Voltage and neutral question

[zapper42]

Hello ,first post so go easy lol.

I am studying electricity and would like a few pointers for my homework.

Am i right in thinking for example say "a cooker oven element". That 240v (uk ) travels from the live wire through the load (element) and back out through the neutral wire..Would the neutral have the full 240v coming out when element switched on ??

We have been set a couple of questions that we have to find out by ourselves using either the net.

I await your response And thank you in advance.

Zap.

 

[riveralt]

The uk standard voltage is now 230v.
I would throw the question back at you and tell you to look up what voltage, current and resistance are and then you will be able to answer your question.
Understanding the underlying principles of electricity will help you solve the problem yourself.
For example what is ohms law?
What is an element constructed of and how does it heat up?
What do the current ratings on an element mean?

 

[EFLImpudence]

Am i right in thinking for example say "a cooker oven element". That 240v (uk ) travels from the live wire through the load (element) and back out through the neutral wire..

No.

Would the neutral have the full 240v coming out when element switched on ??

No.

We have been set a couple of questions that we have to find out by ourselves using either the net.

Or...

I think they probably meant by reading and learning; not just asking someone.

Post some answers and we will tell you whether you are correct.

 

[zapper42]

Am i right in thinking for example say "a cooker oven element". That 240v (uk ) travels from the live wire through the load (element) and back out through the neutral wire..

No.

Would the neutral have the full 240v coming out when element switched on ??

No.

We have been set a couple of questions that we have to find out by ourselves using either the net.

Or...

I think they probably meant by reading and learning; not just asking someone.

Post some answers and we will tell you whether you are correct.

Ok guys lol i did not mean to sound like i am being lazy lol. we were told to find out the answers any way we wanted but needed to understand the principle that got us the answer.


The info of the element that we was given was that it was 2500w .

Now i know using ohms law that the resistance would be just over 21ohms

and the current would be just over 10.869 amps @ 230v.

Voltage is Current x resistance right ? so the element should be drawing just over 10.869 amps if using a clamp on meter set to amps when element switched on .

So voltage would be just under 230v when testing the live circuit using AC voltage setting on meter or am i missing some think here.





p.s by the way why are so many people still saying we are 240v instead of 230v .also this is printed on alot of electrical equipment.

 

[PrenticeBoyofDerry]

p.s by the way why are so many people still saying we are 240v instead of 230v .also this is printed on alot of electrical equipment.

It is so we have harmonised voltage values with Europe, but try measuring the voltage on standard single phase supply in the UK and it will tell you different!
What course are you studying?

 

[sparkiemike]

The nominal voltage in the UK is 230V, in reality it is very rarely that.

Since the 60's the supply voltage for domestic in the UK is 240V, in the late eighties is was harmonised with the EU to 230V +10%-6% (253V-216.2V). As 240V is within the range defined in the EU harmonisation document the UK supply industry has not changed its supply voltage.

 

[zapper42]

p.s by the way why are so many people still saying we are 240v instead of 230v .also this is printed on alot of electrical equipment.

It is so we have harmonised voltage values with Europe, but try measuring the voltage on standard single phase supply in the UK and it will tell you different!
What course are you studying?

Hi this is not a specific course as such ,we are learning the fundamentals of electricity and fault finding in our science class where we are set a number of tasks on various subjects.This months is to do with appliances so hence why i am trying to understand better about the fault finding of the heating element and how to go about testing safely using continuity and voltage testing .Then we have to put what we have learned to the test in the workshop under supervision.It is more interesting this way as our teacher seems to think it keeps us more focused on the topic.Which actually it does !

So just trying to get to grips with some of the questions we were given.

 

[EFLImpudence]

Now i know using ohms law that the resistance would be just over 21ohms

and the current would be just over 10.869 amps @ 230v.

Voltage is Current x resistance right ? so the element should be drawing just over 10.869 amps if using a clamp on meter set to amps when element switched on .

That's all correct.

So voltage would be just under 230v when testing the live circuit using AC voltage setting on meter or am i missing some think here.

Why do you say "just under 230V"?

p.s by the way why are so many people still saying we are 240v instead of 230v .also this is printed on alot of electrical equipment.

Because 230V is the nominal voltage. The actual voltage may never be that low.
This is the figure used to calculate other values.
It was set to "harmonise" with Europe (politics) although nothing actually changed apart from all the tables which were adjusted so that the results are the same.

The actual voltage is, by law, only allowed to fluctuate between 216V & 253V


However, for your element, it is likely that the manufacturer still states 2500W @ 240V. It cannot be 2500W if the voltage is not given.
So, because it is a resistive load, to work out anything else it is necessary to calculate the resistance and use that in other calculations. The resistance is the only constant.

This results in the current increasing when the voltage increases (and vice-versa of course), which is contrary to what you may think.

