3 Phase Electricity Supply

I currently have a 3 phase 18Kva supply, but am reducing to 15Kva.

Can anyone advise how many amps / watts I will now have on each phase?

5kW roughly 20a

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You’ll have 25 amps, 5000 watts per phase.

20A per phase would be a 12kVA supply.

The OP will have 25A per phase with a 15kVA supply (approx. 5,75kW per phase)

Yesterday my supply was reduced to 15kVA.
I suspected that one of the phases is now “overloaded”, so thought that I’d turn on the most commonly used devices on that phase and see what happened. The result was zilch, nothing!???

The devices simultaneously turned on (on the suspect phase) were:

Tumble drier 2500 watts
CH boiler 125 watts
Fridge/Freezer 350 watts
Kettle 2400 watts
Microwave 800 watts
Oven 1450 watts
Toaster 980 watts
Fridge 500 watts
Insect light 40 watts

That’s well over 9000 watts - so why didn’t anything trip?

Very very unlikely, most believe that but thats only the part that hits the food. The rest of the power unit is around 600-700 watts making the average microwave around 1500 watts

It would require absolutely everything to be used at the same time to get to that total.

They were all tuned on at the same time.
I can only assume that they do not always use the full wattage specified on the product labels.

The boiler, fridge (x2 ?)/freezer and oven will not draw power continuously but only when their thermostats call for heat to be generated or moved around which might explain why the total load was lower than expected.

Also are you sure that they are all on the same phase?

Absolutely sure - I was really surprised that the board did not trip.

Current flow in three phases systems is a bit weird. For one thing with a balanced load across the three phases most current flows between the phases and not back through neutral - if you look at a pylon you see the three phase conductors but no neutral (the thin wire at the top is a protective earth/lightening conductor).

It’s possible you could be pulling neutral up away from earth and reducing the voltage on that phase but I’d be surprised if a single domestic installation could do that (have seen it in an industrial environment and the supplier fined us for not doing enough to balance the loads).

@Badger might have some thoughts.

The first thing I did after buying a property was to get shot of a 3 Phase Electricity Supply ( 80 Euros ) and re wire the components were so expensive I do not have a pool or run a workshop and have been able to run any electrical equipment I like at the same time

I’d far rather get rid of the 3-phase once I’m confident that 15kVA is enough.
The other consideration is the cost: I’ve no idea whether this is a simple low cost change or not.

Very true. We have a water heater plainly labelled as being 2,400 watts, but the Linky meter reveals that it only draws 1,500 when it is switched on. Other appliances are similar, such as a 2Kw convector heater that only draws 1500 watts, and an ostensibly 1,800 watt electric kettle that only draws 1,400.

Turned on & actually pulling load? As you rightly suggest, if you were really pulling over 9kW then your Linky (or main disjoncteur de branchement) should have dropped out.

A better test is to put on all your loads & then check the maximum demand per phase before it resets at midnight. It will be like this screen…

As it’s three phase the first “puis max” screen is the grand total, you then keep pressing the button to see each phase individually (the screenshot here shows the load on phase 3).

I’m still trying to find out how Linkys deal with triphasé overload. There’s a possibility that they are more democratic than the old system of limiting load via the disjoncteur de branchement i.e. unless you exceed to overall kVA susbscription the Linky won’t trip, whereas with the older system the main DJ will trip if any one phase is overloaded.

The above theory might explain why @Nigel-at-BUF-House doesn’t lose power when pulling 9kW on one phase or, more likely, the load is actually spread out across the phases after all. Looking at the individual “puis max soutir” screens will confirm this.

My theory is all good until someone with a system that hasn’t got large enough supply conductors tries to use one phase for everything & the neutral overheats.

However, a lot of triphasé supplies are only 18kVA branchements, so the main trip will still drop out if more than 6kVA is drawn on any one phase. I’ll be curious to see what setting @Nigel-at-BUF-House has on their main DJ…?

For a purely resistive load such as a heating element - which all your examples have - I’d expect the wattage to be pretty much “what it says on the tin”. Odd that you are seeing 60-75(approx)% of that over a wide range of appliances.

Yes, I would have thought so as well.
However, I’m not sure that our Linky meter is all that it’s cracked up to be.
We have a 12kVA monophase supply. The ‘Puis Max Soutir’ by my understanding, is supposed to show the max amount of power drawn at any one time during a midnight to midnight 24hr period.
So I can go to the meter and see that the Puis Max Soutir is registering say 3,500.
Then I can increase the load to something in the region of 6kw and I can see the ‘Puis App Soutir’ reading on the Linky increase accordingly. However, the Puis Max Soutir reading stays at the previous amount of 3,500 even when the meter is telling me that we are actually drawing over 6,000.
Once again the numbers on the Linky are not what I would have expected.

Only updated once per 24h ?

That’s what EDF say in their blurb.
If I load the system far in excess of what the Puissance Max reading happens to be, then after about ten minutes or so the Puis Max does start to increase in very slow and small increments, but it would take it ages (probably an hour or so) to register that 3kw extra was being used.
We often have 2 water heaters, washing machine, tumble dryer, and dishwasher all programmed to run at around the same time (3.30 to 5am) and it still just tells me that the max used at any one time is around the 4kw mark.
To be honest, I think that the ‘Puis Max Soutir’ number is not to be relied upon in any way. Perhaps it’s just our particular meter that is faulty in that respect.

Your Linky experience certainly doesn’t reflect mine.

Have you consulted the app to see if your figures make any more sense?