Max draw on a ring?

[martygturner]

Pushing a circuit to nearly the maximum capacity is not a very great idea mate. You've got other factors to consider such as the ring being balanced and the wiring. Assuming if it's a 2.5mm ring circuit it won't be very good running 30A through it (depending on how it is installed.)

Why ? its designed to have 32 amps, not 30 amps plus a bit of wiggle room. A 32 amp circuit must be able to deliver 32 amps, as a ring is already de-rated from its maximum load, depending on installing method, otherwise it has not been properly designed.

I think the trouble always comes when we make broad assumptions about circuits, they are either designed to have a rating or they are not. The op's curcuit has been designed to have 32 amps not 27 or 20 but 32 .If the circuit cannot handle 32 amps it should be de-rated. Whilst we shouldn't overload a circuit if we didn't then many things such as pumps etc would not work.

Mind you it might not be a ring, it could be a 4mm radial.

 

[Jurassicspark]

Whilst we shouldn't overload a circuit if we didn't then many things such as pumps etc would not work.

A pump and an electrical circuit are two complete different things regarding this dilemma.

Mind you it might not be a ring, it could be a 4mm radial.

The OP has stated its a ring. The 32A circuit gives it away.

if you just slightly overload a circuit say at 10% then it will probably never trip.

MCBs are deliberately designed to withstand modest overloads for some time. That’s to prevent nuisance trips for short term overloads. They should not be deliberately overloaded.

 

[Jurassicspark]

I think the trouble always comes when we make broad assumptions about circuits, they are either designed to have a rating or they are not.

Who's making assumptions?
Seen quite a few domestic installations with a modest load connected but due to a high in rush current the MCB had to get changed from a type B to a C.

Care to explain?

 

[flameport]

1) 2000w washing machine
2) 600w tumble dryer and 2400w oven
3) 2400w dishwasher

Is this too much for the circuit?

Not a problem at all.
Those devices are approximately 30 amps in total if all used simultaneously.

The washing machine will be far less than that for 90% of the wash cycle. Same for the dishwasher.
Oven will be 2400W while it's heating, and pretty much nothing when it's not. Unless you like to use it with the door open, once up to temperature the element will be on for a small proportion of the time.

 

[JohnW2]

Run them at different times it should be ok ... Run them together and the fuse will go

As has been said, on the assumption that the device protecting the circuit ("the fuse that will go") is actually a 32A MCB, the loads described should not result in that MCB operating ever - even if (very unlikely) the quoted powers related to 230 V (martygturner assumed 240V, and a 240 V supply, to get 30.83A)), and even if all the appliances were run simultaneously.

The 7,400 kW total load would, at 1230 V equate to 32.77 A but a 32A MCB is required to never operate with currents below 36.16A, even if that current persists indefinitely.

In any event, it is extremely unlikely that the appliances in question would actually draw a total instantaneous current anywhere near 32A for significant periods of time, even if they were all 'running' simultaneously.extremely

 

[ericmark]

I agree with @flameport I get a graph showing what power I have used, One can see the spikes when I made coffee and having viewed the data over months, the only time we tend to exceed the supply from solar panels and battery is when having a shower. Once the sun is shinning the 3kW from battery, and the 1 to 4 kW from solar panels is enough to cover all power requirements. So in the main I do not use over 7 kW = 30.5 A, so one would be very unlucky to cause an overload, and if you did, the worse case is the MCB trips.

Yes, I know that the appendix of BS 7671 talks about dedicated circuits with fixed appliances over 2 kW, but in real terms the only appliance between 2 and 3 kW which draws high current for a long time is the tumble drier and immersion heater, and since heat pump tumble driers arrived, now only the immersion heater really needs a dedicated supply.

 

[EFLImpudence]

...

 

[JohnW2]

I agree with @flameport I get a graph showing what power I have used, One can see the spikes when I made coffee ... and having viewed the data over months, the only time we tend to exceed the supply from solar panels and battery is when having a shower.

Very much so. I think many people seriously under-estimate the effects of 'diversity' (over time)and hence the maximum demand on a circuit or whole installation.

I reproduce below a message I posted about 5 years ago (click here) . Even though in,my very large house, I have a washing machine, dishwasher, tumble dryer, immersion heaters, fan heaters and all the other usual domestic loads (including a good few 'workshop tools0, over an approx 2.5 year period, the total demand of my installation only exceeded 30A on 1,489 out of about 1.35 million minutes (about 0.1%), and exceed 40A for only 6 of those 1.35 million minutes (about 0.0004%).

Those figures are for my entire installation, so those for individual circuits within it will generally be a lot lower.

--------------------- reproduced message -------------------------
In another thread (click here) , there has been extensive discussion about the estimated ‘maximum demand’ of a domestic electrical installation and the associated concepts of diversity. It has been pointed out in that discussion that real-world ‘maximum demands’ are usually surprisingly low.

To illustrate this, I present here some data relating to the last ~2.5 years (about 1.35 million minutes) of my electrical installation. Although data is captured roughly 5 times per minutes, I have it recorded as averages over each 1-minute period, and it is those 1-minute averages which are presented here.

It has to be said that it is a very atypical domestic property. Although now usually only occupied by two people, it is very large, with a 3 x 80A electricity supply and about 30 final circuits. There are no large electrical cooking appliances (only microwave, fat fryer, bread maker, toaster etc.) and the two electric showers are virtually never used. There is, however, a silly number of refrigeration devices! Something like one third of the total electrical consumption results from nocturnal hot water heating.

The first graph below shows the distribution of the instantaneous (1 minute) total demand, indicating that for the vast majority of periods the total demand is under about 5A. The small peak around 15-16A relates to periods when the 3kW immersion is the main load.

The second graph shows the same data, but in terms of cumulative figures, indicating that some 80% of all minutes have a demand below about 4A, about 92% of all minutes have a demand below about 14A and about 98% of all minutes have a demand below about 20A.

The final three graphs are ‘inverted’ versions of the second, the final two being ‘magnified versions’ which show what happens at the extreme tail (moments of highest demand). These show that only about 1% of minutes have a total demand >24A, and only about 0.01% of minutes (about 1 minute every week) have a demand >32A.

Over all the ~1.35 million minutes observed, the mean total demand was 4.35A and the median 2.97A. The lowest demand was 0.35A and the highest 40.36A. Summarising the number/percentage of minutes with total demands above a certain figure. As can be seen, under 2% of minutes had total demands >20A, and almost none had total demands above 30A. For about half of all minutes, total demand was under 3A.

Yes, I know that the appendix of BS 7671 talks about dedicated circuits with fixed appliances over 2 kW, but in real terms the only appliance between 2 and 3 kW which draws high current for a long time is the tumble drier and immersion heater, ...

Indeed - and, in common sense terms, that should only apply to fixed appliances which consume over 2 kW continuously for long periods, which is not the case for things like washing machines and dishwashers or (depending on appliance and usage) not necessarily even true of thjngs like tumble dryers. In my case, even my immersion hetaer rarely draws 3kW continuously for more than about 30 mins.

and since heat pump tumble driers arrived, now only the immersion heater really needs a dedicated supply.