3 phase residential /teleswitch heating

[SparkyTris]

I have a somewhat unusal residential supply question for an elderly friend (at least in my limited experience it is unusual)
3 phases entering the house

I cannot remember the exact setup of the metering at the property (will update when I visit later in the month) but its something like this:

there is a CU for each phase:
L1 - Domestic
L2 - storage heaters (which are energised via a radio teleswitch)
L3 - 24hour low rate

(I might have labelled the phases wrong but that is immaterial)

it has been a "total heating with total control" system since living memory. (which I think is more accurately referred to as total lack of control). that system is fairly common in older properties in this area, north of scotland. the reason this question has come up is that we understand that the radio teleswitches will cease to function shortly owing to the LW signal being stopped (??)

I cannot precisely remember how the metering has been done up to now. I know that there are 2 meters, one for the normal tarriff and one for the low tarriff. what I cant remember precisely now is how the low rate fuseboxes are metered. I would have thought that only 1 meter would do 1 phase but perhaps its a 2-phase meter. (if such things exist)

the owner thought that the simplest thing to do was to just ask for a 3 phase meter but I warned her with a vague thought that it might put her on a commercial rate which would probably be rather high.

what would be the most suitable tarriff & metering arrangement to shoot for here? (I realise that the best thing would be to bite the bullet and move away from these old storage heaters but that is another option altogether)

why the rural property was ever 3-phase is another question entirely. it has only ever been a croft.

 

[ericmark]

I remember the collage lecturer telling us about a large house in the 80's having economy 7 heating fitted and needing a three phase supply due to the load. He was pointing out how daft economy 7 was with larger homes.

As to two phase yes it is done, but actually called split phase, and since the two supplies are in phase with each other, technically not two phase, normally 230 - 0 - 230 to 460 volt line to line.

The limiting factor is a consumer unit which is a type tested distribution unit designed to be under the control of an ordinary person can no be larger than 125 amp, in real terms 100 amp, so if you want more than 100 amp in a domestic you need some equipment out of the control of the ordinary person to split the supply to multi 100 amp supplies. Well that is the theory.

The one domestic I was involved with where we thought it may need over 100 amp, we used a three phase fused isolator supplying three consumer units placed around the house, but all three fuses were supplied by the same phase, it simply allowed over a 100 amp supply. It could have been split into multiphase, but never was.

Split phase is common on farms, but rare in towns.

So it may well be single phase, but multi supplies. In the early days of economy 7 it was common to have a white meter feeding a fuse box dedicated to the storage heaters, so could have 100 amp to storage heaters and 100 amp to home. Then there was a move to use the off peak for washing machines etc, until the series of fires caused by washing machines.

What you need to remember is economy 7 is a tariff not a system, and there are many ways to use economy 7, it was never really a success, we had it at work, and it did what we wanted, during the day when all the machines were running there was very little spare capacity to heat the offices, so the storage radiator worked well, removing the office heating load from the system during the day. The tariff was based on maximum demand and the storage heaters reduced the maximum demand, we had one 300 amp transformer and the room was not big enough to fit a larger one, so we had to keep the day time demand down.

 

[AndyPRK]

An alternative to a radio switch, is a timer fitted by the DNO or metering company which

1. tells the meter to switch over
2. Has a contactor to enable the heating


This is a type they used to fit

 

[SUNRAY]

An alternative to a radio switch, is a timer fitted by the DNO or metering company which

1. tells the meter to switch over
2. Has a contactor to enable the heating


This is a type they used to fit

some energy suppliers are refusing to fit timeswitches now, instead smart meters...

 

[flameport]

we understand that the radio teleswitches will cease to function shortly

There is no specific date, currently they will work up to March 2023. After that is undefined.
However it's inevitable that it will be discontinued, as smart meters can provide far more flexible billing options.

3 phase smart meters do exist, whether they are available depends on the supplier you are using, but you can change to another supplier at any time.

If you want heaters or anything else to switch on at certain times, then you will have to provide your own switching equipment.

 

[Jackrae]

As to two phase yes it is done, but actually called split phase, and since the two supplies are in phase with each other, technically not two phase, normally 230 - 0 - 230 to 460 volt line to line.

? if they are in-phase

 

[JohnW2]

... As to two phase yes it is done, but actually called split phase, and since the two supplies are in phase with each other, technically not two phase, normally 230 - 0 - 230 to 460 volt line to line.

The two phases of 'split phase' are surely 180° out-of-phase (relative to the common point /'neutral), not "in-phase with each other', aren't they?

I know of one installation which, for whatever reason (maybe once was 'full 3-phase'?), has what you would presumably call a 'true 2-phase' supoply - i.e. two of the (120° apart) three phases of a 3-phase supply (plus a neutral).

Kind Regards, John

 

[JohnW2]

... L3 - 24hour low rate ...

What's that, I wonder?

Kind Regards, John

 

[SUNRAY]

I know of one installation which, for whatever reason (maybe once was 'full 3-phase'?), has what you would presumably call a 'true 2-phase' supoply - i.e. two of the (120° apart) three phases of a 3-phase supply (plus a neutral).

