Heating controller/programmer mains power source

niley

Hi,

I'm curious as to others thoughts on this one. The image below is from the manual for an Ariston Microsystem 21 boiler. Mains power comes from the switched spur into the boiler. Power for the programmer is then taken from the boiler via terminals N & 1 through the terminal block and onto the programmer. This means that the programmer loses power when the on/off switch on the boiler itself is in the off position. Is there any advantage (or even requirement) of doing it this way rather than connecting the programmer directly to the switched spur along with the boiler such that the programmer maintains power so long as the switched spur is in the on position? I'm thinking in terms of using some sort of smart hub, and if it's better to keep the thing powered even if the boiler itself is turned off, or if it's better to have the hub turn off with the boiler.

Irish Steve

The main issue with putting the programmer directly on the spur is that unless there's some form of fuse protection with the programmer, you'd end up having to use much heavier wire on many of the interconnections, as they have to be capable of carrying the current that's determined by the breaker on the spur, by using the connect back from the boiler, the 2A fuse there means that much smaller and lighter cables can be used for the interconnections. That makes for much easier wiring in the places where it matters, as space can be tight. It's a viable alternative option to using something like a wiring centre at the location of the timeclock, often in the hot press, depending on where the boiler is located.