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

Who is Online

We have 36 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

Poland

Poland

 

 

Berlin

We were to drive to Poland from Berlin.  In September and October 2014 were in Berlin to meet and spend some time with my new grandson, Leander.  But because we were concerned that we might be a burden to entertain for a whole month-and-a-half, what with the demands of a five month old baby and so on, we had pre-planned a number of side-trips.  The last of these was to Poland. 

To pick up the car that I had booked months before, we caught the U-Bahn from Magdalenenstraße, close to Emily's home in Lichtenberg, to Alexanderplatz.  Quick - about 15 minutes - and easy.

Read more ...

Fiction, Recollections & News

Preface - The Craft

 

 

A Note about Witches

In fairy-tales, witches always wear silly black hats and black cloaks, and they ride on broomsticks.
But this is not a fairy-tale.  This is about real WITCHES
REAL WITCHES dress in ordinary clothes and look very much like ordinary women.
They live in ordinary houses and they work in ORDINARY JOBS.
That is why they are so hard to catch.

Roald Dahl - The Witches

 

The Craft is an e-novel about Witchcraft in a future setting.  It's a prequel to The Cloud, set initially at the turn of 2069-2070 after The Great Famine.

It has adult content.  

As with all fiction on this Website stories evolve from time-to-time.   Unlike printed books that have distinct editions, these stories morph and twist so that returning to them after a period may provide a new experience.

Click here to Read more...

 

 

 

Opinions and Philosophy

A Carbon Tax for Australia

 12 July 2011

 

 

It's finally announced, Australia will have a carbon tax of $23 per tonne of CO2 emitted.  This is said to be the highest such tax in the world but it will be limited to 'about 500' of the biggest emitters.  The Government says that it can't reveal which  these are to the public because commercial privacy laws prevent it from naming them. 

Some companies have already 'gone public' and it is clear that prominent among them are the major thermal power generators and perhaps airlines.  Some like BlueScope Steel (previously BHP Steel) will be granted a grace period before the tax comes into effect. In this case it is publicly announced that the company has been granted a two year grace period with possible extensions, limited to its core (iron and steelmaking) emissions.

Read more ...

Terms of Use                                           Copyright