Wiring up a central heating system

[Pandora]

My proposed central heating system comprises a boiler, four pumps, two zone valves, three mixing valves and two controllers.

What's the best way to provide mains power to this lot? I was planning to install a single "heating system" radial circuit using 4mm=B2 twin and earth. This circuit would start at the consumer unit and snake its way through the house from component to component before being terminated at the boiler. Each component would have its own local fused connection unit to isolate it electrically.

Does that solution seem OK? Any tips?

[Christian McArdle]

Way too big. Use 1mm or 1.5mm. Much easier to work with and will actually fit in the terminals! You can also use multiway flex after the FCU.

Modern boilers usually have an internal isolator, which they like to cut off the rest of the system. Generally, the main supply should direct go to the boiler supply terminals and all other components (pumps, controllers etc) should come off the switched output from the boiler. Don't confuse this switched output with the "pump" output. Your boiler may not have one.

Don't use an FCU for each component. You should have the entire system off a single 3A FCU (or MCB) which comes before the boiler. Individual components may be switched using standard (usually 20A, but smaller is fine) DP switches, rather than FCUs.

Christian.

[Dave Plowman (News)]

I'd say you need to do a bit of learning about current consumption and cable sizes. All the components you've mentioned take a tiny amount of current and could *probably* be fed with the smallest TW&E - ie 1mm.

Which doesn't bode well for the design of a one off heating system.

[Pandora]

My boiler has got this internal isolator. What is the point of it? If you power down the boiler when you service it, you power down all the controllers as well. Isn't there a chance they will lose their parameter settings?

[Andrew Gabriel]

Normally any electronic controls have something like 24h battery backup, unless the rechargable battery has died (which happens).

[Christian McArdle]

It's so that when you turn off the isolator, there are no voltages present on the control wiring. Without it, the call for heat input could be live.

Christian.

[John]

OT but I emailed you 30 days ago Andrew. Today the message came back as undeliverable? Is there a problem with your mail collection?

John

[Andrew Gabriel]

Sorry John. I stopped downloading that mailbox about 5 years ago when it reached 1000 junk mails a day and perhaps only a couple of genuine mails a month. If I've despamtrapped your email address correctly, I've mailed you a usable email address.