Domestic Vs Industrial

[Ryan_Moore]

Hi Sparks!
I am hoping to become an apprentice very soon and I have a question for you all,
What is the difference between the 230v single phase used in domestic buildings and the 415v used in commercial/industrial buildings. Also why is it necessary for there to be a difference, what are the pros and cons of each.


Also I have heard rumours of all new builds now having electric heating, does this mean less work for plumbers and gas fitters and more work for us....or you I should say at the moment, give me a few years

 

[Paul.M]

Each phase is 230V, If connected together on a motor for example or by cross connection by fault it will then become 415V. I haven't explained it very well but that's the basics of it. You will learn all about it once you start your apprenticeship, good luck and ask any questions if/when you get stuck.

 

[topquark]

Hi Sparks!
I am hoping to become an apprentice very soon and I have a question for you all,
What is the difference between the 230v single phase used in domestic buildings and the 415v used in commercial/industrial buildings. Also why is it necessary for there to be a difference, what are the pros and cons of each.


Also I have heard rumours of all new builds now having electric heating, does this mean less work for plumbers and gas fitters and more work for us....or you I should say at the moment, give me a few years

How long have you got

You mentioned an interview in the pm. So I'll try and answer this in terms of a level of knowledge they could reasonably expect you to have.

The main difference between them, as you've probably guessed, is the single versus three (poly) phase. That's probably what they are looking for you to comment on.

Remember that voltage is derived from a difference in potential between two points. In single phase that's between line nominal voltage (230V) and neutral (practically 0V). The word nominal is used because in reality the voltage isn't 230, neither does it stay constant, it fluctuates over time between around 230V and around 240V (and can change if you measure it quickly in succession).

With any (single/poly phase) AC supply the voltage fluctuates a number of cycles per second (Hertz). In the UK that's 50 times a second, in the USA it's 60 times a second. The change from +Ve to -Ve over time would plot a near perfect sine wave (ignoring the voltage fluctuation).

What you get with 3 phase is 3 of those sine waves starting approximately 1 Second / 50 Hertz / 3 Phases) apart from one another IE 0.0067 Seconds (or 6.7 Milli Seconds).

So with 3 phase you get the option of either using one phase only, with the Potential Difference derived between a phase and neutral. Or you can chose to derive the voltage between two phases (which is where the nominal 415V is derived from). The nominal 415V is derived from 240V times the square root of 3 (240V was our old nominal voltage).

With 3 phase you can get away with using (3) smaller sized (cheaper!!) cables, rather than using one large cable capable of handling larger currents driven by a 415V source.

The upshot is it's not "necessary" per se, but certainly cheaper and more flexible.

So 3 phase, some pros/cons, by no means an exhaustive list :

Pros: More power is available to drive power hungry devices like plant/machinery (anything with a motor).

Cons: 3 phase arguably more dangerous (they'll expect you to cite the health/safety issues).

 

[Ryan_Moore]

Thanks very much both of you, the interview I have this time next week(more or less) have asked me to speak for 3 minutes on the reason behind the difference in voltage of domestic and industrial.

So a 3 phase is 3 times that of a single phase, obviously, for something that requires alot of power to run ( Like the shutter in the wholesalers I work in) it pulls some power from each of the phases to opperate, because if it tried to opperate on 1 phase, it would blow the 60A main fuse, right?

 

[Paul.M]

Brilliant answer topquark, much better than my half arsed reply .

 

[Paul.M]

Here is a Wikipedia link to explain it better than what I could over a forum. It's American but the physics are the same. Have a read and come back to here to ask what you don't understand, its not the most simplest of things to understand straight away. Three-phase electric power

 

[topquark]

Thanks very much both of you, the interview I have this time next week(more or less) have asked me to speak for 3 minutes on the reason behind the difference in voltage of domestic and industrial.

So a 3 phase is 3 times that of a single phase, obviously, for something that requires alot of power to run ( Like the shutter in the wholesalers I work in) it pulls some power from each of the phases to opperate, because if it tried to opperate on 1 phase, it would blow the 60A main fuse, right?

Not 3 times, but more power available. I would avoid saying it would blow the fuse, it may (depends on a number of factors, ambient temperature and other considerations).

 

[topquark]

Here is a Wikipedia link to explain it better than what I could over a forum. It's American but the physics are the same. Have a read and come back to here to ask what you don't understand, its not the most simplest of things to understand straight away. Three-phase electric power

It has pictures as well

 

[Ryan_Moore]

You an engineer by any chance Topquark?
ooooh pictures are good, I need all the help I can get

 

[topquark]

You an engineer by any chance Topquark?
ooooh pictures are good, I need all the help I can get

Nope. Just a poor domestic/commercial spark.

