UK Load in Amps on a mains single-phase circuit

[Avo Mk8]

I am puzzled that it is proving so difficult to establish whether the current load on a circuit, hence on its cut-out fuse, is the full current drawn (real plus apparent current) or the net current (real current only).

Stating the obvious - the 100A fuse is there for protection against sustained overload, or some major mishap. Design standards require it to withstand a load of 1.3 x rated current indefinitely. 1.6 x rated current for 90 minutes. You've got to go some to blow it. I feel the power factor considerations you are concerned about are really neither here or there in the grand scheme of things.

I'm already investigating a monitor: Omega OM-DCEV. This uses two clamps on the phase wire:-
Do you have any knowledge of this monitor?

It seems to clip onto Line and Neutral, and use a current transformer.
I'm afraid I'm not familiar with it.
The Omega unit does not appear to monitor power factor, which I thought you were interested in?

The data logger I put a link to is under £22, connects to a PC via USB (with the right model), doesn't use batteries, and it would be the PC that records the data. But probably a lot less user friendly than the Omega!

I've emailed Omega (whose price is £265 (they are - or appear to be! - the manufacturer) to try to establish points such as:
- Will it record total current or only p.f. current?

I hope you get a prompt response.

The second link I posted is a gadget that can be set up to give a real-time display of your overall consumption, including power factor. I though it could answer your concerns about the PF value at your property. It is only £18.

Best regards

 

[Lucien Nunes]

I don't think anybody has adequately answered the original question. The maximum current rating of a conductor or fuse is determined by the heat dissipation within it, which depends on the square of the current through it. There is no relationship between the cable / fuse dissipation and the supply voltage, nor to the phase relationship between current and voltage.

Therefore when considering load power, the fuse / circuit size relates only to the apparent power in kVA and the symbols embody this concept. Apparent power in VA is simply the scalar product of the current and voltage (V and A) without any regard to their relative phase. It is the power that 'appears' to be flowing as observed by means of a voltmeter and ammeter alone.

100A at 230V will always transfer 23kVA because 230 * 100 = 23,000. If the power factor is unity that 23kVA will deliver 23kW of real power; if the pf is zero it will transfer 0kW. But the cables and fuses care nothing for the difference, as their dissipation depends only on the current which is 100A in both cases.

 

[Carl Haworth]

I don't think anybody has adequately answered the original question. The maximum current rating of a conductor or fuse is determined by the heat dissipation within it, which depends on the square of the current through it. There is no relationship between the cable / fuse dissipation and the supply voltage, nor to the phase relationship between current and voltage.

Therefore when considering load power, the fuse / circuit size relates only to the apparent power in kVA and the symbols embody this concept. Apparent power in VA is simply the scalar product of the current and voltage (V and A) without any regard to their relative phase. It is the power that 'appears' to be flowing as observed by means of a voltmeter and ammeter alone.

100A at 230V will always transfer 23kVA because 230 * 100 = 23,000. If the power factor is unity that 23kVA will deliver 23kW of real power; if the pf is zero it will transfer 0kW. But the cables and fuses care nothing for the difference, as their dissipation depends only on the current which is 100A in both cases.

Thanks, Lucien,

Where p.f. is less than 1.0 I still don't understand why the apparent current is part of the overall load on the main fuse. Obviously this current is passing through the fuse to the appliance which is drawing it.

Instantaneously. however, the apparent part of the current flowing through the appliance for whatever reason is - in addition to the real (p.f.) current, but not to perform work - returned to the grid via the fuse.

The returning apparent current cancels out its share of the total current load, so the Watt/hour meter "sees" real (working) current only (unfair on the grid, but nice for consumers).

Is the following a correct layman's understanding of why apparent current is part of VA from the point of view of the supply capacity/main fuse?

The current part of the VA supplied includes both the "arriving" and the lower "returning" current. Although the "returning" current cancels out its own potential share of the power developed by the appliance (Watts), because it does not do any work, it is still loading the fuse on its "way out".

So the total load on the fuse is still the total of the two classes (phass?) of current.

However, I don't understand your comment that an ammeter responds to the combination of real and apparent current. If that were so, surely the current coil of the Watt/hour meter would be developing a magnetic field on the basis of the combination of real and apparent current, so recording VA and not Watts?

In reality, surely, the "negative" effect of the returning apparent current cancels out the relevant part of the total current, so the ammeter reads only in "real" current Amps?

Obviously that is not the case with the load as such on the supply.

