In message , Colin Burchall <[EMAIL PROTECTED]> writes
>Tony Antoniou wrote:
>>
>> But for the sake of common practice for the protection of sensitive
>> electronics, keeping something grounded is a good thing to do. I can
>
>Keeping the negative terminal of a battery connected while the positive
>is disconnected doesn't afford any grounding protection. That
>protection comes from the large mass of metal of the vehicle's body.
>Once your sensitive equipment is disconnected from the vehicle body it
>becomes vulnerable to static discharges etc.
>As soon as one battery terminal is disconnected the circuit is open and
>no current will flow. The only difference between having positive or
>negative disconnected is the potential relative to the car of the
>unconnected terminal, and that is of no consequence.
>
This is not grounding, or here in the UK earthing, as what you are
talking about is the PD (potential difference) between the batteries
negative and positive terminals. The vehicle body does not earth the
vehicle as there are four large insulators between that and the earth.
These are known as tyres. To bring this to earth potential you would
need an earthing strap between the body an earth.
>> you can
>> also face serious consequences when the positive lead is still connected
>> even though the negative lead isn't. I've seen it happen, despite the fact
>> that it shouldn't, theoretically.
>
>What have you seen happen? What are these serious consequences?
>
The vehicle's body may at a different potential to your own body for
instance and a charge may jump from you to the vehicle or vice versa.
(The tools you are using could also be at a different PD to the
vehicle.) If working on sensitive equipment such as electronics then
this could be disastrous. Think about computers and why you should
touch the casing which is connected to earth (ground) via the power
cable's earth prior to working on it.
--
Geoff
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