How To Calculate Your Maximum Demand

[@gordonpullan8336]

Brilliant. When my car charger was fitted 6 years ago the diversity calculation showed max power of 120amps. Not surprisingly the DNO 'blew a fuse'. The DNO then fitted a clamp to measure our actual consumption over a month and gave us permission to use the charger, but did not give us the results from their data logger. Since then we have had a 12kW heat pump fitted, which entailed some work by the DNO away from our property to improve the supply - again we were not told what this work was but there was something vague said about 'harmonics'. There was no charge to us. More recently we have had a smart meter installed, and even in the depths of winter with the heat pump at full bore and the car charging I have never seen consumption above 14kW (say 60 amps). We have a 100 amp fuse to our supply and I am very relaxed that we will never get anywhere that.

[@normanboyes4983]

Good video. This is analogous to Heat loss calculations, where we use theoretical values to calculate accurately and can easily be an overestimate of 30-50% - which then leads to installing larger boilers or heat pumps than are necessary - and then you have to live with the inefficiency. Real world data analysis has to be better than assumptions.

[@Candisa]

Here in Belgium the most common household connections are either 1x40A or 3x25A. I lived for years with a 1x40A connection before I started renovating my home. I didn't have a heatpump, but I did have an electric hob and an oven that was often used simultaneously, an electric hot water boiler, a washing machine and dryer, an electric space heater in the bathroom, a vintage stereo... I could have easily tripped the main breaker with all that stuff, but I never thought about how much I could run at the same time and I tripped that main breaker exactly once in 10 years during a diner party. Many people install heat pumps and car chargers over here without getting their connection upgraded. I personally got an upgrade to 3x32A, but I did that mainly for the 7+kW per phase, not for the 22kW in total.

[@Apym289]

Nice to see you back.

[@m1geo]

I'm sat here in my home, regularly hitting 90A loads. Cheap overnight EV tariffs like Octopus Go and Intelligent Octopus incentivse powering all the high load items together. It's common for me to have many of these on. EV charger, heatpump, tumble dryer, immersion heater, induction hob, home battery charging comes pretty close. The EV charger definitely backs off when the electric shower is on! I went around all the wiring with a FLIR camera to check for hot spots! 😂

[@pete_pump]

Another cracking episode. I was scrawny head about this only a few days ago. I have a heat pump, domestic battery, electric hob oven and 3kW car charger and highest 30 min average over past month was 6kW or 29 Amps. (Max at night whilst recharging domestic battery at 1.5kW and car at 2.5kW with heat pump running at about 1kW draw)

[@richardlewis5316]

I have watched your You Tube videos and now your hat has gone I understand your enthusiasm with heat pumps! I was a plumber for many years then MD of a large computer company so fairly versatile in my thinking. I have recently installed a heat pump which was scrapped but working and dovetailed it into my current combi boiler system with a simple heat exchanger. During the day the heat pump warms the water and radiators and if I want more heat in the house I switch off the heat pump and operate the combi by the thermostat.. Manual controls, no sensors apart from 'common sense! Works well and about £400 to install. In the summer I just use the combi for water so the heat pump is sleeping for 5 months!

[@HeatGeek]

The hat will come back late this year!

[@danoneill8751]

We used a clamp and looked at highest instant value in 3 months, we also looked at highest average over 30min period, and we tried turning everyhting on (had to do it in parts as it was so much). We have elec cookers, two big computers, a microwave, kettle, two power showers (11kw... each!) a heat pump and lots of lights etc. I got to 33kw and I dont think thats everything, thats 143A at 230v. However the highest the actual load hit was 18kw which lasted for 7mins ONCE. The next highest was 14kw and the highest 30min average was 9kw which happens 3 or 4 times a week and is when I'm cooking for about 20mins and the wife is in the shower for 10mins. Anyway, 14kw is 61A so very close to needing to notify. However... we are in the process of replacing the power showers to take feeds from our nice new tank fed from the heat pump and to get so high again we'd need to be cooking very vigorously at the same time as heating. I've worked out that in a 70% duty cycle from the heat pump then it can certainly be drawing about 4.5kw over any 30min period, and that leaves about 9kw for everything else. Even with two rings on the cooker, the oven and the microwave and kettle going, you still cant average 9kw over 30min unless you don't put a pan on the rings so that they just blast heat into the air, leave the oven door open and constantly empty and refill the kettle - if you are acutally heating food with those things, then even rampant cooking averaged just 4kw over 30mins, admittedly peaking at 10kw for the odd 30s. Anyway, data logging is enlightening and if you look at the IEE docs carefully, things like using the breaker values for a cooker are just stupid, unless you are heating your house with your cooker you cant max it out for 30mins!

