Economy 7 / TwinHeat Meter Times + Circuits

[pepsi_max2k]

Hey all, have a question on an Economy 7 style meter that I'm guessing someone here can answer quicker than trying to ask a random CS person down the phone.

I'm moving in to a new property in North Wales with what has been (and may still be) on a TwinHeat B tarriff (basically E7 but between midday-3pm and 9pm-midnight), and has wiring for a couple different fuse boxes (storage heaters, and everything else).

I'm trying to figure out what actually uses the off-peak rate: Everything, or just the storage heaters?

Also, if it is just the storage heaters, presumably they can still be used on-peak too? In which case, can an electrician simply move more stuff (or, I guess, everything) over to the off+on-peak circuit? Which begs the question why it's not like that in the first place

 

[JohnW2]

I'm moving in to a new property in North Wales with what has been (and may still be) on a TwinHeat B tarriff (basically E7 but between midday-3pm and 9pm-midnight), and has wiring for a couple different fuse boxes (storage heaters, and everything else). ... I'm trying to figure out what actually uses the off-peak rate: Everything, or just the storage heaters?

Assuming that the left-hand CU supplies only storage heaters, it looks as if only the storage heaters benefit from the off-peak rate.

Also, if it is just the storage heaters, presumably they can still be used on-peak too? In which case, can an electrician simply move more stuff (or, I guess, everything) over to the off+on-peak circuit? Which begs the question why it's not like that in the first place

That would depend upon what is 'allowed' (by your supplier) with the tariff in question. With true 'E7' is has been the case for many years that the entire installation usually benefits from the cheap rate during the off-peak hours. In an electrical sense, re-arranging for everything to get cheap off-peak electricity would be relatively straightforward, but the supplier would have to be involved, both the indicate whether your current tariff would actually 'allow' that and also because they would have to be involved in altering connections to the meter (and maybe changing the meter).

The simplest solution (if it were acceptable to you) might be to tell your supplier that you want to change to a standard E7 setup and tariff.

Kind Regards, John

 

[pepsi_max2k]

Thanks John, and yes (images updated) the left only has storage heaters.

I'm ultimately trying to decide whether it's worth installing gas for heating, which is getting more likely if nothing else benefits from daytime off-peak. Guess I'll have to speak to the supplier to see what they know.

 

[JohnW2]

Thanks John, and yes (images updated) the left only has storage heaters. I'm ultimately trying to decide whether it's worth installing gas for heating, which is getting more likely if nothing else benefits from daytime off-peak. Guess I'll have to speak to the supplier to see what they know.

You're welcome. If gas is available to you, then it would almost certainly be significantly cheaper to run than storage heaters, and also would provide much more effective and controllable heating. The up-front capital expenditure is obviously the main issue in changing.

However, if you wanted to retain the storage heaters, then I'm sure you could change to a standard E7 setup/tariff, which would mean that everything (as well as the heaters) would benefit from the 7 (nocturnal) hours of cheap electricity (typically 00:30 - 07:30 GMT).

If yiou got rid of the storage heaters, it would almost certainly be financially beneficial for you to change to a 'standard' (single rate) electricity tariff, since things like E7 usually result in higher bills unless at least about 35% of your total electricity usage is during the cheap-rate hours.

Kind Regards, John

 

[crystal ball]

Hard to say from the wiring, its more a paper exercise, you need to speak to your supplier if you half several hours to spare and infinite patience

 

[JohnW2]

Hard to say from the wiring, its more a paper exercise, you need to speak to your supplier if you half several hours to spare and infinite patience

From the photos, I don't think that there is much doubt that the two CUs (one storage heaters, one everything else) are being fed from two different outputs from the meter.

That being the case it would seem that "storage heaters during off-peak periods" and "everything else, 24/7" are being metered separately - but we obviously cannot be sure what that means in terms of tariff/billing (they could just be adding the two meter registers together for a single-rate tariff).

Kind Regards, John

 

[crystal ball]

That switching arrangement is standard off peak, but you cannot see the internal metering, same applies to old tele switch & meter set ups, could be either

 

[crystal ball]

Some info, but not conclusive

https://forums.moneysavingexpert.com/showthread.php?t=5150693

 

[pepsi_max2k]

Thanks. I've had a look at SP website and they class TwinHeat(A or B) as either a meter "type" (with seperate tariffs), a tariff itself, or both - but mostly not much info anywhere. There is a sidenote in a dropdown of an obscure page saying TwinHeat can be used both for heating and anything else, which is useful i guess.

Right now just intrigued as to why the storage heater CU neutral is wired directly to the head and not the meter - anyone care to enlighten me? The meter separation makes sense as it could prevent the storage heaters being used during on-peak times.

 

[JohnW2]

That switching arrangement is standard off peak, but you cannot see the internal metering...

Does not the wiring arrangement, with the two CUs having separate direct feeds from the CU (and no external contactors) imply that usage via the two CUs (one storage heaters, one 'everything else') are separately metered, and also that the output from the meter to the storage-heater CU is time-switched (within the meter)?

