The neutral is a common conductor so is used for both circuits. The separate live conductors effectively become live at different times providing the switch between both. 
Neutral being low (near zero) voltage doesn’t need to be switched

Thanks for pitching in ‍♂️
I would think in this sort of scenario that the ‘main’ circuit was always live, with only the off-peak one being switched on and off at the appropriate times. 

Yes, the additional switched off-peak circuit feeds the needs of the storage heaters/hot water or whatever as appropriate 

Thanks, what I’m struggling with is that it appears to me that the heater circuit (with its own fusebox) and the main circuit for the rest of the flat are physically separate so I can’t see any way they can share a neutral. I’m fully prepared to believe I may be being a bit thick and hopefully the soon to arrive installers will explain all! I have attached a photo.

The main input into the building would bring the common neutral in and that connection, wherever it is picked up will provide the ‘return’ connection for the live circuit. 
Will wait to see the result 

Thanks, I will keep the forum posted, watch thios space, installation due on31/8

Aclara 5port meter now installed, see pic

However despite appearing correctly wired and having been quoted a day rate and a night rate, the storage heater circuit is not activating.

“unit rate1” display shows 7Kwh used since installation yesterday.

“unit rate2” display shows 0Kwh used despite my switching on 2 of my 3 storage heaters overnight.

I will be passing this to my complaints handler in the meantime, anybody got any suggestions?

Get them to configure the ECAUL/ALCS :)

Yes, there’s a relay which switches the off peak circuit.

We’ve seen a few where this isn’t set up properly so as Blastoise says, ask them to update it 

Like this for instance? Photo taken at 5.30, I assume at midnight it should show relay II as closed and relay I open if I’ve understood correctly? I will check just after midnight.

Best to check after 00:30 - otherwise the random offset might not have allowed the relay to close yet.

No, I think (hope) you’ll find that Relay I stays closed all the time. Otherwise, you’d have a lot of soggy stuff in your freezer and all your electric clocks would blink at you in the morning. 

Yes, it should just be the extra circuit that switches on for that off peak time. 
As has been mentioned, things don’t switch at exactly the same time otherwise there would be a power surge locally from all those using the same system

Not silly at all - it’s a common misconception. There was a user complaining in this forum a few weeks ago that his off-peak (E7) usage was incrementing overnight even though the off-peak (heating) circuits were switched off at the consumer unit. He had difficulty understanding that his always-on stuff’s usage was being recorded on the ‘E7 meter’ and charged at the cheap rate during the night. I’m not sure he was convinced ...  

So eyes propped up with matchsticks I checked the meter at 00.29 this morning (2nd Sept). Below is a composite of the 2 photos I took. It clearly shows that the active rate is still the standard one and that in both photos you can see the night rate relay is still open. I shall be passing this evidence onto my complaints handler asap. I will post what happens.

That looks like a very low off-peak rate to me, so it depends what you mean by standard. I don’t know whether those rates are shown including or excluding VAT, but single-rates these days are around 29p. I’d expect the peak rate for a dual-rate tariff to be well over 30p. Who did you bribe to get prices like that?

Do you know for sure when your peak and off-peak times are? They vary a lot around the country, 

The tariff is probably changing (or not, if you’re still not on an E7 plan) at the right time; it’s just the Load Control that’s not being switched. As Blastoise said, ask them (!) to resend the ALCS commands. 

aPS We’ve seen a couple of cases where the installing engineer did this and had confirmation that it was all OK (a green light on his dashboard), when it turned out not to be OK at all. Not only that, but the fix that the metering people then applied also had a (different) fault. This means that they should now know how to deal with this situation, although how far down the totem pole this knowledge trickles is anybody’s guess. My suggestion would be to write up your situation in detail in a text file, then contact a Support agent via webchat, paste the text into the chat and add your (timed) screenshots, with a request that the agent pass the whole lot on to the metering team. Be sure to include both the MPAN and the meter serial number (MSN) in the details. The MSN is visible on the meter itself, above the barcode above the window, starting with 21M.]

Yes thanks i got a bit confused over which rate is which and it bears no relation to what was quoted to me, so that’s another thing to sort out. As regards this whole sorry mess I have a dedicated complaints handler as this matter of changing 2 meters for 1 has been going on since January of this year. So I have emailed her over the weekend with the latest screen shots and text.

You are filling me with dread, as I will need to combine my 2 meters into one dual rate at some time too.  Much prefer it separate so you can see at a glance what the THTC reading is and the day rate on the other.

If you have THTC right now, you’ll stay on the exact same metering setup until Smart Meters are ready to support it. Once they’re ready, you’ll be migrated over to Smart - and only then will it be collapsed into a single meter.

OVO’s team already confirmed to me that keeping it on two separate meters and/or using Twin-Element meters will be asking for trouble. This was confirmed in-person by a senior manager when I was at OVO’s HQ last year and during a recent forum event.

With solar and a small battery considering changing to a  smart meter, currently on standard tariff but considering changing to Economy 7. Does OVO provide this funcionality or do I have to change suppliers to get it?

OVO isn’t quite ready to move folks to <> from E7 yet. However, I must advise that I don’t think Economy 7 is right for your setup - you need to shift an awful lot of usage to overnight to justify it.

I take your point. However, I am considering increasing the size of my battery and grid charging at night for use during the day in Winter, in Summer I generate enough to cover my night time usage and day time on an average sunny day.

In that case, this may need some number crunching. @juliamc @BPLightlog and @Firedog are good at that. 

Hi @tiredteddy , I was in a similar situation with a single rate meter and had been looking to use lower cost electricity to power various systems, especially as you mention, during the winter months. OVO will get there but I’m not sure when so I’ve recently switched to a provider who offers time of use (ToU) tariffs. 
It is important that you look at what you use during peak, not only 4-7pm but also during the morning from around 6-9 as these times can be higher, the evening significantly so at times. 
I believe that calculations suggest that you need to ensure that less than 30% of your usage will be during peak times but that will depend on which tariff you choose. E7 can work but it’s a little more tricky as some find that they need a boost in storage just before evening peak to last through the night