Mike Humphrey wrote:

Roger Hayter wrote:
Mike Humphrey wrote:
It's something to be careful of in multi-rate installations that there's
often not a single switch to cut all power to the building. My house
used to have THTC, which meant there were *four* main switches
(general supply, 24 hour heating, water heating, timed heating). Unless
all four were off, something was still powered or could become powered
under timeswitch control.

That's complicated, did you have four separate incoming cables and main
fuses, or was it all done after the meter?

There's one incoming cable with a main fuse. This then fed a pair of
henley blocks, which split the supply to two meters. One was just a
single-rate mechanical meter, which did the "general supply" and fed a
consumer unit for everything that didn't involve heating. The other
meter included a radio timeswitch, with one continous output and two
switched outputs. Although this was actually a multi-rate meter it
only recorded one rate - all heating was charged at the same price.
The three live and one neutral tails from this meter fed a second
consumer unit with three independent main switches (each feeding their
own bank of MCBs) that powered all the heaters.

The two switched outputs turned on and off according to a schedule that
SSE set - it changed regularly, potentially being different every day,
and customers weren't told what the schedule was. So unlike Economy 7,
which is unlikely to turn on at a random point in the day, it's
extra important to make sure that the relevant main switch is off - as
you never know when the timeswitch will switch on!
Just to add to the confusion, the immersion heater and some of the
storage heaters had a boost facility - fed from a different circuit on a
different main switch.

Mike
That sounds confusing. But versatile for heating, I suppose. They
presumably had to trust you not to connect everything to the cheaper
heating always on supply.

--

Roger Hayter