Calculating the maximum demand of a single circuit is pretty straightforward, figuring out maximum demand for an entire installation is very tricky.
Even the official guidelines from industry bodies state that it's difficult to find maximum demand accurately. This might be the reason why when you follow the official guidance you sometimes get a really high figure.
In this video Joe Robinson discusses some of the problems with calculating maximum demand and shows how different approaches can give you different values for the same installation.
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🕐 Chapters 🕕
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00:00 Are you calculating maximum demand properly?
00:13 Full free CPD Module on Circuit Protection: 👉 training.efixx.co.uk/course/c...
00:22 Double stacking consumer units, will they increase maximum demand?
00:40 Practical experiment on maximum demand.
01:16 What's in the real world installation?
01:30 How to calculate maximum demand using traditional guidance.
02:01 Calculating maximum demand on circuits not connected to fixed loads.
02:51 A change to calculating maximum demand for lighting circuits.
03:53 Should small loads be included in maximum demand calculations?
04:15 Cooking appliances and how they affect maximum demand.
05:00 How do you factor socket circuits into maximum demand?
05:14 Bringing diversity into play on our calculation.
07:18 Finally arriving at socket circuits for maximum demand.
08:14 The maximum demand figure for this three bedroom property.
08:29 What are the actual measured figures for this property?
09:17 Why is the calculated value so different to the measured value?
10:08 The IET Design Guide 'fesses up!
10:19 An interesting alternative method to calculate maximum demand.
11:04 What difference does the alternative method make for our installation?
11:29 Can we use any other methods?
11:53 Next video in the series: 👉 • How Can You Protect Me...
12:01 Full free CPD Module on Circuit Protection: 👉 training.efixx.co.uk/course/c...
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❌ This content on this channel is for electrical professionals.❌ ==================================
📹 Presented by
Joe Robinson - Technical Editor
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#electricaldesign #electricians #electricalinstallation
Doing my AM2 in 3 weeks, so brushing up on as much info as possible. Efixx are the greatest! Thanks guys
Thanks Matthew, best of luck!
Good luck...
Also I've been told by DNO workers if sticker says 100amps, the standard is a 80 amp fuse and stickers not always correct
The point about maximum demand is about what "could" be being drawn not what actually is being drawn. A house with 12 rooms would likely be calculated to have a maximum demand that is higher than a house with 6 rooms - but if both properties have the same number of occupants and same appliances the actual demand in that circumstance might be the same - but what if the owner of the 12 room house sells it to a large family - the actual demand would likely increase - the electrical installation must still be able to handle this safely. The demand calculations include lots of spare capacity for this reason - relying on actual usage isn't safe as actual usage changes with circumstances.
I have always used the second method in this video, and was even told by an NICEIC inspector that this was the preferred method
Clicked on this as I was curious how it was done there. I teach Code at a local college for apprentices and we do load calculations for homes in a far different way, and the only reason we do it is to determine the electrical service size (main breaker to feed the home) A massive difference we have is ALL lighting and general use "sockets" are simply calculated based on the square meter area of the home (5000w per 90m2, than 1000w for every additional 90m2 or portion of), Ovens, electric heating, electric car chargers all have specific requirements afterwards we add any other load over 1500w at 25% demand if an electric oven has been accounted for. quick and simple.
When I was in the trade many years ago, I discussed this with the NICEIC inspector, who said that the electricity boards, who had far more experience, rated domestic installations at 6 watts per square foot - far easier, and more accurate.
The Shelly 3EM can monitor three-phase current or single-phase current. The power supply for the device is on phase A. The newer Shelly PRO 3EM, on the other hand, is power supplied on phase C. The power clamp must be attached correctly. On the Shelly 3EM the arrow points from the fuses to the electricity meter. On the PRO 3EM the arrow points from the electricity meter to the fuses.
Very important to get the figures correct for a whole premise load as you don't want a burning smell as you shake hands with the Customer after completing your install
True, true.
Provided all load devices are appropriate to this should not happen. Nuisance tripping is more likely...
Brilliant information chaps. Im sure historically I have not been too far of declaring an installations max demand on an EIC certificate. Next video, could you provide details of a portable version of a data logging device, as I would use for sure.....a device such as this, if affordable and accurate too, would help me sleep better at night.............;)
When I first started did maximum demand once for a rewire on a 4 bed house, 4 rings, electric shower, electric cooker etc. Came out at like 96A, the fuse was only a 60A, called up DNO and asked them to upgrade the head to 100A, a specialist came out, I explained my maximum calculation via BS7671, the response was: "Nah its fine, we don't use that, tell you what if you ever blow the main fuse tell the guy that comes out that I said you can upgrade it to 80A, it will be fine".... What a waste of time..
