dual boiler supply

[mackeral]

A chap has a garage which is being converted into an office. Standard set-up of boiler in garage and central heating controls in the house (timeclock).
At the boiler he has a 'house pump' and 'boiler' switch and also a separate 'garage pump' for the rad in the garage. The idea being to run the CH in the garage separate from the house CH.
However, the supply to the burner and 'garage pump' will need to be from a different circuit.
Is there any special precautions that need to be taken when feeding an appliance (the burner) from 2 different circuits?

thanks

 

[plugwash]

unless you know exactly what your doing you should put everything related to the central heating on the same cuircuit.

is there any special reason why you can't do this?

 

[mackeral]

Plug,

the CH is controlled via a timeclock fed from in the house. so timeclock OFF, no supply to the boiler. Therefore to turn the supply on in the garage without turning the timeclock on in the house 2 supplys are needed...

thanks

 

[kevplumb]

why not just use an s plan +

if the boiler live is fed from two different places surely once it fires both lines will be live

 

[Lectrician]

It is possible with the use of a relay. This would need to be put in an enclosure, and suitable warning notices used. Dont like the idea myself though

Does the boiler not have a constant live?? Many do, and this could then be used as appropriate.

 

[Big_Spark]

If your talking about what I think your talking about then the clear, simple and only answer is an indefatigable NO.

Equipment must not be fed from two sources of energy unless there is an interlock in place to prevent dual energisation simultaneously. Timeclocks etc do not qualify. The interlock would need to be mechanical and unable to operate on both circuits simultaneously.

 

[mackeral]

thanks guys,

Lectrician - Is the constant live not at the timeclock? So there would only be a switched live running through from the house to the boiler/pump?

[why not just use an s plan +

if the boiler live is fed from two different places surely once it fires both lines will be live ]
Kev, maybe you could explain this one out to me?[/quote]

 

[Lectrician]

Many boilers require a constant live, and a switched 'fire' live.

 

[Big_Spark]

As Lec has said, most boilers have a permanent live feed, this is for pumps, internal controls etc, and a switched live that is the triger for the boiler to fire up. However they will be fed from the same source, just one will be interupted by controls (The switched live) and one will be direct to the boiler.

In order to comply with regulations these must come from the same source, ie: Switched Fused spur.

 

[Lectrician]

Yep, that is how it would be wired, (if yours has a constant live). This constant live could then be utilised to open a second valve via a second time clock/switch.

If you have just two pumps, one for each rad circuit, you would then need a relay to isolate the two pump lives from each other. Otherwise everytime one pump comes on in parallel with the boiler, so will the other.

Starts to get a little involved to simply talk about. A diagram would be better.

Why don't you se what cables come into your boiler and let us know??

Chances are even if your boiler doesn't need a constant live, the nice sparky will have installed a 3core or 2x2cores anyway

 

[kevplumb]

s plan + is here

 

[mackeral]

There is a supply from the t/clock to a 2 gang switch. 1 switch controls the pump and the other the burner. A 3 core flex goes to each. Surely then there is no permanent feed at these points, only a swiched feed from the t/clock?

thanks for the info so far...

 

[Lectrician]

Sounds like the original wiring is a bit of a bodge? Why a 2 gang switch? Whats it's purpose? The time clock should be doing the switching.

 

[mackeral]

thanks for your patience Lec...

Seen this many times. Im assuming for local isolation (although the neutral wont be switched)