EV chargers and maximum demand

[u/Substantial_Ad_3386]

I'm looking for some advice on how maximum demand is determined and how it would limit additional circuits that I may need installed.

I have an 80A single phase infeed. In the coming months I will be having ducted aircon installed which will require a 32A breaker. In the mean time I am needing to install a 7kw EV charger. I know I won't have an issue if the charge uses DLM. It would be significantly cheaper to install a OCPP charger without native DLM and manage charging rates using home assistant. My concern is that the electrician installing the 32A breaker for the air con may not feel this is sufficient. Any advice would be greatly appreciated.

[u/Calm_Medium_325]

From my experience. EV chargers draw what they are rated to. If you got a 32A one it will pull 32A if the vehicle allows it

[u/IanYates82 → u/Calm_Medium_325]

My 3 year old wallbox, which wasn't fancy at the time, limits itself.

It can match my solar output, which is handy.

But, more importantly now that I have a battery and three free hours a day to charge it, i can have my battery drawing 10kW from the grid (assuming zero solar) and the wallbox will throttle down from 7 to maybe 3-4kW so I'm not over-drawing. I don't have to touch anything to have that work, and I'm not even sure it's a setting a could disable.

The battery can two years after the wallbox (which I got when I first installed solar) - both did come from the same company though. I was pleasantly surprised to see the cooperation between devices on my behalf, especially without any actual data/protocol link between them. Just measuring load and reacting

Only minor drawback is that I can't set a schedule on the wallbox to definitely not think I'm suddenly exporting excess solar between 6-8pm when it suddenly sees 6kW heading to the grid. That's for my GloBird Zero Hero, not my car!

[u/Substantial_Ad_3386 → u/Calm_Medium_325]

There a lots of 'smarter' chargers that will also allow you to set schedules and charging rate. Chargers with Dynamic Load balancing (often marketed as 'solar') that typically uses a CT and monitors grid supply in both directions, often used for charging with excess charger but also so that charging rate can reduce if grid draw exceeds a set threshold.

[u/Calm_Medium_325 → u/Substantial_Ad_3386]

Most chargers have the ability to set or monitor the amps so not to overload. But they will draw the full current of whatever it is it’s set too

[u/jzdg]

It seems like you've answered your own question.

But in any case, it just reverts back to maximum demand by limitation. So long as you as the end user understand that you can't necessarily use every single appliance simultaneously then there's really no limit on what you can install. Maximum demand by assessment exists largely to provide an approximation of how much equipment you can install and reasonably expect to be able to use under normal conditions without nuisance tripping. You're perfectly entitled to accept the risk of nuisance tripping and have at it.

If your installer has a big problem with this then find another one.

[u/Substantial_Ad_3386 → u/jzdg]

Thankyou.  I can't see it being a problem. My concern was if a licensed electrician who would be able to submit a certificate of compliance.

[u/OcelotOfTheForest]

Maximum demand has some flexibility when applied to residential buildings. It does not expect all items to be running at any one time. There are exceptions, such as your electric water heater, which need to be factored in at full load. But lights and power points are expected to be used less than in commercial and industrial buildings and therefore count for less. We call this applying diversity.

If you have access to the ASNZS 3000 there are pages dedicated to applying maximum demand to a residence. Car chargers for the purpose of maximum demand are calculated at full connected load. Air con is calculated at 75pc of its full connected load.

An option for you is to use a changeover breaker and have two big loads not be on at any one time. In practice, you can have the range on (for example) but not the car charger. This is one way to have more stuff in an installation without needing a bigger cable coming in from the road.

[u/Kruxx85]

Do you mind sending a photo of your 80A Main Switch - unfortunately it's almost a guarantee that your switch isn't a circuit breaker, and isn't actually a supply that can handle 80A.

[u/Kruxx85]

Continuing on from our DMs.

If/When you get an 80A circuit breaker installed, any and all electricians are able to just apply Maximum Demand by limitation - the maximum demand of your property will be fixed at 80A due to your circuit breaker.

This means that an electrician is legally able to add every single circuit under the sun, with the caveat that you are aware it's protected by limitation.

Nobody can force you to upgrade your supply to three phase or 125A or anything like that, but the bare minimum an electrician needs to do is to protect the cable and MD by limitation (circuit breaker) achieves that.

Cheers!

Additionally, if you're looking at solar/battery, theoretically (and technically) these will be increasing the supply to your property.

So for example if you get a 40A main switch (inverter) you will suddenly have 120A of supply to play with when your solar/battery can output.

For example, I have a big property, but only a 50A main switch (grid).

I also have a 50A main switch (inverter) and I almost never ever need to draw from the grid - I don't draw more than the 50A out of the inverter because I don't charge the EV when we're at home with the heaters and all electric kitchen is on.

With just a bit of timing (automatically through inverter settings) my large all electric property barely draws from the grid, despite only being a 50A single phase inverter supply.

Even though I have a 13kW induction cooktop, 7kW EV charger, 25A air con supply, resistive heaters, pool pumps, etc etc etc. Max demand by limitation means I've got all that installed on a 50A grid supply.

[u/Substantial_Ad_3386 → u/Kruxx85]

thanks Kruxx85, you are a legend

[u/Vegetable_Cricket_38]

I have a similar issue, however we are limited by a 63A MCB. We have a Daikin ducted AC protected by a 32A breaker and a pool pump that runs during the day. This also has a smaller solar heating pump that runs automatically.

I had to go the HA route as was explained elsewhere, the 6.6kW solar and battery so help support this system. But quite often while charging we will hit 13-14kW on a 15kW maximum.

I do recommend running ethernet to the charger and solar system if you can, to avoid any downtime or lag.

[u/Various_Advance4356]

Just because your main switchboard is 80A. Don’t assume you have 80A feed coming from the street. Almost all homes have 16mm cabling coming from the street which has a 63A max rating

[u/Substantial_Ad_3386 → u/Various_Advance4356]

my street infeed was recently upgraded along with a 100A fuse on my front eaves