Perhaps, but the practical application of experience is still a valuable commodity often overlooked in today's 'over educated', but mostly theory based electricians world...
@@dougle03 Yep exactly this, although I created 4 rings, Kitchen, Utility, upstairs and downstairs, originally it had just one ring for the whole house which had been fine for 60yrs, even though I increased the number of circuits does not mean I actually increased the load.
This topic is very important, please more calculation topics
Pro tip for calculation: lights -ignore. IT -ignore. -smoke -ignore. Number of socket circuits - ignore. Walk around the house and find all appliances that can create significant heat (at least 1000W) and will run for at least 30 minutes. Multiply by 10. Done.
But I've seen some places with well over 1kW computers.
@@lua-nya Residential.
@@lua-nya Yes 2 computers in my property are running on 1200watt power supplies but they're only normally running at 1000 watts each when their users are gaming. For 6 hours straight. Computers should be included.
As I’ve had a few issue’s now with AFDD’s “nuisance” tripping. Working as it should but certain items plugged in on one circuit don’t trip but on another circuit with some white goods, say fridge on once item plugged in the AFDD trips anywhere from 5-30secs. Should we (electricians) 1st fix to European radial circuits as AFDD’s were designed for said Euro circuits in the first place.
If I am doing a new build I do this but if I am doing an EICR I often will state 100A if a 100A fuse is fitted, 80/80 etc. One it's not possible to monitor when carrying out an EICR for a duration long enough to simulate a true load and 2 because the majority of properties are now having Heat Pumps or EV Chargers or both fitted the majority of the time we're spiking to 96 Amps in detached and semi detached properties. When designing from scratch I was taught 5 watts/ft or 80 watts/meter rather than relying on arbitrary loads, sadly this calculation now comes in well under what I am actually finding during testing.
What data logger did you use as I was thinking of getting the PEL 51 but over £1200
When calculating maximum demand should we include the mcb supplying surge protective device?
Nope
When Calculating the maximum demand for UK Power networks for 4 properties I used the 2nd method, only to be told by UK Power Networks that they work off 2kw Per Property, your 39A equates to roughly 9KW 🤔🤔
Interesting take on the subject. The guidance is to reach a max demand for the property, not for your living arrangements. Add an EV and a heat pump which is the direction of travel and you will see that demand is a critical calc.
But that demand calculation must be re-done when introducing large energy consumers that are only installed officially by competent persons...! Determining a demand that is far higher than practically needed increases costs in a way that's not necessary. the difference might be a property needing 3 phase or not. Actual use must factor into the equation or, as this video highlights, homes would need +100 amp incommers which in the UK at least is unlikely to be possible without significant additional costs... and all for an overzealous demand calculation... If additional high current consumers are introduced, then sure the demand calc should be reconsidered... Catering for tomorrow's' theoretical needs is today's expense; and it's a luxury most consumers would prefer not to indulge in...
it's amusing the 5A is still allowed for the socket outlet on a cooker control unit.... that was for a 1200w kettle back in the 50s!
Unsure how 82.66 A max demand was arrived at in the final Max demand calculation? I cant seem to quite get to that figure.
Even at that demand on the first calculation, the header fuse would take a ridiculous amount of time to blow. ~100,000 seconds according to the big brown book.
I think people underestimate just how much power 100a really is. You need to be doing something pretty abnormal to get anywhere close in a normal home.
🌱🪴🌱
Take the 39A he measured here, add 32-40A for an EV charger (his peak was just after getting home from work, so exactly when you would expect the car to be charging if you haven't set it to charge off peak) and maybe you jump in the shower while your partner is cooking dinner and suddenly you are getting very close to 100A. EV chargers change the calculation enormously.
Being able to use an alternative method if approved by a competent electrical design engineer is great, but how many people consult a competent electrical design engineer when adding an EV charger, which probably the most important time to be charging maximum demand?
Easy, we have 150% PV, And over 400% groups. My primary rail is limited to 40A per building while mid day 80A would be available. The 80A can flow, but never will there flow 80A on any rail here due to the way I've centered both solar-pv and grid supply.
