1. #1
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    Default BTB (Back To Basics)- Disconnecting a Car Battery

    When youre done bitching about the Web Team, maybe you can join us over here. Lets do some back to basics (BTB) please.

    Its been awhile, but disconnecting the starndard car battery- Negative first right?

    And why?
    Last edited by CALFFBOU; 10-07-2006 at 01:09 PM.

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    I believe that it is negative first.

    And I was taught to cut a 1-2" section out of each cable so that if the cables were to touch after being cut they would not reenergize the car, even for a moment.


    I dunno, just what I have been taught.
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    The theory behind "negative first"is this: Almost all modern cars and trucks are negative ground,making anything metal in the body grounded(or a return path to the battery)(negative earth to our brothers across the pond).If you cut the POSITIVE first and touch anything metal with the cutters you will create a spark.Usually a pretty big one.By cutting the negative you lessen the possibility of this by greater than 80%.Like anything else it isn't completely foolproof but that's why it's taught that way.Likewise on an OLD vehicle(pre 1954ish)with POSITIVE ground you would cut the positive first.The key here is to remove the GROUND from the equasion.Clear as mud? T.C.

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    Quote Originally Posted by CALFFBOU
    And why?
    200 years of tradition thats why

    Honestly Bou I do not know. It is just something that was always taught but the other replies make since to me.
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    Quote Originally Posted by BFDLT32
    200 years of tradition thats why

    Honestly Bou I do not know. It is just something that was always taught but the other replies make since to me.

    200 years ! Cars have only been around since like 1885 ! LOL
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    pointless...

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    Disconnect the GROUND first. Usually negative, but as R101 mentioned, some older cars may still have a positive ground. For today, we'll assume it is a modern negative ground.

    The why is simple:

    Removing either contact will achieve the goal of disrupting the flow of power.

    However, if you chose to remove the positive first, and hit any part of the mangled car body with your wrench, you could accidentally create a circuit between the terminal and the body that would result in a strong current and major light and smoke show. In rare cases, in that instant where the wrench or tool touches the body it is even possible to instantly "weld" the metal implement to the body, causing a sustained reaction, and possible fire or battery rupture.

    If you remove the negative ground first, and you accidentally touch the body, nothing happens. That is where that line goes anyway. Just remember to steer clear of the positive terminal while doing so.


    And as for cutting out a section; we don't. Nothing really wrong with doing so, but you may find that you or the wrecker WANT to re-energize the car at some point, and you have just removed your ability to do so.

    We try to remove the cable neatly, but fold the end back and duct tape it off so it can't reach the terminal either way.

    Never argue with an Idiot. They drag you down to their level, and then beat you with experience!

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    Quote Originally Posted by Ron3427
    pointless...

    And this comment isnt? Contribute to the thread or go away. There. Now we dont need to worry about the webteam!

    as for disconnecting....if you didnt destroy the connections, just tape the ends off so they cant touch metal again, instead of cutting them.
    Last edited by nyckftbl; 10-07-2006 at 06:55 PM.
    Proud East Coast Traditionalist.

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    Quote Originally Posted by BFDLT32
    200 years of tradition thats why

    Honestly Bou I do not know. It is just something that was always taught but the other replies make since to me.

    Ugh...

    First- The phrase goes- "150 years of tradition..." Please get it right.

    Second- I hope you now know that its black/ground first.

    Lastly, I knew the answer all along, just wanted to let other people chime in first.

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    The disconnection of the negative lead will cause a much shorter and cooler arc and lessen the chance of igniting any vapors.

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    When you remove the negative cable first you will get NO sparks while removing it. If you remove the positive cable first you WILL get sparks just from removing it as it is still in a closed circut. Also there is some mis-information in a few of the above threads....Regardless if the negative cable is removed or not, IF you touch any metal part with your wrench while removing the positive cable, you will get sparks. You are creating a dead short between the positive and ground.

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    Quote Originally Posted by CALFFBOU
    Ugh...

    First- The phrase goes- "150 years of tradition..." Please get it right.

    Second- I hope you now know that its black/ground first.

    Lastly, I knew the answer all along, just wanted to let other people chime in first.
    First- I know, but I like change

    Second- I do know

    Lastly that was nice of you to make this a good training exercise
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    Let's go a step further. Do you disconnect the battery cables or cut them?

    Look at the car. You don't have to work in a body shop to be able to tell when a vehicle is drivable or not. If it looks like it can be driven away, or even driven out of the road and into a nearby parking lot, just disconnect the battery cables.

    If the damage is so severe that it will need to be towed, save the time and cut the cables. This is when you will cut the 2 inch chunck out of them like it was mentioned above.

    Don't play games with wrenches and neatly disconnect a battery from a car that clearly has so much damage that it has to be towed anyways. And whatever you do, don't cut the cables and find out that another family member is planning on driving the car away from the scene.
    Chris Shields
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    I've always been taught to avoid cutting the cable for the same reason mcaldwell stated. At the same time, I was taught a long time ago to slip a latex glove over the cable ends to prevent any accidental arcing.

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    Depends on if you even can get to the battery. If you can reach in with snips but not a wrench then go for a cut cuz thats the only thing yo can do.
    J

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    First of all... you have to know where the battery is!