Kind Regards, John

I've come across the same thing, Equally also a 3ph head feeding a 3ph meter and onto a 3ph board with all 1ph circuits.
Customer purchased a second hand 3ph machine, wired it in and it wouldn't start and trips the MCB - even a bigger bigger size I think about 25A for a failry small motor, around 2KVA or so, he called us in to fix the machine.
Motor static resistance/IR etc tests looked good.
Meter shew 240V on each phase and 415V across phases... exceptp h2-3 was 0V, a call to DNO to report the fault revealed they had it recorded as Red, Blue & Blue service.

 

[JohnW2]

I've come across the same thing, .... Meter shew 240V on each phase and 415V across phases... exceptp h2-3 was 0V, a call to DNO to report the fault revealed they had it recorded as Red, Blue & Blue service.

If I understand correctly. that's not really the same thing as I was describing - in fact, yours sound pretty bizarre. Are you saying that there was a 3-phase service head, with three fuses, but two of them were fed by the same ('blue') phase? If so, I wonder why on earth they would have done that since, as you saw/discovered, it would cause complete confusion (and 'failure to work' in some situations') if someone tried to use it as a 3-phase supply!

The installation I was referring to may have a 3-phase supply to the service head (can't tell), but it only has two fuses and two phases coming out of it to the installation.

Kind Regards, John

 

[SparkyTris]

What's that, I wonder?

Kind Regards, John

Yeah, Ive always wondered that too.
the "Total Heating with Total Control" branded scheme I think is (was) perhaps peculiar to Scotland and possibly had something to do with a way to use the white elephant of hydro-electric pumped storage in the remote highlands. Im sure others will comment.
Anyway it (the THTC) had its heyday when I was too young to be involved or interested in the technicalities. The "24 hour low rate" fusebox is common around here on properties of a certain age. as far as I can see, it is a round-the-clock supply from the low rate meter. I guess that the rules were that you could only put certain "lifeline" circuits on it, maybe 1 convector heater and a small boost immersion, not sure. perhaps others can comment?

 

[SparkyTris]

So it may well be single phase, but multi supplies. In the early days of economy 7 it was common to have a white meter feeding a fuse box dedicated to the storage heaters, so could have 100 amp to storage heaters and 100 amp to home. Then there was a move to use the off peak for washing machines etc, until the series of fires caused by washing machines.

The supply arrangement in question is certainly full 3 phase & neutral. 400V between the line of all 3 fuseboxes. 400V exists within the single dwelling house. each phase has a 100A cutout. I have done work on the property and measured it myself.

and Yes - regarding the "24 hour low rate" washing machines were/are definitely another thing that were commonly on that box too.

 

[Harry Bloomfield]

As to two phase yes it is done, but actually called split phase, and since the two supplies are in phase with each other, technically not two phase, normally 230 - 0 - 230 to 460 volt line to line.

I cannot get my head around that Eric - is that in the UK? How can two phases be in phase with each other, yet produce 460v between them? The same phase split two ways will have zero volts between.

230 - 0 - 230 reads like a centre tapped transformer, as used for a yellow building site transformer and that would produce 460v between the outer tappings.

 

[SUNRAY]

If I understand correctly. that's not really the same thing as I was describing - in fact, yours sound pretty bizarre. Are you saying that there was a 3-phase service head, with three fuses, but two of them were fed by the same ('blue') phase? If so, I wonder why on earth they would have done that since, as you saw/discovered, it would cause complete confusion (and 'failure to work' in some situations') if someone tried to use it as a 3-phase supply!

The installation I was referring to may have a 3-phase supply to the service head (can't tell), but it only has two fuses and two phases coming out of it to the installation.

Kind Regards, John

It certainly did cause confusuion, the story started with a colleague going to look at it, his initial tests measured the 240's and 415 between ph1-2 & ph1-3, he assumed ph2-3 was OK. He phoned me for assistance removing the motor with the intention of taking it back to the workshop and by the time I got there he had partially stripped the machines panels, removed a number of the motors mounting bolts and disconnected the wiring. We removed the final bolts and in the workshop did the static tests with a better tester and found it to be as expected and is span freely by hand.
Applying power it ran smoothly so we returned to the customer, I suspected the DOL starter - which tested fine without motor connected to it but as soon as the motor was reconnected it tripped the MCB. I reckon we'd been back there for an hour going round in circles before we decided to 'move the wires round one' with the result the 415V contactor coil was then between ph2-3, that was the first time we measured the 2-3 voltage.

In essence it amounted to a similar scenario to yours where only 2 phases were available within the system, albeit for a different reason.

I think I recall a similar experience in this forum a year or so back with a burnt fuseway in the cutout.

 

[SUNRAY]

I think I recall a similar experience in this forum a year or so back with a burnt fuseway in the cutout.

Does anyone else remember the overheated/failed cutout at fast food/take away?