I’ve managed 63A averaged over a half hour… that was an interesting night…
Dare we ask what you were up to? 🤔 Keep in mind it's a family show! 😂
@@efixx car charger (32A), Storage heater (10A), then the dishwasher, washing machine and tumble dryer (since replaced with a less inefficient model) all managed to spike at the same time. Along with the baseload of fridge/freezer and network gear. Note that other than the storage heater … there is no water or space heating. Heat pump definitely on the cards though. But nowadays most people should be able to look at smart meter data for an absolute peak, and a typical peak over the last n years.
@@JohnR31415That's basically the same as he was getting plus the EV charger (39A+32A would be 71A). EV chargers change everything.
@@JohnR31415 Plunge electric pricing is introducing all sorts of unusual loads into the average domestic electric arrangements. I've heard stories of people causing their main fuse to blow trying to use as much as possible during a plunge pricing event (Negative import rates for those that don't know)...
@@efixx Someone getting an electric shower while someone else is cooking a meal on an electric hob while the EV charges would easily get well past 63A.
Finally, i still ignore those recommendations. 30W LEDs😅
I remember the old electricity boards used to say 40A was what the average house was as a maximum demand.
A high power (> 10 kW) electric shower uses more than that. (OK, it only runs for a few minutes at a time). Add in cookers, immersion heaters,, heat pumps and electric car charging and we are heading for values about double that.
@@roberthuntley1090 I did mention that old electricity boards so don't know now but the supply still was 60,80 or 100 A
Ah calculating MD... my least favourite topic 😅 I recently was asked to come up with a figure for an install at a luxury leisure park, it has multiple 400A 3ph origins and I was going to be working on one of these. I started on the 225A sub-main feeding the site of the install and came to a figure of 75A spare after 2 days. When I mention that I have to carry out the same calculations for every sub-main on the origin I was told they were going to remove a 36kW heater from the spec and just go ahead blindly
I do this every day. Caravan parks are more challenging to work out max demand than any other installation.
🙏🙏🙏
Common method used by Housing Associations just looks at breakers: largest cct +40% of all other cct's. Quick and dirty.
The message I get from this is that there are too many desk jockeys sitting on their arses dreaming up ways of justifying their existence. I have a 10.3KW instantaneous electric shower and an 11.3KW electric hob, the chances of both of these being in use at the same time is ZERO! I have oil fired central heating (with immersion backup in the event of boiler failure - yet to happen after 21 years) which provides around 50 gallons per day of hot water, if the water runs out (very rare) I just switch on the boiler for an hour. Use common sense; if it is a 3-bedroom semi it is not going to need as much power as Buckingham Palace!
Yes, but now add a second person to the household. You come in from a run and get a shower while your partner is cooking the evening meal and boom both are in use at once.
Completely glossed over the fact that in one table for diversity for cooking appliance states, take first 10A and 30% of remaining current wheres the other table states, take 10A and 30% full load of appliance. Can anyone clear this up?
Could we solve this with one book that givesyou all the info you need.
ok, but it will be out of date at some point or will only offer technically specific information, predominantly applying to each level of electrical position. Designer/installer/Inspector or all 3. I think the book you desire would be twice as big as an old argos catalogue......;)
Add mcbs x 0.4
Yaaay first comment!
Well done you! 😃
If I use any of these methods on my own home the numbers are just bonkers. How can any methodology proposed by these (almost historic) documents be credible when they can end up overstating maximum demand by multiples of what the actual typical values are? Looking back this year I can find 8 kW as my peak load... for the whole house... in one 30 minute period. I have a double CU and a sub-panel CU and loads of circuits (20+ I think). Realistically the peak load for me is when exporting power at around 9.5 kWh - under 40 Amps at my supply voltage. I feel no need to count the over-provisioned wall sockets or the number of lamps. Add in the modern reality of the dishwasher, washing machine etc timed to run in the early hours (to take advantage of cheap rates) the 'latest' guides are just swept into irrelevancy.
Is it really acceptable for the main fuse to blow out just because it’s unlikely that you’d turn on the shower put a pan on all four hobs and crank both ovens, turn on the kettle and flick on the toaster and washing machine. Maybe you don’t do that, but the next person in your house might.
@@edc1569factor in the tripping curve on a BS1361 100A incomer is such that a 200A load passing through that fuse will take just over 30 minutes to trip. None of those loads with the exception of a constantly running water heater, eg the shower, will run at full power for more than 5-10 minutes before starting to cycle, or turn off having completed it's task.
