CH and HW wiring

[Fred]

Hello,
As you may know from my other posts, I am converting my gravity fed
CH/HW system to a fully pumped solution by moving the pump, adding
2-port valves etc.
I have bought a cylinder stat and a smart pump but neither has any
wire pre-fitted. Do I use "standard" 2-core mains cable for the stat
(there is no earth terminal inside the stat) and 3-core for the pump
(which is earthed)? Or do I need special cable that can withstand high
temperatures, like immersion cable?
I have bought some Horstmann 2-port valves from Screwfix and they do
have pre fitted wire with tinned ends. Is the idea that these are the
correct length already and you do not trim them further? It looks
quite tough wire to cut.
I also bought a CH wiring connection box (SF code 18884) to wire them
into. I know that I need to knock out the tabs along the top and
bottom to let the wire in but I am unsure: how do I stop the wire from
chaffing against the box. I'm thinking back boxes have rubber grommets
but these plastic boxes have nothing. How do I keep the cables neatly
in the box; there are no clamps or anything to hold them, so is it
just a matter of cutting the wires to the right length (the pump cable
doesn't look easy to trim; see above) so that none protrude from the
box? Is there nothing stopping them from falling out if you
(accidentally) tug them?
Thanks again.

[David Hansen]

On Thu, 31 Jan 2008 09:18:42 GMT someone who may be Fred wrote this:-

Both should have come in a box with instructions inside which will say what sort of cable is recommended. People have got away with standard cable types to both, but heat resisting cable is the thing for a proper job.

The general advice is to cut off the tinned ends. However, some disagree and many don't bother.
Cables should be suitably supported. If they are clipped to the surface then place a clip near the box. If flex is being taken in it should be clamped inside too. If inside (horizontal) trunking it doesn't need clipping.
There shouldn't be much rubbing. If you think there will be then put the cable in trunking to protect it.

[Roger Mills]

In an earlier contribution to this discussion,

Aren't there any installation leaflets with the pump and stat which specify the wiring requirements? If not, I would use heat resistant (flexible - not house-wiring) cable.

You *could* shorten them - but having them a bit longer is often useful if you ever need to remove the actuators without disconnecting them electrically. You can usually find somewhere to tuck the cables out of the way.

You need strain relief of *some* sort on the cables. Is there any provision in the box for using cable ties to clamp the cables to the back? If not, I would *drill* a hole for each cable (rather than removing the knock-outs) and then put a cable tie round each cable just inside the box, to prevent it being pulled out.
[There's been some discussion in another thread about the merits - or otherwise - of tinning the ends of cables, but I don't think it's likely to be a problem with low current applications such as this]

[Fred]

Instruction leaflets yes, but nothing about wiring in them.

I was thinking long these lines myself.

I'll hunt that out; any idea what it was called?
Thanks.

[Fred]

Oh I forgot to ask:
Is it ok to use two core (brown and blue) to go to the cylinder stat. I'm unhappy about using the blue, which should be neutral, as a switched live. I'll obviously flag it with a bit of tape.
Thanks.

[Roger Mills]

In an earlier contribution to this discussion,

It was in a thread called "Warm! 13 amp UK style plugs etc." Tinning is first mentioned by 'jrwalliker'.

[ARWadworth]

No problems doing that. Most households have lighswitches done the same way.
Adam