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Old 05-06-2017, 07:34   #1
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Fire Risk in High Current 12V Wiring

FWIW, I recently had a small fire in the FACTORY INSTALLED wiring for my bow thruster. The negative and positive wires crossed at one point, and the fuseable link was installed "down stream" of the crossing point (close to 2 feet away). In short (no pun intended), I needed to continuously run the bow thruster for an extended period of time (less than the time period where the thruster automatically times out). Apparently the heat generated in the conductors first softened the insulating jacket, then the compression pressure at the positive / negative wire crossing deformed the insulating jacket, and a dead short occurred. The fuseable link never melted to protect the wiring (of course it didn't, see above note about wiring details). Net result was melted wires, two boiled group 31 FLA batteries creating a cloud of water and ACID vapor inside my sealed sail locker (yes, each battery was in a battery case and the cases were in a glassed in enclosed wooden box) and a small fire in the supporting wood bulkhead. I am rewiring with heavier 4/0 wire, placing a 400 amp "T" class fast fuse (instead of a fuseable link) immediately after the battery in the positive wire, placing a TWO POLE disconnect (opens both the positive and negative side of the circuit) by the deck hatch to the sail locker (OEM was buried at the bottom of the locker, not that opening the circuit would have helped in this instance), and ensuring that a NO POINT DO ANY OF THE CONDUCTORS CROSS.

BTW, the Admiral and I executed our "fire procedures" and were able to minimize the damage. Do you have a fire fighting plan in place and do you ever review it with your crew ?????
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Old 05-06-2017, 08:57   #2
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Re: Fire Risk in High Current 12V Wiring

Quote:
Originally Posted by Jeanneau 45.2 View Post
FWIW, I recently had a small fire in the FACTORY INSTALLED wiring for my bow thruster. The negative and positive wires crossed at one point, and the fuseable link was installed "down stream" of the crossing point (close to 2 feet away). In short (no pun intended), I needed to continuously run the bow thruster for an extended period of time (less than the time period where the thruster automatically times out). Apparently the heat generated in the conductors first softened the insulating jacket, then the compression pressure at the positive / negative wire crossing deformed the insulating jacket, and a dead short occurred. The fuseable link never melted to protect the wiring (of course it didn't, see above note about wiring details). Net result was melted wires, two boiled group 31 FLA batteries creating a cloud of water and ACID vapor inside my sealed sail locker (yes, each battery was in a battery case and the cases were in a glassed in enclosed wooden box) and a small fire in the supporting wood bulkhead. I am rewiring with heavier 4/0 wire, placing a 400 amp "T" class fast fuse (instead of a fuseable link) immediately after the battery in the positive wire, placing a TWO POLE disconnect (opens both the positive and negative side of the circuit) by the deck hatch to the sail locker (OEM was buried at the bottom of the locker, not that opening the circuit would have helped in this instance), and ensuring that a NO POINT DO ANY OF THE CONDUCTORS CROSS.

BTW, the Admiral and I executed our "fire procedures" and were able to minimize the damage. Do you have a fire fighting plan in place and do you ever review it with your crew ?????
Wire must have been undersized. Shame but pretty common. Any idea what size the original circuit protection was?
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Old 05-06-2017, 12:27   #3
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Re: Fire Risk in High Current 12V Wiring

Cables that cross, touch, or are even touching for the entire length of the run are not uncommon or even necessarily to be avoided. I think your problem is that the cable was perhaps not sized correctly and it was certainly not fused correctly. There may be a problem with your bow thruster to cause it to draw too much current, but the fire was caused by lack of over current protection adequite for the installed cables.
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Old 06-06-2017, 05:46   #4
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Re: Fire Risk in High Current 12V Wiring

Thank all the fallen angels you are safe and uninjured. Installing a fuse at the battery was the only way to correct this problem. I hope all will learn from your misfortune. Install catastrophic fuse protection at the battery terminal, within 7 inches.
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Old 06-06-2017, 19:15   #5
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Re: Fire Risk in High Current 12V Wiring

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Cables that cross, touch, or are even touching for the entire length of the run are not uncommon or even necessarily to be avoided.
Yeah I fully agree. Cables running together is perfectly normal.

All wire needs to be protected by a fuse. We cant control what happens in the bow thruster and if it has an internal failure it's entirely possibly for it to pull more than the rated current of the cable. This then causes the fault you experienced.

The solution for this is to have a fuse or breaker as close to the source as practical, rated to the same amps or lower than the wire. In case of an overload the fuse or breaker will trip first and the wire will never get hot enough to cause a problem. Note that cable manufacturers will take the temperature rating of their insulation into account with this, and also give you derating factors to use when the cables are in bundles rather than free air.

For instance you might have a battery with a thick 100A cable leading to a distribution box. The 100A cable might have a 100A fuse right at the battery terminal. The distribution box will then have a fuse or breaker on every outgoing circuit, rated the same or less than the wire on each circuit.

You may choose to rate the fuses/breakers according to the rated load on the end device (if it's lower than the wiring of course) but this is not strictly necessary, the fuse is there first and foremost to protect the wire and prevent fire.
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Old 06-06-2017, 19:21   #6
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Re: Fire Risk in High Current 12V Wiring

A perfect example of why ABYC requires fuse protection within 7" of the battery.

I hope you are not paying for this, it should be an insurance claim and if the God's are awake your underwriter will go after the vessel manufacturer.
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Old 11-06-2017, 22:17   #7
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Re: Fire Risk in High Current 12V Wiring

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A perfect example of why ABYC requires fuse protection within 7" of the battery.

I hope you are not paying for this, it should be an insurance claim and if the God's are awake your underwriter will go after the vessel manufacturer.
The OPs boat is a 2000 model. My 2005 Catalina didn't have fuse protection at the batteries until I added it (terminal fuses, really easy). I am not sure that manfucturers were doing that back in 2000? I know that on my current boat, there is fuse protection for the wiring, but it isn't at the battery but maybe 6' down the cable. This boat was built in 2010. I will be adding terminal fuses when I redo my battery bank.
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Old 12-06-2017, 04:35   #8
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Re: Fire Risk in High Current 12V Wiring

Thanks. A good reminder of the importance of safe wiring practices.
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Old 12-06-2017, 07:13   #9
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Re: Fire Risk in High Current 12V Wiring

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Originally Posted by dhays View Post
The OPs boat is a 2000 model. My 2005 Catalina didn't have fuse protection at the batteries until I added it (terminal fuses, really easy). I am not sure that manfucturers were doing that back in 2000? I know that on my current boat, there is fuse protection for the wiring, but it isn't at the battery but maybe 6' down the cable. This boat was built in 2010. I will be adding terminal fuses when I redo my battery bank.


Is the profit margin, on a vessel, so small that a few fuses or relays to protect the vessel and it's occupants are too much to ask of the manufacturer.?
Or are these used vessels that the previous owner/diy guy removed these safety devices.?
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