UK Load in Amps on a mains single-phase circuit

[Carl Haworth]

I have a 230 Volt single-phase circuit with a 100 Amp cutout fuse and a 100 Amp MCB switch, so the supply is rated at 23 kVA.

Only about 13% of my total energy consumption is electricity. The remaining 87% is natural gas, supplying the following appliances (kW figures are net output power):-

22 kW boiler, 3 kW fan-flued convector heater. 8 Kw cooker.

After (if?) natural gas is turned off some time in the 2030s I can have 3-phase installed (at vast cost) to give me total kVA 55.15 at 230 Volts. As you can see, this offer is tied to reducing the supply capacity per phase to 80 Amps. So a connection from one phase (and the neutral) to my existing single-phase consumer unit would be rated at 18.40 kVA, leaving (I presume) 36.60 kVA for the 3-phase, once this is balanced (how is balancing achieved in this sort of situation, by the way?).

I will also, by then, need a powerful EV charging wallbox. An 11 kW one is for 3-phase only, as would be a 22 kW electric boiler (heat pump technology is not suitable for our home). If these two appliances consume 33 kVA, the 3-phase will be used to over 80% of its capacity, but it could be arranged that the two would never be on at the same time.

The 23 kVA single-phase circuit, with capacity reduced to 18.4 kVA, will need to carry extra loads:-

Cooker (12 kW maximum, 7 kW diversity), 3 kW convector heater.

I have done calculations of the peak consumption of the circuit as it stands now. I need to be confident that these are reasonably realistic, so that I can add the extra loads to the existing ones, and calculate the much higher peak consumptions with the extra loads added. I need to know if the total is likely to be within the reduced 18.40 kVA capacity of this circuit.

If this is relevant (please see below), the additional appliances mentioned for the single-phase, and both those for the 3-phase, have power factor 1.

As regards the existing load on the single-phase circuit, if a p.f. should be applied, it should be reasonable to use 0.8.

To work out first the load on the increased-load circuit as regards the its capacity/the capacity of the cutout fuse, I need to know if I should increase the kW of the total existing load by 1/0.8, so as to include apparent as well as real current, and get a figure in kVA. Or should use the total kW. At that point I would add the extra loads of the cooker and convector heater, as kVA and kW are identical.

Calculating Amps using kVA increases the load on the existing circuit by 25% if p.f. is 0.8, so, after adding the extra proposed loads, there is unsurprisingly considerably more "headroom" left in the circuit capacity if I calculate using kW.

I suspect that kW is the correct basis to use, because apparent current passes back into the grid after passing through the circuitry of an appliance. An appliance may draw, say. 10 Amps. If its p.f. is 0.8, 2 Amps are returned to the grid instantaneously as the 10 Amps are drawn. This is why a Watt/hour meter records using the voltage times the net current used up by loads, and so reads in kWh and not kVAh.

So I suspect that the cutout fuse draws the net current (full current less apparent current).

Which should I use for my calculation: kW or kVA? If the answer is kVA, then, in view of my comments just above, where have I misunderstood things?

I've tried to find an answer to this, but can't find any focussed guidance.

Can forum members enlighten me reliably, please?

Carl

 

[Lucien Nunes]

But how is that the Watt/hour meter (I mean the meter which supplies data for consumption charging purposes to the energy supplier), is driven, at the supply voltage and frequency, by only real power?

Is it because the current which is the basis of the apparent power is out-of-phase with the current basis of the real power?

If so, why does the power developed by the out-of-phase current not do work in the meter's current coils?

The watt-hour meter (not watt/hour. that's watts per hour) performs real-time vector multiplication of current and voltage to resolve only the in-phase, real power component. In a traditional spinning-disc meter this is done magnetically by the interaction of the two fields set up by the voltage and current coils. Only the in-phase component of the field created by the current coil generates nett torque on the disc. In a smart meter the same multiplication is done electronically.

It is equally possible to arrange the meter coils to register only the reactive component. Both instantaneous kVAr meters and kVAr-hour meters are used on industrial supplies to monitor reactive power flow, because this is chargeable on large consumers' tarriffs. Not as energy supplied, of course, but to defray the cost of installing oversize transformers and cables to carry the reactive component of the current that does not pay for itself with energy supplied. Chargeable reactive power incentivises customers to maximise their power factor, i.e. minimise the current needed to supply their real power demand.

