Working a PC on a single phase

you must be making a mistake. it seems no home computer work at 3p station. unless large frame in the past.

Yes, Houses are never 3 phase. They are often 2 phase, with each phase 180 degrees out of phase with a neutral connector = 2 phase wires plus a neutral = 3 wires to the house.

For 120 volts you use a single phase wire to neutral. For 240 volts you use the two phase wires only as they have the full 240 volts between them.

An emergency supply may power a single phase and the house owner keeps critical equipment on that phase (refrigerator, radio, TV, etc). in that case some power sockets may not be powered

Plus a house lamp into a socket...if it lights, plug your computer, monitor, printer etc into that socket.

Large houses & Industrial units are mostly 3 ph [In Pakistan]. Lighting & power distributed in different rooms may be on different phases or lights in each room is on 3phases to minmise flickering in the work places.

Of cource there is no PC which works on 3ph. The gentleman is confused as he may have 3ph connections but how these are distributed, he may not be aware of.

aurizon:

The so called 3 wire 220-240 VAC system you are referring to, with 2 110-120 V legs, 180° apart is considered a single phase system.

Confusing, yes ... but that is what it is.

Whether using one leg and the neutral for 110-120 VAC, or both legs together for 220-240 VAC, it is always one phase. Real two phase is different altogether, and seldom used anymore.

Regards,

Greg

"Never"? There is a house at postcode CM3 4RU that has a 3-phase supply, to cope with the loads presented at that location. All the domestic sockets are single phase. Some of the electricity is red, some yellow and the rest of it is blue...

to complete your rhyme -

and when it is rewired*, it will possibly kill yue

*because of current E.U. regulations on cable colours.

You misunderstand my intent or maybe I misled. I said if his home PC would work in his home that is wired for three phase, it is likely that it is being operated on single phase.

I know of at least one house in the US that was wired for three phase (input wye 208/120). Even then, you get your 208 across two phases and 120 from one leg to neutral. So unless your computer is made to operate on 208/240 you should be able to power your computer from your single phase generator. I remember there used to be a selector switch on the back of the CPU box that would switch from 120 to 240. Look and see. Also, as has been mentioned, find a receptacle that has a lamp plugged in to it and use that (IF the lamp is 120 volts). However, depending on where you live, you may have all your single phase loads operating on 240 volts then your generator would output the same and you should be good.

Do you mean that if the generator provides an output of 240v to all the home appliances, my computer will work irrespective of whether single or 3 phase?

What does the label information regarding the mains input it requires actually say?

I apoligize in advance for this long missive.

Perhaps I should make some assumptions to fully answer your question. You say your generator outputs 240 volts single phase. When you hook up your generator to your house, how do you do it. Do you use a suicide wiring (what we call a cable with a male connector on each end) and plug one end into the generator outlet and the other into a receptacle in your house. This is usually the way many folks in the US do it and is dangerous as hell. With the generator turning you are putting power on exposed prongs and if it becomes unplugged you could get a nasty shock or killed.

On a normal US home system, three wires enter the house, two hot wires and a neutral. The electrical breaker panel in the home is split with one hot wire going to each side. A two-pole breaker will connect across both sides and provide 220 volts nominal to a connected load. A one-pole breaker will connect to one side and only one wire connects to the load side. In the wire going out to the single phase load, the second wire is connected to the panel neutral. This will give you one-half of the line to line voltage. These power receptacles and overhead lights, on a normal US home system. I saw that someone had spoken about red, yellow, and blue electrical wires. In the US, again on the normal home system, the hot wires are black and red and come off the secondary of a center tapped transformer. The center tap being the neutral and is only grounded at the transformer. On a three-phase system in a home, the transformer hookup is usually a three phase wye with the center tap being the neutral. The normal output voltage is 208 line to line (phase to phase) and 120 line to neutral (line divided by the square root of 3). The wire colors are brown, orange, and yellow with the neutral being grey. Industrial wiring for motor control is color coded black, red, and blue with a delta connected transformer. Industrial lighting is 3-phase wye connected 120/277. Again, this is US based power.

If you have four wires coming into your house, not including the ground, you probably have a 3-phase system. My assumption is that your receptacles have 240 nominal voltage at them since you are saying your generator outputs 240 volts. Does this mean your home wiring is 220/380 volts? If you are connecting this to you home wiring, either by the suicide wiring or wiring the generator into the electrical panel you are only powering up one third of your home wiring. I am confused though by your comment that all your lights work. The only ones working should be those on the same circuit as the receptacle you plugged your generator into. I assume that you have switched off all the panel circuit breakers except those on that receptacle circuit and if not, you should, or at least the three-phase breakers. If my assumptions are correct and the voltage output at your receptacle is 220, your computer will work when your 240 volt generator is connected.

