UK Load in Amps on a mains single-phase circuit

[Carl Haworth]

While you are concentrating on the heating output and trying to achieve something similar to what you have now in the future you have to bear in mind a lot of the newer technologies rely on an increased level of property insulation to deliver the most effective results
I was always a bit sceptical of the passivhaus building methods until I got involved in a project that a local vet was building, he is very into the eco concept and built a new surgery to passivhaus spec with heat recovery, ASHP, solar panels and masses of insulation, the end result is very effective and costs very little to run but it does involve more cost. One of this guy's other projects was renovating his own house Low Energy Building Consultancy | Kingsleypassivhaus | Frodsham - https://www.kingsleypassivehouse.com/ it might seem a bit extreme but with the ever rising energy costs it has to be an option

Several vectors have been generated by my original innocent question of whether the maximum current load on a domestic circuit, in relation to the maximum amperage limit (or 80% of that) of the supply, should be calculated on from the peak use in kW (dividing Watts by the supply voltage), or, if there is reason to consider the particular installation to have a power factor of less than 1, in kVA (finding the higher amount of Amps from this in the same way).

I still don't have an answer to that question, but I have had several "non-answers" which are very interesting.

Your intervention is among these vectors.

We don't want to rebuild, or move, but we do accept that the already well-above-average performance of our 1968 house could be further improved. You imply that this should not necessarily be done only if clearly cost-effective over a reasonable term. We are prepared to look at this, although we do not see at present how this house could be made substantially more suitable for our needs, even with major disruption.

But we will look at the website whose address you have provided. Many thanks!

RE YOUR FIRST WORDS ABOVE

My original question to members of this website arose from the task I had set myself of trying realistically to assess how many extra Amps could be absorbed safely by our existing single-phase 23 kVA mains circuit.

That was with the view of trying to establish:-

What extra electrical load would be involved by replacing by electrical appliances our gas boiler, a gas convector heater in our lean-to utility room (this heater may no longer be strictly necessary due to substantial improvements to the insulation of that room post-dating the addition of the heater in 1997), and our venerable but brilliant Cannon gas cooker (with fold-way high level grille/rotisserie: 5.275 kW, but that will be the energy input figure).

Additionally I would need to take into account that an electric c.h. boiler, replicating the 22 kW output of our gas boiler, would need 3-phase current. This, according to our DNO, would reduce the kVA of the single-phase input from 23 to 18.4. Not good news!

I know our typical annual gas consumption over enough years to have a realistic estimate of it for one year.

With the well authenticated figure of 76% for the output of our gas boiler in relation to its 28 kW input, I used, as you noticed, the same rating (22 kW to be on the safe side) for a proposed electric boiler.

I have now been struck by how much greater is the annual requirement for kVA if we went "all-electric" than it shows when adding our current consumptions (in kVA for present single-phase installation to our gas consumption.

I estimated consumptions for the three appliances which would be replaced, and added these to our current single-phase consumption in kVA. I calculated the consumptions of the replacement electric appliances, with use periods and levels of power drawn to match what I estimate applies now to our mixed installation.

The total known annual consumption of gas as useful energy is around 20,000 kWh.

But I found it impossible to arrive at a figure as low as 20,000 kWh/pa for the present boiler alone with what seems to be its work pattern Modifying this pattern to produce a suitable figure (well below 20,000 because I have to include figures for the heater and cooker) have made it pretty clear that the present boiler is too powerful for our 2019-21 needs, even if was only slightly OTT when specified and fitted in 1997.

In fact, it looks as if we need only about a 15 kW boiler, or even less. Interestingly, our local service man spontaneously declared last year, when he serviced the boiler, and changed the gas valve (the only major component that this boiler has ever needed - apart from flue fans, which I can fit legally myself, that 15 kW was "quite enough for a house of this size and kind".

So we'll try to find someone qualified in energy assessment to produce a heat requirement for our home before I do much more work on my forecast.

 

[plugsandsparks]

The hot gas recovery is currently piped just to DHW cct. The tank temp of 74 is measured half way down the tank. The pump that failed is used to circulate around the DHW circuit. Even when the tank is not calling for heat the hot gas recovery is so strong it conducts through the pipework. As mentioned its an issue that is ongoing.

You asked a question re-KVA loads etc etc . I cannot work out what you are trying to work out but FWIW.

