Good afternoon all,

for a particular application I am looking for a combined central heating
digital timer-controller/thermostat unit (wall-mounted), preferably
mains-powered although I would consider one of those handy roving
battery-powered ones if necessary...

My question relates to the wiring of the output switch. Traditionally a
central heating controller has a SPDT switch providing both a "CH on"
and "CH off" signal, and the pole of the switch is usually wired to
live, to provide the mains supply to the zone valve, and so on.

However, I need to find a unit specifically in which the pole of the
switch (and it must be SPDT, SPST) is not hard-wired to Live, such that
I can wire it to something else.

Does anyone who has fitted such a unit recently know if it is usual for
the manufacturers to hard-wire the switch pole to Live? Obviously for
the battery-powered ones this isn't an issue but for the mains-powered
controllers there is the possibility that the live power for the unit
and the switch pole are connected internally, which scuppers my plans.

thanks,

Michael

"Michael Kilpatrick" wrote in message
...
Good afternoon all,

for a particular application I am looking for a combined central heating
digital timer-controller/thermostat unit (wall-mounted), preferably
mains-powered although I would consider one of those handy roving
battery-powered ones if necessary...

My question relates to the wiring of the output switch. Traditionally a
central heating controller has a SPDT switch providing both a "CH on" and
"CH off" signal, and the pole of the switch is usually wired to live, to
provide the mains supply to the zone valve, and so on.

However, I need to find a unit specifically in which the pole of the
switch (and it must be SPDT, SPST) is not hard-wired to Live, such that I
can wire it to something else.

Does anyone who has fitted such a unit recently know if it is usual for
the manufacturers to hard-wire the switch pole to Live? Obviously for the
battery-powered ones this isn't an issue but for the mains-powered
controllers there is the possibility that the live power for the unit and
the switch pole are connected internally, which scuppers my plans.

thanks,

Michael

I believe many are termed "Volts Free" which means that the switching
contacts are independent of the control circuit - most will be SPST.

John wrote:
"Michael Kilpatrick" wrote in message
...

However, I need to find a unit specifically in which the pole of the
switch (and it must be SPDT, SPST) is not hard-wired to Live, such that I
can wire it to something else.

Does anyone who has fitted such a unit recently know if it is usual for
the manufacturers to hard-wire the switch pole to Live? Obviously for the
battery-powered ones this isn't an issue but for the mains-powered
controllers there is the possibility that the live power for the unit and
the switch pole are connected internally, which scuppers my plans.

thanks,

Michael


I believe many are termed "Volts Free" which means that the switching
contacts are independent of the control circuit - most will be SPST.

"Most will be SPST"? It strikes me as odd. For a typical Y-plan system
with a mid-position valve, for example, the hot water circuit is
required to have an SPDT switch. So why not make all controllers SPDT by
default.

Surely most mult-zone controllers (i.e. one zone for HW and one or more
zones for CH) have all their switches as SPDT, no?

I definitely need to have a CH zone with an SPDT switch on my main
controller (which will have two CH zones and one HW zone).

Michael

"Michael Kilpatrick" wrote in message
...
John wrote:
"Michael Kilpatrick" wrote in
message ...

However, I need to find a unit specifically in which the pole of the
switch (and it must be SPDT, SPST) is not hard-wired to Live, such that I
can wire it to something else.

Does anyone who has fitted such a unit recently know if it is usual for
the manufacturers to hard-wire the switch pole to Live? Obviously for the
battery-powered ones this isn't an issue but for the mains-powered
controllers there is the possibility that the live power for the unit and
the switch pole are connected internally, which scuppers my plans.

thanks,

Michael


I believe many are termed "Volts Free" which means that the switching
contacts are independent of the control circuit - most will be SPST.

"Most will be SPST"? It strikes me as odd. For a typical Y-plan system
with a mid-position valve, for example, the hot water circuit is required
to have an SPDT switch. So why not make all controllers SPDT by default.

Surely most mult-zone controllers (i.e. one zone for HW and one or more
zones for CH) have all their switches as SPDT, no?

I definitely need to have a CH zone with an SPDT switch on my main
controller (which will have two CH zones and one HW zone).