 

[Carl Haworth]

The watt-hour meter (not watt/hour. that's watts per hour) performs real-time vector multiplication of current and voltage to resolve only the in-phase, real power component. In a traditional spinning-disc meter this is done magnetically by the interaction of the two fields set up by the voltage and current coils. Only the in-phase component of the field created by the current coil generates nett torque on the disc. In a smart meter the same multiplication is done electronically.

It is equally possible to arrange the meter coils to register only the reactive component. Both instantaneous kVAr meters and kVAr-hour meters are used on industrial supplies to monitor reactive power flow, because this is chargeable on large consumers' tarriffs. Not as energy supplied, of course, but to defray the cost of installing oversize transformers and cables to carry the reactive component of the current that does not pay for itself with energy supplied. Chargeable reactive power incentivises customers to maximise their power factor, i.e. minimise the current needed to supply their real power demand.

 

[Carl Haworth]

The watt-hour meter (not watt/hour. that's watts per hour) performs real-time vector multiplication of current and voltage to resolve only the in-phase, real power component. In a traditional spinning-disc meter this is done magnetically by the interaction of the two fields set up by the voltage and current coils. Only the in-phase component of the field created by the current coil generates nett torque on the disc. In a smart meter the same multiplication is done electronically.

It is equally possible to arrange the meter coils to register only the reactive component. Both instantaneous kVAr meters and kVAr-hour meters are used on industrial supplies to monitor reactive power flow, because this is chargeable on large consumers' tarriffs. Not as energy supplied, of course, but to defray the cost of installing oversize transformers and cables to carry the reactive component of the current that does not pay for itself with energy supplied. Chargeable reactive power incentivises customers to maximise their power factor, i.e. minimise the current needed to supply their real power demand.

I agree that Watt/hour is not correct. It is Watt-hour (or Watt hour).

My mistake arises from" /" interpreted, very reasonably, as "per".

One Watt-hour is one Watt of energy exerted over a duration of 1 hour. 1 Watt PER hour suggesst a continuing power of 1 Watt for one hour and for each subsequent hour.

Thanks for picking me up on the sloppiness!

And thanks for explaining precisely why the Watt-hour meter is driven by only by in-phase current (x Volts).

I guess, sooner or later, that domestic consumers will also be charged for total power, depending on the p.f. of their installation. Inductive devices multiply "exponentially" (may not be a totally sloppy term here!), and not necessarily just ones with tiny power ratings. LED bulbs are no better than fluorescent tubes (in p.f.), and are worse than latter with electronic ballasts, but, fortunately, consume much less current per lumen emitted.

All very interesting, and illuminating!

 

[Lucien Nunes]

one Watt of energy

Did you plant that for me?
Power / watts
Energy / kWh or joules

Sorry, but I know you know what you are talking about fundamentally and can't let you get away with it

 

[Carl Haworth]

Oh, dear, another boo-boo! I didn't plant it. I wouldn't be so foolish!

Yes, I see my error! The Watt hour (Watt-hour) is the unit of energy (so what is the Watt on its lonesome?)

We are dealing with a relationship between force and power very like that (torque and power (work)) in engines/motors which exert a rotating force, and develop power, and so perform work, over time and distance.

This explains why the Watt has fairly recently become a common unit for work done, but it's just plain Watt without specifying the time/distance over which the underlying force is exerted. As you will know, It originates in the differently named unit that James Watt devised to persuade farmers to swap their horses for a Boulton and Watt one or two horse-power static steam engine.

That old unit has stuck. You still rarely find even aware motorists quoting engine power in Watts, and the same is presumably true where they don't call a horse a horse (eg, Germany, France, Italy).

THOUGHT

I still don't know what to do to estimate reasonably reliably the peak power consumption of our single-phase circuit. The monitor which I found proved unsuitable for long-term monitoring, and the same seems to apply to the two suggested by our good friend Avo.

Do you have any suggestions - apart from a LOT of very wearisome, and probably inaccurate, counting and adding up?!

All the best,

Carl

 

[Avo Mk8]

Do you have any suggestions - apart from a LOT of very wearisome, and probably inaccurate, counting and adding up?!

I think I have a slightly clearer idea of your requirement now. I was focussed on PF before, but for kWh there do seem to be a few products out there.

