quetions

[snowplough]

Hi there,
Im new to this site but woould appreciate if any of ou could answer one of many quetions i have about electrics as i am currently doing m y level 2 electrics course.

 

[snowplough]

Many thanks for that reply ,ill try and get my head around it.

Second question, in a single load circuit say alioght boulb in the house, if its supplied b the normal 230 volts if ou measured the voltage just across the light bulb wire would thi measure les then 230 volts , and if so what would it measure. after the light bulb if oumeasured the voltage in the netral wire would this measure 230 volts or would the voltage or pressure now be less because it as loss presure going throught the light bulb. If you measured the voltage at an two points in the line would this meassure 230 volts just before the load?.

Hope u can answer this as i am a little confused.

Regards

Snow plough

 

[Morty]

I would say just concentrate on learning how to graft for now. You'l learn all this if you listen and take notes at college, dont be afraid to say when u don't understand things coz the teachers are trained to help you understand, unless they are failed sparky's which most of em are but that's another issue. Just coz no one else makes a noise when the teacher asks if everyone understands it doesn't mean they actually know coz ive been there and done it and they don't.

This site is good for sparkies to refer to info they need and general convo's about whats right and whats wrong but the stuff your looking for is much easily learnt through a teacher. Lookin at a load of jargon these sparkies are writing down for u (as helpful as they are) probably isn't doing you much good.

The more experience you get the more you'l understand how electricity works then it will be much easier to make head and tail of the technical side of things.

I'l give it to ya tho it's good that you wana know it all already lol most ppl at college are absolute numpty's that dont really give a ----

 

[pushrod]

Second question, in a single load circuit say alioght boulb in the house, if its supplied b the normal 230 volts if ou measured the voltage just across the light bulb wire would thi measure les then 230 volts , and if so what would it measure. after the light bulb if oumeasured the voltage in the netral wire would this measure 230 volts or would the voltage or pressure now be less because it as loss presure going throught the light bulb. If you measured the voltage at an two points in the line would this meassure 230 volts just before the load?.

a good way of thinking about voltage is as potential energy that is given up in the circuit. If there is just a bulb in the circuit then all the energy will be released at the bulb and the voltage is dropped across the bulb ie the 230 V. The line is not a load and so no voltage is dropped along it so a voltmeter measuring across 2 points on it would read zero volts. Equally measuring the voltage across 2 points on the neutral would also read zero V.

In reality there would be a very small resistance in the wires so there would be a very small voltage dropped along them. A very sensitive voltmeter would therefore show that maybe only 229V was being dropped across the bulb the rest being dropped as heat along the wires.

Electricity is very complex to understand, but to be able to install it safely does not require that you understand every aspect of it completely. If you go deep enough into it you you will find that electons don't behave as particles but waves! But really that is not that important. There are various good analogies that help you think about electricity- find ones that you are happy with and stick with them, but as mentioned earlier keep asking the questions and reading

 

[snowplough]

Thank for the repl although im still a little confused, are you saying that the electrons flowing through the light bulb are being pushed by 230 volts which is all the supply voltage, i no you said it might be 229 with it loosing one vault in the cables, and are you saying that once the electrons have been pushed through the bulb element all the pressure in the neutral wire is lost so measuring the neutrel on a volt metre would give you 0 volts.
I would have thought tho that measuring two points on the live or line cable would give you 230 , im still unclear.

Thanks for your patience

snowplough

 

[pushrod]

Thank for the repl although im still a little confused, are you saying that the electrons flowing through the light bulb are being pushed by 230 volts which is all the supply voltage, i no you said it might be 229 with it loosing one vault in the cables, and are you saying that once the electrons have been pushed through the bulb element all the pressure in the neutral wire is lost so measuring the neutrel on a volt metre would give you 0 volts.
I would have thought tho that measuring two points on the live or line cable would give you 230 , im still unclear.