    Some cars have them in the trunk, such as BMW.

    Sme are in the front wheelwells, like many Daimler Chrysler cars.

    Some are under the rear seat, as in the old school VW Beetle.

    Some cars have more than one battery.

    Holmatro's auto extrication guides give you the location of the batteries, air bags and other pertinent information.
    ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
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    Quote Originally Posted by CaptainGonzo
    First of all... you have to know where the battery is!

    Some cars have them in the trunk, such as BMW.

    Sme are in the front wheelwells, like many Daimler Chrysler cars.

    Some are under the rear seat, as in the old school VW Beetle.

    Some cars have more than one battery.

    Holmatro's auto extrication guides give you the location of the batteries, air bags and other pertinent information.
    this is 100% true.
    J

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    Quote Originally Posted by SIGNAL99COM
    Let's go a step further. Do you disconnect the battery cables or cut them?

    Look at the car. You don't have to work in a body shop to be able to tell when a vehicle is drivable or not. If it looks like it can be driven away, or even driven out of the road and into a nearby parking lot, just disconnect the battery cables.

    If the damage is so severe that it will need to be towed, save the time and cut the cables. This is when you will cut the 2 inch chunck out of them like it was mentioned above.

    Don't play games with wrenches and neatly disconnect a battery from a car that clearly has so much damage that it has to be towed anyways. And whatever you do, don't cut the cables and find out that another family member is planning on driving the car away from the scene.
    this is kind like the Try before you pry thing. why cause more damage if you dont really have too. i knew the negative cable was disconnected first just not why. now i know!!!!
    " IF GUNS KILL PEOPLE THEN I CAN BLAME MY MISSPELLINGS ON MY PENCIL" -Larry The Cable Guy-

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    Our SOP calls for removal of the Negative post first, then the positve. we never except in extreme situations cut the cables. You never know when you may need power back on, for instance if power seat has to be moved back, or forward. Its just easier if you keep it simple everytime. Having said that we had a wierd one happen to us a few weeks back, 2 vehicle MVC head on @ about 35-50 kmh, average amount of damage nothing unfixable. FF removes the neg cable first, goes about removale of pos. cable, wrench grounds out against frame, car starts up!!! Holy batcrap, suprised the h out of everyone. Turns out the battery was punctured underneath out of site and was grounded. Still cant figure out why the car started, keys were on the front seat out of ignition, put keys back in ignition, turned ignition to start and then turned ignition to off, car shut off. A mystery! Life went on.

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    What about Hybrids???
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    Default Nice Try

    Quote Originally Posted by Frmboybuck
    When you remove the negative cable first you will get NO sparks while removing it.(wrong) If you remove the positive cable first you WILL get sparks just from removing it as it is still in a closed circut. Also there is some mis-information in a few of the above threads....Regardless if the negative cable is removed or not, IF you touch any metal part with your wrench while removing the positive cable, you will get sparks. You are creating a dead short between the positive and ground.(Wrong again)

    First, if there is any draw on the battery, both the + and - will spark.
    Second, if the - cable is removed then there is nothing to complete the circut.
    Nice try though.

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    Default And don't forget....

    Airbags are more likely to be triggered if you disconnect the positive first. Neat show, but not fun.

    At least that was what i was told in my lessons on vehicle extrication.
    Jason.
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    I've always been taught and practiced and taught to disconnect the ground cable first.
    Now as to the question of cutting or disconnecting, I have tried to make it a habit to always disconnect, not cut the ground cable. The reasoning: One day a nice lady (who happened to be a dispatcher of ours) was pulling through the local bank ATM when she did not see the bright yellow 4' high barricade that would prevent her from running into the side of the building. Brand new Ford F-350 powerstroke crew cab. Took the pillar right on the blue oval. Major fluid leak. No injuries, minor crash. Fixable by many opinions. The engine crew (young crew, no experianced officer supervision, volunteer crew) CUT 2" out of the cables while they mitigated the fluid leak.
    Nicely disabled, good job fellas! But the truck just needed a new hood, new grill and a couple of whapps of the hammer and bammo! Brand new truck again! Except for the $400 the autobody shop charged the insurance company for new cables and labor.
    Needless to say the insurance company reviewed our SOP's and wished reimbursment from the VFD for the amount of approximately $400.

    Someone has already said TRY BEFORE YOU PRY. Use some common sense and think before you do some of the things we do commonly.

    As for cutting, there are just certain times you NEED TO CUT! Extrication (not extended) is a cuttable instance. Life before property.

    Batteries are spread out all over. My wifes 2005 Chevy Tailblazer has a battery under the back seat. Wouldn't have known that if not for an astute observation by her extremely curious husband!

    *Mark
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    Quote Originally Posted by SIGNAL99COM
    Let's go a step further. Do you disconnect the battery cables or cut them?
    Are you assuming no life threatening injuries with this question?

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    My point was that just because the negative is "unhooked", that dosent assure you that NO sparks will fly. I was not assuming there was draw on the battery either but in that case then yes you will get sparks from either cable because you have current flowing and you are breaking the chain

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