 

[Deleted member 26818]

I believe this is one of those questions where the answer can be never ending.
In general power is generated and distribute as 3 phase. Typically every 3 houses will be fed 1 phase from a 3 phase supply cable in the street. Every third house being on the same phase.
Each phase is 230V to earth or neutral, but is 400V between phases.
Where an installation is expected to have a high current demand, such as some shops, blocks of flats, factories etc. all 3 phases will be fed to the installation.
Equipment that uses 3 phases as opposed to single phase, is more efficient.
If you consider a large engined motorcycle traveling at 70mph, the engine will just ticking over, hardly any strain at all.
Wheras a small engined motor cycle will be revving it's nuts off at the same speed.
Sorry have to go.

 

[Ryan_Moore]

Lot of maths in that description, I like it, bit of a maths nerd B-)
I am sure between now and my interview I will have alot of questions, I gotta get this apprenticeship!
I really am grateful of any and every bit of help you can offer and I will let you know how it goes.

 

[Paul.M]

Lot of maths in that description, I like it, bit of a maths nerd B-) I am sure between now and my interview I will have alot of questions, I gotta get this apprenticeship!I really am grateful of any and every bit of help you can offer and I will let you know how it goes.

Once you've done your research for this 3 minute talk on 3 phase motors post up what you are going to say and we will have a look at it for you and see if there is anything you've missed out. Hope you get the apprenticeship.

 

[Des 56]

]Lot of maths in that description, I like it, bit of a maths nerd [/B]B-)
I am sure between now and my interview I will have alot of questions, I gotta get this apprenticeship!
I really am grateful of any and every bit of help you can offer and I will let you know how it goes.

Do yourself a favour and mention your interest in maths during the interview

When you start ingesting electrical theory,a large proportion of that theory requires a lot of use of maths, and a good understanding of it

It is the conerstone of electrical theory, from the very basic, to the higher levels probably attained by those who responded to your questions

 

[topquark]

As you like maths (mad fool) if you're up on your trig, you can use Sin(2pi x freq x time) to plot out what happens on the fluctuating voltage over time for each of the 3 phases, convert that to a current (assuming resistance of 1 Ohm). Then add up the current across all 3 phases at each point in time and amaze yourself that no current is flowing in the neutral ! That's one of the other advantages to a (perfectly) balanced 3 phase system.

With tau = 2pi (for all the newbie nerds).

Voltage at point in time t would be 230V * Sin(tau x 50Hz x t)

Assuming you have access to a spreadsheet.

 

[Des 56]

Voltage at point in time t

Isn't "Instantaneous value",easier for us to say when we are drunk

 

[topquark]

Voltage at point in time t

Isn't "Instantaneous value",easier for us to say when we are drunk

But, but I haven't had a drink for ages sir

 

[Des 56]

But, but I haven't had a drink for ages sir

I trust for the benefit of Ryan J Moore,that was the only post you made that was a little short on the truth :8:

 

[Ryan_Moore]

Or very true, a drunken spark giving me advice might not be the best thing

 

[topquark]

I trust for the benefit of Ryan J Moore,that was the only post you made that was a little short on the truth :8:

I have to say I've been good ... haven't posted any obviously misleading information for a long time. (It's been alleged I have a wicked sense of humour ... don't know where anyone would get that idea from).

 

[Ryan_Moore]

Maths question: the sine graph passes through 0 and peaks at 1 and -1 on the y axis, applying this to our electricy stuff, it would pass through 0 ( ie no volts at no time) and peak at 240 and -240 right?

On a single phase this is fine, you have 1 sinx graph and that is that, however when you have 3 phases you end up with 2 translations of the sine graph along with the original, if you translate sin by (-90,0) (I think it my translations arent great) you get the graph of cosx so on 1 axis you have sinx,sin(x+a) and cosx. and each of these represents a phase? At any time(any x value) you have 3 possible solutions(one per graph)

you know what I am gettin too much into this, I need to be patiant and wait til I am actually a apprentice, I am too damn excited now!

 

[Ryan_Moore]

I have to say I've been good ... haven't posted any obviously misleading information for a long time. (It's been alleged I have a wicked sense of humour ... don't know where anyone would get that idea from).

With a tag that says "children on backseats cause accidents, accidents on backseats cause children" I think that is an awesome sense of humour

 

[topquark]

Maths question: the sine graph passes through 0 and peaks at 1 and -1 on the y axis, applying this to our electricy stuff, it would pass through 0 ( ie no volts at no time) and peak at 240 and -240 right?

Yes, but remember that's just a voltage that's present. It has to be measured between that point and somewhere else, either 0 volts or one of the phases to derive the potential difference and hence be able to drive a current (remember it's Alternating Current we're interested in, not the voltage).

