3 Phase electric supply

[Jacqui Too]

We are in the middle of a total rewire. I have just found out that we have 3 phase and wanted to know the pros and cons of such a supply.

Our electrician tell me its OK but I don't know any thing about it, and I am one of those people who has to know about things that concern me, plus if it is not good then can we change it now?

[WJT]

JaquiiToo, hopefully someone with more knowledge will post but we have recently changed from 3 phase to single. We were told that unless you have large machinery that you were using externally it was probably best to go with single. I really don't understand it fully but we were having cuts in our power because of the 3 phase.

We have 9kw from EDF and with 3 phase only 3kw was entering the house, now on single phase all 9kw are and it seems to be better. But there appears to be pluses and minuses with both. I would say if you are having no problems with your supply and your electrician can balance your supply with the 3 phase perhaps it is a good idea to stay with it.

[Jacqui Too]

Thank you WJT

Just to add a little more info:We were reconnected last summer with the old wiring and used a plug situated in an out building for power.

We have used this now on and off for 5 weeks using washing machine, kettle, hairdryer, etc. when we arrived this last time we could not get the power point in the out building to work so had to run an extension from a plug in the house, when the electrician came to start the work we found out it was 3 phase and 2 were already blown! (obviously they had all worked last summer when EDF reconnected) so until we finish the rewire and get EDF out again to sort us out we only have 1 phase left! We are on a 9kw supply.

[WJT]

I guess you could say that if you were on single phase and it blew you would have nothing instead of having three chances for it to blow on 3 phase.  Hopefully someone with more knowledge will show up soon. [:)]

[Clarkkent]

[quote user="Jacqui Too "]

We are in the middle of a total rewire. I have just found out that we have 3 phase and wanted to know the pros and cons of such a supply.

Our electrician tell me its OK but I don't know any thing about it, and I am one of those people who has to know about things that concern me, plus if it is not good then can we change it now?

[/quote]

I think that from a safety point of view you should know that the potential difference between any two phases is 415 volts, if you have a single phase supply this is only (!) 220 volts between supply and earth. Three phase supplies are potentially more dangerous than single phase supplies.

In Britain it is the usual practice to distribute phases so that each house receives only a single phase. This means that the supply will be balanced between different properties. In some houses in the country in France, the phases are distributed within the house and balanced across eg heating circuits. This is the case in my own rather small French house. If you have the opportunity to replace a three phase supply with single phase then take it.

[powerdesal]

[quote user="Clarkkent"][quote user="Jacqui Too "]

We are in the middle of a total rewire. I have just found out that we have 3 phase and wanted to know the pros and cons of such a supply.

Our electrician tell me its OK but I don't know any thing about it, and I am one of those people who has to know about things that concern me, plus if it is not good then can we change it now?

[/quote]

I think that from a safety point of view you should know that the potential difference between any two phases is 415 volts, if you have a single phase supply this is only (!) 220 volts between supply and earth. Three phase supplies are potentially more dangerous than single phase supplies.

[/quote]

You still die. Just as a point of useless information, did you realise that 50 hz frequency (Europe / UK) is actually more dangerous than the 60 hz used in USA. 

Not a lot of people know that [6]

[Clarkkent]

You still die. Just as a point of useless information, did you realise that 50 hz frequency (Europe / UK) is actually more dangerous than the 60 hz used in USA. 

Is that a consequence of the frequency or the higher voltage? (USA domestic voltage is 110)

[Martin963]

If you have no existing three phase equipment then probably it is simpler to shift to single phase.

Just to explain - in very simple terms - a three phase supply arrives at your house using three "live" cables and a neutral (and some sort of earth).   The three lives are kept separate,  and all carry conventional AC but each "phase" or cable is 120 deg out of sync with the others - so as one peaks +ve the other two are a bit negative (although one's rising from zero and the other is dropping from peak -ve),  then the + ve one goes negative and the other two come up.    It's like a constant dance where the dancers never meet but circle round each other.

Now you may ask why the complication - well certain things work rather well (such as three phase motors) when fed power on this basis,   but the main reason for using it in France profonde is that the cable runs to houses are often long and if you divide the current across three conductors the heat (resistance) losses are not just divided by three,  but by much more.   So on long cable runs you can use three thin cables instead of a single phase thick one which has to be much much thicker and expensive.    In addition the neutral doesn't have to be three times as large as the three single phases because other things being equal it carries very little current (for reasons too complicated to go into,  but reliant on the loads on the three phases being reasonably well balanced the neutral only carries the inbalances).

Now in our case our pool pump and our hot water cylinder are three phase and it would be complex and expensive to modify them.   But - knowing Jacqui as I do that you are starting from scratch - it probably would be worth going to single phase.   You'll need an electricain and EDF at separate times to achieve this though.