Thanks for your patience

snowplough

Remember that voltmeters are connected in parallel across 2 points

It's is not really correct to think of voltage as a pressure, but many find it useful. Try to think of it as a difference in energy between two points. If the energy is be used in the lamp then at the start of the line it has 230 bits of energy - a bit further along the line (but still before the bulb) no energy has been used . So the difference between the two points (potential difference) on the line is
230 - 230 = 0V
Since all the energy is given up at the lamp then across the bulb the voltage ( or potential difference)
is 230 in the line and 0 in the neutral. So
230 - 0 = 230V

Measuring 2 points on the neutral, after all the energy has been given up is
0 - 0 = 0V

so measuring the voltage on 2 points on the line, and then measuring the voltage across 2 points on the neutral will both give you a zero reading.

Hope that helps, if it doesn't i haven't explained it well enough

 

[snowplough]

Many Thanks push rod for our reply,

I think yoy explained it as easy as u can its just me me who i thought i had the basic concepts when i havnt and i still struggle to get my head around it. i assumed that the pressure between any two points in the light bulb circuit ie live or neutral , or even one end of the voltimetre at the begining of the circuit in line and the other at the end in neutral would measure 230 volts but im way out and need to start again in understanding the theory.
Thanks for your patience any way.

Snowplough

 

[electricAl]

Pushrod explained it pretty well i thought - even i understood it (sort of )

As stated, Snowplough, the voltage analogy to pressure can help to a degree - but there are significant differences. It may help you if you don`t regard pressure in such absolute terms - when we measure pressure it`s relative to the surrounding air pressure. The Difference in pressure of the opposing sides.

Pushrod introduced an important element when he mentioned Potential Difference. The `thing` we refer to as voltage is actually a measurement of the electrical potential difference between various parts of a circuit.

Basically it`s the difference in the state of electrical charge. Think of those electrons (but don`t think too much about `em ) When they are at a certain `pressure` (say 230v) they`ll escape to somewhere where they are under less `pressure` (0v) if they can. When you close the switch contacts in your lighting circuit, they have a path to a place of lower pressure, so they take it. That results on them passing thru the filament & lighting it on the way.

If you measure between two points at differing `pressure` (voltage/potential) you are measuring the difference between those 2 points - if between Line (@230v) & neutral (@0v) the voltmeter will read 230v in difference. Between two points at Line voltage (230v & 230v) it`ll read 0v difference. That doesn`t mean there`s no voltage, just that there`s no difference between the two points. But a difference does still exist between the Line @230v & neutral/earth @0v.

If you measured the output of a 110v transformer it would be 110v between the Line (aka live) & the neutral you`d get...yes, you guessed it - 110v. But if measuring between the input side (@230v) & the output (@110v) your voltmeter would register 220v - the difference in `pressure` (potential difference) between the 2 points.

Hope you follow that young man...

My suggestion to you would be to aquire or make a breadboard (google it if unsure) & a power source (looooooow voltage ) & drop in various resistors in series. Measure to destruction between the various parts of the circuit until you can confidently predict, knowing the volts supplied/resistance offered, what the voltage will likely be if measured. (remembering that the source voltage will be dropped (shared) betwee ALL the resistors in that series circuit)

As said, comparing voltage to pressure may help you to a degree, but the comparison breaks down in many areas so don`t depend on it totally.

Hope this helps you & don`t stop asking the questions...

Al

 

[snowplough]

Man Thanks Elccal al , im till trying to get my head around it and will bombard ou with loads of questions no doubt.
one of man things im trying to get my head around is if there 0v on any two points on the line and neutral, then why would you get 230 vaults if you measured two points on the light bulb filament as the the other guy told me?.

many thanks

snowplough

 

[DPG]

Don't forget a voltmeter doesn't measure the voltage at a point as such, it measures the difference in voltage between any two points. If you measure between the live and neutral of the bulb then the voltmeter is showing you the difference between neutral (theoretically 0V) and live and will therefore show 230V (approx).

