2 phase supply

[Harnoor]

I am working on a site, 5 new build domestic 3 bed house, dno is only supplying 2 phase supply (33kva max load) is this enough for connecting 5 properties?

 

[JohnW2]

I am working on a site, 5 new build domestic 3 bed house, dno is only supplying 2 phase supply (33kva max load) is this enough for connecting 5 properties?

I may be wrong, but I think that 6.6 kVA per house is well above what they consider to be adequate.

Kind Regards, John

 

[Murdochcat]

A little surprised given the impending need for EV chargers and heat pumps

 

[ebee]

I may be wrong, but I think that 6.6 kVA per house is well above what they consider to be adequate

Yes I think you are correct initially.
However I think that is intended originally as say 2 or 3kw per home for a more substantial number of homes, meaning less chance of greater variation of probabilities into the higher side of the graph.
With the number of possible EV chargers as the "new kids on the block" we surely must consider their effect too as Murdochat mentions.
So 2 to 3 times of what we had not so long ago might not be actually that high at all when you filter in both of those reasons.
To what extent you`d calculate heat pumps to be more like a 24/7 kind of load and renewables to be a bit of a saviour of balance (although very variable indeed), well I`ll leave that to those in charge and their best guesses.
The chances are that they indeed have far better answers than we could guess at.

 

[ericmark]

So 3 x 24 amp and 2 x 36 amp when we normally fit a 60 amp fuse minimum. OK I have lived in a caravan with a 10 amp supply, but not shower, and cooking was gas. A cooker is normally given a 32 amp supply, I know we have diversity and all three homes are unlikely to use 24 amp at the same time, my house has a 60 amp fuse, two cookers, two electric showers and touch wood as yet not blown.

But I have oil central heating, 19 kW so that's another 80 amp, OK heat pump a bit better so likely only 16 to 20 amp for heat pump, but only 24 to start with, so 4 amp for the rest, not going to work.

Remember split phase has to be split into 2 you can't have homes with split phase supplies in the UK, alright in France the pay for power in a different way, the lower the supply the lower the standing charge, so you do get homes with a 16 amp supply, it did work OK until the smart meter, as one could draw 20 amp and long as not for long, but when the smart meter came in, instead of a fuse to disconnect on overload they used the smart meters internal relay, so over 16 amp, and power disconnected.

I use every day around 16 to 20 kWh, so average between 3 and 4 amp, so using an inverter, battery, and solar panels to take away the peaks yes it is do-able, with the battery absorbing the peaks, as long as no heat pumps or EV charging, heat pump 16 - 20 amp, EV 30 amp so before counting the cooker, sockets, lights etc, you need 50 amp, so even with a 60 amp supply one is on the edge. And your looking at 24 amp, that is not really going to work.

 

[Murdochcat]

There was a programme on TV a year or so back about a new estate in wales where ALL the homes had 3 phase supplies - and these were small family homes.

 

[ericmark]

Sorry I read "dno is only supplying 2 phase supply (33kva max load)" to be total for the 5 homes, so my central heating boiler is 19 kW OK heat pumps are more efficient but 19 / 5 = 3.8 kW which is around 16 amp. We can expect each home to have occupants arriving home around same time so all heat pumps working together. As to EV changers that 35 kVA so impossible to have EV charging.

Have a split phase supply to each home could be done, alternate each house as to which feeds upstairs and which is down stairs, but still 33 / 5 = 6.6 KVA and most EV chargers are 7 KVA it does not work.

 

[flameport]

We can expect each home to have occupants arriving home around same time so all heat pumps working together.

No.
Heat pumps and modern heating systems in general are not 'crank the heating to max when people get home' and then switch it off when done with it.

(33kva max load) is this enough for connecting 5 properties?

Could be. What does the design specification for the development say?

Or is this a case of the developer is too tight to pay for local network reinforcement costs?

 

[JohnW2]

Yes I think you are correct initially. However I think that is intended originally as say 2 or 3kw per home for a more substantial number of homes, meaning less chance of greater variation of probabilities into the higher side of the graph.

Agreed.

With the number of possible EV chargers as the "new kids on the block" we surely must consider their effect too as Murdochat mentions.
So 2 to 3 times of what we had not so long ago might not be actually that high at all when you filter in both of those reasons.

Again, agreed.

Kind Regards, John

 

[SUNRAY]

I wonder if somewhere along the line a typo has occurred and it should be 3 phase.

It would be a little unusual to run just 2.

Far from unknown of course.

 

[JohnW2]

I wonder if somewhere along the line a typo has occurred and it should be 3 phase. It would be a little unusual to run just 2. Far from unknown of course.

I also wondered that. However, on reflection, it occurred to me that if the plan is to do the usual thing had supply just one of the phases to each house, in turn, then three phases for just 5 houses might perhaps have been regarded as unnecessarily 'OTT'?

Kind Regards, John

 

[SUNRAY]

I also wondered that. However, on reflection, it occurred to me that if the plan is to do the usual thing had supply just one of the phases to each house, in turn, then three phases for just 5 houses might perhaps have been regarded as unnecessarily 'OTT'?