Take your heat loss for the house, add a portion of your DHW demand, based on heat exchanger capacity and usage / now many people are in the house, this will give a base demand in KW, lets say its 24KW.
If you use a heat pump at 50 degrees, check the COP for the heat pump at 50 degrees against various environmental conditions, so lets say use a COP of 3. Divide your 24KW by 3, this gives 8KW, lets say PF is 0.9, then your KVA for your heat pump is 8 divided by 0.9 = 8.9KVA Nett. If using a TP supply then this will draw approx 15A. If on a single phased supply it will be approx 40A.

Now of course you need to find a specific heat pump that has a small excess above your worst case heat demand of 24KW, this could be a 30KW heat pump, whatever it is you can proportion the above figures accordingly or simply choose the heat pump and look at the manufacturers data for max current draw .

The ground loops were designed by the manufacturer so again you need to talk to them.

Heat pumps can be quite simple and output direct to radiators or UFH, you can use mixers to ensure the temp around the rads or UFH are to the designed temp, e.g. 40 degrees for UFH and 50 for rads.

Buffer tanks are used in more complicated systems when the demand can be very variable and it stops the heat pump cycling on low demand and can give a more immediate response to sudden high demand

 

[Carl Haworth]

The hot gas recovery is currently piped just to DHW cct. The tank temp of 74 is measured half way down the tank. The pump that failed is used to circulate around the DHW circuit. Even when the tank is not calling for heat the hot gas recovery is so strong it conducts through the pipework. As mentioned its an issue that is ongoing.

You asked a question re-KVA loads etc etc . I cannot work out what you are trying to work out but FWIW.

Take your heat loss for the house, add a portion of your DHW demand, based on heat exchanger capacity and usage / now many people are in the house, this will give a base demand in KW, lets say its 24KW.
If you use a heat pump at 50 degrees, check the COP for the heat pump at 50 degrees against various environmental conditions, so lets say use a COP of 3. Divide your 24KW by 3, this gives 8KW, lets say PF is 0.9, then your KVA for your heat pump is 8 divided by 0.9 = 8.9KVA Nett. If using a TP supply then this will draw approx 15A. If on a single phased supply it will be approx 40A.

Now of course you need to find a specific heat pump that has a small excess above your worst case heat demand of 24KW, this could be a 30KW heat pump, whatever it is you can proportion the above figures accordingly or simply choose the heat pump and look at the manufacturers data for max current draw .

The ground loops were designed by the manufacturer so again you need to talk to them.

Heat pumps can be quite simple and output direct to radiators or UFH, you can use mixers to ensure the temp around the rads or UFH are to the designed temp, e.g. 40 degrees for UFH and 50 for rads.

Buffer tanks are used in more complicated systems when the demand can be very variable and it stops the heat pump cycling on low demand and can give a more immediate response to sudden high demand

My original question posted on this website is ("is" because it hasn't been answered! yet!):-

I need to be able to compare the present peak load of my single-phase circuits with the capacity of the supply (80 Amps. at 80% of the maximum supply capacity of 100 Amps), in order to see how much "headroom" there is for additional single-phase appliances needed if we change our fuel from the present combination of electricity and gas to electricity only.

I know what my present load is in kWh per year, so I can divide that figure by 365 and then 24 in order to find the load per hour. From this, I can estimate likely peak loads.

However, should I be calculating the load in Amperes obtained from the consumption recorded by the domestic meter, if the installation operates, which seems very likely, at a power factor of less than 1? If I need to take p.f. into account I must calculate the load as kVA (real current plus apparent current), and find the Amps from that figure.

For example, if my annual consumption is 4,500 kWh, at p.f. 0.8 the consumption of real plus apparent current is 4,500/0.8, which is 5,625kVA.

The current for 4,500 kWh at 230 Volts over 1 hour (divide by 230 x 365 x 24 and multiply by 1,000) is 2.233 Ah.

For 5,625kVA it is 2.79 Ah.

If I quadruple the mean Amps to estimate peak instantaneous current, we have 9.32 Amps where the base unit of power is the kW. and 11.166 Amps where it is the kVA

This difference between 9.32 and 11 66 Amps is immaterial on my present consumption.

But if I want to increase the load on this circuit by adding new appliances with a total load of 16.250 kW and p.f. 1, I have to add (16,250/230) Amps:. That gives 70.652 Amps as a possible extra peak load.