[@vivhenderson8628]

Electric showers are the main problem where maximum demand is concerned. You can apply diversity to most circuits and you will never get any where near 80 or 100 amps But an electric shower can draw up to 40 amps which could cause potential problems if charging an EV or powering a heat pump.

[@HowsieBob]

Quality as always Adam. 👏

[@vandit83]

When I got my heatpump installed I got a survey by the DNO and they recommended a 3phase supply. But I feel it’s been a bit pointless as I don’t have a 3phase heatpump or battery system so it’s all working off one of the phases 🤷🏻‍♂️ I got 13kw demand when I had my car charging, battery charging and dishwasher on. But I don’t think the heatpump was on.

[@FatMise]

We've got a heat pump, EV, induction hob, solar battery storage (no gas at all, only electric in our house) and our max draw is 17.1 kW over the past year. This is using a Hildebrand Glow smart meter that sends live reads every 10 seconds, which I log using Home Assistant. The highest number it's logged over the past year is 17.1 kW, which is approx 75 A. We do, in fact, run lots of appliances (dishwasher, washing machine, tumble drier, dehumidifier) at the same time -- overnight on the cheap rate tariff, which is also when the EV and solar battery storage is set to charge. I also set the heat pump to a higher flow temperature during the cheap hours, so that I can "pre-heat" the home on the cheap rate. However, we're not using the induction hob at the same time as charging the EV, or boiling a kettle in the middle of the night, so that's a pretty hard cap on how much we would realistically draw at once. I think 75 A measured peak gives a good headroom vs the 100 A main breaker.

[@JP-zd8hm]

Similar situation, max has been 15kW, the big hitter out of everything is the EV charger

[@SolAce-nw2hf]

Correctly estimating a maximum load can be quite hard. Needs may change over time, so planning ahead for what you want to use and when you want to use it is always a good idea. A smart meter will give you some insight, but these often produce averages that are simply unusable. With peak loads, you can trigger a circuit breaker or worse, even if the average load isn't al that high. So make a spreadsheet with what is on your circuit breakers, and when you will use it. Try to use powerful appliances on solar power if you can. This will reduce the load on your grid connection. You can also spread their usage over the day or week and make this a habit, so you don't need to worry about losing power. And when you have a collection of power tools or other heavy appliances that should not run simultaneously, combine them on a dedicated circuit breaker, so the impact of a mistake is limited. Induction cooking tends to make only very short peak loads, but charging an EV takes very long. So that's the one to worry about if you also want to run an ASHP at the same time.

[@graemeross1998]

Running a car charger generally through the night 32A running heat pump max 25A

[@SolAce-nw2hf]

@@graemeross1998Car chargers in the Netherlanda generally use 11 kW (3x 16A). The newer heat pumps are now able to stay well below 16A providing you don't have a huge home.

[@kosiranze]

Not exactly a regular clamp meter, but a meter like shelly PRO EM series are quite affordable, connect to their cloud platform via WiFi (or completely locally to home assistant and similar) and offer readouts by up to a second resolution.

[@ianskeet]

Just used the smart meter calc. Looks like my highest load was 78amp on my 100amp supply. That's an EV, ASHP, Powerwall and a tiny bit of home use in the off-peak hours. Best not be cooking a Christmas dinner between 4 and 7am.

