Re: Why ground the neutral?


> Yeah now we drill into live circuits behind the drywall with
> "double-insulated" drills and electrocute ourselves becasue we have
> dispensed with the grounding.
Cordless drills. That's why they still need to be insulated.
Reply to
Paul Hovnanian P.E.
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I have never seen an insulted drill chuck yet except for the Fisher Price Model 28. I got a real one when I turned 8 years old though.
Reply to
Gym Bob
Have you seen a Makita cordless? The only exposed metal is the 3 clamping jaws. I imagine most "keyless" chucks are made that way.
Reply to
Gfretwell
The Makitas we have are not like that. They have silver metal chucks and not gun-blackened metal or are you telling me they are plastic?
Reply to
Gym Bob
Norway in fact has a system where the transformer is isolated from earth (ground). In this case there isn't even a neutral, just the three phases with 230V between them.
Of course, there are still earth wires that tie together all the sockets in the house. The breaker won't trip on the first fault to earth like in a conventional grounded system, but if a second fault on a different phase occurs the two faults will short-circuit tripping the breaker(s).
It definitely works, but in practice it isn't quite as simple as in theory. In reality there is no such thing as a perfect insulator. Every wire and every appliance is leaking a little bit to earth. This means that a large system will always have a phase to earth voltage. What this voltage will be is determined by the impedance between the different phases and earth. If the impedances are equal, this voltage will be about 133 volt if the phase to phase voltage is 230V.
I better point out that this has no effect on the appliances.
/Clas-Henrik
Reply to
C-H Gustafsson
Double-insulated doesn't mean all exposed parts are plastic. A drill with a metal chuck can still qualify as 'double-insulated'. The term simply means that if an internal wire's insulation should fail and energize the motor frame or other internal metal, it still won't be conducted to any exposed part. The metal chuck of a drill can easily be insulated from the motor via nylon gearing. So you would need a wire fault to the motor case, and another fault somehow electrically connecting the motor case/shaft to the output shaft.
Metal screws holding a casing together are another common one. They go through holes in the plastic casing to self-tap threads in a molded piece of plastic on the other half of casing. If the motor frame becomes 'hot', the screws are still safe.
daestrom
Reply to
daestrom

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