[Gllug] OT: Mains electricity colour coding.

[Alain Williams]

On Sun, Oct 24, 2010 at 06:58:44PM +0100, general_email at technicalbloke.com wrote:
> Hi All,
> 
> For time immemorial I have been told brown is live, blue is neutral and 
> yellow/green is earth. Mains electricity is AC so it oscillates between 
> the positive and negative 50 times a second right? In that case why does 
> it matter which way you wire the blue and brown cables to the nominally 
> blue and brown terminals in a plug? I always assumed you could 
> electrocute yourself equally well by touching the blue terminal, maybe 
> even better as the brown's got a fuse that might protect you!
> 
> I'm slowly working my way through W.P.Jolly's seemingly excellent "Teach 
> Yourself Electronics" so maybe it'll all become clear soon, having said 
> that - I'm also impatient!
> 
> I'm wondering now if and how the notion of "live" and "neutral" is 
> different to that of "positive and negative". If so can anyone breifly 
> explain or point me to a website that explains? Haven't had much joy 
> with google so far :/
> 
> Yours ignorantly,

Don't worry - you understand a lot compared to some people...... something
that I saw about a month ago:

I am not sure if I should laugh or cry at this, I suspect cry.  The complete
lack of understanding that it shows is astounding.  Did they author ever do any
science at school ?

See:

	http://www.bestbrandtobuy.com/car-power-adapter/

They seem to have becom sufficiently embarassed at the article that the removed
much of it. I have copied it as it was originally below.

Regards

****************
Car Power Adapter

The reason normal electrical appliances dont work in vehicles is because the
power source isnt the same. Cars use AC power instead of DC, which is what we
have in our homes. The electricity can still power your machine, but the power
plug it uses wont consume the power correctly. Car power adapters are basically
just power plugs that are designed to take in your cars AC power. They adapt to
your machine in the same way, but they end differently, as they are designed to
plug into your cars cigarette lighter, as opposed to a normal wall outer.

AC stands for alternating current, and DC stands for direct current. The reason
cars use AC power is because of the battery. An alternating electrical current
basically means that the power can, in laymans terms, go in two directions. In
the case of cars, the battery needs to be able to both receive and dispense of
power. Direct electrical current can only power an application; the power source
itself cant receive power as well. Because a battery needs to receive power, it
has to use AC power. However, AC power exists at a different frequency than DC
power, so an appliance that is set up to receive AC power cant receive power
from a DC power source, and vice versa.

Another reason why regular appliances cant use the car as a power source is
because of the shape of the power connector. Cars power supplies were originally
intended to light cigarettes, which is why theyre still often referred to as
cigarette lighters. A cars power source is still shaped for the cigarette
lighter, and so in order to access the power source, a car power adapter has to
be shaped to fit it correctly. Because the USA doesnt use AC power for regular
appliances, theres no need to fit a car power source to a regular electrical
cord shape.


When it comes to buying a car power adapter, there are two main issues to
consider  compatibility and adaptability. If youre able to attach a car power
adapter to your appliance, which means that the power cord is detachable. At the
opposite ends of a power cord are the end that connects to the power source and
the end that connects to the appliances power input. The shape of this input, as
well as the amount of power the appliance consumes, dictates the type of power
adapter you need.

If the appliance you want to power in your car is a mainstream appliance, like
an iPod, you wont have any trouble with finding the correct cable to connect it
to your car. But for something more unique, like a set of speakers, youll need
to find an adapter that both fits it correctly and sends out the correct amount
of voltage. There are a number of car power adapters that have replaceable
#heads, meaning that they can connect to a number of appliances that have
standardized power inputs. These are very useful for people who are alternating
between a few low-power appliances.

As for affordability, whether car power adapters are worth it just depends on
your situation. If youre only trying to power one application, or a few that can
use the same cord, then the $10 to $20 youll spend on an adapter is well worth
it. If, on the other hand, you want to power a few different appliances in your
car that would require you to buy several adapters, it might be worth it to
spend the $40 or so it costs to buy a power inverter. This will convert your
cars AC power to DC power, and allow you to plug in your electrical appliances
in the same manner you usually would.
****************

-- 
Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/
Parliament Hill Computers Ltd. Registration Information: http://www.phcomp.co.uk/contact.php
Past chairman of UKUUG: http://www.ukuug.org/
#include <std_disclaimer.h>
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