On 15 Feb, 21:44, wrote:
On the advice of this group I'm about to make some changes to my
thermal store and boiler configuration, which will also need some
changes to the electrical configuration, (see thread "Need help
setting up thermal store" started last december for all the details);
I'm after some advice as to how best to complete this.

The current electrical setup is this:
A mains circuit feeds a switched FCU which then provides power towards
the wiring centre.
From the wiring centre the time switch, pump, boiler, cylinder stat,
room stat and zone valves all hang off in a fairly standard fashion.
i.e. This FCU, (lets call it "A"), isolates all of the items above.

There is a second switched FCU which provides power to my solar
controller, (Resol BS), and then onto the solar pumping station.
i.e. This FCU, ("B"), isolates power to the solar controller and the
solar pumping station.

So far so good.

What I want to achieve is that a currently unused relay closure on the
Resol BS will be used to fire the boiler, (which in turn will run the
pump). *The simplest way of achieving this would be to provide a live
from the time clock / cylinder stat, (via the wiring centre), into the
Resol BS and out again back to the wiring centre.
The problem I see with this is that isolating FCU "B" would then
potentially leave a live on one of the terminals within the Resol if
it is opened up for maintenance.
Is it sufficient to attach a label to the Resol to the effect that
"This unit may need isolating in two places to render it safe for
maintenance"?, [I'm sure I've seen such a notice elsewhere in my
travels].

NB. The 'obvious' answer is to power everything from one FCU, but I
don't favour this plan as I don't really want to solar controller
depowered during boiler and heating maintenance.

Any ideas?
Mike

Is the resol arranged such that the "other live" parts can be enclosed
in a separate section or effectively made inaccessible by the use of a
fingerproof screen with appropriate warning labels. Many motor control
centres and industrial panels employ this technique which allows
maintenance on the major part of the panel without necessarily
shutting down critical sections. Another method would be by the use of
a separate means of isolating device such as a plug-in relay in
another enclosure outside the resol unit but with its coil supply
derived from the resol. The possibilities are endless!
Its only the current blame culture and the jobsworths busily creating
rules about problems which "might" cause a problem one day which leads
us into the situation where we must try to prevent damage to idiots
poking around in electrical stuff where they should not be. I am now
retired but spent many years working on systems which contained live
parts which were recognised as such and only touched using appropriate
devices with care. Death or pain is natures way of improving the
intelligence of the human race!