface of the object. It makes sense that, since charge is only on the surface of metals, a flow of charge must take place only on the surface of metals, right? Unfortunately, the word "charge" refers to two different things. When electric charge is placed on a metal object, the added charge is just a drop in the bucket compared to the amount of charge already in the neutral metal. "Uncharged" wires contain an enormous amount of charge inside, even though they may have "zero charge" on average (net charge). Are you confused yet?

All metals contain huge amounts of movable electrons. During an electric current it is these electrons which flow. However, each electron is near a proton, and so the metal is said to be "uncharged." Now if we were to place EXTRA charge upon a wire, that would be like pouring a teacup into the ocean. The "water level" would rise a tiny bit. Yet extra charges on a wire create a very noticeable electrical imbalance (they attract lint, deflect electroscopes, make sparks, etc.)

It isn't so strange that we might accidentally assume that the extra charges are the only charges on the wire. Yet in reality, electric currents happen in the "ocean" of the wire, and the extra "teacup" on the surface has little effect on the charge flow. The charge flow (current) is not just on the surface, and the whole "ocean" flows.

A second source of misunderstandings: during high frequency AC, the electric current on the surface of a conductor is higher at the surface than it is within the bulk of the metal. This is called the "skin effect." It is not very important for thin household wires at 60Hz. Perhaps some people heard about the Skin Effect but did not realize that it only works for very thick wires or for high frequency AC. At extremely high frequencies, the current does flow as a "skin" on the surface of large wires. For circuits involving high-current and high-frequency such as radio transmitters, it makes sense to use copper pipes as conductors. All the charge flow is on the surface of the conductors. All the heating takes place on the surface, and not deep within the metal. </i> http://www.amasci.com/miscon/elect.html

Edited by - on

deastburn
Captain

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USA
334 Posts

Response Posted - 05/16/2004 : 20:34:37

Dick:

Consider yourself fortunate. I read last year that two thirds of all boat fires are caused by faulty wiring. Also, if your engine was getting no current from the battery because of wire corrosion, it is likely the battery was getting no charge from the engine's alternator (assuming you have one). That usually translates into a blown alternator in very short order.

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