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Old 09-09-2009, 10:41   #1
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AC Wiring Shocker

I've decided to replace the AC wiring in my boat. It was built using 14/3 Extension cords. I asked the surveryor about it when I saw them and he said that it was typical practice in the 80's when my boat was built. I didn't like the idea but bought the boat anyway. I've slowly been replacing the wire with 14/3 tinned marine wire.

As i started removing some of the wire from a particuilarly difficult location my hands come out of the hole covered in black soot. In looking at the wire it is covered in black soot. The only conclusion that I can come to is that the wire had either been on fire or close to it.

Ok time to speed up the replacement process.

I hae two fifteen amp circuits on the boat and the 14/3 tinned wire is fine according to the code. It worries me that the 14/3 extension cord almost (or did ) catch on fire. I only have four outlets on each circuit so am comfortable that I am not overloading the wire.

Do you think it is worth moving up to a #12 wire?

Why didn't the breaker blow when the wire caught on fire?
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Old 09-09-2009, 11:07   #2
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It is hard to know the condition of the cord before it died. It could have had broken wires in the bundle. The cover may have cracked and moisture got to it thus making the cross section area smaller. The current load goes up but below the breaker load yet too much load for the cord.
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Old 09-09-2009, 11:17   #3
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Hi Charlie!

If you don't already have a copy - I recommend getting Nigel Calder's: Boatowner's Mechanical and Electrical Manual.

I'm not a certified electrician, but I would definitely go to 12 gage for internal wiring and wire your boat at least for 30 amp service. Note 30 amp service cordsets use 10 gage wire.

Be careful wiring and follow the ABYC recommendations otherwise you can cause a slew of problems and possibly kill somebody!
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Old 09-09-2009, 12:04   #4
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it sounds like there was no evidence of the wire failing...? If the soot was from a wire fire, the cover should be melted...Maybe the soot is from something else? if the run length is appropriate for 14 gage rating, and you are using good wire, it should be fine. IF you are going to use a hevy draw appliance l ike an electric heater, I would make that particular run to that outlet larger....
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Old 09-09-2009, 12:14   #5
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I wouldn't run a coffee pot on 14 gauge wire, except in emergences
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Old 09-09-2009, 12:18   #6
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Ampacities of copper wire, in free air at 30o C:
================================================== ====== | INSULATION TYPE: |
| RUW, T THW, THWN FEP, FEPB | | TW RUH THHN, XHHW | ================================================== ======

SizeAWG

Current Rating@ 60 deg C @ 75 deg C @ 90 deg C ================================================== ====== 20 -------- *9 ----------------------------- *12.5
18 -------- *13 ------------------------------ 18
16 -------- *18 ------------------------------ 24
14 --------- 25 ------------- 30 ------------- 35
12 --------- 30 ------------- 35 ------------- 40
10 --------- 40 ------------- 50 ------------- 55
8 ---------- 60 ------------- 70 ------------- 80
6 ---------- 80 ------------- 95 ------------ 105
4 --------- 105 ------------ 125 ------------ 140
2 --------- 140 ------------ 170 ------------ 190
1 --------- 165 ------------ 195 ------------ 220
1/0 ------- 195 ------------ 230 ------------ 260
2/0 ------- 225 ------------ 265 ------------ 300
Derate 15% for being part of a loom/cable. See a problem with 30A and #14 wire?
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Old 09-09-2009, 12:49   #7
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Hi Charlie. Sounds like you've got quite a project going, and another great opportunity to learn something new (boats are overflowing with those kinds of opportunities!!). As RaptorDance suggested, a copy of Nigel Calders' book is a must.
When selecting the right wire guage for the job at hand, it's important to know the voltage, current, length of wire run, and how much voltage drop (or loss) you'll experience in that circuit.
Let's assume you're working with 120vAC as voltage, you want to run a 1500 watt heater on the circuit. 1500 watts divided by 120 volt = 12.5 amps. That's your current. Now let's say you'll be running a 25' wire run (continuous). According to the table in my ABYC standards (and Nigel Calders Book); 14ga wire will safely handle 15 amps up to a 25' run, falling within the 10% loss catagory.
Why the concern about loss? Electrical devices that are considered absolutely necessary for the yachts operation and survival should be wired with a maximum 3% voltage loss (bilge pumps, nav. lights, VHF radio, etc...)
Be sure that the circuit breaker you'll be tying to is sufficient for the load also.
Would I rewire my boat using heavier wire? Probably, but I'm always accused of "over-engineering" my boats!
Have fun, but do read up on marine electrical systems.
Bob
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Old 09-09-2009, 12:52   #8
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I disagree with the above tables. Where are they from S&S? Those are some unacceptably high voltage drop percentages for AC circuits.

For AC circuits on something as small as most pleasure boats, you do not need to worry about increasing the wire gauge diameter for lengthy wire runs. For DC circuits, its a very different story.

For 120VAC, at the minimum, you run 14 AWG for 15 amps, 12 AWG for 20 amps and 10 AWG for 30 amps. This is the minimum though. In your situation Charlie, I would run all 12 AWG to your 15 amp electrical outlets with a 15 amp double pole breaker at your AC panel. By wiring this way, your AC breaker will pop before your wire overheats. Running 10 gauge wire for a 120V/15 amp circuit like yours would be overkill and a waste of money.

