AC Wiring Shocker

[Cheechako]

Ahhh, there you go... the Ham thing...

[seandepagnier]

I just scored pounds of wire in the sf bay area for my boat various sizes on spools. There is a used building supplies Building REsources with wire, and they also have teak boards and other useful stuff for cheap. I even got 15 feet of 00 (double 0) gauge wire to connect the wind generator to the batteries.

[Charlie]

Hi All here is a link to the wires that I pulled out pretty scary when I look at the fire they could have caused -- Picasa Web Albums - mckenzie.charlie - burnt wire

[Rene]

The amperages for a given wire size in AC systems are correctly quoted as 15 amps for #14 awg, 20 amps for #12 awg and 30 amps for #10 awg. Voltage drop is not usually a factor in these short runs. However #8 awg might be a better choice for main runs to your breaker panel. Using a larger wire size than necessary does not save electricty. The wiring that appeared to be extension cord was likely marine cable. This cable is used on ships and devices such as sump pumps and float switches and is an approved wireing method. Marine grade wire is not only tinned but is constructed with finer wire strands, this reduces metal fatigue caused by vibration. Joints, splices and terminations are responsible for more fires than wire size when the wire is protected by the correct fuse or breaker. Improper crimping, loose screws and the wrong wire connectors are the usual culprits. Unless you are dealing with fixed resistance heating ( baseboard heaters etc.) devices can only be rated for 80% of rated breaker capacity or 12 amps (1440 watts). If you have a device rated at 15 amps or 1500 watts it must be plugged into a 20 amp recpticle on a 20 amp circuit. Not enough emphases is placed on the use of anti-corrosion compounds on splices, joints and terminals. These compounds help to exclude oxygen and salt controlling corrosion and overheating.The ball game is entirely different when dealing with DC circuits and a manual like the one by nigel calder is a major help even to a retired elecrtician like me. Marine wireing has many nuances not found in normal residential or industrial electrical applications.

[GordMay]

Originally Posted by Rene

... The wiring that appeared to be extension cord was likely marine cable. This cable is used on ships and devices such as sump pumps and float switches and is an approved wireing method...

Charlie’s picture seems (to me) to be depicting a (portable) Flexible Cord. Note the poly’ filler strands, a characteristic of flexible cords (and extension cord), not normally found on modern cables.

Extension cords are convenient ways to provide power to portable equipment. Extension cords are intended only for temporary use with portable equipment.

Flexible cords and cables are attached to appliances, and can be used as pendants, for the wiring of fixtures, for the connection of portable lamps and appliances, for the connection of stationary equipment that is frequently moved, and to prevent transmission of noise or vibration and allow movement. Flexible cords (& extension cords) are NOT an approved wiring method.

Most Codes, Standards, & Regulations prohibit the following uses of flexible cords (and extension cords):

- as a substitute for fixed wiring (i.e. permanent)

- when run through holes in walls, ceilings, or floors

- when run through doorways or windows

-when attached to building surfaces

- when concealed by walls, ceiling, or floors

[senormechanico]

The "soot" seems to me to be oxidized black wire insulation. I don't see any evidence of overheating, just soot tracks. The plastic on the terminal ends looks ok and the polyester filler isn't damaged.

It's not approved wiring of course, but I don't think the boat was in danger of fire.

Steve B.

[Charlie]

Senor M:

I don't know enough about electrical fires to know for sure on this one but it sure looks like the wire was hot enough to leave a black stain on the yellow insulation of the extension cord. I am goign to replace the wire regardless of what happened but am curious as to whether this was a fire, overheating, or just oxidation.

Gord May is correct on this cable it says that it is extension cord right on the yellow jacket.