 

[Spark123]

Volts are the pushing force, Amps are what flow around a circuit, resistance is just that - something that restricts.
In reality we still tend to find that a majority of appliances are 240v even though someone decided it would be a good idea to start using 230v to bring us into line with Europe, I take it that you are doing GCSE? I wouldn't be too worried which one you use however you need to keep using the same one throughout.

In your original post the volts are across the element (AKA potential difference). The potential difference causes a current to flow in the element, the current (I) being restricted by the resistance (R) of the element. The current flowing in the element causes it to heat up (I²R = Watts).

The end to end resistance of the element can be measured using an ohm meter. It might be above what you are doing in your course but one thing we need to know is that a an element heats up the resistance changes (and goes up) hence what you measure when the element is cold doesn't correspond directly to ohms law for when it is in use and hot.

 

[zapper42]

Thanks everyone for the insight .The cooker we have in the school workshop does say 240v on the label and we were told to use this figure when working out our answers.

The reason i originally asked was that the element we have has 4 terminals, wires going to and from it... Brown wire i assume is live to one terminal a yellow and green wire which is earth ,a yellow wire which goes to thermostat and fan and a blue neutral wire .

The question asked on our sheet was - which wire carries the voltage to the element and what is that voltage? brown wire,yellow or green wire, yellow wire or blue wire.

I put brown wire carries incoming voltage to element.


Which one is the earth wire ? i put yellow and green .


what does the yellow wire do ? i put this controls the thermostat and the fan.


What does the blue wire do and is there any voltage across the terminal when element is on.


I put blue wire is neutral . but i was not 100% sure if voltage is present at the neutral wire because i assumed that voltage would go from the yellow wire to thermostat and fan to turn the fan on .


I was confused with this because i read that some elements can be fed from the neutral wire



I should have probably explained all this in my first post

 

[RF Lighting]

Normally when a cooker element has four terminals it will actually be a dual element i.e. it's actually two seperate elements, but they are both attatched to the same back plate where it bolts onto the cooker. You can see here one element around the outside , and a second smaller element on the inside.

Normally there will be two seperate lives to the element, and they will both have gone through some sort of control such as the control knob on the front of the cooker, and a thermostat inside the oven. It in not wired as you suggest with one wire bringing power in and the other one doing the control.

The neutral terminals of the element may or may not be joined together depending on how the cooker was manufactured.

 

[zapper42]

Normally when a cooker element has four terminals it will actually be a dual element i.e. it's actually two seperate elements, but they are both attatched to the same back plate where it bolts onto the cooker. You can see here one element around the outside , and a second smaller element on the inside.

Normally there will be two seperate lives to the element, and they will both have gone through some sort of control such as the control knob on the front of the cooker, and a thermostat inside the oven. It in not wired as you suggest with one wire bringing power in and the other one doing the control.

The neutral terminals of the element may or may not be joined together depending on how the cooker was manufactured.

Ah i am starting to understand now lol .Thank you.

Zap

 

[TicklyT]

As far as the terminal allocations you mentioned go, here's a few questions to ask yourself that may help:-

Is mains voltage present anywhere in the oven even when all the oven controls are turned off?
What turns the oven on and off?
Does the fan run all the time, only when the oven is turned on, or only when the element is working?
How is the oven temperature control achieved?
What parts of the oven continue working even if the heater element isn't working?

 

[zapper42]

As far as the terminal allocations you mentioned go, here's a few questions to ask yourself that may help:-

Is mains voltage present anywhere in the oven even when all the oven controls are turned off? yes at the terminal block .
What turns the oven on and off? The user lol
Does the fan run all the time, only when the oven is turned on, or only when the element is working? If it's a fan oven then fan runs when oven is on to distribute the heat.
How is the oven temperature control achieved? via a thermostat sensor in oven cavity.
What parts of the oven continue working even if the heater element isn't working? fan

.

How did i do

 

[ericmark]

Voltage is measured between two points normally line (or phase) and neutral both are regarded as live.

Although volts squared divided by watts = ohms in practice this does not work out because of two factors. One the resistance changes according to temperature and the element may be coiled so has an inductance as well.

As a result we normally start with DC when we are learning and use test resistors in a bread board which will not get hot.

Most elements are controlled by switching on and off and the time on (Mark) is varied in relation to time off (Space) but this is not always the case.

The AC voltage will peak at around 325 volt but we calculate at the root mean squared (RMS) value of 230 volt.

Another reason why we normally start learning with DC. With DC Watts = Volts x Amps simple but with AC Watts = Volts x Amps x Power factor correction so we have VA and Watts which are similar but not the same.

The problem with a lot of schooling is the difference between AC and DC is ignored so one needs to be careful to work out the level of the student as it is easy to talk about things which are beyond what is required.

We have things like conventional current flow and electron flow which are opposite. So to do an internet search can bring up items which can completely confuse.

So you need to state what level you are working to. i.e. what course or exam are you working towards and age also helps.