'pump plan' type wiring with 1 relay?

[John Stumbles]

I need to fix up proper controls on a CH system that has separate pumps
driving CH and DHW. At the moment there is no stat on the HW cylinder so
$DEITY knows how it's wired. (The wiring seems to be crammed into a back
box behind the programmer so I haven't investigated yet, but my money
is not on it having proper interlock between CH and DHW systems and the
boiler.) The pipework layout makes conversion to a Y plan or a packaged
Grundfos Pump Plan (tm) a very unattractive option so I need to arrange
proper temp control on the DHW and interlock with the boiler.

I know I can do it with 2 relays with their contacts wire-ORed to drive
the boiler Switched-Live:

<pre><tt>

Programmer Room stat
---- ----
L ---o o-----------o o--------+--------+
| |
CH pump (>) | RLA |
| |
N ------------------------------+--------+


Programmer Cyl stat
---- ----
L ---o o-----------o o--------+--------+
| |
DHW pump (>) | RLB |
| |
N ------------------------------+--------+


L ----------------+--------------+
| |
o | o |
A | B |
o | o |
| |
+-------+------+
|
---------
| SL |
| boiler |
| N |
----------
|
N ------------------------+

- but ISTR seeing somewhere a single relay solution. I'm damned if I can
see how that would work but willing to be proved wrong

Incidentally has anyone grokked how the Grundfos pump plan wiring centre
does it? IIRC there's no relay in the box so presumably it's some sort of
triac cct with wired-OR to the gate.

 

[raden]

I need to fix up proper controls on a CH system that has separate pumps
driving CH and DHW. At the moment there is no stat on the HW cylinder so
$DEITY knows how it's wired.

Are you sure you are inside the legal envelope (so to speak) doing this
?

 

[John Stumbles]

Are you sure you are inside the legal envelope (so to speak) doing this
?

I assume you mean wrt Part P? As I read it (unfortunately 2 slags'
numpties have disabled ^C on the AD but the words I want are 'replacing
any fixed electrical apparatus' and 'not include ... any new fixed
cabling') my wiring centre with the relay in it are my 'fixed
electrical apparatus' and as long as I only use flex (preferably bellwire
(joined with choch-blox) rather than T&E to hook everything up I
should be OK.

 

[John Stumbles]

Are you sure you are inside the legal envelope (so to speak) doing this
?

I assume you mean wrt Part P? As I read it (unfortunately 2 slags'
numpties have disabled ^C on the AD but the words I want are 'replacing
any fixed electrical apparatus' and 'not include ... any new fixed
cabling') my wiring centre with the relay in it are my 'fixed
electrical apparatus' and as long as I only use flex (preferably
bellwire (joined with choch-blox) rather than T&E to hook everything
up I should be OK.

Oops, reading further it advises that 'new CH control wiring installations
are notifiable'. Bummer.

 

[raden]

Are you sure you are inside the legal envelope (so to speak) doing this
?

I assume you mean wrt Part P? As I read it (unfortunately 2 slags'
numpties have disabled ^C on the AD but the words I want are 'replacing
any fixed electrical apparatus' and 'not include ... any new fixed
cabling') my wiring centre with the relay in it are my 'fixed
electrical apparatus' and as long as I only use flex (preferably
bellwire (joined with choch-blox) rather than T&E to hook everything
up I should be OK.

Oops, reading further it advises that 'new CH control wiring installations
are notifiable'. Bummer.

Hmmm, there you go

 

[Roger Mills]

In an earlier contribution to this discussion,

Are you sure you are inside the legal envelope (so to speak) doing
this ?

I assume you mean wrt Part P? As I read it (unfortunately 2 slags'
numpties have disabled ^C on the AD but the words I want are
'replacing any fixed electrical apparatus' and 'not include ... any
new fixed cabling') my wiring centre with the relay in it are my
'fixed electrical apparatus' and as long as I only use flex
(preferably bellwire (joined with choch-blox) rather than T&E to
hook everything up I should be OK.

Oops, reading further it advises that 'new CH control wiring
installations are notifiable'. Bummer.

Yes, but what reaction are you expecting from your local Builing Control
department when you submit a Building Notice saying "I am going to replace
my CH controller" or whatever?

If you know what you're doing, just *do* it! Unless you're selling your
house next week, it will get lost in the noise.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

 

[John Stumbles]

If you know what you're doing, just *do* it! Unless you're selling your
house next week, it will get lost in the noise.

Gosh, I'm shocked!

The thought never even crossed my mind