Kind Regards, John

I wondered that too but I find it quite hard to believe it's cost effective to bury a cable containing 3 conductors when 2 or 4 are very standard and 3 is likely to not be a stock item. Then hooking 3 of a 4 core cable into 2 of the 3 phases is... well to be frank it doesn't add up.

Thinking about this over night neither does it add up to provide only 16KW to 3 houses these days when, as has been mentioned 3 EV's at 7KW each are potentially going to be running simultaneously and with the keen interest in doing away with gas appliances there is significant possibility that electric heating is not that far away.

I haven't looked recently, certainly not since before Covid but I have very crude plug in meters which display highest and lowest current and voltage, peak total and average power over the measurement period. This sort of thing

Bearing in mind this is a 13A unit to plug a device into, and I added a 10:1 current clamp which may or maynot be calibrated accurately but does give a believable result (let's be generous and say within 10%) I measured the 6 week lights period one winter our peak power was close to 25KW (I suspect we are on a 60A fuse as we're a looped supply) but I had no idea how many times or what duration, our average was below 1KW.
Another way of looking at that is we were peaking at 80% of the total supply for 5 properties.

 

[ericmark]

I have looked back over whole of December and my peak use was 10.8 kW, can't remember what I was using, but the solar panel software allows me to look back to when they were fitted, and in general 8 kW is about the only peak which lasts any length of time, the scale changes depending on peak use that day, and many days show it with 6 kW as top of scale, I would assume it is my electric showers which give me the peak, so seems my peak 50 amp, and I have a 60 amp fuse.

I have wondered if it was to rupture what it would be replaced with, I would think without changes 80 amp is my limit, as the consumer unit is rated at 100 amp, and there is no fuse supplying the consumer unit as such, so it can have the solar plus grid supply, so unless extra fuses fitted 80 amp would be about the max.

If I want easy enough to see if my daughter is having a shower in the flat before I go for a shower myself, as to if two used it would blow fuse I don't want to test, it had two electric showers well before I bought the home.

So with showers running from the domestic hot water which would make more sense, I would think my peak would be below the 6 kW mark, specially having a battery and solar panels.

However if I bought a house with less than a 60 amp fuse I would be asking what is going on here.

 

[JohnW2]

I wondered that too but I find it quite hard to believe it's cost effective to bury a cable containing 3 conductors when 2 or 4 are very standard and 3 is likely to not be a stock item. Then hooking 3 of a 4 core cable into 2 of the 3 phases is... well to be frank it doesn't add up.

If, as one presumes,they are just going to supply one phase to each of the five properties, this discussion is really only of theoretical (or even 'terminological') interest, since it doesn't really matter whether the supply cable carries 2 or 3 phases. If (as, like you, I suspect is the case) it is actually a 3-phase supply, one of the phases would only be supplying one property.

...... I measured the 6 week lights period one winter our peak power was close to 25KW (I suspect we are on a 60A fuse as we're a looped supply) but I had no idea how many times or what duration, our average was below 1KW. Another way of looking at that is we were peaking at 80% of the total supply for 5 properties.

Transitionally, DNOs rely extremely hevily on 'diversity' (across timeeee and properties). With just a shower and a large cooker, peak instantaneous loads in an individual property can easily exceed 80A,perhaps exceed 100A, but the average ('after-diversity') figure they work with has only been 2 - 3 kW per property.

As raised above, the question is whether the appearance of EV charging (and,to some extent, heat pumps) has totally moved the goalposts of that traditional approach - since,uniquely, EV charging can represent a large load which persists for long periods of time, hence potentially having a major impact on the average ('after diversity') demand.

Kind Regard's, John

 

[SUNRAY]

If, as one presumes,they are just going to supply one phase to each of the five properties, this discussion is really only of theoretical (or even 'terminological') interest, since it doesn't really matter whether the supply cable carries 2 or 3 phases. If (as, like you, I suspect is the case) it is actually a 3-phase supply, one of the phases would only be supplying one property.

Transitionally, DNOs rely extremely hevily on 'diversity' (across timeeee and properties). With just a shower and a large cooker, peak instantaneous loads in an individual property can easily exceed 80A,perhaps exceed 100A, but the average ('after-diversity') figure they work with has only been 2 - 3 kW per property.

As raised above, the question is whether the appearance of EV charging (and,to some extent, heat pumps) has totally moved the goalposts of that traditional approach - since,uniquely, EV charging can represent a large load which persists for long periods of time, hence potentially having a major impact on the average ('after diversity') demand.

Kind Regard's, John

This may all very well be the case but the supply does need to cope with the peaks. If my understanding is correct the DNO only permits fusing to be twice the supply capacity so 16KW ~64A maximum fuse = 64*2/3 = 43A. So getting home from work, putting the car on charge, putting a load in the washing machine and starting to cook dinner ~60A or to put it another way 50% overload of the fuse and all of the allowance for all 3 properties. It smacks of a mistake to me.