[@anthonydyer3939]

My Maximum demand = 50 amps. On the Zappi charger you can throttle the current flow to the car in order to keep the grid import below a configured amount. So my house has a fuse cutout of unknown rated value. Therefore it’s assumed to be 60amps. It’s probably higher, but I don’t want to find out the hard way that it isn’t. At home in the winter time, it’s perfectly feasible for me to be running overnight: 32amps for car charger, 20 amps for the battery charging and 13 amps for the hot water heater without any current limitation. It’s easy for current to be flowing for over an hour at 63 amps. So by configuring a grid import limitation of 50amps on the Zappi charger, I’m confident the maximum demand can be configured rather than predicted. So adding a heat pump I hope should be easy. If I keep the hot water heater off, and any backup heater for the heat pump off, then I should simply substitute the existing hot water heater with the heat pump current draw.

[@blobstrom]

I still love the term Hoover for a vacuum cleaner. I wonder how many actually have a Hoover? My last Hoover product was a tumble dryer 🤣

[@philspiegel2476]

14.3kW was our peak demand at 02.00 on 17th Oct .a cold night ...5kW into a Powerwall and the remaining 9.3kW heating a 3kW immersion, 4kW Electric Boiler and probably some underfloor and miscellaneous [we are all electric with 3.2kWp solar since 2005 but with powerwall battery since June 2023 ... [OctopusFluximport 2-5am] Now, at least, we use almost all of what we generate 8-) PERHAPS the DNO/ max demand is of concern for immediately after a power cut...when interrupted devices and thermostatic heating will all turn on ( unless they are intelligent Dynamic Demand controlled devices ). Our peak time demand 16-19.00hrs is the opposite = zero with the 13.5kWh battery falling to 20% about 20.00hrs and dropping back to grid usage until after recharging again between 2-5.00hrs.

[@markrainford1219]

I'm an electrician and maximum demand, along with seventy five percent of the rest of the regs, are just an exercise in wasting ink.

[@Umski]

Pretty good breakdown - you missed electric showers - that could be make or break if you consider a 10kW shower may run for say 5 minutes, but if that kicked in with the oven, toaster, HP and charger it may take it over even with a 30 minute window from the smart meter - it's a judgement based on what the homeowner has and states they use...a clamp meter might be a good indication but ideally recording over a period of time would be better. I've monitored my use via Open Energy Monitor for over 10 years and the max peak was 4.5kW once when both ovens were on...realistically even with all the 13A plug-in stuff on, I doubt I could get to more than 20kW but that's without a HP or EV (yet)

[@MikeBookham]

I also have a Open Energy Monitor and a previous Christmas day I wondered high I could get the peak and with the EV charging, electric shower, kettle, espresso machine, double oven & electric hob as well as a multitude of other electric items concurrently on it peaked around 12kW.

[@Umski]

@@MikeBookham that's curious - how powerful is the shower and presumably the car charger is 7kW? Were the other loads cycling on/off on their thermostats e.g. ovens, hob? Conservatively, I'd total those loads to 7+10+2.2+2?+4+3? = 25ishkW which would be the 100A limit? if they were all drawing at the same time

[@MikeBookham]

@@Umski We no longer have an electric shower but it was around 9-10kW. Other than the EV charger & kettle the other items cut in and out, so it would be very rare for all to draw full power at the same time, especially with an induction hob & oven. Also I’ve just discovered (after the SD card corrupted a couple of weeks ago) that my EmonTx only samples the mains for 200ms every 10s, as it still runs the JeeLabs classic radio driver and not continuously so if there’s any draw during it’s ‘sleep’ period then that’s not captured. The new LPL radio drivers run in continuous mode so would capture all power consumption.

[@effervescence5664]

I have to do this every time for customers wanting to go full electric EVs/induction hobs/electric showers and heat pumps. Honestly most of the time it's better to just meter it for a couple of weeks in winter, or where possible in the summer and add 30% to summer value. I have come across many a property that have blown their main fuse due to engineers using diversity and not taking into account Christmas Day family gatherings. It's almost exclusively a Christmas call out. Not the best time to lose power especially in a bad winter, even more so when the DNO decides to charge for their call out.

[@Apym289]

Totally agree, if you ever want a worst case scenario, Christmas Day is the day.

