Another battery disconnect question

[stvaughn]

Standard procedure for disconnecting a battery is to remove the ground connection first. My question is do you switch the ground circuit or the hot circuit or does it really matter?

 

Steve

[joe_padavano]

28 minutes ago, stvaughn said:

Standard procedure for disconnecting a battery is to remove the ground connection first. My question is do you switch the ground circuit or the hot circuit or does it really matter?

 

Steve

 

This is like asking a religion or politics question - or worse, like asking which way the toilet paper should hang off the roll!

 

I look at it this way.  If you disconnect the hot side, a tool dropped against the + terminal will still arc to ground.  If you disconnect the negative side, that is not a possibility. The latter seems safer to me.

[PFitz]

3 hours ago, joe_padavano said:

 

This is like asking a religion or politics question - or worse, like asking which way the toilet paper should hang off the roll!

 

I look at it this way.  If you disconnect the hot side, a tool dropped against the + terminal will still arc to ground.  If you disconnect the negative side, that is not a possibility. The latter seems safer to me.

 

This is the safer way, ..... whenever possible.  Sometimes batteries are grounded with a short strap and it may not be easy to run heavy cables to a switch.

 

Paul

[Joseph P. Indusi]

Steve:

Save yourself some trouble and buy a heavy duty cutoff switch especially for a 6 volt car.   

Joe, BCA 33493

[lozrocks]

As stated, when disconnecting a battery, always disconnect the earth cable first. (irrespective of negative earth or positive earth)

If you are asking about inserting a cut off switch into the circuit, then a cut out switch should always be in the hot side.

[stvaughn]

2 hours ago, lozrocks said:

As stated, when disconnecting a battery, always disconnect the earth cable first. (irrespective of negative earth or positive earth)

If you are asking about inserting a cut off switch into the circuit, then a cut out switch should always be in the hot side.

Why should the switch “always” be on the hot side since standard procedure is to disconnect the ground side first. 

[bob staehle]

The Caterpiller factory has been installing batt. disconnect switches on the ground cable, of their heavy equipment for years & years & years.

           for what its worth   Bob  

[joe_padavano]

3 hours ago, lozrocks said:

As stated, when disconnecting a battery, always disconnect the earth cable first. (irrespective of negative earth or positive earth)

If you are asking about inserting a cut off switch into the circuit, then a cut out switch should always be in the hot side.

 

You might want to go back and re-read what you wrote...

[lozrocks]

What is the purpose of a battery disconnect switch?

Primarily to prevent theft. Disconnecting power to the fuses.

Second to reduce the drain of the battery whilst standing for long periods.

More modern cars have circuits which need to be kept active. Central locking for example. So a bypass circuit for the disconnect switch is used to keep power to these circuits. That's not possible if the switch is on the earth side.

In the USA for diesel engines the disconnect switch is required to be on the earth side. In Europe the disconnect switch is required on the positive side. The reason for both is to prevent fires if the ignition or battery switch fails.

In race cars and drag cars I believe it is mandated that the disconnect switch be on the positive side and must be negative earth.

In an early car with very simple wiring, there is no advantage or disadvantage to having the disconnect switch on negative or positive side.

[Curti]

In a restored car with all NEW wiring, competently rebuilt starter, generator, diode in cutout, etc. I see no reason for a battery disconnect.  That being said,  a disconnect can be useful while building the car. 

[stvaughn]

I agree with both lozrocks and Curti, however for me reason number three is my justification for a switch. 

#3 Peace of mind. 

 

[Curti]

I suggest putting one in ALL of your cars, particularly the new ones, there is miles more wiring .

[stvaughn]

42 minutes ago, Curti said:

I suggest putting one in ALL of your cars, particularly the new ones, there is miles more wiring .

😎

[joe_padavano]

1 hour ago, Curti said:

I suggest putting one in ALL of your cars, particularly the new ones, there is miles more wiring .

Unfortunately, new cars do require power to retain memory in certain units, maintain the radio theft lock code, and to allow remote key fobs to work. Yeah, you can power those systems separately, but where do you draw the line?

[PFitz]

Some of the cars from the 20s and 30 are a nightmare to get to the battery terminals. A battery disconnect switch makes life easier when working on the car necessitates shutting off all the power,.... as long as the switch isn't as equally tough to get to. 

 

Many cars have the battery under the front seat. And many of those have reupholstered front seat cushions that are often overstuffed and tough to get back into the seat base frame without risk of damaging the upholstery.

 

Another pet peeve is some cars where the battery is in through a small door in the running board splash apron where easy access to the battery terminals was not part of the design. It's a challenge to get a wrench on the terminals - all while working on hands and knees.

 

Paul

[Spinneyhill]

On 11/20/2018 at 11:19 AM, PFitz said:

all while working on hands and knees.

and trying to see it by looking out the bottom of one's multi-focal glasses. My neck doesn't go back far enough.

[Frank DuVal]

On 11/19/2018 at 2:58 AM, lozrocks said:

In the USA for diesel engines the disconnect switch is required to be on the earth side. In Europe the disconnect switch is required on the positive side. The reason for both is to prevent fires if the ignition or battery switch fails.

 

Required by what person/code/government rule?

 

Steve, it does not make a difference for your collector car. Whatever is easier to wire.😉

[PFitz]

12 hours ago, Spinneyhill said:

and trying to see it by looking out the bottom of one's multi-focal glasses. My neck doesn't go back far enough.

 I feel your pain. I use full frame plastic reading glasses for shop safety glasses so that in instances like that hidden battery I can see what I'm doing at arm's working length when I have to have my head tilted.

 

Reminds me - had to borrow the wife's bifocals once to do a similar look-in-and-under type task. Found they worked better when I put them on upside-down.

 

Paul