[Roy M]

Funny to have run into this thread, today. Over the weekend, I did some AC repairs on a friend's boat. It's a thirty-plus year old Islander that was exhibiting some failures of its AC circuits. I opened up the breaker panel and found several of the Marinetics (popular in those days) breakers, covered in black soot. All of the original wiring, basically a three wire zip cord, 14 gauge, untinned, red-black-green, was stiff, and green corroded at all the lugs. I replaced the entire panel with a new Blue Sea unit, added temporary pigtails to the existing wiring (I'll strip out all the original later) because the corrosion had capillaried back some ways, then replaced the Marinco shorepower plug with another, due to scorching of the terminals and some melting of the plastic. Miraculously, the water heater now works.

Old wiring systems should be replaced with newer, all-tinned stranded wires, such as Ancor. Old breakers do age as well, reducing their ability to conduct current and creating heat. All of the paper labels on the old breakers had charred. Moisture, salt and heat affect the older wiring over time, reducing their capacity to carry rated current, creating heat and mysterious failures to conduct.

I have completely replaced all of my original wiring and distribution system over the last couple years, upgrading in the process from a six-circuit DC system (enough in the 70's) to a sixteen circuit system for the 21st century's demands of nav electronics, saltwater washdown pumps, electric windlasses, refrigeration, and all those wonderful electric and electronic servants that make our cruising so special. If any of you have old AC or DC circuits, whether or not you ever leave the dock, they have been subjected to the abuse of time and the environment. Inspect the components, as well as the associated wiring and distribution, for signs of deterioration. Transplants are better than cardiac arrest. And if you are going to take shortcuts, as I am doing with my customer, make sure they are temporary, as in a couple months, at most.

[Cheechako]

Yeah, when you think about it, a wiring fire is probably more likely a cause to need to abandon ship than a weather problem.....

[GordMay]

Originally Posted by senormechanico

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

True, in a practical sense, for most applications. Not quite technically accurate, though.

The tendency of alternating current flow to crowd towards the external conductor surfaces is called Skin Effect. The higher the AC frequency, the more pronounced that tendency. These considerations become important for 60 Hz when conductor diameter exceeds about 1.25 inch (± 1500 MCM, where 1 MCM = 1000 Circular Mils).

[Rene]

Gord; The cable in the picture may be cabtire it isn't very clear. The code rules you allude to do apply to certain types of flexable cables in residential and industrial applications. The use of approved flexable cables in the mining code and shipboard codes is not only common but is the norm.

[GordMay]

Originally Posted by Rene

... The use of approved flexable cables in the mining code and shipboard codes is not only common but is the norm.

Most cruising boats don't have "festoons" or "pendants", where cabtire is most often used.
Are you Cdn? ("cabtire")

If you get stuck for a temporary repair, and must use a flexible cable (extension cord, or cabtire), try to get a cord with the letters “T” (high temperature) & “W” (wet locations) in the type designation.
Hence, for instance, type “STOW” as opposed to the cheaper “SO”.

[S&S]

Stop reading the NEC Gord! You'll go blind!

[GordMay]

It’s been nearly a decade since I’ve studied the Canadian Electrical Code or the NEC, and I never even knew that the City of Chicago had it’s own Code; which (if the Ampacity Table is representative) certainly isn’t very stringent.
I don’t work in electrical design any more.
Even so, I am slowly going (slightly) blind.

[S&S]

Originally Posted by GordMay

It’s been nearly a decade since I’ve studied the Canadian Electrical Code or the NEC, and I never even knew that the City of Chicago had it’s own Code; which (if the Ampacity Table is representative) certainly isn’t very stringent.
I don’t work in electrical design any more.
Even so, I am slowly going (slightly) blind.

That's quite a leap of logic going from an ampacity table to a comment about a whole code.

The Chicago Electrical Code is the strictest in the country. The table I posted is not from the CEC- just a representative sample off the net, In any event #12 AWG is standard wiring in THHN and the like for 20A free air circuits on shore and same for MTW in applications calling for it. Note I didn't post bundled conductors or length corrections
Come on, lighten up, I was just razzin' ya.

Say "festoon" 3 times.