Adding this to:-

9.32 Amps, where the base unit for the existing consumption is the kW, gives a total instantaneous load of (9.32 + 70.65) 79.97 Amps, which is within 80% of the maximum capacity of the 100 Amp maximum supply.

But adding it to:-

11.166 Amps. where the base unit for the existing consumption is the kVA because the installation is estimated to operate at power factor 0.8, and because current loads have to include apparent as well as real current. This gives a total instantaneous load of (11.166 + 70,65 Amps) 81.82 Amp, which exceeds 80% of the capacity of the 100 Amp maximum supply.

So it makes what can be a very significant difference to establishing what peak current can be added to an existing installation if the current load on the supply has be calculated including apparent current, where the current installation operates at a power factor of less than 1, compared with assuming that the p.f of the installation is 1, where kW and kVA have the same value.

SIZE OF PIT FOR THE GROUND CIRCUIT OF A GIVEN GSHP

What firm do you suggest that I contact?

You are right that I need to establish the heat energy requirement for our house. 22 kW was calculated by the firm that installed the present boiler in 1997, converted gravity DHW heating to pumped, and modernised and slightly extended the original twin single pipe circuits by putting some radiators onto two-pipe.

This house had had cavity wall insulation injected by its previous owner in 1972 (I have the certificate). The U value of the cavity walls was already much better than average due to the use of lightweight (aerated) blocks for the inner leaf of these walls, and for internal partition walls.

Loft insulation was vestigial. We upgraded most of the windows to double glazing before 1997. But, since then, we have had much better high-performance Upvc double glazing installed throughout and have greatly improved the loft insulation to a standard where it has a performance similar to that of 300 mm mineral fibre blanket laid on the top of the upstairs ceilings.

In 1998 we added large and well insulated porch, giving us a direct route to the forward section of the garage, and separated the back section of the garage from the boiler/utility room, which opens into it, by a very substantial double-skinned-with-cavity partition (this created a workshop/utility extension room, leaving a large garage forward of it)

The very large flat roof area covering porch, garage, workshop and the main utility room was re-roofed in 1998 using insulated boarding.

Between 1997 and 2004 I completed the modernisation of the radiator circuits which had been started in 1997.,but left as "hybrid pipework".

So the heat requirement of the house should be considerably lower now than the 22 kW which was calculated (rather generously, I suspect) in 1997.

We had our boiler serviced last October. The service man (who, as usual, is always looking for the opportunity to change an "old" boiler") commented that he thought our existing boiler far too powerful for our house (as far as he knew anything about it!). He considered that we should not need more than about 15 kW.

He may be right, and the requirement is probably a lot lower than 22 now, but this needs establishing against a full U-value calculation for the house.

I intend either to do this calculation myself, or get it done by an energy assessor.

 

[James]

You should not be trying to calculate maximum demand by dividing daily consumption by 24 or any other period like a month or year.

for example if you have a 70A constant draw from a heat pump, a shower whilst boiling the kettle or cooking dinner could blow the main fuse even though your daily average will be well below the maximum available supply.

 

[Carl Haworth]

You should not be trying to calculate maximum demand by dividing daily consumption by 24 or any other period like a month or year.

for example if you have a 70A constant draw from a heat pump, a shower whilst boiling the kettle or cooking dinner could blow the main fuse even though your daily average will be well below the maximum available supply.

Thanks!

I do realise this. I gave notional peak consumptions to highlight the issue raised by my original question posted on this website, which has not been answered (yet).

I will probably eventually monitor consumption over at least a year, using a current monitor which plots a graph, and whose output can be connected to my PC. The monitor will probably have to be re-set after its maximum run time, but I think that I will end up with a series of graphs stored on my PC, each for a period of well under a year. and which, even if they are not absolutely contiguous at the joins, should tell me what I need to know

If you know of a neater and quicker way of doing this, do please tell me.

Can you also answer my kW/kVA question?

 

[Avo Mk8]

I'm not able to answer your question I'm afraid, but have a comment or two:

You mention assuming a PF of 0.8 in your calculations.
I think it's most unlikely the PF would be as low as 0.8. Reports on the interweb (therefore must be true ) suggest a typical UK domestic figure for a household of around 0.95.

For a modest outlay you could purchase a meter to find the current position (sorry!) - just an example below:
(there are many cheap direct reading displays, but most seem to have a current transformer that is a rigid toroid, so cannot be placed on incoming tail - maybe through design!)

