three phase dual rate meter for Economy 7 use

[robincls]

Hi there,

I'm new on here and just came across this forum on the web, I've been fighting this question / problem ever since I moved into my house in 2013 - so here goes!

My house has a three phase supply due to the blown air night storage heating that we have running on the Economy 7 tariff. 

When the system was put in (~1965) it was set-up as follows:

phase 1 440v supply to the night storage heater ONLY

phase 2 240v domestic supply

phase 3 not connected

The timing for the Eco7 rates are managed by a Venner time switch.

The problem with this set-up is that phase 1 & 2 are two separate circuits (two meters, two MPAN serial numbers etc). This means two standing charges and even worse I cannot benefit from running my appliances or water heater during the night as the domestic supply circuit and associated meter are charged at the full day rate. 

Before I contact my supplier I want to understand if such a product even exists that could replace both my analogue meters and the time switch, like a digital Eco7 meter would in a normal single phase house i.e. with the timer and R1, R2 rates all in built? 

Unfortunately I'm not an electrician so I hope this makes sense?  

Many Thanks

Robin Coles

 

[Tony S]

They are available, as to whether you supplier will fit one is a different matter. Give them a call and I wish you well trying to get any sense out of them.

 

[robincls]

Hi Tony, 

Yes, I know what you mean. I have the advantage of knowing the bloke that does all the meter installations around my way so am planning on getting him in first 'off the record' to get what is actually required down to a tea before I call them. But even he is not overly familiar with the idea hence I'm trying to find out myself.  

Cheers for replying

 

[SLIPSHOD & SLAPDASH]

Hi Robin

Your descriptions are wrong for the phases.  Any phase to neutral is 230v and between any 2 phases is 400v. No such thing as 440v single phase.

 

[binky]

and the 3rd  phase is not in use, so you have what is generally described as a 'dual supply' 

 

[ProDave]

What is the rating of the blown air storage heater? Plenty of them around here in use on single phase. Most seem to be about 15Kw input

The heater can clearly run from a 100A supply and at night you don't normally use much domestic stuff.

What you describe is not economy 7 but the old white meter tariff that preceeded it where even on a single phase supply, it was only the storage heaters that got the cheap rate at night.

You are probably best talking to your supplier to upgrade to a different tariff, i.e get onto Economy 7 or even E10

 

[robincls]

Thanks for all your replies (and corrections re the phases!), very informative. Wish I had found this forum in 2013 when I moved in.

W.r.t the rating see below from the data plate:

Creda Electricaire Type AB

Volts = ~240 / 50 Hz

Supply Phase 1

Restric. 10kW

Unrestric. 300W

A.S.C 70 kWh

I'm already on Economy 7 but my issue is the metering; I have one meter for the storage heater and one for everything else. So despite my water tank being timed to come on between 00:00 and 07:00 (and also the timed use of appliances i.e. overnight dish wash etc) none of this consumption is being logged as on the cheaper rate.

I think I either have two options: 1 to look into a dual rate three phase meter that can monitor usage over both phases or 2: to suggest to the utility provider to fit two new meters, one for each phase and just add the R1 from phase 1 to the R1 from phase 2 and the same for the R2 reading.

I guess option three would be to see if the whole lot could be run on a single phase. Would certainly half my current standing charge! 

 

[SLIPSHOD & SLAPDASH]

Do you know what your main fuse size is. It may say 60, 80 or 100 A on the outside, or it  may say nothing or be wrong but it will give us a clue. 

However it seems so far quite posdjble to run your whole house of one phase & meter

 

[Tony S]

There may have been a reason the DNO split the load between two phases such as load balancing. You don’t say where you are, if you’re in a rural area you may be on a split phase supply. Split phase uses a 3Ph service head as they’re standard stores stock.

Only your supply company can answer the questions.

 

[SLIPSHOD & SLAPDASH]

There may have been a reason the DNO split the load between two phases such as load balancing. You don’t say where you are, if you’re in a rural area you may be on a split phase supply. Split phase uses a 3Ph service head as they’re standard stores stock.

Good point. As i have never seen a split phase installation i forgot about it. Its 460 V ? or is it now 440  with the 'harmonised'  wording. 

Even so, something is not correct wirh the 440 & 240v supplies

 

[ProDave]

At 10Kw that Electricaire will be quite happy with the rest of the house load on a single phase feed.

I still contest that despite what it may say on your bill, you are NOT presently on economy 7.  A key feature of E7 and E10 is the WHOLE house gets metered at the cheap rate at the appropriate times.  Since this is not so here then you are not really on E7 and I would be taking THAT up with the supplier and demanding they sort out the metering so the whole house gets the cheap rate at night. It is not your concern exactly what they do to achieve that.

 

[Andy™]

Good point. As i have never seen a split phase installation i forgot about it. Its 460 V ? or is it now 440  with the 'harmonised'  wording. 

Even so, something is not correct wirh the 440 & 240v supplies

split phase is 230/460. you also need to check voltage of anything used too since most stuff is 400v. 2 phases off a TP system would be the usual 230/400 so its possible that it what he has, and unless he's out in the sticks, thats what id expect it to be

 

[Ardet R]

If you are only using two phases then the simplest thing for the supply company to do would be to change your tariff on the supply that is not for the storage heater to economy 7, however this may not be financially sensible for you if you do not use a significant proportion of your standard power overnight as the calculations would be independent for each supply.  With two service heads I think it would not be possible to combine the costs.

Changing your supply to a three phase or split phase with three phase meter would allow the E7 costs to be combined but would necessitate terminating one of the MPANs which I can see would not be the supply company's preferred approach as they would then be receiving less income.

The installation could be run effectively from a single supply though because you presumably only have electricity service to your house without additional utilities then I would suggest a 100A supply would be the most sensible choice.  From a practical perspective this is also very straightforward to implement but would require consultation with your supplier to find out why this was not done in the initial instance, as said above there may be problems with load balancing across phases.

However if your house as a whole does not use a large amount of power there would be the possibility to transfer the house supply to the existing E7 supply, if it has a large enough fuse, without supply company input, though this may not go down well with your supplier.

 

[Tony S]

split phase is 230/460. you also need to check voltage of anything used too since most stuff is 400v. 2 phases off a TP system would be the usual 230/400 so its possible that it what he has, and unless he's out in the sticks, thats what id expect it to be

250-0-250V

 

[binky]

Good point. As i have never seen a split phase installation i forgot about it. Its 460 V ? or is it now 440  with the 'harmonised'  wording. 

I've only come across split phase about 3 times in big houses. These days WPD prefer to run a 3 phase in - just as cheap apparently.

As the standard supply is 80A, which is roughly 20kW, a single phase supply and dual tariff meter will probably work fine. I can't see load balancing from the DNOs pont of view being a problem, as this is their standard supply for a domestic house, but I could be totally wrong about that. Contact your DNO and ask, they are generally very helpful.

 

[Tony S]

I've only come across split phase about 3 times in big houses. These days WPD prefer to run a 3 phase in - just as cheap apparently.

As the standard supply is 80A, which is roughly 20kW, a single phase supply and dual tariff meter will probably work fine. I can't see load balancing from the DNOs pont of view being a problem, as this is their standard supply for a domestic house, but I could be totally wrong about that. Contact your DNO and ask, they are generally very helpful.

Balancing the load wouldn’t be a problem as the primary side is just a single winding. The load of the two coils of the secondary may be out of balance, the primary will only see one load.