Here's one which uses a current transformer connected to a 'hub', that uploads usage data to their platform. You interrogate the data on your phone/ tablet/ laptop, and can download accumulated data (In CSV format if you want to play with it in Excel!)
I haven't looked at this in detail, so may still not be suitable. I see the current transformer 'dongle' is battery powered, but I suspect those batteries should last a good time, say 6 months or a year?

Engage Sub-metering Kit - Efergy

Multi-Circuit & Solar Upgrader Kit for Engage

uk.efergy.com

There are also professional data loggers from Fluke etc, but I was concerned both the cost of the hardware plus software licensing might make such equipment prohibitvely expensive.

PS. I'd just buy the £18 display, see what the figures look like, including PF, and if happy with the outcome (!), proceed with the logger above. It's only money

 

[Carl Haworth]

Thanks very much.

I will have a look.

You'll be surprised to hear that I don't have any experience of CSV format. I have looked up what this is, and don't feel much the wiser!

I don't have Excel installed on my PC, because I don't pay for MS Office, but I DO have LIbreOffice, which includes a spreadsheet program similar, I suspect, to Excel.

But I've never used it because I like a manual to consult when writing a spreadsheet, and, to my knowledge, there isn't one for LibreCalc. Possibly there is a "Dummies" manual, If not, I would have to keep looking elsewhere on line while working to find out how to operate this program smartly.

Would I be able to load data downloaded from the logger in CSV format into LibreCalc, do you think? I believe the free program is a clone of an unlatest version of Excel.

I create spreadsheets for various purposes quite frequently. I use a brilliant very old spreadsheet program SuperCalc5. It's only shortcoming is the limited memory that it is able to apportion to a single spreadsheet, but, so far, I've not found this a problem in practice.

It's a DOS program, so won't run in any version of Windows after XP, and it can't intercommunicate with any Windows program, or email.

I started using SuperCalc on our first computer, an Amstrad, in 1987, and have stuck with it in PC format (the last version being 5) since.

So how can I be able to use it when my PC runs Windows 10?

I have a Windows 98 computer. and a Windows XP one, where it is installed and usable. But, ironically, it runs best, and prints fastest, in my version of XP installed as a virtual machine within Oracle Virtual Box on the hard disk of my W10 machine. Although SC5 can print only through a parallel printer port, and these are now long defunct, I run an Italian software program that enables DOS programs to print through a USB port.

Curiously, although SC5 runs better in XP VM than in real XP, the memory size is still limited, as dictated by the program. But, also curiously, the program apportions a larger memory when it is running in XP VM than in XP itself.

Could I load CSV data from the logger into LibreCalc? I think that this program is a clone of an old version of Excel.

As already mentioned, I've never dealt with data in CSV format, so this would be a new learning experience!!

 

[Avo Mk8]

.Could I load CSV data from the logger into LibreCalc? I think that this program is a clone of an old version of Excel.

As already mentioned, I've never dealt with data in CSV format, so this would be a new learning experience!!

Yes you could.
Libre Calc guide here:

Welcome to the LibreOffice Writer Help

help.libreoffice.org

It's much simpler than it sounds, especially after you have done it a few times!

 

[Carl Haworth]

Fuse responds to the VA load, real and apparent

Thanks again for your help, and your very interesting account of the gshp job. Hope the over-heat problem has been sorted by the designer/supplier.

I did ask you who you would suggest to size up the feasibility of gshp for our own home. That question probably got buried under the other issues, but, if you can spare the time, I'd appreciate a lead. It would seem that a firm specialising in the remarkable Stiebel pumps that you described would be a good starting point.

Here's hoping for a suggestion made with the benefit of your experience of the market.!

All the best,

Carl

PS thanks to various contributors, yourself among them, I now know for sure that the supply fuse load is the kVA h of the the supply, not the kWh. And I also now understand why this is, counter-intuitive though it first seemed to me!

 

[plugsandsparks]

The process works something like this:
1. Choose a GSHP installation company. ( DM if you want a suggestion for your area)
2. Said GSHP installation company will have knowledge, experience and service from their chosen GSHP manufacturer, e.g. Siebel (there are many others)
3. Engage said company for a design, this will generally be backed off to the manufacturer, e.g. "Install Co" backs off design to "GSHP Manufacturer Co"
4. Based on your local environmental conditions, e.g Land Area, soil type, availability of ground water, the manufacturer of the GSHP will design the ground loop.
5. Install Co then installs to GSHP manufacturers design -

Hope this helps and glad you are in sync with the electrical engineers nightmares of dealing with the plethora of AC electrical loads and its impact of current carrying infrastructure (and we have not even mentioned harmonics yet), lol

