Hi,
As I understand it CT clamps are used to monitor the power being used in the property and the charger is limited if the current drawn gets close to the incoming fuse rating 60, 80 or 100A. They are slso used to monitor solar so that the car is charged only using that.

 

I think it depends on if you plan to take advantage of the OLEV / OZEV grant for the charger install.

If you do then you need to fit a CT and have internet connectivity. If you are not claiming the grant you definitely do not need the connectivity, and I don't think you need the CT.

AFAIK the Zappi can use Harvi as its CT without needing a hub - the hub is only required for internet connectivity and to be able to use the MyEnergi app.

 

I think it depends on if you plan to take advantage of the OLEV / OZEV grant for the charger install.

If you do then you need to fit a CT and have internet connectivity.

Why do you need a CT clamp for the OZEV (neé OLEV) grant? The OP may need one to restrict the total load but that's a different issue. OZEV have an obsession with "smart" but that's for different reasons.

 

Thanks for the replies. I intend to claim the OLEV grant and I would need the app to schedule charge times. Ideally the Hive charger would allow the CT clamps to talk to the Hive hub but there doesn’t seem to be much detail about the Hive charger.

 

Ok, so to claim the grant and use the MyEnergi app you would need a Harvi and a Hub. The Hub needs a power supply and a wired Ethernet connection. This is the system I have , and it works well for me.

I am not familiar with the Hive system or other alternatives, but there may well be options.

Bear in mind it may be easier to manage charge times in your car rather than in the charger (that is what I do with my VW, assume the Merc would be similar). On this basis you might be able to get a simple dumb charger installed without the grant for not much more (or possibly less) than an 'intelligent' charger with the grant.

 

I prefer the smart option so I can see exactly what it is costing me, this is partly a money saving exercise after all. Coincidentally I have been switched over to OctopusEnergy after my energy provider went down so would be looking to use their low off peak tariff. A little irritating having to get a hub as I have no spare ports on my Sky router so will need to get an Ethernet switch, that’ll be two more power connections behind the TV 🙄

 

So do you actually need the CT clamp installed? Do some installers just leave off any CT clamps from the installation?

 

It's only required when the current drawn by the car could take the theoretical total drawn by the house above the limit imposed by the supply fuse. You really need to get a decent charge point installer to advise as the calculation involves looking at all of the other electrical loads in the house, applying diversity where appropriate, and finding out what the incoming limit is, what fuse is actually fitted, and possibly negotiating with the DNO to get it raised.

 

It’s not a requirement but is advisable. If you’ve got electric shower/big oven/hob/Outbuildings it all adds towards the load so a bit of thought has to go into maximum demand.
I’ve done a couple without CT clamps but now I’ll always put them in unless it was impossible. The last thing you want to tell a customer is ‘make sure you don’t have a shower whilst your charger is on and someone is cooking the dinner’.

 

Yeah, got electric showers, two ovens and induction job. The car will mostly be charged overnight but I’m edging towards the Zappi as this has the Harvi wireless CT clamps.

 

Have you got the Zappi and Harvi ? and how's it performing?
Thanks

 

My property has an 100 amp cutout and we never go anywhere near the current load. We charge off peak 32amp, night load on house 1 amp so no ct (current transformer) no problem due to diversity. My sister has an 60 amp cutout and she chargers during the day sometimes, so she has a ct.

 

Having a 100A main fuse does not mean that you have a supply capable of delivering 100A for any length of time, though. The highest capacity domestic single phase supply, that will have a 100A main fuse protecting the incoming cable, is 15kVA. This is why there is a need for load management, as 15kVA equates to about 65A, the default load management current for modern charge points with a CT.

More significantly, the local LV distribution transformer will most likely only be able to supply around 5kVA per home continuously, perhaps less, as it relies on demand diversity at the LV grid level to remain within it's thermal limit. We're a reasonable example, along with 21 other homes we are fed from a 100kVA PMT. Some simple arithmetic shows that 22 homes supplied by a 100kVA transformer should only have about 4.5kVA per home. Yet we have a supply rated at 15kVA. The reason this works is LV network diversity, the system relies on not every home drawing a lot of current at the same time, or for long periods of time. This is the issue with EV charging, it involves both drawing a high current and over a long period of time, so causing the diversity allowances used by the DNOs for determining capacity to fall over.

 

There is no way the grid can limit your load except by dropping the voltage, therefore your load can be anything you put on it until cutout falls over. As consumers we do not worry about load. The grid have to manage it. Drop voltage drop load.

 

It's not about doing the impossible like that, it's about limiting the charge point max advertised current to keep the total demand of the installation within a limit. That's what the CT does, it gives the charge point the total load at the incoming supply to the installation and the charge point can then change the Control Pilot advertised current to the charger in the car in order to force it to lower the charge current if needed. This is very easy as it's just an SMPS, so it can very easily just modulate down the current to the HV battery..