Current transformers

I haven't looked at the specs for the French system but from what you have said it sounds very sensible.

I did read the the SMETS2 spec and have concluded that it is a massive missed opportunity.  It was clearly written based on a very narrow set of requirements, purely around metering.  For example, there is no requirement for a SMETS2 meter to provide details of the current measured at all (only power and voltage but not not necessarily corresponding instantaneous values are available).  If we are going to install a digital current meter in every home, not providing any access to that data is quite frankly ridiculous.

To those who say "just install a separate shunt" then remember that this is a domestic setting with electricians used to working with domestic supplies.  I would be quite happy mounting a din rail Modbus based digital power meter in a suitable enclosure and wiring the necessary 25mm sq cable to it but (a) those are more high current connections which can potentially cause fire if poorly made, (b) making such an assembly is probably outside the (assessed) competence of most domestic electricians, (c) it takes up space and (d) it is extra unnecessary cost.

In the vast majority of cases, what needs to be measured (certainly in the clip on CT case) is the whole house load.

Are there any current green funding initiatives which rely on measuring what is generated rather than what is exported?  Historically, where measurement of generation has been required for subsidy purposes, the requirement has been for a meter where the accuracy / tamper resistance requirements preclude clip on CTs as part of the measurement arrangements.

Clip on CTs are generally used for load / export limiting rather than accurate metering.

SMETS2 meters will cope with export quite happily, which makes it all the more frustrating that the specifiers of those meters omitted the ability to avoid potentially dangerous CTs.

DShutt said:

In the vast majority of cases, what needs to be measured (certainly in the clip on CT case) is the whole house load.

That could be challenging when the power is coming into both ends of the busbar.

Isn't the requirement not to export until the battery is full, and not to import until it is empty. So the inverter balances the voltage so that there is no current in the consumer's tails until there is a surplus or none left respectively. It does not have to be as precise as a meter.

If you do not have a battery, is there any need for this monitoring?

DShutt said:

In the vast majority of cases, what needs to be measured (certainly in the clip on CT case) is the whole house load.

There are other installations than domestic.

DShutt said:

lip on CTs are generally used for load / export limiting rather than accurate metering.

load curtailment can be applied to a circuit ... or an installation.

I agree that in the case of domestic EV charging installations, where the existing demand is large, or the supplier might take some extensive period to uprate the fuse, the quick and easy method used is load curtailment.

Similarly, clip-on current transformers offer a quick and easy method for export limitation, and probably all that's needed for energy management.

DShutt said:

SMETS2 meters will cope with export quite happily, which makes it all the more frustrating that the specifiers of those meters omitted the ability to avoid potentially dangerous CTs.

Yes, the reason for mentioning this was people often ask why we don't use the smart meter for some of this ... why is a separate CT necessary. There are, of course, many reasons for this, including GDPR and information security, in the layers of the smart metering protocols ... and as mentioned, earlier versions of SMETS being 'import only' ... which may be OK for the EV case, but other difficulties (and hence costs) also get in the way.

Chris Pearson said:

Isn't the requirement not to export until the battery is full,

This doesn't cover the complexities of schedule based pricing. There is a competition between the middle-men/women and the users as to who gains the benefit of the overall grid variable pricing. Users with large battery stores want to charge while cheap and feedback while costly, much to the chagrin of the "eco-suppliers" offering loss-leader overnight pricing.

Even with a simple Solar - Battery system (8 panels, 5kWh) and a Gas tariff (cheap 4h on Sundays), I'm being asked to 'flex' the charging regimes .

Maybe all the RCBOs need a second CT for just the supply side (rather than the L-N difference), with cheap consumer units pre-populated with 100% monitored circuits.... Brave New World?

DShutt said:

In the vast majority of cases, what needs to be measured (certainly in the clip on CT case) is the whole house load.

Well, I've got two active clip-on CTs at home, and only one of them is on the meter tails - the other on the PV circuit. Had the HP gone in before the monitoring system rather than after, there would likely have been another on the HP circuit as well. Granted this is all on the "management" rather than "control" side of things - but such setups are far from uncommon For example: https://openenergymonitor.org/

   - Andy.