3 phase mains..?

Steve

The 240 volts AC we normally get in our homes is one of the three such supplies that run to our homes along with the neutral. The neutral is a common return cable. These three supplies are each generated from different windings on the generator at the power station. Each is 120 degrees out of phase with the next. If you were able to look at the voltage of all three you would see that each peaks at a different time, one third of a 50th of a second apart.
The voltage between each phase is 415 volts so it is not normal to connect more than one phase to a single residence. Normally you will get say the blue phase, your neighbour the yellow and his the red phase and so on. In theory over the whole country the demand on each phase balances out. All three phases are normally used together in industry to supply much higher power levels and much smoother supplies without wrecking the balance of the phases. This is because the voltage peaks three times as often. There are clever ways of connecting the three phases to allow a 12 times smoother supply, but only normally for industrial use.

Before this all gets too complicated perhaps I should say what these two phases mean for you.

Firstly each will be shared with a different group of houses down your street. Sometimes only one phase will get a power cut- you may have seen this as every third house down the street will loose its power.

If you connect one of the phases to your HiFi only then it will be largely unaffected by interference generated by your own domestic appliances, heater motors, fridges. I'd be surprised if this was much of an advantage though compared with a separate spur off the same phase. The only bit of cable which is no longer common is the "tails" cable from the meter to the fuse box and this is nomally 25mmsq cable and of very short length.

What would really be good would be to have all three phases available. This would allow the design of a 12 times smoother supercap supply, and a three phase turntable motor-3 times more smooth running.

Can't think of any other advantages. Sorry if it was a bit heavy. It is right at the limit of my knowledge.

John

The technical stuff is explained above.

I have 3 phase in my workshop. I use one phase for hi-fi and one for the rest, leaving one spare phase. I was strongly advised that only a single phase should be used for the hi-fi rather than what seemd logical to me which was to use both phases available (one for the power amp, say). I haven't a clue why I was given this advice and was much too dumb to question it. . .

Alex

PS very sorry to hear about your diminished CD collection (hopefully it was kate's half ;-)

Tha answer to the question about different pahses for different pices of kit is simply one of safety.

3 Phase is not designed for domestic installations.

If you wired your CD to one phase and your amp to another. In a fault condition you have a potential 415 volts between boxes. Ouch !

The three phases come from the way electricity is generated using synchronous motors. I strongly recommend you check local building regulations as to how to correctly install multiple phases in your home (especially if your sparky is a little vacant). I can imagine some potential dangers of having more than one phase:
1. Someone might accidentally connect them together
2. If someone touches two phases
3. If someone tries to disable power to the house and only switches off one of the phases.
4. If there are two outlets in one room using different phases then someone might connect one to one piece of equipment and one to another and then a fault situation could present a very large voltage between the two pieces of equipment.

Sonic benefits? Who knows. A separate spur ought to be better in the respect that your other household appliances do not add noise to it.

Are you sure you have three phase? If the not very bright electrician has told you so, maybe he is wrong. For safety reasons alone I would employ a competent electrician to check it out his work.
I doubt very much that your electricity supplier would go to the expense of supplying three phases to the service head in a domestic dwelling, although as stated previously they are supplied to business premises.

I did a barn conversion where my wiggly amps came from a remote overhead line. The distances involved meant I was suffering occassional large voltage drops.

The local Board put me a three phase supply in from the outset just in case it was a long term problem. When I asked whether we could connect one end of the barn to one phase and the other to a different phase was told NO..... too dangerous for the reasons outlined above.

IEEE regulations cover it if you're prepared to dig a bit

Try this for interest.

http://www.southernelectricaudio.com/images/mayer2.pdf

Regards

pm

As always, many thanks to you all - John, it may have been at the edge of your knowledge, but excelently explained !
I do have 3 phase, and have seperate supplies to each spur, so will reconnect the hi fi to one, and get it checked out by a more alive sparkie !
Unfortunatly, Alex S., kate´s half of the cd collection consists of a David Soul CD and a "now that´s what" compilation...nuff said ??

No progress yet with the insurance claim, but boy, is iy hard to remember what discs you had..

Steve