Is your boat in the SF Bay Area by any chance?
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Old 09-09-2009, 12:55   #9
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Originally Posted by S&S View Post
Ampacities of copper wire, in free air at 30o C:
================================================== ====== | INSULATION TYPE: |
| RUW, T THW, THWN FEP, FEPB | | TW RUH THHN, XHHW | ================================================== ======

SizeAWG

Current Rating@ 60 deg C @ 75 deg C @ 90 deg C ================================================== ====== 20 -------- *9 ----------------------------- *12.5
18 -------- *13 ------------------------------ 18
16 -------- *18 ------------------------------ 24
14 --------- 25 ------------- 30 ------------- 35
12 --------- 30 ------------- 35 ------------- 40
10 --------- 40 ------------- 50 ------------- 55
8 ---------- 60 ------------- 70 ------------- 80
6 ---------- 80 ------------- 95 ------------ 105
4 --------- 105 ------------ 125 ------------ 140
2 --------- 140 ------------ 170 ------------ 190
1 --------- 165 ------------ 195 ------------ 220
1/0 ------- 195 ------------ 230 ------------ 260
2/0 ------- 225 ------------ 265 ------------ 300
Derate 15% for being part of a loom/cable. See a problem with 30A and #14 wire?
I am running 15 amps on 14/3. Even derated it is still well under the limit. 30 amps was the total going into the boat not running on the 14/3 wire.

Ok I replaced two runs. Now just need to put in the receptacles. It is alot harder to do on a boat as opposed to a house. Crimp on fitting, het shrink etc. We'll see how it goes.

I've decided to run one side of the boat in 12/3 and the other in 14/3. Plus no hair driers on the Starboard side of the boat. LOL
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Old 09-09-2009, 13:18   #10
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Its pretty easy attaching stranded wire to 15 amp outlets. You use a crimp on ring terminal and back the screw all the way out, even though you have to force it a little towards the end. I know you know Charlie, but for others, never wrap stranded wire around the screw. Always use a crimp on ring terminal.
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Old 09-09-2009, 14:48   #11
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I donít think it is worth moving up to a #12 wire on a 15 Amp circuit, in most cases.
A #14AWG copper wire is suitable for a 12.5 Amp / 1500 Watt load (maximum Iíd apply on a 15A Breaker) over a distance of 50 to 90 feet.

Itís almost certain that the wire didnít catch fire due to an overload that didn't trip the breaker. As Cheechacko indicates, the wire likely didnít burn, and the surface contamination is likely from a different cause.

Extension cord is not suitable for permanent installation, anywhere.


Yes (S&S) I see a problem with 30A and #14 wire, just as (I presume) you do.
The Ampacity table that S&S contributed looks like it has been adapted from the ABYC Ampacity ratings. ABYC allows higher Ampacities than do shore-side codes, such as the NEC & CEC. I donít approve of the ABYC tables, which I believe are too liberal, and always recommend utilizing NEC/CEC Ampacity tables.
#14 to 15A
#12 to 25A
#10 to 30A

A 1500W CoffeMaker will operate just fine on #14 AWG Cu wire feeding a 15A duplex receptacle.
Stranded conductors (recommended) cannot be connected directly to wiring device screw terminals. Crimp on a ring or captive fork terminal, which goes under the binding screw.

The voltage drop of a circuit is in direct proportion to the resistance of the conductor and the magnitude of the current. If you increase the length of a conductor, you increase its resistance; and thus increase its voltage drop. If you increase the current, you increase the conductor voltage drop.

The NEC recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn't exceed 5%, and the maximum on the feeder or branch circuit shouldn't exceed 3%. This recommendation is a performance issue, not a safety issue.
5% Voltage Drop @ 120VAC Applied = 6.0 Volt Drop (114 V at load)
3% Voltage Drop @ 120VAC Applied = 3.6 Volt Drop

A maximum distance of 53.73 feet will limit the voltage drop to 3% or less (89.56 feet @ 5% drop) with a 14 AWG Copper conductor delivering 12.5 amps on a 120 volt system. A #12 Conductor would be recommended for 15A Ccts longer than 50 - 60 Feet.

Engineering Basis:
* 15 Amps Rated ampacity of selected conductor
* 2.9495 Ohms Resistance (Ohms per 1000 feet)
* 0.058 Ohms Reactance (Ohms per 1000 feet)
* 3.6 volts maximum allowable voltage drop at 3%
* 0.9 Power Factor
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Old 09-09-2009, 14:54   #12
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IMHO, going a wire size bigger than the chart is good practice. The resistance is lower (uses less juice) and there is some margin for error. The cost of the wire compared to the labor is not that much.
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Old 09-09-2009, 15:00   #13
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I disagree with the above tables. Where are they from S&S? Those are some unacceptably high voltage drop percentages for AC circuits.
They are standard tables( off the net) but they are in confromance with my copy of the Chicago Electrical Code. The issue is not voltage drop but resistive heating. 14 ga. wire is fine for 15A, 12 for 20 and 10 for 30 (at 120V). Remember Ohm's Law.

It pays to be conservative and go with a larger gauge. Standard practice is to derate the free air ampacity when the run is confined (or combined with other wires). The CEC has tables for this but they are only available in hard copy. I don't particularly like the AYBC ratings either.
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Old 10-09-2009, 10:13   #14
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"ABYC allows higher Ampacities than do shore-side codes...." Is it possible that stranded wire has different ratings than solid core wire? Seems like I remember that electricity moves on the surface of the wire not "through" the wire...? If that is the case, then stranded wire may have more surface area.... thus the up rating... am I remembering this right?
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Old 10-09-2009, 10:34   #15
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"ABYC allows higher Ampacities than do shore-side codes...." Is it possible that stranded wire has different ratings than solid core wire? Seems like I remember that electricity moves on the surface of the wire not "through" the wire...? If that is the case, then stranded wire may have more surface area.... thus the up rating... am I remembering this right?

Current only travels on the surface of a conductor when it's at RF frequencies.

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