As said before if you measure at two points on the same live wire then the meter will show you the voltage drop, which may not be visible unless its a long run, but at most will only be a few volts. So even though the cable is at 230V relative to earth, the voltage between the two points is not 230V.

Hope this helps. Daz

 

[snowplough]

Hi Daz, thanx for the reply,
Im tring to get my head around all this stuff, so like the other guys said if u put a volt meter on the line you would get 0volts and same just on the neutral, but if u put one lead on line and ond on neutral ou would get 230volts. what would ou get as a reading if you put the voltimeter with the two leads on the filament inside a light bulb say wouldnt you get ovaults same as when ou put them both on the line.

Secondlywhen the current comes out of the lightbulb into the neutral wire is it coming out at the same pressure as when it was forced into the light bulb through the line, so im tring to sa is the current going bacck to where its source at the same force back through the neutral as it came out of the line through the bulb .

Man THANKS

SNOWPLOUGH

 

[pushrod]

Hi Daz, thanx for the reply,


Secondlywhen the current comes out of the lightbulb into the neutral wire is it coming out at the same pressure as when it was forced into the light bulb through the line, so im tring to sa is the current going bacck to where its source at the same force back through the neutral as it came out of the line through the bulb .

Man THANKS

SNOWPLOUGH

Hi Snowplough you haven't fully appreciated Daz's answer and as such your question doesn't really make sense. Partly because of the pressure idea not relating perfectly to voltage as Al said earlier.

Try this it might help - think of a voltmeter as a little calculator that checks the energy at 2 points and then takes one away from the other to give its reading. This is why a voltmeter is not connected in series but in parallel ie with 2 leads to check the energy at the 2 different points.

Strictly speaking in your domestic lighting circuit the current is not flowing all the way around the circuit as it is AC - only with DC eg a circuit with a battery is the current flowing in a single direction.

Can i ask are you at college or doing some sort of distance learning/ correspondence course?

 

[snowplough]

Cheers Push rod,
As i said before excuse my inbility to make sense of it all, ill just keep on reading over what you have wrote to see if owt clicks, while you mentioned A.C , does A.C flow up the neutral wire and down the live and vice versa or does it only flow one way down the live and through the neutral?.

Many Thanks

Snow plough

 

[Darkwood]

I hope all this theory brushing on the quantum level isnt going to divert your attention from the electrical theory that you need to revise to pass your exams, although your enthusiasm is good i think you should learn to walk before you run, that way it will be easier to understand but good on yer for your dedication to your interests --- its a rare thing to see nowadays.

 

[pushrod]

with AC the electrons constantly change direction in fact they compelete 50 full changes of direction every second - this gives you the frequency of 50 hertz.

don't know if you do ebay but this book would answer all your questions for c&g 230 level 2 and it is dead cheap at the moment Basic Electrical Installation Work by Trevor Linsley on eBay (end time 12-Jul-09 19:50:42 BST)

another good book is electrical installation by Scadden which will cover level 2 and 3.

 

[Darkwood]

with AC the electrons constantly change direction in fact they compelete 50 full changes of direction every second - this gives you the frequency of 50 hertz.

don't know if you do ebay but this book would answer all your questions for c&g 230 level 2 and it is dead cheap at the moment Basic Electrical Installation Work by Trevor Linsley on eBay (end time 12-Jul-09 19:50:42 BST)

another good book is electrical installation by Scadden which will cover level 2 and 3.

Hi pushrod, i see you made a common mistake when you visualise electrons whizzing round a circuit but may i correct you and hopefully enlighten you.
Electrons do move/migrate in a d.c. circuit due to a constant attraction but at a snails pace (in the region of mm per second) but in a.c. they tend to just sit there and vibrate with the changing direction what you are mixing it up with is the propagation of the electro-magnectic field which flys round at near light speed.
Check out this link....Speed of electricity - Wikipedia, the free encyclopedia
At 50 hertz it would change direction 100 times a second as it completes a positive and negative cycle in 1 hertz.