Exporting power at 9.5kWh? Peak power of 8kW in 30 minutes? Hmmmm
Hmm, a very basic assessment and overview, given that most new household loads have significant Power Factors (meaning low); induction hobs, led lamps, heat pump compressors, EV charge points, to name a few, so therefore circuits need to be matched according to the PF adjusted current values, so a PF of 0.5 will require conductors to be sized at double the normal rating. I’m surprised the guidance makes little reference to PF adjustments in load currents, it seems to be somewhat out-of-date or written by people who don’t understand the topic or how modern property loads are evolving.
EV chargers (the actual charger is actually in the car, the charge point is just a fancy socket) have active power factor correction which gives it a power factor of 0.95+. This is the same for other things with significant load that also have switch mode power supplies such as your TV, laptop, pc, high power LED supplies, PV inverters, battery chargers etc. I’m pretty sure at least some heat pumps have this too
Regulations ensure there are very few high power devices with low power factor, even a crappy power factor cheap gu10 is still less than the old halogen lamp.
@@TheAviation101 eVSE’s have OF correction, I think your way off subject there. All compressors have non-unity PF. The EV charger will not have a unity PF, tend the Renault Clio as an example, it won’t start charging until the PF is above 0.8 and yet there are countless examples of where it won’t start charging, indicating that typical house loads are a cumulatively PF. Whatever, even modest PF values below unity should be taken into account even at 0.9 the actual load current t will be 10% higher, still whether do I know!
@@G6EJD I’m talking about the charger itself, not the house. Given it has active circuitry to correct the power factor (of the charger, not the house), the Renault Clio has a power factor of 0.96
How do you measure power factor?
what about an EV on top of this.
Load management via CTs etc to manage ev load when the rest of the property is using power.
This video makes very little sense. You talk about *maximum* demand (what you might have to contend with when *all* the high-current devices are on), so you have the capability of supplying them without failure (wiring and fusing). But then you're calculating some kind of average (assuming that not everything is on, or not running at full current). It's certainly NOT a given that someone won't be using an instant heating electric shower while someone else is using the electric stove and one or more hotplates, and electric room heaters are in use around the property. Not to mention that electric ovens of the old design, with simple resistive elements, are either using full current or next to none, as the thermostat cycles, rather than some variable power output inverter. They don't use variable amounts of current, when the heater is on, depending on what temperature you've set them to. If you *are* calculating *maximum* demand, then actually do so. Calculate the highest current that could reasonably be in use at the same time (the shower in use and the stove, a couple of hotplates, one or more room heaters). The average is, of course, going to be lower - the stove is on a thermostat, likewise for room heaters, which individually switch on and off at various times unrelated to each other. But they *can* all be on at full power at the same time. Overall, your electrical system needs to be able to cope with that (fusing and wiring). Our house failed in design to cope with real world situations, such as electric fan heaters running in two bedrooms (incidentally, that's already higher than the fuse rating for the sockets circuit), plus an electric kettle boiling, and the microwave oven at the same time. At some moment everything was drawing full current, and the fuse went. This is a 1965 house, with all wall sockets on one radial going around the house, on a 16 amp fuse. Yes, real fuses - and I prefer them, breakers can fail to break, a fuse wire *is* going to blow. And I don't hold truck with any arguments that some dimwit could put something other than one strand of the correct fuse wire in it. That isn't going to happen here. Anyway, people do force breakers on, and breaker switch parts can weld together, or simply fail to release. Properly wired fuses fail "safe," they don't not blow. But the house was never designed well. All the sockets on one fuse, and a house with no central heating. Of course you're going to run electric heaters in bedrooms, unless you like wrapping up like an Antarctic explorer to try and keep warm, while still breathing in chilly damp air. And most portable electric heaters are very high current devices. Power requirement calculations that aren't based on reality lead to this kind of stupid electrical design happening.
Great video. What it shows is that the maximum demand as shown needs quite a bit of updating. In a commercial premises I rewired there are 20 circuits. - each treatment room has a radial circuit - the lighting is separated across 4 circuits - emergency is on its own. - alarm - cctv - fire alarm Etc etc. on max demand traditionally it’s a huge amount, but in reality is nowhere near that and is far better for the customer because it offers better continuity of service in the event of a fault. And when testing in the future it’s easier to work around.