[@MrKlawUK]

assuming overnight EV charging at 7kw + maybe some washing/dishwasher if you’re moving those to your off peak window - thats your likely max peak at night. Daytime if you have electric shower may be similar. Heat pump I wonder if there is value in having smart clamped sensors to control diversity? Although probably not necessary for most users

[@HenryOCarmichaelSmith]

I'm not sure you can use the smart meter data in the way you suggest to calculate maximum demand. It is showing KWh not KW. i.e. the amount of power consumed in a given amount of time and not necessarily the maximum amount of power you demanded from the grid at any given time. For example pulling 100A from the grid for 30 minutes and then zero amps for another 30 minutes will result in 50kwh energy used, but if you were to pull 50A for a full hour you'd still only use 50 KWh. The difference is in the first example you've blown the main fuse.

[@HeatGeek]

It’s an incredibly simple calculation to convert energy over time to power

[@HenryOCarmichaelSmith]

@@HeatGeek Put another way, a smart meter reading will only tell you how much energy you used in a given time. It won't tell you what the maximum load was during that time. Unrealistic example but hopefully you can understand my point here ..If you pulled 200A for 5 minutes and then blew the main fuse, what do you think the smart meter reading would be ? Clue, it's not 200KWh...

[@HeatGeek]

@@HenryOCarmichaelSmith that’s one of the main points of the video… a 1 second max demand is meaningless and useless

[@DuncanKEdinburgh]

Problem is, you don't know what people are going to plug in... Maybe Mr Homeowner gets carried away in Lidl one Saturday afternoon and comes home with a welder, a plasma cutter, and a couple of big fan heaters... Me, I've got 55A worth of storage heaters which all go from 0 to 100% simultaneously when my off-peak supply kicks in around 10:30pm. Fortunately I'm usually not having a shower whilst cooking dinner at that time.

[@paullongley1221]

Measuring consumption of washing machines and dishwashers is tricky as they’re only drawing max load for a random period in a couple of hours cycle, ie pump/spin+element and hitting maybe 15amps

[@gino2465]

Electric car chargers and heat pumps require a ena application. Properties need upgrading to 3 phase to allow more than one ev charger. Stop and think about all your cars in your family being charged at once. Most gas appliances will end and your home will be all electric. So max demand in most cases with homes on 80 amp supply would most likely be OK. Any more ev chargers may be an issue. Thinking ahead long term people will want 3 phase 22kw chargers over the 7.2 kW chargers we have now. So 3 phase is the solution for the future in my opinion.

[@deanchapple1]

Yep clear as mud!

[@TheBadoctopus]

Great video. Just a note to say induction hobs are potentially very high draw - mine is rated at 7.5 kW max, though running it at that for an hour would probably melt the kitchen.

[@SolAce-nw2hf]

I have a 11 kW 3 phase induction hob. It can draw a lot of power, but not for long without having to order take out 😂

[@TheBadoctopus]

@@SolAce-nw2hf wow, I expect you can smelt iron on that thing 😱

[@SolAce-nw2hf]

@@TheBadoctopus Not really. As impressive as 11 kW sounds, it's nothing compared to natural gas. Basically it's just a big 16A induction zone in the middle and two 8A zones on each side. It does go fast, but it will not burn your house down to ashes (unlike the first attempt at pancakes in boost mode).

[@LauraJim-nf5ef]

Great video. Somehow you translated kWh per half hour incorrectly (6:18) to kW but got the right A so all good :D :D

[@caterthun4853]

Think.. In France you pay a fixed yearly charge for your max demand. The higher max demand the more you pay. As a rule of thumb in UK 1kw is 3 amps

[@doakley1987]

No, 4 amps

[@pt6423]

When we had a car charger from Podpoint installed at 7kW, they insisted we had our incoming fuse upgraded to 100A. No upgrade, no charger !

[@HeatGeek]

They may have been correct..

[@Richardincancale]

6:16 How do you get 20 amps from 2.3 kW? Power is volts multiplied by amps so with a nominal 230 volts that gives 10 amps? Here in France our smart meters give 10 minute reading and also daily maximum which makes monitoring a bit easier. But supplies are usually 6, 9 or 12 kW, ie up to 45 amps, but this is generally fine for an all electric home, heat pump and EV charger.

