@
JoeSoap @
meldrewreborn
Sorry chaps...I've been driving most of the evening and not long arrived at the digs so only just picked this up.
There are three types of Economy 7 or 10.
The first type is bog standard day/night rate. Four terminal meter and the only difference is the meter records consumption on two different registers or sets of dials. Nothing is switched and there is no separate output to run heating. All usage on any circuit is charged at the prevailing rate for the time of day.
The second type is a switched system. This will either use a mechanical time switch (Smiths or Sangamo) which is use to control heating and or hot water, or the Radio Teleswitch System. The meter itself is still a four terminal meter but the timeswitch controls the live feed to the heating/water circuits so they are only powered during off peak hours. Some water tanks are fitted with dual immersion heaters with the lower element wired to the switched off peak supply and the upper one wired to the regular supply so you can boost the heat in the tank during the day if need be, but at on peak prices.
This can be replaced with a five terminal meter which only energises the heating circuits at off peak times.
The third type of system uses two separate meters, or two separate switching systems and is only found in regions served by the former regional boards, Southern Electricity and Scottish Electricity. Which is why the current strange combination Scottish And Southern (SSE) exists today.
They have two meters each with a separate MPAN number, sometimes referred to as a 'black meter' and a 'white meter' because they came in those colours. One meter was the meter for E7 and the other was for heating and hot water. Remember the Heat Electric adverts back in the 70s? These systems, called Flexiheat or Heatsave, worked on a four rate system where you had a day and night rate for regular electricity and an off peak third rate for heating and hot water plus an extra few hours a day of heat on a fourth rate. These so called 'complex sytems' were only installed and supported by Scottish and Southern regional boards and if any still exist in the wild can ONLY be properly managed and supported by SSE or OVO. The reason they were installed in these two board areas was because of the availability of excess power in these regions available from the Magnox nuclear power stations of the time.
In theory, a modern 5 terminal or even six terminal smart meter is capable of replacing the system...but in practice it rarely works properly unless installed and managed/supplied by SSE or OVO. But since the Magnox fleet have now all been taken off line, the system is obsolete. The systems by default all have two MPAN numbers so you pay two lots of standing charges, and no other companies can offer a complex tariff for different heating on peak and off peak rates.
If you have the third type of system, your only two choices are to sign up with SSE or OVO, or to convert to a standard E7 system and rip out all the oddball timers and meters and have the heating system modernised. In which case, a bog standard four terminal smart meter will be fine and you can arrange to have the additional MPAN and second set of standing charged removed.
I did this in a previous property a few years ago so a reasonably savvy electrician can do the job easily enough, but saving on the second set of standing charges more than compensates for the slight loss of the four time periods.
RTS is scheduled for switch off in April 2024 but my bet is it will be extended until early 2025, so no need to worry just yet.