Some friends had it done,   and as far as I remember the electrician disconnected the supply,   did the work to convert from three to one,   then left it diconnected until EDF came and did their bit (new meter,  new disjoncteur).   Then it was all turned back on.

I would try and get EDF or your sparks to check what's happened to the other two phases,   there is a small risk that in the absence of the other two you may be putting undue strain on the neutral and possibly getting the wrong voltage as well in the event of a fault.    They shouldn't just disappear.

Sorry to ramble,  it's a complex subject that I am not an expert on - someone can explain it better no doubt.

As others have said,  there is a hazard of mixing phases together,  but in your case if everything is running off one plug then you are fine.   Although be careful not to draw too much through your extension lead and adaptors.

(A classic case of danger is in the theatre lighting area where different spot lights may be connected to different phases.   In the event of a fault,  and assuming the earth has failed,  a technician may end up touching two lights at the same time and having the 415 V difference passed through their body,   and 415V is a lot more dangerous than 230 V.   However in the average French home this is unlikely to be a consideration.)

[Gluestick]

There is a good primer on Three Phase here.

[powerdesal]

[quote user="Clarkkent"]

You still die. Just as a point of useless information, did you realise that 50 hz frequency (Europe / UK) is actually more dangerous than the 60 hz used in USA. 

Is that a consequence of the frequency or the higher voltage? (USA domestic voltage is 110)

[/quote]

Apparently 50 Hz is very close to the human bodies natural frequency and because of this it is more dangerous than a frequency further away, ie 60 Hz.

I seem to remember this as one of those choice pieces of information that you get, in my case, many many years ago. Equally, its not the volts that kill you but the current.

Both the above bits of info are pretty irrelevent if you get a hard 240v or 415v belt, you end up dead.

as they say, you cant see it, you cant smell it, you cant hear it  - but it kills you.

[Gluestick]

So how do High Frequency Car Ignition Systems kill people then, Steve?

Tens of thousands of volts at microscopic current.................

 

 

[powerdesal]

I have no fixed idea at the moment but give me a few minutes to check and I will post why / how.

[Gluestick]

I believe it is because like Tasers it can stall the sinusoidal rythm of the heart, Steve, by "stalling" the pacemaker trigger.

And this is why some illegally imported Asian manufacture "Stun Guns" are so dangerous.

Which of course run on a 9 volt PP3 battery!

 

[powerdesal]

GS,

A high voltage is not necessarily dangerous if it cannot deliver substantial current. .  Physics demonstration devices such as Van de Graaff generators and Wimshurst machines

can produce voltages approaching one million volts, yet at worst they

deliver a brief sting. These devices have a limited amount of stored

energy, so the current produced is low and usually for a short time.^[3]

During the discharge, these machines apply high voltage to the body for

only a millionth of a second or less. The discharge may involve

extremely high power over very short periods, but in order to produce

heart fibrillation, an electric power supply must produce a significant current in the heart muscle continuing for many milliseconds,

and must deposit a total energy in the range of at least millijoules or

higher.

I would suggest that the discharge energy from the high energy ignition systems, when directed to earth through the resistance of a human body  is sufficient to produce a current that is enough to cause fibrillation.

edit. Just seen your post above, exactly, the current causing fibrillation could be classed as 'stalling' the heart rythm

[Callie]

We have been on 3 phase since renovating our house over 10 years ago.  We live in a large house in the country and are at the end of the line.  After the electrician had finished his work, we found that he had balanced everything across 2 phases and just the septic tank pump was on the 3rd phase !  We rebalanced everything, and we have never had any problems.

[Jonzjob]

18 milli amps is all it takes to stop the heart.  Lethal voltages are 150V AC and 50 V DC...[:D]

[trees 2]

[quote user="Jonzjob"]18 milli amps is all it takes to stop the heart.  Lethal voltages are 150V AC and 50 V DC...[:D][/quote]

If that, above, is correct, why are RCD's set to trip at 30mA?

I had always had it drummed into me that a killing current was of the order of 250mA.

[Jonzjob]

I was taught that 18 mA for more than a very short time would arrest the heart, but an RCD will trip within a couple of m/seconds. Not enough time for the heart to arrest, but long enough for you to say 'golly gosh' !!

[Jacqui Too]

Thank you Gluestick and Martin for your very interesting replies [blink]

[quote user="Gluestick"]There is a good primer on Three Phase here.[/quote]

Hmmm just a little more info than I can cope with[:$]

[quote user="Martinwatkins"]

I would try and get EDF or your sparks to check what's happened to the other two phases,   there is a small risk that in the absence of the other two you may be putting undue strain on the neutral and possibly getting the wrong voltage as well in the event of a fault.    They shouldn't just disappear.

[/quote]

When the electrician said we only had 1 phase left and the other two had blown, I took it that we had somehow inadvertently fused them whilst doing some work! He did say that he could get EDF out to reinstate the fuses for us then, but we said as long as we had power in at least 1 plug we could survive until the end of the rewiring.

