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Discussion Starter · #1 ·
Hi,

Planning on getting an EV charger fitted to our home and had our electrician out in January to discuss. He's qualified for the installation work but we'll be his first install so it seems some of the bureaucracy is new to him.

I found the EV charging installation form on our DNO's website (WesternPower) which suggested we should have a load survey to correctly calculate the new maximum demand. The electrician came around and we did this together by turning on all the large electrical appliances in the house (range cooker with induction hob, kettle, underfloor heating in garage etc..) whilst the electrician read the load out from the clamped cable. Add 32A for the new EV charger and we were about 105A.

That meant an application to Western Power who came out and conducted a survey for upgrading us to three-phase for around £1,900.

My question is whether we've gone about this incorrectly... should/could we be looking at load limiting devices to avoid the need to go upgrade to three-phase or should the electrician have applied some diversity in those calculations which would have kept us below the 100A limit?

Or is it just better to have the three-phase upgrade? Many new houses around here seem to be built with three-phase anyway so is this a worthwhile investment?

Thanks,
Chris
 

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LEAF N-TEC 62KW
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Why do you need a 3phase supply?
A single phase supply is more than adequate for 32amp/7kw charger.
If you use one of the off peak tariffs, you won't have any issues with needing an uprated supply should it be limited to 60 or 80 amps.
 

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Hi,

Planning on getting an EV charger fitted to our home and had our electrician out in January to discuss. He's qualified for the installation work but we'll be his first install so it seems some of the bureaucracy is new to him.

I found the EV charging installation form on our DNO's website (WesternPower) which suggested we should have a load survey to correctly calculate the new maximum demand. The electrician came around and we did this together by turning on all the large electrical appliances in the house (range cooker with induction hob, kettle, underfloor heating in garage etc..) whilst the electrician read the load out from the clamped cable. Add 32A for the new EV charger and we were about 105A.

That meant an application to Western Power who came out and conducted a survey for upgrading us to three-phase for around £1,900.

My question is whether we've gone about this incorrectly... should/could we be looking at load limiting devices to avoid the need to go upgrade to three-phase or should the electrician have applied some diversity in those calculations which would have kept us below the 100A limit?

Or is it just better to have the three-phase upgrade? Many new houses around here seem to be built with three-phase anyway so is this a worthwhile investment?

Thanks,
Chris
My understanding is that the loading calculations should include diversity - see this thread for discussion about the approach 32A query on a 100A fuse board
 

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My understanding is that the loading calculations should include diversity - see this thread for discussion about the approach 32A query on a 100A fuse board
In the past this was the case. I have no idea whether the application of diversity calculations has been changed in recognition of the demands of EV charging. But even so, if the OP is charging his own vehicle, it's not too difficult to avoid using both shower and cooker at the same time and of course off peak tariffs are a much cheaper way to charger. (Octopus Go is 5p/kwh for 4hours - enough for my 7kw charger to add about 40% to my Leaf's 62kw battery at a cost of £1.20 compared to £3.25 during the day)
 

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When electricians assess the installation, they can apply diversity factors to the calculation. In simple terms, they look at the likelyhood that all devices in the home will be switched on all at once. Some loads can have diversity applied to them, others such as EVSE chargers cannot.

If you really want to know more about diversity then watch John Ward's video on the topic:

Your electrician should have already applied diversity rules where he could, but if you are at risk of going over the service head cutout limit, then it will almost certainly be cheaper to buy an EVSE charger box which can sense the load and throttle the car's charging current. I think that Zappi can do this, using a CT clamp around the main supply, but you are wise to check with them first.

Another option if you have say an electric shower which you know cannot run whilst the EVSE charger is running, then perhaps fit something like this:
which is a bit more clunky but still has its place in some installs.

All of which are likely to be cheaper than the DNO fitting 3-phase!
 

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Yes a changeover switch on the shower supply is a good way to avoid exceeding the supply limit.
 

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Discussion Starter · #9 ·
Thanks, I've spoken to another installer now who has recommended the Zappi unit with load limiting and so I'll explore this with them. The way I understand the comments above RE diversity suggests that you can apply it to calculating the existing MD in your home (I'm not going to turn everything on at once as you say) but when a car charger is added it of course needed to assume a full 32A draw in any MD calculations. Thanks
 

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If as an electrician if he can’t calculate maximum demand correctly I would walk away from using him.
A load survey on a house can be carried out using a clamp meter with a peak hold function over 24/48 hours. That’s far more realistic then turning every load on.
As others have suggested a charger with load limiting feature is probably your way forward.
 

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If you fit a changeover switch for the power shower, you might be in the middle of a 32A charge, then someone suddenly cuts the power to the car, whammo. Not a nice thing to do! Yes the kit should survive as it's no different to the grid suddenly stopping, but even so, you can expect induction surges etc inside the car's charger maybe. Contactors will open suddenly, while a large current is still flowing, so sparks will happen.

If you fit a Viridian EVSE, you can then add a resistor internally to tune the max current to anything between 6A (the minimum any EVSE runs at) and 32A. So if you're 5A over the limit, a small resistor of 590 Ohms connected across 2 terminals will reduce the max to 27A. Here's the link to the manual itself.
https://cdn.shopify.com/s/files/1/1...2.0_EPC_2.0_Manual_-_Iss_1.2.pdf?v=1592218842
and the website for Viridian is ecoHarmony
 

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The changeover switch / garo shower priority switch is clunky. If you make the EVSE the priority circuit, you would conciously have to disable EVSE charging to take a shower, preventing that unexpected loss of power to the car.

The better option is to dynamically adjust the EVSE permitted charge based on a CT readout, like Zappi. Most of the time the house wont be using all these other appliances at once and the EVSE can run at the full 32A, but if they do, the EVSE can throttle or halt its charging dynamically. The Viridian is not automatic, its a manual adjustment. I can see grid load monitoring being a selling point in more EVSEs in the future, where there is a reluctance by DNOs to fit larger service head fuses. Western Power already won't fit anything above an 80A fuse in a lot of cases without exceptional circumstances.
 
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