I suppose it would be theoretically possible that just the output to the heater CU could be time-switched, but with the metering of both outputs being time-switched (so that both enjoyed cheap-rate electricity during the relevant periods), but I've personally never seen or heard of a meter which behaves like that (or has provision to do that) - but maybe that's due to my lack of exposure/experience!

Kind Regards, John

 

[JohnW2]

Right now just intrigued as to why the storage heater CU neutral is wired directly to the head and not the meter - anyone care to enlighten me?

Electrically speaking, it doesn't matter where the neutral is connected - the 'in' and 'out' neutral connections to a meter are simply connected together inside the meter.

Although there are two L outputs from your meter, there's probably only one N one - which could be the 'practical' explanation for what you describe.

Kind Regards, John

 

[pepsi_max2k]

I suppose it would be theoretically possible that just the output to the heater CU could be time-switched, but with the metering of both outputs being time-switched (so that both enjoyed cheap-rate electricity during the relevant periods), but I've personally never seen or heard of a meter which behaves like that (or has provision to do that) - but maybe that's due to my lack of exposure/experience!

Not quite the same model but from a similar era (mid 2000s).

similar wiring, from https://talk.electricianforum.co.uk/topic/33283-storage-heater-problem-no-power-at-night-to-charge/

from meter's tech spec https://www.landisgyr.com/webfoo/wp-content/uploads/product-files/5246_Technical_Specification11.pdf

basically shows metering comes before the switch for the seperate cu line, which i would assume means the metering of both is time switched, with the switch for the heater cu there purely to avoid useage during on-peak times (can't think of any other reason to separate it).

i mean really i should just go over there boil a kettle and watch what the reading does but this is much more fun and educational

 

[JohnW2]

View attachment 175128 from meter's tech spec https://www.landisgyr.com/webfoo/wp-content/uploads/product-files/5246_Technical_Specification11.pdf ... basically shows metering comes before the switch for the seperate cu line, which i would assume means the metering of both is time switched, with the switch for the heater cu there purely to avoid useage during on-peak times (can't think of any other reason to separate it).

I'm a bit confused. That appears to be a single-rate meter (i.e. everything metered together, 24/7) with a contactor switching one of the outputs, which really makes no sense to me - I must be missing something! Do I take it that your meter is able to display both peak-rate and off-peak rate usage figures? If so, that doesn't seem to correspond to that 5246 meter.

i mean really i should just go over there boil a kettle and watch what the reading does but this is much more fun and educational

Yes, provided you have cheap and non-cheap meter displays (which I don't think the 5246 has), then that would be the simplest approach, although I'm not sure that boiling a kettle once would be enough to see (a 2kW kettle for 5 mins would be under 0.2 kWh) - a 2kW fan heater for an hour would be 2kWh, which would probably be enough to see.

Kind Regards, John

 

[crystal ball]

Does not the wiring arrangement, with the two CUs having separate direct feeds from the CU (and no external contactors) imply that usage via the two CUs (one storage heaters, one 'everything else') are separately metered, and also that the output from the meter to the storage-heater CU is time-switched (within the meter)?

I suppose it would be theoretically possible that just the output to the heater CU could be time-switched, but with the metering of both outputs being time-switched (so that both enjoyed cheap-rate electricity during the relevant periods), but I've personally never seen or heard of a meter which behaves like that (or has provision to do that) - but maybe that's due to my lack of exposure/experience!

Kind Regards, John

I worked for local electricity board for a number of years, during that time I must have 100s of tariff changes from normal single rate to E7, originally using mechanical time switches then on to tele switches, E7 then was midnight to seven GMT, at midnight the teleswitch changed the two rate meter to off peak and also switched on the off peak CU with its internal contactor, the whole installation was on off peak for seven hours then the reverse happened at 7 am.

Then came combined teleswitch and meter which did the same thing, which is what our op has in his picky, although with the advent a smart meters this may be changed but from the pic it is not possible to say what is happening

 

[JohnW2]

I worked for local electricity board for a number of years, during that time I must have 100s of tariff changes from normal single rate to E7, originally using mechanical time switches then on to tele switches, E7 then was midnight to seven GMT, at midnight the teleswitch changed the two rate meter to off peak and also switched on the off peak CU with its internal contactor, the whole installation was on off peak for seven hours then the reverse happened at 7 am.

Fair enough. That would be the arrangement which I said I supposed "... would be theoretically possible", but that I had "personally never seen or heard of a meter which behaves like that (or has provision to do that)"! Put it down to lack of experience.

As I previously reported, although I rapidly had it changed, the E7 installation I inherited in 1987 was not like that. Off-peak usage was metered by separate meters (one for each phase in my case!) fed via time-switched (00:30-07:30) contactor, with those meters feeding only the storage heaters (through switch-fuses) - so only the storage heaters (which, by then, were not being used anyway!) benefited from the off-peak rate.

As I wrote above, a bit of extra confusion seems to have been introduced by the OP posting details of what appears to be a single-rate meter with a contactor (which I don't really understand!).

Kind Regards, John