Michael

Perhaps I am wrong. Mine is SPST - the switch in the motorised valve takes
care of other switching:

http://www.horstmann.co.uk/downloads...sDatasheet.pdf

On Thu, 08 Oct 2009 12:46:10 +0100, Michael Kilpatrick wrote:

Does anyone who has fitted such a unit recently know if it is usual for
the manufacturers to hard-wire the switch pole to Live? Obviously for
the battery-powered ones this isn't an issue but for the mains-powered
controllers there is the possibility that the live power for the unit
and the switch pole are connected internally, which scuppers my plans.

The Honeywell CM927 wireless programmable thermostat has a SPDT switched
output which is independent of the receiver unit's mains supply. The
Honeywell progstat itself is my favourite device for being pretty flexible
and easy to install and program for the user to use.



--
John Stumbles -- http://yaph.co.uk

An atheist is a person with no invisible means of support

In article ,
YAPH writes:
The Honeywell CM927 wireless programmable thermostat has a SPDT switched
output which is independent of the receiver unit's mains supply. The
Honeywell progstat itself is my favourite device for being pretty flexible
and easy to install and program for the user to use.

The Honeywell ST699 which was fitted here before I replaced it
with my own computer control had a pair of SPDT volt-free contacts.
They were labelled 240V 3A. When you followed the tracks back to
the relays on the board, you find the relays were rated 120V 1A
(or might have been 2A, I can't recall now), but not 240V at all.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Michael Kilpatrick wrote:

However, I need to find a unit specifically in which the pole of the
switch (and it must be SPDT, SPST) is not hard-wired to Live, such that
I can wire it to something else.

Not a problem if you find a unit that you like which has a hard wired
live - just use the switched live to drive a relay with a mains rated coil.

Use one myself in a home brew lashup to release the three way valve when
the CH goes off at night.

--
Scott

Where are we going and why am I in this handbasket?

In article ,
Michael Kilpatrick wrote:
My question relates to the wiring of the output switch. Traditionally a
central heating controller has a SPDT switch providing both a "CH on"
and "CH off" signal, and the pole of the switch is usually wired to
live, to provide the mains supply to the zone valve, and so on.

However, I need to find a unit specifically in which the pole of the
switch (and it must be SPDT, SPST) is not hard-wired to Live, such that
I can wire it to something else.

The Honeywell I had before fitting a new system had a link from mains to
the two SPDT relays - you could remove it if you wanted to switch say 24
volts.

--
*Frankly, scallop, I don't give a clam

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Andrew Gabriel wrote:
The Honeywell ST699 which was fitted here before I replaced it
with my own computer control had a pair of SPDT volt-free contacts.
They were labelled 240V 3A. When you followed the tracks back to
the relays on the board, you find the relays were rated 120V 1A
(or might have been 2A, I can't recall now), but not 240V at all.

Probably couldn't be bothered testing them at 240 volt. Or simply didn't
mark them as such. Many US firms are a bit insular. ;-)

--
*When I'm not in my right mind, my left mind gets pretty crowded *

Dave Plowman London SW
To e-mail, change noise into sound.

On Thu, 08 Oct 2009 12:46:10 +0100, Michael Kilpatrick wrote:

Good afternoon all,

for a particular application I am looking for a combined central heating
digital timer-controller/thermostat unit (wall-mounted), preferably
mains-powered although I would consider one of those handy roving
battery-powered ones if necessary...

My question relates to the wiring of the output switch. Traditionally a
central heating controller has a SPDT switch providing both a "CH on"
and "CH off" signal, and the pole of the switch is usually wired to
live, to provide the mains supply to the zone valve, and so on.

However, I need to find a unit specifically in which the pole of the
switch (and it must be SPDT, SPST) is not hard-wired to Live, such that
I can wire it to something else.

Does anyone who has fitted such a unit recently know if it is usual for
the manufacturers to hard-wire the switch pole to Live? Obviously for
the battery-powered ones this isn't an issue but for the mains-powered
controllers there is the possibility that the live power for the unit
and the switch pole are connected internally, which scuppers my plans.



The Salus RT500RF is available on ebay at a very reasonable price (about
40 quid delivered). That has a spdt contact which comes with a removable
link to allow volt-free operation. It's quite a nice little unit but a
bit basic in operation (if that matters). It works in the 800MHz band, so
no interference problems for most people with computers/networks.


--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.