New socket from spur

[JohnNox]

My house's central consumer unit is located inside the under-stairs cupboard. Recently an alarm engineer installed a fused spur in order to power up an alarm control panel.
So now there is:

[Consumer unit]->spur cable->[3A FCU]->cable->[alarm box]

I was wondering what is the best way to get a single power socket inside the cupboard, in order to power a Nest wireless thermostat (to be fixed outside the cupboard).

Would it be lawful and "ok" to install a connection box and a single socket on the cable between the consumer unit and the existing FCU ?

That would make the system as follows:

[Consumer unit]->spur cable->[connection box]*-->[3A FCU]->cable->[alarm box]
                                             *-->[socket]->cable->[nest thermostat]

Any thoughts or alternative ideas welcome. One alternative I thought would be to use the existing FCU box as a connection box and get another cable out going to a socket. It'll be a 3A fused outlet but that would be fine for the Nest thermostat.

Like so:

[Consumer unit]->spur cable->[3A FCU]*-->cable1->[alarm box]
                                     *-->cable2->[socket]->[nest thermostat]

 

[EFLImpudence]

What rating of fuse/mcb does the new spur run off?

 

[EFLImpudence]

The Nest thermostat should be on the same circuit as the boiler and heating.

It should be connected near the boiler or wiring centre.

 

[JohnNox]

What rating of fuse/mcb does the new spur run off?

The new spur runs of a 32A MCB (along with a couple of downstair socket rings).

The Nest thermostat should be on the same circuit as the boiler and heating.
It should be connected near the boiler or wiring centre.

The boiler-side part of the thermostat is wired next to the boiler. The wireless part can be moved from room to room and the place I decided to install it is outside of the under-stairs cupboard. That's the most efficient place in terms of temperature and being able to 'see' movement and do it's smart things. Unfortunately there's no extra cabling running from the boiler to this location, so I'd like to power it via a normal socket. I do this already, the Nest wireless part is installed on a socket inside the kitchen, but that placement is suboptimal.
So it's just a matter of providing a socket inside the cupboard!

 

[EFLImpudence]

Ok (as it's on 32A circuit).

Then there is no need for a connection box.

Just connect your new socket cable to the supply/feed/in terminals of the FCU.

 

[JohnNox]

Ok (as it's on 32A circuit).

Then there is no need for a connection box.

Just connect your new socket cable to the supply/feed/in terminals of the FCU.

Thank you very much, I'll do that! Just out of curiosity, what is the reasoning behind using the supply side terminals of the FCU instead of the load side? So that the socket is unfused?

 

[EFLImpudence]

So that the socket is unfused?

Well it is at 32A - until you put in a plug.



Before someone else says something.

The regulations actually state that you can only have one socket on a 32A spur with (what I presume you have) 2.5mm² cable.
However, this one socket can either be a single or a double socket - 2 x13A = 26A and the cable is rated at 27A but you are not, strictly speaking suppose to plug in two 13A appliances on one double socket but that's another matter.

Anyway, the alarm circuit will use so little current that it will not really matter.

 

[EFLImpudence]

Oh, that's a point -

Has the alarm fitter used 2.5mm² cable? I think he probably would.

 

[JohnNox]

Oh, that's a point -

Has the alarm fitter used 2.5mm² cable? I think he probably would.

Yes he fitted normal 2-core and earth 2.5mm cable from consumer unit to FCU. A smaller cable from FCU to alarm box.

 

[EFLImpudence]

That's alright then.

 

[Blueflash]

Does that mean you have a spur from a spur

Dave

 

[EFLImpudence]

It does but with an alarm and a thermostat, there is no problem.

Or you can treat it as a (very short) radial circuit - albeit 32A OPD on 2.5mm² - with overload protection by two 3A fuses.


Would you be unhappy with it?

 

[winston1]

Does that mean you have a spur from a spur

Dave

Indeed, and not allowed. It is all very well saying it is only an alarm and a nest, but there is nothing to stop someone plugging in a 13 amp load.

 

[EFLImpudence]

...and what dire consequence would that cause?

 

[Blueflash]

Do you just make up your own regs then ?

Dave