RE: Heating relays and CAT5 power

["Nigel Giddings" <nigel@xxxxxxxxxxxxxx>]

Simon,

I have built a VIOM based CH controller and used the matching relay
boards which are rated at 1 amp d.c. at 24 Volts d.c. /110 Volts a.c.

http://photos.corbenic.co.uk/dcp02093jpg.html

I suppose it really depends what you will actually be switching, that is
to say what is it connected to in your heating system. My system
controls wax filled zone valves, these then operate a switch to operate
the pump...

A 3A relay should have no problems at all, you will probably find that
your spur unit feeding mains power to the existing controls is only a 3A
anyway...

Running your proposed relays over CAT5 should be no problem but make
sure you fit diodes across the coils to prevent back EMF caused when the
relays magnetic field collapses when de-energised...

HTH

Nigel

-----Original Message-----
From: Simon McCaughey [mailto:simonmcc@xxxxxxx]
Sent: 27 October 2006 10:10
To: UK Home Automation List
Subject: [ukha_d] Heating relays and CAT5 power

I have finally got round to starting my heating control project using
the
VIOM I got about 2 years ago!

I have most of the software written, so it's time to turn to hardware -
couple of questions :
1) I am basically replacing the standard heating controls with a relay.
What
sort of relay should I use? I see normal timers seem to be rated at 3A,
would
this do the job : http://tinyurl.com/y5afgh <http://tinyurl.com/y5afgh>

2) The connection between the VIOM and the relay will be about 20 metres
CAT5 cable. Will CAT5 carry enough power safely to power 3 relays? The
coil
on the above relay takes 37.5mA according to the maplin page. From
googling
it seems to be somewhere around 1A, so this should be absolutely no
problem.

Any advice or experience appreciated!

Thanks

Simon

---
"I refuse to tip toe through life only to arrive safely at death"

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