Electrical System... inadequate wiring?

[sfreihofer]

Now that my CD 25 (#794) is stripped, I am beginning the restoration by updating the 12 volt electrical system.

I was intending to reuse the original wiring for the existing circuits (cabin lights, running lights, etc.) since they are imbedded, and run new wiring for those circuits I plan to add.

However, after inspection the existing 16 AWG wiring appears inadequate in the designed circuits. For example, the cabin lighting circuit encompasses 5 incandescent lights in parallel, off of a 20 amp circuit breaker.

According to Don Casey's book, 16 AWG is only suitable for carrying a load of 5 amps up to 10 feet round trip, or 2 amps up to 30 feet round trip.

In the extreme, if all lamps were lit, the circuit would certainly be overloaded for 16 AWG wire, long before the 20 amp circuit breaker would trip. In fact, I don't see how you could trip the 20 amp circuit breaker WITHOUT frying the wiring first.

In other words, as designed, the 20 amp circuit breaker does not seem to adequately protect the circuit because of the wire size, and the anticipated load could exceed the capacity of the wire.

Am I right, or am I missing something? Should I replace all of the original wiring also...?

[JBondy]

You are correct that the idea of the breaker is to protect the wire. Individual fuses can be installed close to an electronic device to protect it, but the main breaker is protecting the wiring and to prevent it from possibly causing a fire.

20A is a lot for a lighting circuit. Most of mine are 10A.

Also, a shortcoming in many older boats is the lack of a main fuse between the battery and the main breaker panel. This is to protect the wire that runs from the battery to the panel. My Ty didn't have any electrics, so I don't know if CDs have this aspect covered. My Pearson did not.

Joel
Pokey III
'78 Pearson 323
Bayside, NY

[tartansailor]

S,
OK, you have 5 interior lights, and let's assume that
they are 10 watts each. Divide 50 watts by 12 volts
and you get a little over 4 amps.

Say also that the round trip circuit is a ridiculous 40 feet.
Now 16 gauge wire has about 0.004 ohms per ft. Multiply that by 40 ft and that by 4.1 amps, and I get a little under 0.7 volts voltage drop. Well within 10% allowed.

I agree with Joel, a 10 amp breaker would be more appropriate, although max amps for 16 wire is 25 amps.

Now the big concern is corrosion at the terminals. That adds unacceptable resistance.

If your wires are tinned, and the insulation is intact, enjoy.

There are some here who advocate switching to LEDs'.
With those you can really brighten up the cabin.

Dick

[sfreihofer]

Thanks for the input Joel and Dick. The table I am relying on for wire sizing is based on a 3% (0.36v) voltage drop, as required by the ABYC.

To run 2 amps from the control panel, 10 feet to the mast and 27 feet up the mast, requires 12 AWG wire. This admittedly seems like overkill, but I'm going by the book. Thus, the original 16 AWG wiring is marginal at best, and the original 20 amp circuit breaker will not protect the circuit.

I thought other Cape Dory owners may find these facts of interest, and possibly relevant to their own boats.

I am converting the running lights to LED, so the existing wiring is sufficient for that circuit, but I'm replacing the wiring for the deck light and cabin lights to bring the boat up to ABYC standards.

Thanks for your input. I now understand the reason for the discrepancy.

[Jim Davis]

Unless there has been a change, the 3% is for electronics and 10% is fine for lights and other circuits. 12 Gauge for the mast light on a 25 isn't just overkill.

[sfreihofer]

Hi Jim;

To quote Casey, p. 458: "... a drop greater than 3% is not allowed (by American Boat and Yacht Council standards) for essential electrical items such as bilge blowers, running lights, and navigation equipment. While some items, such as cabin lights can tolerate lower voltage, it is almost never a good idea to use the smaller gauge wire."

I'm replacing the wiring anyway because the original wire is not boat wire (not tinned), not sheathed, and not safety color coded (red and yellow). The heavier wire doesn't cost that much more (pennies per foot), and doesn't take any longer to install. I see no reason not to upgrade the wire gauge.

Stan