I forgot to add, if you plan on wiring your 240 single phase generator into your three phase panel, do not connect the two wires from the generator to the line bus terminals in the panel (these would be 380 volts across them when the power grid is operating). It is safer to find an unused single pole breaker (or purchase one) sized for your generator. If the output amperes is listed on the generator, buy one equal to or less than what is listed. If you don't know what the amperes are but do know the generaor KW and output voltage, divide the KW by the voltage. It is a straight division and you don't have to worry about anything else (e.g., KW=5500 watts divided by 240 volts = 22.9 amps. Buy a breaker for 20 amps.). If your generator has three prong receptacles, use a three conductor wire. On the opposite end from the plug, strip them out and connect one of the conductors from the generator to the load side of the single phase breaker, one to the neutral bar and one to the ground bar. Always make sure your panel main breaker is switched off when back-feeding the panel from your generator. Otherwise, you are pumping electricity outside your home. The good thing about back-feeding through a breaker is that you can leave the wire connected and switch it on-off when you lose power or it is restored.

Suicide wiring is the easiest was to back-feed your home but you need to be careful. And always remember to ensure the main breaker is switched off.

"I have a home computer which normally works on a 3-phase AC supply."

What sort of computer is this? I have never seen a home computer that uses three phase power.

I have worked on systems that do use three phases but these have all been super mini to mainframe computers. These systems usually don't use phase to phase power but rather use each phase separately to neutral. The only reason they use three phases it that they would pull too much on a single phase so they spread the load. If it is wired like this there shouldn't be a problem but keep in mind you will be pulling the total load on one phase and this could overload the phase.

Be warned thou that it may actually be wired as cnpower and aurizon have said to use a two phase system with 180° between phases. This is used because of the 110V supply in the states and by using two phases like this you can get 220V.

Pakistan uses 220 V 50 Hz so that it more than likely wired to use each phase separately to ground and you should be able to use it on a single phase. In any case you wont damage the computer by trying to run it all on a single phase, it just wont work if it actually uses the 380 V that you get between each phase.

Your address is Pakistan so maybe things are different there, but here in the US it is single phase = 110-120v. In Europe the single phase voltage is 240v. This should not be confused with a US 220v line which is a 2 phase circuit with a total of 220v across the 2 live conductors. A 3 phase supply has an additional 120v conductor. The voltage across any 2 conductors is still 220v. As mentioned above in 3 phase 3 live conductors are used to spread the load.

As for your computer the key question is what voltage is it designed to operate at. 110 US or 240v European. If it is a home computer it will operate on single phase 110 or 240v power. Some computers have a switch so you can travel with it. There is no such thing as a home computer that requires 3 phase. Moving a multiphase mainframe into a home does not make it a home computer. All home computers will work off of 110 or 240v depending usually upon the standard voltage of the country they are sold in.

"A 3 phase supply has an additional 120v conductor. The voltage across any 2 conductors is still 220v"

Not true, if you check you will find that phase to phase is 190V. In a three phase system each phase is 120° out of phase with each other so the phase to phase voltage is √3 times the phase to neutral voltage. The 220V phase to phase that you referred to earlier is generated from a single phase with a 1:2 transformer with a center tap on the secondary side that is tied to earth and counts as the neutral. This is in fact a two phase system with each phase 180° out of step.

masu:

"The 220V phase to phase that you referred to earlier is generated from a single phase with a 1:2 transformer with a center tap on the secondary side that is tied to earth and counts as the neutral."

You are correct (as usual).

However:

"This is in fact a two phase system with each phase 180° out of step."

Again, I know it confuses many, (and everyone here so far) but the 220-240 VAC "hot" to "hot" (120 to 120, 180° opposite) system is a single phase system, NOT a 2 phase system. No matter how you wire it, you never have more than one phase.

One link:

http://www.behlman.com/applications/AC%20basics.pdf

Regards,

Greg

Hi Greg,

Very true, it is actually incorrect to refer to the 220 volt system used in the US as a two phase system. You are quiet correct in saying that it is in fact a single phase and at best you should only call it a split phase system.

