3 phase residential /teleswitch heating

[JohnW2]

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?

Interesting - it's certainly not something I can recall ever (in many decades ) having seen or heard about in England. Do I take it thst there is/was a separate meter for the "24 hour low-rate" supply, since the usual dual-rate meter can only meter to one of its registers at any particular time?

I wonder how on earth they 'policed' the usage of the "24 hour low-rate" supply?

Kind Regards, John

 

[JohnW2]

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

Yes, in some senses similar to the situation I described (an installation I've seen, not 'mine' - I have '3 proper phases'). The big difference is that the installation I described did not pretend/claim to have a third phase (within the installation), and so no-one would have been able to even think of/trying to connect any 3-phase loads or 3-phase sockets.

It (what you described) does seem to be a rather silly thing for a DNO to do, since I don't really see any point, yet there clearly are some significant downsides - so it's difficult to understand why they would have done it. If it had initially been a proper 3-phase supply and one of the phases had 'failed', they surely would/should have 'mended' that phase, not done what you describe?

Kind Regards, John

 

[SUNRAY]

Yes, in some senses similar to the situation I described (an installation I've seen, not 'mine' - I have '3 proper phases'). The big difference is that the installation I described did not pretend/claim to have a third phase (within the installation), and so no-one would have been able to even think of/trying to connect any 3-phase loads or 3-phase sockets.

It (what you described) does seem to be a rather silly thing for a DNO to do, since I don't really see any point, yet there clearly are some significant downsides - so it's difficult to understand why they would have done it. If it had initially been a proper 3-phase supply and one of the phases had 'failed', they surely would/should have 'mended' that phase, not done what you describe?

Kind Regards, John

I agree it does seem silly but have absolutely no knowledge of any previous history of the installation or the reasons etc.
As it happens the DNO came round a few days later and were able to make the change quite easily as the cable originated from a cast iron cabinet (junction box) within the little industrial estate of small units.

 

[SparkyTris]

Interesting - it's certainly not something I can recall ever (in many decades ) having seen or heard about in England. Do I take it thst there is/was a separate meter for the "24 hour low-rate" supply, since the usual dual-rate meter can only meter to one of its registers at any particular time?

I wonder how on earth they 'policed' the usage of the "24 hour low-rate" supply?

Kind Regards, John

there were (are!) 2 meters - 1 for normal rate, and 1 for low rate.
the main low rate load (heating) would energise using the long-wave controlled teleswitch (sometimes via a separate contactor)
the 24-hour low rate fuse box would be permanently energised, and metered via the low rate meter.

the domestic fusebox would be permanently energised and metered via the normal rate meter

this system did NOT use the "normal" dual-rate meter to which you refer, which I suppose is more of an Economy-7 or Economy-10 scheme, which I think is far more common.

it always seemed odd to me as well.

From recent dialogue with the DNO / energy suppliers, I am starting to think that they are no longer very sure of who's got what any more, not how it all works.
I would love to find out who organises the radio teleswitch scheduling. I know that some switch on at 8pm and some switch on at 10pm in my immediate area.

it seems that SSE are the only organisation who can offer the "Total Heating With Total Control" tarriff. and that if you have a THTC system, and you attempt to go elsewhere for your energy, they threaten that the system will no longer work. - That threat implies that SSE have the ability to remove individual teleswitches from the LW schedule which seems unlikely but not impossible. I don't think that there is enough bandwidth in the LW signal to be able to address individual receivers quickly enough....

 

[SparkyTris]

supply at the property in question is arranged as follows:

L1, L2 & L3 are connected into a 3-phase mechanical meter, out of which only L1 and L2 are utilised. L1 energises storage heating via a radio-teleswitch/contactor arrangement. L2 supplies the "24 hour low rate" fusebox which is feeding I think a freezer and an electric fire. big freezers are (or at least were) popular in rural scotland.

L3 alone energises the normal rate domestic fusebox via a more modern electronic meter (which probably has the capability to be a dual rate timed meter). it looks as if that has been replaced fairly recently.

so the 3-phase meter is the nominally low-rate meter.

 

[jelliottelectrical]

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

yep.

I think the supplies originate from the days of DC supplies, which were often two lives and a neutral. Most supplies of this age have now had new cutouts fitted, and I don’t know any DNOs that stock the cutouts with two fuses and a neutral (though they are readily available) most likely they have used a stock 3 phase cutout and linked two fuses to one phase. Sometimes you do come across three phase cutouts with one fuse not connected or blanked off. Depends who did it on the day. You can also have this problem after a fault. Sometimes two conductors short phase to phase, which either blows one fuse and not the other, but the fault causes the two phases to continue working, as they are shorted. On a residential street no one may notice unless the have any three phase equipment.

I did come across a fault once where this occurred, the red and yellow phases shorted together, however the red had burnt through, severing it from the rest of the main, past this break it was joined (via the burnout) to the yellow, so at the transformer, three healthy fuses and network operating as it should be, but past the break (feeding just one three phase service) had red and yellow at same potential. So effectively L2 L2 L3. Was quickly noticed when three phase machinery failed to work, and one faulty joint cut out and replaced with 3!

 

[Harry Bloomfield]

Was quickly noticed when three phase machinery failed to work, and one faulty joint cut out and replaced with 3!

I came across similar in Scarborough, affecting an entire block, all but one single phase supplies, or only using single phase equipment. The one a 3ph bullion hoist, which just wouldn't run. 240v between each phase and neutral and each phase to neutral, but a strange voltage between two of the phases and zilch between the other two. It took an enire afternoon for the DNO to eventually track the issue down from the sub, under a disused and locked building, rather longer before access was gained and it was restored. I was the only one who had noticed the missing phase, in the entire block.

 

[SparkyTris]

enough bandwidth in the LW signal to be able to address individual receivers quickly enough

I guess that there might be a period available (when no other switching is taking place) where individual teleswitches could be "stunned" by the LW signal

 

[Harry Bloomfield]

I guess that there might be a period available (when no other switching is taking place) where individual teleswitches could be "stunned" by the LW signal

I would assume, that rather than them all switching at the time the system is triggered remotely, that they use a variable delay after the signal, to switching on ot off.

 

[plugwash]

one faulty joint cut out and replaced with 3!

I'd imagine that is the norm when dealing with faulty tee joints, because once the bad part is cut out the cables will no longer reach the jointing location.