 

[pc1966]

Is the following a correct layman's understanding of why apparent current is part of VA from the point of view of the supply capacity/main fuse?

The fuse reacts to the heating effect of I^2R and are not considering if that I is in phase with the supply V (for real power) or at 90 deg to V (for the imaginary power).

What is actually used to deliver useful work is the real part. The imaginary part simply contributes to heating of the supply cables, etc, which is why large industrial users often have capacitor banks to compensate for this (brining PF closer to 1) as the supply company charge them otherwise, basically to keep their network operating efficiently.

 

[Carl Haworth]

Stating the obvious - the 100A fuse is there for protection against sustained overload, or some major mishap. Design standards require it to withstand a load of 1.3 x rated current indefinitely. 1.6 x rated current for 90 minutes. You've got to go some to blow it. I feel the power factor considerations you are concerned about are really neither here or there in the grand scheme of things.

View attachment 94374


It seems to clip onto Line and Neutral, and use a current transformer.
I'm afraid I'm not familiar with it.
The Omega unit does not appear to monitor power factor, which I thought you were interested in?

The data logger I put a link to is under £22, connects to a PC via USB (with the right model), doesn't use batteries, and it would be the PC that records the data. But probably a lot less user friendly than the Omega!

I hope you get a prompt response.

The second link I posted is a gadget that can be set up to give a real-time display of your overall consumption, including power factor. I though it could answer your concerns about the PF value at your property. It is only £18.

Best regards

I will now look at the links which you so kindly supplied, because the Omega continuous current monitor which I was looking at is not suitable for my needs (it has a memory capacity equal, at the highest sampling rate (once per second), to only about 9 hours' connection time, after which it switches off, and, as regards battery life, it can't, as it stands, be run from a mains-powered UPS,

And, it appears, it does not have CE approval so can't legally be sold in the UK - until there is a post-Brexit British Standard drawn up for the compliance to which it can be approved.

I was surprised by this, because, as with so much which was supposed to be part of "our own sovereignty" post-Brexit, I was under the impression that the UK was still recognising CE compliance, at least for devices which already have it.

I did have to ring Omega to discuss this monitor, but the technical man, Alex, was so pleasant and (within reason) helpful, that I did not grumble about not having had a reply to my message.

 

[Avo Mk8]

it does not have CE approval so can't legally be sold in the UK

It is possible the device does not fall under any Directives that require it to be CE marked.
It is battery powered (under 50V), so does not come under the LV Directive
It may be regarded as electromagnetically 'benign' so would not come under the EMC Directive,
Alternatively, like many electronic sub-assemblies, it may be for incorporation in an overall system, and thus be outside the scope of the CE Marking Directive itself.

With regard to post-Brexit arrangements, the process is in hand.


If UK manufacturers want to sell in Europe, they will still have to comply with EU CE marking procedures.
To sell in the UK they will from 2023 comply with UKCA marking procedure.
Until 2023, both schemes are valid in UK

 

[Lucien Nunes]

Is the following a correct layman's understanding of why apparent current is part of VA from the point of view of the supply capacity/main fuse?

No. First, there is no such thing as apparent current. The current is the current, There is apparent power which is the figure obtained by multiplying the current by the voltage and which makes up the full VA figure (not part of it.) Apparent power can be resolved into two parts for the purpose of analysis; real power delivered to the load, and reactive power which flows from source to load and back again every AC cycle. Reactive power flow to and from the source 'cancels out' because the current is out of phase with the voltage, but the current does not itself cancel out.

Any current that flows in the conductor, regardless of which way it is delivering power or how much of the power is real, causes voltage drop along the conductor that is in phase with the current. The phasing of the load voltage, which governs the real power, is unrelated.

 

[Carl Haworth]

No. First, there is no such thing as apparent current. The current is the current, There is apparent power which is the figure obtained by multiplying the current by the voltage and which makes up the full VA figure (not part of it.) Apparent power can be resolved into two parts for the purpose of analysis; real power delivered to the load, and reactive power which flows from source to load and back again every AC cycle. Reactive power flow to and from the source 'cancels out' because the current is out of phase with the voltage, but the current does not itself cancel out.

Any current that flows in the conductor, regardless of which way it is delivering power or how much of the power is real, causes voltage drop along the conductor that is in phase with the current. The phasing of the load voltage, which governs the real power, is unrelated.

That is a beautifully lucid (no pun intended!) explanation - and - indeed, I should not have used the term "current" with "apparent".

Now please excuse the following uneducated further questions, and suggested answers (I prepare to be shot down again!):-

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?