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

AC Digital Multimeter Ammeter Voltmeter 80-260V Current Transformer LCD Display | eBay

Excellent Visual Experience - The LCD HD display screen, combined with the backlight function, makes it easy to read the displayed data, giving you an excellent visual experience. Monitor AC circuits more comprehensively!

www.ebay.co.uk

If you have a smart meter, depending on the model, you may find sequencing through the displays shows not only the usual kWh, but kVArh as well, in which case you could work out PF from that.

 

[Carl Haworth]

I'm not able to answer your question I'm afraid, but have a comment or two:

You mention assuming a PF of 0.8 in your calculations.
I think it's most unlikely the PF would be as low as 0.8. Reports on the interweb (therefore must be true ) suggest a typical UK domestic figure for a household of around 0.95.

For a modest outlay you could purchase a meter to find the current position (sorry!) - just an example below:
(there are many cheap direct reading displays, but most seem to have a current transformer that is a rigid toroid, so cannot be placed on incoming tail - maybe through design!)

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

PEACEFAIR 100A Multi-function Meter Voltage Current Power Factor Frequency Energy Tester physical parameters(1*Meter+ 1*open type CT) : Amazon.co.uk: DIY & Tools

www.amazon.co.uk

AC Digital Multimeter Ammeter Voltmeter 80-260V Current Transformer LCD Display | eBay

Excellent Visual Experience - The LCD HD display screen, combined with the backlight function, makes it easy to read the displayed data, giving you an excellent visual experience. Monitor AC circuits more comprehensively!

www.ebay.co.uk

If you have a smart meter, depending on the model, you may find sequencing through the displays shows not only the usual kWh, but kVArh as well, in which case you could work out PF from that.

Thanks!

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).

However, your suggestion of 0.95 p.f. for a typical domestic installation is not only less pessimistic than my 0.80, but may be more realistic. If the latter, it makes it less critically important to know whether I should be working in kW or kVA!

I will ask Octopus Energy about the Smart meter that they say they want me to agree to have. I would normally resist this to the wire (sorry!), because I fear large and disruptive implications (eg, meter position, and so on) for an installation like ours. I suppose(!) that we wouldn't have to meet the cost of replacing the supply over a distance of around 8 metres under our drive in order to bring it to a new, external meter box, but we would be left with a load of fall-out as regards "making good".

It would be crazy to get involved in this unless we were installing 3-phase at the same time. And we're certainly not ready to make a decision on this at the moment. In any case, if our DNO means what they say, our supply amperage would be reduced to 80 Amps per phase, rather than the present 100 Amps of our single-phase, so we'd be obliged to have whatever form of electrically powered heating we might decide on (when we are ready!) on 3-phase. New large loads would be needed for the single phase, which would be at (safe level) 80% of 80% the present capacity (64 Amps).

CURRENT MONITOR

Many thanks for the links, which I will follow.

I'm already investigating a monitor: Omega OM-DCEV. This uses two clamps on the phase wire:-

https://uk.farnell.com/omega/om-dvcv/data-logger-ac-voltage-current/dp/3410288?gclid=EAIaIQobChMIrJaL9uTP9QIV2MLVCh22wQyYEAQYAiABEgIMBfD_BwE&mckv=_dc|pcrid|565467377247|plid||kword||match||slid||product|3410288|pgrid|125527087130|ptaid|pla-301834726710|&CMP=KNC-GUK-GEN-SHOPPING-SMART-EDMIUMROAS-Test821&gross_price=true#anchorTechnicalDOCS

Do you have any knowledge of this monitor?

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?

_ With a PSU replacing its AAA batteries, has it enough memory to log current over a year, or will it have to removed at intervals (what intervals?) to transfer the data collected to date to my PC, and then be replaced and re-started.

I'm hoping for an answer! (I'm sure you know the feeling!)

Best wishes,

Carl





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[plugsandsparks]

Fuse responds to the VA load, real and apparent

 

[Carl Haworth]

Fuse responds to the VA load, real and apparent

 

[Carl Haworth]

Thanks very much - as I feared!

However, AVO 8 MKO (hope i've got that right) considers that 0.95 is a more realistic p.f. for a domestic installation than 0.60, so the difference between the two narrows considerably!

Whew!