shorting a wire and fire

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Belgian1979
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shorting a wire and fire

Post by Belgian1979 » Wed Sep 07, 2011 5:38 am

This is a work related subject : the car in question has a batterij in the trunk and a big 121 Amp kabel to a distribution point under the hood. The car burned out completly and based from what we can see it started at the junction point under the hood. Possible caused by a the 121 Amp cable loosening and shorting out on the shell of the car.
I would assume a high enough current through this cable is possible to cause enough heat to start a fire.

However the other parties involved say the battery would desintegrate before enough heat would have been generated.

Any ideas on this ?

BCLS776
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Re: shorting a wire and fire

Post by BCLS776 » Wed Sep 07, 2011 8:26 am

Car batteries have plenty of power to start fires and not only do they create tremendous heat from a short circuit, but they sometimes explode from internal heating while shorted too.

One of the best safety devices you can install on a car is an inline fuse very close to the battery on the (+) terminal. If there is a short somewhere downline from the fuse on the main power wire, the fuse will blow. You need a large (100 or 200A) fuse, and these are available at shops that sell automotive electrical supplies. The fuse needs to be big enough to handle your starter cranking over the motor.
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BCjohnny
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Re: shorting a wire and fire

Post by BCjohnny » Sun Sep 11, 2011 6:02 pm

Belgian1979 wrote:This is a work related subject : the car in question has a batterij in the trunk and a big 121 Amp kabel to a distribution point under the hood. The car burned out completly and based from what we can see it started at the junction point under the hood. Possible caused by a the 121 Amp cable loosening and shorting out on the shell of the car.
I would assume a high enough current through this cable is possible to cause enough heat to start a fire.

However the other parties involved say the battery would desintegrate before enough heat would have been generated.

Any ideas on this ?
OK, I'm assuming a '121 amp cable' is a cable rated at about 120 amps, but over what distance? Even if the cable was rated at that over the full length used, shorting a battery (obviously depending on the battery capacity) to earth would allow five, maybe ten times that amount of current to flow, instantaniously, and in the case of a well charged battery for ten, maybe twenty seconds or more, the current only lessening inversly to the cable conducter temperature. If so the cable would be toast in much less than that, and more than likely alight.

Though theoretically possible, I very, very much doubt doubt the battery would 'disintigrate' in the manner described. In fact I'd say almost impossible, in practice.

Putting any kind of fuse in the starting circuit is not best practice. Conventional petrol/gas engine starter motors can draw up to 800 amps under lock torque, geared ones maybe just over half that. It would have to be a very big, very slow burning fuse to be of any use.

JMO.
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Mmfh
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Re: shorting a wire and fire

Post by Mmfh » Wed Sep 14, 2011 11:17 am

Batteries most definitely have the power to start fires!!

I saw a nice'67 Nova burn to the ground by a wire that had shorted. As best as we can tell going from the battery through the firewall and into the back of the fusebox.

The wire got hot, melted off the insulation and somehow caught stuff on fire under the dash. Not exactly sure what started it as by the time it was out everything was pretty much gone. We are sure though the fire started under the dash.

Very sad!

Mm

Kevin Johnson
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Re: shorting a wire and fire

Post by Kevin Johnson » Fri Sep 16, 2011 5:11 am

If the cable loosened at the attachment point any resultant arcing could easily start a fire. Watch the McGyver episode where he welds a connecting rod with a battery and a quarter.

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