As far as I know he has almost finished the 1st. fix by now, but will not be connecting any of the new wiring to a fuse board until we have dug up the floor and buried the cables in their trunking under the new floor.

I am sure that the temporary supply he has left us with is safe and as you say we must just make sure we do not overload the single plug and extension lead.

Not sure if I got the answers I was expecting! for eg. 'We have 3 phase and its a nightmare, get rid' or  'no problems you will be able to have X,Y, Z.........' or 'stay with it, it'll cost you a fortune to change now'.

 

[Gluestick]

Jacqui:

Simple time!

I like simple: the keynote to success.

Unless you plan to use some pretty heavy industrial type kit, such as things that essentially require large electric motors above say 2 HP, then single phase is your best bet, for the following reasons:

1.    A single Phase does not require careful balancing between phases, thus wiring and the installation is simpler and therefore ought to be cheaper:

2.    Any future expansion of your existing requirement is again far simpler and therefore cheaper:

However: One Caveat.

I do not know the answer to this, re your own circumstaces, so please do check before making any commitment and decision!

If a domestic user in France stays on an original supply contract with EDF, then by statute, any future cost increase is strictly limited.

Some users have switched to an alternative supplier to find that after the honeymoon, their electricity prices have gone through the roof!

I am not sure whether or not your specific situation qualifies: please do check as it is very much to your advantage.

If your house is covered by the statutory regulkation and switching to Single Phase takes you outside the price protection, then stay with three phase.

Hope this assists.

 

 

[Nick Trollope]

[quote user="Jonzjob"]18 milli amps is all it takes to stop the heart.  Lethal voltages are 150V AC and 50 V DC...[:D][/quote]

It is not about current (or voltage) it is about energy. The amount of current needed depends on the energy needed to stop, damage or start the heart - or summat like that. Interesting to note that an electric chair is several magintudes more powerful than a defibrulator (or is it defibrilator?).

That said, the actual current can be as little as 6mA....

[AnOther]

Just to add a point, in the US I believe they have both 110 and 220v, the latter being used for things like airconditioners.

Not quite sure how that works, phase to ground for 110 and phase to phase for 220 maybe ?

I agree that subject to your supply cable being up to it conversion to single phase is probably a good idea, especially so if you are faced with a rewire anyway.

I have both. The house is single phase but in my barn I have 9kw 3ph, handy for when I start up my factory [;-)]

 

[Gyn_Paul]

extract from

http://www.3phasepower.org/1phaseloadson3phasepower.htm

In multiple-unit residential buildings in North America, lighting and convenience outlets can be connected line-to-neutral to give the 120V utilization voltage, and high-power loads such as cooking equipment, space heating, water heaters, or air conditioning can be connected across two phases to give 208V. This practice is common enough that 208V single-phase equipment is readily available in North America. Attempts to use the more common 120/240V equipment intended for three-wire single-phase distribution will likely result in poor performance since 240V heating equipment will only produce 75% of its rating when operated at 208V.

Where 3 phase at low voltage is otherwise in use, it may still be split out into single phase service cables through joints in the power supply network or it may be delivered to a master distribution breaker panel at the customer's premises. Connecting an electrical circuit from one phase to the neutral generally supplies the country's standard single phase voltage (120VAC or 230VAC) to the circuit.

The power transmission grid is organized so that each phase carries the same magnitude of current out of the major parts of the power transmission system. The currents returning from the customers' premises to the last supply transformer all share the neutral wire, but the 3 phase system ensures that the sum of the returning currents is approximately zero. The delta wiring of the primary side of that supply transformer means that no neutral is needed in the high voltage side of the network.

[Punch]

In reply to the OP.....

This must be one of the most misunderstood things of French electricity supplies that crops up time and time again on many French related fora.
There is absolutely no benefit whatsoever in having three phase in a domestic enviroment, unless you are running industrial type equipment or machinery, have a particular need for it such as a heat pump etc; or you have a large group of properties on the same site.

You may not have a choice in some instances. The EDF will often insist on three phase for supplies over 12KW as it helps balance their loads on their supply network. It also can depend on the distance you are from the nearest supply transformer. The EDF would also prefer you to stay on three phase for the same reasons. There is recent scenario that I have had for a client in which the distance between the EDF coffret and the house is quite a long distance and because of the voltage drop reasons, single phase cable sizes ( 2 core) are prohibitive.

Basically if your EDF supply is 9KW you can draw up to 9KW ( about 45 amps) on a single phase supply before your EDF disjoncteur will trip. In an equivalent three phase supply of 9KW, you can only draw up to 3KW on any one phase, before the EDF trip will go. This means you have to balance your installation very carefully and this is sometimes difficult to do.

There is no difference whatsoever in monthly standing charges  or units cost for either type of supply.

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