*take nothing for granted!
Unless otherwise indicated all photos © Richard McKie 2005 - 2015

Who is Online

We have 82 guests and no members online

Translate to another language

Hot wires

 

Pushing a current through a conductor requires energy.  The difficulty in doing this is called resistance; and is measured in Ohms.  For each Ohm of resistance an electromotive force of 1 Volt is required to cause a current of one Amp to flow.  In other words Resistance = Voltage (drop across the conductor) divided by the current (Amps) in the conductor.  This is called Ohms law and is obvious, a priori, from the definitions of these quantities.

The important things to know about conductors are that: resistance varies depending on the material that the conductor is made from; and the electrical energy used to overcome resistance becomes heat. Read More...

Electrical conductors get hot depending on the current flow; and the heat generated goes up exponentially as the current increases in a wire.

Suppose the lead to a power board in your kitchen is carrying 2 amps and consuming 5 Watts per metre as heat.  This is so small you don’t even notice the lead getting warm. If you add a few more appliances taking the total to 10 amps the heat in the lead will jump, not to 25 watts per metre as you might expect (5x5), but all the way up to 125 watts per metre; at which point it will probably burst into flames. This is why commercial power boards have a big safety margin with wires around twice as heavy as those in this example; so there is only moderate heating even at 15 amps.

Resistance falls as conductors get fatter, in proportion to cross-sectional area. This is obvious because two identical conductors (or water pipes) side-by-side carry twice the current of one.

You may have noticed that the cord to some high current appliances, like heaters, kettles and vacuum cleaners, gets warm.  To avoid heating the wires in your house too much and possibly burning it down, properly installed wiring has current ratings well above a safe limit; electricians are careful that all strands of a cable are terminated; and the current is limited by fuses and other kinds of current breakers. 

 

image014

 

We often want some wires in home appliances to get hot:  electric heaters, kettles, toasters, and so on work on this principle; an incandescent light bulb generates so much heat that the filament glows white hot; a fuse wire melts if the current gets above a certain limit.

But unless you want a bit of extra warmth, heating wiring in buildings is wasteful and a fire risk.  It is particularly wasteful in the street or in wires running for miles in the country.  Many millions of kilowatt hours of electricity can be lost heating the countryside.

The actual losses are equivalent to approximately 10 percent of the total electricity transported between power stations and market customers.  In long links and in those carrying high currents, from time to time, the losses can be much higher than this.

 

 

Add comment


Security code
Refresh


    Have you read this???     -  this content changes with each opening of a menu item


Travel

Berlin

 

 

 

I'm a bit daunted writing about Berlin.  

Somehow I'm happy to put down a couple of paragraphs about many other cities and towns I've visited but there are some that seem too complicated for a quick 'off the cuff' summary.  Sydney of course, my present home town, and past home towns like New York and London.  I know just too much about them for a glib first impression.

Although I've never lived there I've visited Berlin on several occasions for periods of up to a couple of weeks.  I also have family there and have been introduced to their circle of friends.

So I decided that I can't really sum Berlin up, any more that I can sum up London or New York, so instead I should pick some aspects of uniqueness to highlight. 

Read more ...

Fiction, Recollections & News

A Discourse on History

 

 

On Australia Day 2011 again we hear the calls: Change the Flag; become a Republic; reparations for the White Invasion...

There are strong arguments for progress in each of these areas but as the following article discusses we first need to ensure that the changes that must be made are indeed progress; that we don't sacrifice that which has been achieved already.

Read more ...

Opinions and Philosophy

Sum; estis; sunt

(I am; you are; they are)

 

 

What in the World am I doing here?

'Once in a while, I'm standing here, doing something.  And I think, "What in the world am I doing here?" It's a big surprise'
-   Donald Rumsfeld US Secretary of Defence - May 16, 2001, interview with the New York Times

As far as we know humans are the only species on Earth that asks this question. And we have apparently been asking it for a good part of the last 100,000 years.

Read more ...

Terms of Use                                           Copyright