On a single phase this is fine, you have 1 sinx graph and that is that, however when you have 3 phases you end up with 2 translations of the sine graph along with the original, if you translate sin by (-90,0) (I think it my translations arent great) you get the graph of cosx so on 1 axis you have sinx,sin(x+a) and cosx. and each of these represents a phase? At any time(any x value) you have 3 possible solutions(one per graph)

Stick to using Sin, that's all you need. The phases are 120 degrees out of phase with each other. If we label them P1 P2 and P3 then when P1 is at 0 degrees, P2 will be at 120 degrees and P3 at 240 degrees.


you know what I am gettin too much into this, I need to be patiant and wait til I am actually a apprentice, I am too damn excited now!

Keen is good ... just don't come across as hyper or impatient in the interview

 

[Ryan_Moore]

So for a fraction of a second, 1/50 of a second I think, according to the sin graph, something can have 0v?

 

[malcolmsanford]

Nope. Just a poor domestic/commercial spark.

To quote a Western movie Idiom.

" You speak with fork tongue" Just a poor domestic/commercial spark,:devilish:

 

[topquark]

So for a fraction of a second, 1/50 of a second I think, according to the sin graph, something can have 0v?

I'm being cautious with my wording now, as it wouldn't be for a whole 1/50 of a second (as it's continually changing and will complete one complete cycle from 0 to +240 to -240 and back to 0 in 1/50th of a second). The accuracy of the time period at which it is 0V would also be reliant on (but not depend on) the sampling rate you use and accuracy of voltage measurement when measuring it. IE the more samples you make in a given time period the more accurate the result.

Lets agree that at a point in time, for a period of time, each phase can be at 0V. So between that phase and 0V, then YES (no potential for work on that phase, at that point in time, between that phase and 0V).

However, if you see where the other two phases are at that point in time, then there is potential between that phase (currently at 0V) and either of the other two phases (+120degrees and -120degrees ... you can work out the voltage).

 

[Paul.M]

I hated motor calculations back at school, find them not too taxing now but its been a long day, im off for a drink :21:

 

[Ryan_Moore]

First draft of my 2-3 minute presentation.

Q. Find out what Voltage is used for the following:
a. Domestic electricity supply
b. Commercial/industrial electricity supply

Ans.
a. 230v single phase.
b. 400v 3 phase.

Q. Why is there a difference between these types of supply?

Ans.

Domestic- Because of the appliances, the most demanding of which being cooker, shower etc(requiring 6mm/10mm T&E 40A breaker) single phase, neutral and earth is sufficient for the demands of a domestic home.
However in a commercial or industrial environment a much greater voltage is required to power machines and equipment(such as one with a motor, the shutter in an electrical wholesalers) this therefore requires 2 phase, neutral and earth system, which allows the machine to draw upon 3 phases in order to gain the required voltage for it to operate. *graph handout and explanation*


note: I have a small question regarding the 3 phase graph, which is 3 sin graphs with a space of 6.4 ms between them(I think)
If you consider the graph and say you need 300v at time x, you can add the 3 values(one on each curve) to achieve this correct? However the single phase graph is just the sinx graph, so if at time x you only have a very small amount of volts the appliance wont work, so if my maths is correct, I am obviously missing something can anyone see what it is?
I understand it is very difficult to explain what I am talking about without a graph to see, tell me if I am not making sense and I will try an think of a better way to word it.

 

[topquark]

Here's something I produced a while ago. You'll need to smarten it up and ensure that the voltages and units of time are appropriate to your usage.
It should give you a start.

 

[topquark]

Have a look at the data under the graph that the graph is plotted from. Remember it's the current that we are interested in (ie a flow of electrons past a point) not the voltage. The voltage is simply there to overcome the resistance and produce the current that we need. For example to drive out motor.

 

[Ryan_Moore]

Can I not be your apprentice Topquark I will bring your company to liverpool, it will be a blast!

 

[topquark]

If there was oodles of work around I wouldn't be on here so much. I'd love to be in a position to take on an apprentice, but no chance of that for the foreseable future

 

[Ryan_Moore]

Every spark that walks into the shop says the same thing, especially the ones that stay all day for the free cups of tea! Tough times

 

[Big n Daft]

Ryan,
To be a top class spark you will have to be able to drink every other trade under the table and be last to bed, then first up in the morning saying what a lovely day it is.

 

[Ryan_Moore]

Sounds like what you need to be a top class fella, not just a spark!

 

[Silly Sausage]

Read up on 3 phase induction motors!
These machines are the workhorses of industry, brilliant invention.
Briefly...a 3 phase supply generates a rotating magnetic field in the stator windings which induces an opposing field in the (essentially) solid rotor, producing torque.

 

[topquark]

Here's a nice little animation showing the generation:

Three Phase AC Generator