I live in Australia but I have worked in both New Zealand and Papua New Guinea but all three use a 240 V 50 Hz 3 phase supply so the split phase systems are pretty much unheard of in this neck of the woods. I have however seen it use in marine applications in an attempt to reduce the hazards associated with electric shock. During my time I have worked mainly for US companies so most of the equipment that I have worked on is set up for 110 V 60 Hz and has been modified to cope with 240 V. One of the problem is that the leads are so thick that they wont fit into our sockets, it usually means replacing the leads not just the plugs. Another hassle is that the conversions are for 220 V not the 240 and the peak phase to ground voltage of 340 V and is dangerously close to the breakdown voltage on many line filters.

By the way thanks for the link, it's very useful and I have book marked it as I can see it being very useful in answering the many power supply questions that crop up here at CR4. You may also be interested in this link, it a list of Mains_Systems and the types of plugs that are in use in many of the countries around the world.

Hi masu,

Thank you for the useful link!

Regards,

Greg

I have set a link that should clear everything up. It's a little more complicated than one might think. There are a lot of different scenarios.

http://www.woodweb.com/knowledge_base/Threephase_motors_101.html

Hi Sail4ev,

I had a quick read of the link you supplied and some of it is icorrect. For example

"Three-phase power has three legs carrying power, each with the same sinusoidal wave form, but 120 degrees out of phase with each other. When one leg is at the peak of the wave, another is 2/3 the way towards the bottom on its way down, and the third is 1/3 the way *up* from the bottom on its way up. In a generated 230 or 460 VAC 3 phase system, you should always measure about the same 230 or 460 volts between any two legs, (unless your supply power factor is way off). "

With a three phase system if you measure the phase to phase voltage you do not get twice the phase to neutral voltage. You get √3 times the phase to neutral voltage. The voltages you will see for the different supplies are 110-190, 220-380, 230-400 and 240-415. Also the supply factor has absolutely no effect on the voltage that you will see. The power factor is related to the angle between the current wave form and the voltage waveform. If you measure the current and voltage by themselves you will always see the RMS value. I havn't read the whole article but if it makes mistakes this fundamental in the first few paragraphs I would treat the rest of it with extreme caution.

You know...When you can't even believe a link these days, things are really getting bad. Some things I will have to leave to the battle of the experts and keep my little fingers to themselves. I'm certainly not the final word.

All I can claim is that 110-120v devices worked fine on any of the individual legs of a 3 phase panel.

My computer is a common 1.5Mhz Pentium-4 that runs on a 240v input at its power box

So it definitely does not fit the category of computers that you mentioned you have used. Yes, the mains electricity supply in this country is a 3 phase 240v. But does that make the PC run on single phase......how?

Is the supply 240V phase-to-phase or 240V phase-to-neutral?

If the supply voltage is 240V phase-to-phase then there is scope for connecting the 240V computer across two phases. If the supply voltage is 240V phase-to-neutral then it must be connected across phase and neutral to avoid damage to the equipment. In both cases the earthing ought to be checked to ensure safety of the user and others nearby.

Some equipment power requirements have a large tolerance of voltage: 110-240VAC may be stated on the label for an appliance suitable for use across many countries; many industrial instruments are stated thus for application in a global market place. It may be that the computer has a wide tolerance of input voltage, in which case there would appear to be no issue with the power voltages available.

Other appliances may have a voltage change selector of some sort built into them to suit international application; an electric shaver would be an example.

Some might suggest that if the mains power has failed and the home is running on a generator there will be other things of higher priority than the continuing use of a home computer, in which case why does the computer's supply voltage matter (rhetorical question)? The priority would be to cope elsewhere in the home with the loss of power and to re-energise the main supply with all speed.

The distribution in nearly all countries is three phase. But it is very unusual to have more than one of these phases connected to an inidividual domestic dwelling. Unless it is a very special special "special", your computer uses so-called single phase. If it was multiphase, it would have been supplied with a multi-phase plug; I believe these are almost invariably 4-wire, to provide an earth (ground) connection. The bigger risk would be if your generator output Voltage exceeds the nominal rating for the property - but you'd probably notice that because any tungsten lamps would glow too bright.

If indeed your house is wired for 3phase then you must really be careful about proper grounding or you may find as much as 167 volts between your computer ground and your phone or T-1 line. Perhaps your best bet is let a competent electrician hook up your generator, provide an automatic powerline disconnect (required by law in many areas) and assure proper grounding for the generator supplied appliances. Through the efforts of the previous owner of our home we had 117 volts between the newly installed electric clothes dryer and the washing machine. When my usually demure wife tried to unload the washed clothes into the dryer she let out a shrieking litany of expletives worthy of an ancient sailor. I called an electrician even though I'm sure I could have found and corrected the problem. He also discovered other grounding issues. The electrician was familiar with the original housing tract builder's attempts at shortcuts in all the other houses in the neighborhood. I have often found my scholastic achievements (and ego) are not a substitute for seasoned experience LOL.