[@HowardBurgess]

UK smart meters measure in half-hour periods. The max usage in one period was 2.3 kWh and hence 4.6 kWh for a whole hour. This is 4600/230=20A

[@Richardincancale]

@@HowardBurgessAh - makes sense

[@tagware]

Electric Shower 😮???

[@HowsieBob]

As Adam mentioned, each home is different. An immersion element😉

[@MarkoCosic]

Do you cook (hob) on gas?

[@HeatGeek]

Currently. You are supposed to recalc everytime you add a significant draw

[@yngndrw.]

Maximum demand calculation is an absolute mess, best thing is to measure IMO. Not "cheap", but the Fluke A3001 FC can log current over a long period of time. Our maximum demand came out to be 34A before the heat pump. (Which added 14.3A)

[@redshift3]

I reckon that lighting and appliances have become more efficient since the guidance documents were drafted

[@SolAce-nw2hf]

LED has changed everything. It is no longer a real factor. Televisions, fridges, dishwashers and dryers are also much more efficient, but they do add up. Microwaves, electric water heaters, induction hobs, electric ovens and coffee machines still have very high peak loads because there's no real way to improve on them. I'm not worried about ASHP systems as they have gotten very efficient.

[@mentality-monster]

What a ballache. Surely the easiest thing to do is in the first place buy a heat pump and car charger which are capable of reacting to house load. If the load spikes because an electric shower is running whilst someone is using the oven and four hobs simultaneously, the charger should stop charging the car for a bit and the heat pump should turn the heat down until the load drops to compensate. Must be simpler that all these shenanigans!

[@HeatGeek]

Yes. But your max d calc has to include those appliances anyway though for some strange reason

[@richardlewis5316]

You missed the highest individual wattage item - a 10.5kw shower.

[@jacko101]

I never iron my hair and blow dry my clothes at the same time! 😆

[@ef7480]

Residential 3 phase commeth....

[@AntonyWhite]

My Moixa energy manager has a decent resolution read of energy flow from grid, solar and battery to my house or car. No ASHP yet, that’ll be going in next summer now I’ve insulated properly. However, with everything drawing at the same time, I can get it up to 75A. I have a 100A supply though, so even with no diversity I have capacity, and I’ve insulated well enough to only need a 5kW ASHP, so I’m still just under the 100A even with that going full chat

[@yngndrw.]

You have to assume 60A, unless you contact the DNO and get confirmation from them. (Even if the sticker on the cutout says 100A.) The assumed rating is also less (30A) if it's an older cut-out)

[@yngndrw.]

Here's a document showing the various cut-out types and the assumed ratings: www.energynetworks.org/industry-hub/resource-library-old/low-carbon-technologies-cut-out-rating-guidance-to-electric-vehicle-or-heat-pump-installers.pdf

[@AntonyWhite]

@@yngndrw. I have previously confirmed that my service is 100A with my DNO

[@dbat3291]

I'd be more worried about flooding! If you have all that lot switched on to measure it you'd have to be an octopus!! My assumption is the measurement is based on what comes out of the supply from the grid how would having solar panels effect such calculations?

[@normanboyes4983]

It doesn’t because you are trying to determine maximum draw.

[@ecybernard-com]

The empoiria vue can log 1,2, or 3 phase for the mains plus 16 circuits for about $150 usb. Results on your phone or their website, and can be connect to home assistant.

[@yrification]

Firstly. Ask a qualified electrician. It’s a case by case basis. A 4 bed with an elderly couple in, isn’t the same as a 4 bed with a young family with 2 kids. Your video is relatively good, but I think details such as plugging all items in isn’t really necessary. A “downstairs socket circuit” is generally much higher usage than up, especially if the kitchen/utility isn’t on a separate circuit. I agree the guidance is dated but as you state it is just guidance, but I would strongly recommend a qualified person look at it or someone who has been informed by an ‘electrically skilled’ person. It is a hard subject to broach because in todays houses, there’s so many variables. Here’s one for you. Typically, no more than 20 Led downlights should be installed on 1 circuit in one location. This is because led lighting has a huge peak inrush for a fraction of a second and can cause nuisance tripping. A fine example of the variety of intricacies electricians come across.

[@HeatGeek]

I approached several electricians about this vid. There was not much help. Electricians have been doing our md calcs for years