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# Explain Three Phase?

Discuss Explain Three Phase? in the Commercial Electrical Advice area at ElectriciansForums.net

#### LukeScotty

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Arms
Welcome to ElectriciansForums.net - The American Electrical Advice Forum

Hiya all, Could someone possbile explain 3 phase to me, or link us to a decent website which could tell me. I work for an industrial electricial company, but funnierly enough we havnt done much on 3 phase

Cheers Luke

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#### TonyM58

Ok, VERY briefly:-

The substation transformer supplying your house is three phase, exactly as if a factory was being supplied.

The three windings are star connected, cand draw it here but put a dot in the middle of a page. Draw a line vertically up from it . Go clockwise one third (120 degrees) and put another line from the central dot, then draw another at a further 120 degrees. you should now have three lines spaced at one thrid intervals around a circle. the first label L1 at the end, the second L2 and the thrid L3 going clockwise.

You now have a respresentaion of a three phase supply (the lines are the windings) From the central dot, draw line horizontally accross the page, this is the neutral. Also draw another line from the central dot and connect tit to earth. The central dot is called the 'star point'

ok, you know what a sine wave looks like? well each of three phases produces an identical sine wave, but they are 120 degress apart. So when the first sine wave peaks, the second is at a different point in the cycle, as is the third wave.

So, if you was to measure between any of the Lines (L1, L2 or L3) as shown on your diagram and Neutral you would have 230V, but iff you was to measure between any of the Lines (Like L1 to L2) you would measure 400V.

With your house supply they just run the first block of houses off L1, the second block off L2 etc.

Now think if you has a 100A supply coming n to your house, then so would the next block etc. Now think of the same supply coming in to a factory, you would now have three 100A supplies (so obviously you have more available power)

Now you can either use this from a three phase dis board as three seperate single phase supplies (shared out so they are loaded equally) or take it off as a three phase 400V supply (for industrail machinery, motors etc). In practice you would use both the three pases and individual single phases in an industral phases.

Main thing you need to know if you start working on three phase equipment is mortors will run in one direction using L1, L2 and L3 (or red yellow blue, or brown black grey using new colours), and if you want to run it in the other direction, you simply swap any two of the phases at the motor. (i would explain why but its another story, and you need good motor principles)

I can expand on any of this or can answer specific queries you have, no probs. i seem to remember you are doing 2391 soon? You will be testing on a three phase dis board, and three phase contactor with BS4343 outlet when you do it. Its all the same principles, but the PFC is twice the single phase value

Good luck!

#### Martin

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Three phase power is the most efficient way to generate and distribute electricity. The basics are easy, but it gets more complicated when you start taking about 3ph phasor diagrams, phase balancing and looking at how three phase motors work.

Three phase motors are perfectly blanced loads, in that they draw the same current from each phase, so they don't need a neutural. Each live takes it in turns to act as the neutural return path for the other lives. This happens 50 times a second or 50Hz.

If you are drawing different currents from each live then you need a neutural to return the difference in current between all the phases.

Three-phase electric power - Wikipedia, the free encyclopedia

and deals with some of the scary maths here:
Three-phase - Wikipedia, the free encyclopedia

Also HowStuffWorks has some info here:
Howstuffworks "How Power Grids Work"

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#### fusion

hi giuys,,,can any one explain how 3 phase supply works and can a 240 volt consumer unit be fitted to a 3 phase supply..

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#### Mac

hi giuys,,,can any one explain how 3 phase supply works and can a 240 volt consumer unit be fitted to a 3 phase supply..
Have you read the thread above.You can connect a 230V CU from one of the phases but not to a 3 phase.You would have a 3 phase supply coming in,supposedly commercial or industrial.You can then take a supply to a 230V CU if it is feeding-ie an office or something along them lines

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#### Sparky-Tom

hi giuys,,,can any one explain how 3 phase supply works and can a 240 volt consumer unit be fitted to a 3 phase supply..
Hi Fusion,

There are two very good three-phase descriptions above, is there anythiong you want know specificly about three-phase that is not mentioned?

And as to wheter a three-phase supply will work with a 240 volt consumer unit. Yes it will aslong as the dist board is made for three phase, I.E. a 3 or 4 pole main incomer and 3 pole lugs for 3-phase MCBs to be fitted. You can also pull single phase (240VAC) from a 3-phase dist board by fitting a single pole MCB onto one of the lugs in the distboard, but when doing this, it is important to ensure that all phases are balanced (all pulling the same current) so as not to put any strain on the cable and to maximize its CCC.

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#### deakin09

Agreed although personally If it was me I would just fork out for a proper 3 or 4 poll distribution board

Get one built for the job as you would have to change practically every thing in the board in any case to take 3 phase.

Regards chris

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#### lost-sole

I have my 2391 and didn't really do any practical on 3 phase, or was i missing that week!!!. I would n't mind getting on a short course to install a 3 phase board coz i want to get into commercial and industrial coz i stick to the treeth with house bashing anyone got any info thanks in advance

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#### Andy Smith

I have my 2391 and didn't really do any practical on 3 phase, or was i missing that week!!!. I would n't mind getting on a short course to install a 3 phase board coz i want to get into commercial and industrial coz i stick to the treeth with house bashing anyone got any info thanks in advance
What do you specificaly want to know or not undersatnd, ill be pleased to help if i can

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#### lost-sole

Guess what Andy Smith is also my name LOL was looking for some experience really so if you are within 40 miles of stockport and fancy some free help on a saturday then get in touch

regards

Andy

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#### Andy Smith

Guess what Andy Smith is also my name LOL was looking for some experience really so if you are within 40 miles of stockport and fancy some free help on a saturday then get in touch

regards

Andy
Hello Name sake, sorry not with in 40 miles, but pleased to answer questions PM if you wish

Cheers

#### Funky Gibbons

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I bought a DL6790 Combivolt 2 when I tested it on the Red positives at the back of the socket the LED for Continuity lit up and bleeps, but the LCD for voltage display didn't indercate anything I then tested it on a known spur from an exsiting socket by testing the Red cables and the LED for Continuity lit up and bleeped, Am I right in thinking when I tested the spur the tester should not of indicated anything and why does the LCD voltage display not indercate anything when I test the sockets.

#### trev

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Kudos for thread resurrection though Funky

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Try reading it again, and again, and again. If you still don't understand what you are doing, sell it before you kill you're self.

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#### Silly Sausage

deleted, Tony's already done the joke!

Last edited by a moderator:
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#### Geordie Spark

A politician has two faces and electricity has 3.

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#### Silly Sausage

Hahaha.....
while your looking left or right, you're being shafted up the arse!

Nice one G!!!

K

Are you allowed to say that Archy?

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#### Geordie Spark

Are you allowed to say that Archy?
The mods are not so strict over here.

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#### Essexboy7

just come across this thread.Please tell me the OP was having a wind up?

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#### DJ Ovengloves

Indercations are unclear
just come across this thread.Please tell me the OP was having a wind up?

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