 

[Carl Haworth]

The process works something like this:
1. Choose a GSHP installation company. ( DM if you want a suggestion for your area)
2. Said GSHP installation company will have knowledge, experience and service from their chosen GSHP manufacturer, e.g. Siebel (there are many others)
3. Engage said company for a design, this will generally be backed off to the manufacturer, e.g. "Install Co" backs off design to "GSHP Manufacturer Co"
4. Based on your local environmental conditions, e.g Land Area, soil type, availability of ground water, the manufacturer of the GSHP will design the ground loop.
5. Install Co then installs to GSHP manufacturers design -

Hope this helps and glad you are in sync with the electrical engineers nightmares of dealing with the plethora of AC electrical loads and its impact of current carrying infrastructure (and we have not even mentioned harmonics yet), lol

Many thanks. I've printed off your suggestions for future reference.

Where do you yourself operate (if you are effectively a GSHP company)?

 

[Carl Haworth]

Yes, you on the right lines. This is a 59KW GSHP, brine is the medium circulating in the ground loop. The difference in temperature brine in/out maybe only a degree or two, but all it needs to do is turn the Fgas inside the GSHP from liquid to gas so it can run through the heat exchanger and give up its heat and turn back to liquid. Admittedly the unit has a large compressor to push the Fgas around the heat exchanger and normally heat pumps are more efficient in heat mode than cooling mode as the heat generated by the compressor easily provides some extra heat transfer into the Fgas too aid liquid to gas transition. What Stiebel have done is more formalise this heat recovery into direct hot water to aid both DHW and CH and breaks the temp barrier that normally makes heat pumps most efficient at 35 degrees. The system i am working on is set to 50 degrees fixed value direct to buffer tanks which then heat the house, hot water tank, swimming pool and warm air heat exchanger for the swimming pool air handling unit, so it has alot to do and raising the temps available means i dont need electric immersion for Legionnaires and provides hot water at a high temp for mixing further down the line. As mentioned the issue i was wrestling with was because the hot water tank rose to 74 degrees which is too much for bog standard pumps.

Very belated response - got side-tracked by other issues!

You are in Chesterfield. We are in Retford - about 35 miles away.

If you are willing for me to do this, how can I contact you direct (say, by email)?

I'd like to investigate with you in much more depth the practicalities, if necessary with the addition of 3-phase electricity, of installing ASAP for our existing (current gas-boiler-powered) wet central heating circuits, and without or with heating of DHW.

 

[plugsandsparks]

Just DM your email, it should be secure and not open to spamming, appear to having quite a few of these types of conversations, cheers P&S

 

[Carl Haworth]

Just DM your email, it should be secure and not open to spamming, appear to having quite a few of these types of conversations, cheers P&S

Just DM your email, it should be secure and not open to spamming, appear to having quite a few of these types of conversations, cheers P&S

I didn't know what DM means. I've Googled it., where the explanation is "direct marketing".

If that's the meaning, the result of your search does not surprise me:-

I use an old email address (@waitrose.com, not the @gmail.com address that I have had for well over a year now) for my postings on Electricians Forum. That was simply so I could find the messages from the forum easily.

That old email address now only receives mail, which is transferred into the email Client where I still have an account for the address , with a separate one for my gmail address. Since @waitrose.com (aka @johnlewisbroadband.com) ceased to be my ISP I have not been able to use that address, at least via my email Client. for outgoing messages.

I gave up on @waitrose.com for three reasons:-

1. Inbox of limited, and small, size;

2. POP3 incoming email server only;

3. Absolutely NO spam filtering.

My contact at the email Client that I have been using ever since Microsoft stopped offering a decent one of their own (eg, Outlook Express in W. XP. Windows Mail in W. Vista) suggested moving to gmail as email provider because their spam filtering is very thorough.

So all that now arrives in the @waitrose.com inbox in my Client is occasional spam, that I always junk as soon as I see it, plus emails from Electrician's Forum (and newsletters from a financial site).

Trust you're now satisfied that I am not some dubious crank, or worse!

If you are satisfied, how can we get in touch directly?

Needless to say, for a direct conversation by email, the address which I would give you to use would be my @gmail.com one!

 

[nicebutdim]

In this instance DM would be direct messaging as in forum member to member messaging.

Hover over (or click on) the member's name and then click 'start conversation'.