Is this because the work done to drive the meter by the total current is reduced by the effect of the out-of-phase current which lags by 90 degrees behind the total current?

 

[Carl Haworth]

It is possible the device does not fall under any Directives that require it to be CE marked.
It is battery powered (under 50V), so does not come under the LV Directive
It may be regarded as electromagnetically 'benign' so would not come under the EMC Directive,
Alternatively, like many electronic sub-assemblies, it may be for incorporation in an overall system, and thus be outside the scope of the CE Marking Directive itself.

With regard to post-Brexit arrangements, the process is in hand.
View attachment 94410

If UK manufacturers want to sell in Europe, they will still have to comply with EU CE marking procedures.
To sell in the UK they will from 2023 comply with UKCA marking procedure.
Until 2023, both schemes are valid in UK

 

[Carl Haworth]

No. First, there is no such thing as apparent current. The current is the current, There is apparent power which is the figure obtained by multiplying the current by the voltage and which makes up the full VA figure (not part of it.) Apparent power can be resolved into two parts for the purpose of analysis; real power delivered to the load, and reactive power which flows from source to load and back again every AC cycle. Reactive power flow to and from the source 'cancels out' because the current is out of phase with the voltage, but the current does not itself cancel out.

Any current that flows in the conductor, regardless of which way it is delivering power or how much of the power is real, causes voltage drop along the conductor that is in phase with the current. The phasing of the load voltage, which governs the real power, is unrelated.

That is a beautifully lucid (no pun intended!) explanation - and - indeed, I should not have used the term "current" with "apparent".

Now please excuse the following uneducated further questions, and suggested answers (I prepare to be shot down again!):-

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?

Is t

It is possible the device does not fall under any Directives that require it to be CE marked.
It is battery powered (under 50V), so does not come under the LV Directive
It may be regarded as electromagnetically 'benign' so would not come under the EMC Directive,
Alternatively, like many electronic sub-assemblies, it may be for incorporation in an overall system, and thus be outside the scope of the CE Marking Directive itself.

With regard to post-Brexit arrangements, the process is in hand.
View attachment 94410

If UK manufacturers want to sell in Europe, they will still have to comply with EU CE marking procedures.
To sell in the UK they will from 2023 comply with UKCA marking procedure.
Until 2023, both schemes are valid in UK

I knew vaguely about the above, so your neat diagram is useful. Many thanks!

Do I understand you correctly that CE approval is probably irrelevant to this device, anyway?

I'm merely curious about this, because the monitor is apparently on sale (at both Omega and Farnell), even though it seems not be what I should be buying!

The phone connection with the guy a Omega was not good, so he might have been referring to a different monitor, with a larger sampling memory, which he mentioned as one that they could not currently sell in the UK (or in the EU??).

But I pressed him on this block, and he seemed to be sure that it applied to the OM -DCVC. Seems odd, when it is for sale.

I've followed your two links. As far as I can tell, they show instantaneous data only, and do not display current etc over time in graphical form. Apologies if I have not understood correctly.

My energy company's website has some wordy (but not very worthy!) pages on its smart meter, but betrays little of of what this can and can't do beyond what most informed people already know. I'm reluctant to ask for full technical details because (a) the customer service staff seem to know only about supplying and charging for electricity, and (b) I don't want to unleash the remotest risk of my home's frontage being excavated to fit a new single-phase supply, probably with a lower amperage main fuse., all to leave me with a downgraded version of my existing supply, and a meter which does not provide a key thing that I want - only to have to repeat the exercise in a few years' time to install 3-phase!

in any case, it seems highly unlikely that a smart meter would have a memory to hold several months' record of current consumption rates and which I could transfer to, and keep in, my PC

I suspect that the question "how much spare capacity is there in my supply at recorded peak instants" is going to be asked with increasing frequency if energy consumers want, or conclude that they are going to be obliged, to switch to all-electricity from gas. Ideas floated by our government about first mixing 20% H2 with NG and eventually moving to all-H2 may prove impossible to realize for cost reasons (eg, replacing mild steel pipelines with ones of a steel resistant to H2, and/or no prospect of being able to manufacture enough "green" H2, and so on). And the net-zero date, to which the UK has signed up, looms!

So I suspect that interest will soonbe awakened fairly widely - among suppliers of electrically-powered heat-generating equipment, if not consumers - in being able to work out how much extra load a given single-phase installation can safely stand, and whether an expensive upgrade to 3-phase is needed (and if this would be enough).

 

[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 Hub Kit - Efergy

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