"home computer " means a PC Personal Computer. There is no PC running on 3phase.

Actually you are confused that you have 3ph supply @ your home, but PC is running on a single ph. See your power Plug of PC. Is it not a normal Plug to go to wall-outlet?

How you connect your total house wired for 3ph on a single ph?

"I need to turn on a generator to power my house on a single phase current. The lights and all the electrical gadgets seem to work fine then..... but I'm not sure about the computer."

"My computer is a common 1.5Mhz Pentium-4 that runs on a 240v input at its power box"

I think I know what is going on here. Firstly Pakistan works on a 230 V phase to neutral 3 phase 50 Hz mains system. Most of the time houses are wired to a single phase but sometimes when you have high drain items like large water heaters, electric ovens, air conditioners etc the bring all three phases in. The three phases are only used for these high drain items and the rest of the house is wired to a single phase.

What I think is going on is that when you say everything is working you are only partly correct. All the lights and power points may be operating but if you check any of the three phase items these will not be working at full output.

Another possibility is that you may not actually be using the three phases that are connected to your house. Some time in the past there may have been a high drain item that used all three phases but it has since been removed. The three phases are only connected to the switch panel and are just weren't removed when the equipment was.

The third possibility is that you only have a single phase supply running to your house.

There is an easy way to check if you do actually have a three phase supply and that you are using all three phases. If you have a three phase supply there will be three watt hour meters at the switch board, one for each phase. If you do not have three meters then you don't have a three phase supply. If you do have three meters check that all three are registering power consumption, this will tell you if all of the phases are actually used.

In any case all this doesn't matter in answering you initial question. You will have no problems running you PC on a single phase supply, it's has a single phase 220/240V 50/60 Hz power supply and only needs one phase to run.

Or could take the cover off his electrical breaker panel and look inside. If there are three buss bars running vertically (or horizontally) with circuit breakers connected to them, he has three phase. Also, could probably check the pole outside and see if there are three transformers hanging there, at least that is the way it is here in the states. Three single phase transformers are connected together to give a delta-delta or delta-wye configuration. Usually, wye on the secondary for homes. If a single residence, the number of service entrance wires coming in is a dead giveaway.

That clears everything for my understanding. The power outlet in the wall that I plug my computer into, has holes for 3 pin plugs and was once used with an air conditioner. But I plug into it a 2 pin adapter to use it for my computer ...... so it doesn't matter if I connect my computer to that socket when it provides a single phase?

THANK YOU

masu

Bingo Now I know what is going on. The outlet you are plugging you PC into has a neutral and two separate phases one to each pin. When you start your generator you are only supplying power to one of the phases and hence only one of the three pins will have power on it. If your computer is connected, via the adapter, to the pin that is not powered it won't work. If this is the case you will need to modify the adaptor so that it uses the other in to supply power to your computer. Be careful though because if you move the wrong wire you will end up supplying 400 V to your computer when the mains power returns.

You will need to refer to the diagram at right and a multimeter to check this.

Firstly with the mains connected check the voltage between each of the pins with respect to the other two. You should see 400 V between two pins and 230 between these and the third as in the diagram on the left. In this case the red and blue pins are active and the green is neutral.

Now with the mains disconnected and you generator supplying the power check the voltages again. Where you originally had 400 V you will more than likely see 230 V but this could be anything as one of the pins is no longer being supplied with power. Where you originally saw 230 V now only one will show 230 V the other will show 0 V. It the diagram on the right the red conductor is the phase that is supplied by your generator and mains while the blue pin is only supplied by the mains alone.

In this situation your adaptor needs to use the red and green pins to supply power to your PC and what I suspect you will find is that it us actually using the blue and green. If this is the case your PC will work when the mains is on but not when you are running on the generator. If this is what is happening you will need to modify the adaptor to use the other phase or in other words move from the blue to the red pin.

Be careful though and make sure you modify the adaptor correctly as if you move the wrong conductor you will supply your PC with 400 V when the mains is on. If you do modify the adaptor then make sure that you use a multi meter to check that there is only 230 V coming from the adaptor with both mains and the generator supplying power before connecting the PC.