3 Phase balancing

Postby curious1 » Fri Jan 25, 2008 6:01 pm

not sure where my topic questions are going as cant see them on here...so forgive if they get duplicated.

Q. If you have 3 phase supply as your incommer "France for instance" and you shared the circuits loads across the board over the 3 phases by way of washing machine on one , water heater on another etc and power equally spread across too, that its balanced that way??

can you clarify on the balancing side or is this the correct way?


Curious 1
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Simply Build It

Postby ericmark » Fri Jan 25, 2008 7:34 pm

Since the items are not likely to be used together it would not balance as such. You would really need a bigger group on domestic like No1 house on Red and No2 house on Yellow and No3 on Blue No 4 on Red etc. Since each house is likely to have similar loads at same time this will work. This is of course what does happen.

Postby curious1 » Sat Jan 26, 2008 5:14 pm

Hi thanks for the reply, makes sense and sounds very similar to our main street supply in uk being 3 phase in the road but only one of the phases going to an individual house.

Would it be correct to think that in say a kettle is on and then an immersion heater also cuts in and then main breaker then tirps out.. (as it does in this case) that if a split load board was used it would solve this problem?


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Postby ericmark » Sun Jan 27, 2008 12:03 am

Not quite. An immersion heater is normally 3Kw and the same give or take for kettle total is 26 amp and normally 32 amp on consumer unit so even if on same fuse it should not trip with load. Plus normally the immersion heater would be on its own 16 amp supply. But there are two things which can cause tripping the other is earth leakage and if kettle is leaking 15ma and immersion heater 15ma then both together could trip the RCD. But both should be less than 1ma so again should not really happen.

The split load board is designed to allow some items to have different earth leakage protection to others it does not affect the total load on the board.

Most houses have only overload protection on lights, immersion heater and cooker but also earth leakage protection on sockets which could be used outside. (TN-C-S) some houses often with overhead supply have two levels of earth leakage using 30ma and 100ma trips.

Old houses only were protected with over current.

This is of course UK system. In the USA you do have two 110 volt phases a completely different system. So don't bother looking at USA web sites.

Some times caravans do have a lot lower supply to houses and I have seen overload problems with caravans but you should not have a problem with a house.

What trips? Most miniature circuit breakers MCB's look like a switch and have amps and rating marked on them i.e. B32
Most Earth leakage trips RCD's have a test button fitted to them. Also marked 30ma or 100ma as well.
Most Isolators have Red switch and may be marked 100A but do not trip as such and are protected by fuse.
There is an new type which combines both MCB and RCD called RCBO these have ratting i.e. B32 plus test button. Should also be marked 30ma.

If you identify what trips maybe we can guide you better.

Postby curious1 » Mon Jan 28, 2008 5:52 pm

Thanks ericmark for your reply,

the old board has switch type mcb's and I traced the circuits back to the board, it would appear that the immersion is wired in on the same circuit as the sockets on thar floor (16amp mcb) so ive now changed it over to the one spar way i had left so its now on its own 32amp mcb which hopefully will solve the problem.

The RCD on this property is not combined into the distribution board like the uk ones but is a big black seperate one in between the board and supply and belongs to EDF so when i change the fuse board over i'll be putting one of the combined RCD protected boards in for extra piece of mind.

I was starting to get concerned with the overhead supply (PME)? and thought that this may also be causing the tripping as when it rains for prolonged time the RCD also trips out! and as the supply is running through some conifer branches i've asked them to come and check it / trim the branches away from it. (Will take them ages no doubt as it always does i france)

Anyway thanks very much again for your valued help.


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Postby ericmark » Mon Jan 28, 2008 10:59 pm

You did not say France was really were you lived. I thought just an example. Immersion heater on 32 amp seems OTT and I would have expected 16 amp. And France does not use ring main system or have fuses in the plugs so sockets would also be 16 amp. Overhead supplies are rarely PME now called TN-C-S. I would expect TT but being non UK IT or TNC could also be used. I have only worked in Algeria not France so I don't know the system but we are supposed to be "Harmonized" so same rules apply to France as UK except for ring main and fused plugs.

Postby curious1 » Sat Feb 02, 2008 1:44 pm

Hi again ericmark, thanks for your reply.

Yes france is the place but its only a holiday home. the immersion is on a 32amp fuse as until I change the board it was the only on spare as when its on the 16amp it causes it to trip. All seams well since changing thou so fingers still crossed.

Q. Why does the french system not use ring mains? Some places i've seen have been wired up recently using ring mains and were connected and passed by the local EDF, which did supprise me as I knew they dont have rings.. in france?


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Postby ericmark » Sat Feb 02, 2008 5:12 pm

The ring main system was first used when copper prices were high and it does use less cable as first used but modern regulations controlling where beams may be drilled have removed this advantage to some extent. For the ring main to work is must have local fusing. Either in socket or in plug as we do. It allows many sockets to be installed on one fuse and relies on the fact not all sockets are used together. But it has a number of flaws the main one is identifying when the ring has been broken which can produce overload as the single cable is only ratted at 22 amps and also sockets being fitted too close to the consumer unit. Plus people taking spurs from spurs and then the first spur being mistaken for at ring. Although the reason it was banned in many countries like USA is they don’t allow parallel circuits of unequal length.
The idea of local fusing is a good one but this can also be applied with radials using 20 amp supply onto many outlets in a smaller area.
This is thought by many as being a better system and as our power usage grows splitting a house into more areas becomes an advantage in fault finding.
The introduction of the RCBO has resulted in the ring main getting a new lease of live. This again is all down to cost a RCBO costs about £30 against the £4.50 for a MCB but splitting the sockets into two independent circuits as far as earth leakage is concerned does reduce nuisance tripping. If using two power circuits then price of RCBO’s = 2 x 32.89 = £65.78 minus the two MCB’s and RCD = £22.65 which is not too much extra but splitting into 4 circuits the extra jumps to £79.29 which has extended the life of the ring main. Because of new UK rules (BS7671:2008) on RCD’s on cables in certain types of wall etc. this may change?
Because we in the UK have fuses in the plug the socket with a fuse is never seen but in industrial premises MCB’s built into same unit as the socket is common but expensive. People of course also cheat and I have seen many 110 volt 16 amp supplies in the UK where two sockets are supplied from one 20 amp RCD. Many consider it is close enough but of course one gets the cumulative effect where some one has also used 1mm cable on a 10 amp socket (As used with computers and kettles) in turn connected to 16 amp plug. So we have double the ratted current able to reach the 10 amp socket. Our fused plugs removes to a great extent these problems.
We are suppose to be “Harmonizedâ€

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