Conservatory electrics - extra double socket question

[shd1970]

Hi all,

Can anyone advise on on the following 2 quick questions please.

I have a conservatory with 3 double sockets off a 5 amp spur and i am planning on putting 2 x 1250 watt radiant heat electric radiators on the outside wall.

I need a further double socket so first question is.....

1 - Can i just take a feed from the closest double socket ?

and finally,

2 - Can i drop the cable in the cavity between the brick and block work on the dwarf wall of the conservatory, rather than chip out the plaster work on the inside wall ? Is this safe to do ?

Thanks in advance.

rgds,
Sean

 

[disinfo]

2500W / 230V = 10.8 amps so thats your first problem.

Secondly, its not a good idea to run cables in the cavity because of the possiblitiy of it being filled with foam insulation at a later date (causes pvc cabling to break down)

 

[shd1970]

Hi disinfo,

Many thanks for taking the time to respond.

So, upon checking further the electrics for the conservatory is seperately fused on the RCD but there is no indication as to the fuse size at that point, but the fuse in the spur is definately 5 amp.

Can i just replace the spur fuse with a 13 amp fuse ?

Secondly, we had the conservatory built and are planning on replacing the shelves anyway that span the cavity so it would be ok then if i then use say, use polystyrene insulation, or the rigid insulation blocks that you see used ??

Many thanks,
Sean

 

[disinfo]

Hi disinfo,


Secondly, we had the conservatory built and are planning on replacing the shelves anyway that span the cavity so it would be ok then if i then use say, use polystyrene insulation, or the rigid insulation blocks that you see used ??

Many thanks,
Sean

Sorry, I did actually mean polystyrene.

Installing cabling into plaster is extremely easy, and if cut away neatly it only takes minimul skill to repatch.

So, upon checking further the electrics for the conservatory is seperately fused on the RCD but there is no indication as to the fuse size at that point, but the fuse in the spur is definately 5 amp.

Can i just replace the spur fuse with a 13 amp fuse ?

Im a little unclear about what you mean here, do you mean that the conservatory is on its own fuse / mcb / rcbo at the consumer unit? If so I dont understand where the spur comes in.

What size cable is in the conservatory?

 

[shd1970]

thanks again disinfo for your input and apologies for any confusion.

with regard to the insulation, i know what you mean about chipping out a channel of plaster but the cavity really does seem the best approach as the decor inside the conservatory is pretty good (even if i do say so myself). Presumably, i could run it through some plastic conduit to give it some increased protection and then add some insulation boards (dense loft style blocks that i've seen) ?

regarding the fusing in the conservatory , i have just had a brain wave and checked.....the 5 amp fuse is for the fan in the ceiling ! (apols for the confusion)

So, i guess in just need to find out what fuse is on the RCD, correct ?

Sean

 

[Chri5]

Is the fused spur the ONLY spur off your main ring ? (because some fit a spur off a spur).

If so then running a 13a load is allowed and 13a x 230v = approx 3000w of use.

Since you intend to use 2500w of electric heating that doesn't give a huge amount for the other socket, which you haven't told us what it's going to be used for.

In a 'nice' world you should provide the sockets as part of the ring circuit which should be rated at 32a and will allow for a 13a load at each socket position.
Design wise that's the best option, but if you can't do that then the spur feed will be ok, even if it has the 3000w restriction.

Generally it's not a good idea to have cable placement between wall cavities. The cable is more prone to cold and damp, it can bridge the inner and outer walls causing damp and the insulation around it (be it fibreglass, kingspan or anything else) means the cable will over heat and fail.

The current regs derate the cable when it's run with insulation and since you pushing the capacity of the cable very close to it's limits, it's not advisable.

Surface trunking, conduit or chasing the plaster is the only real options that insure a correct design.

If you really must use the void then I'd suggest you increase the cable size to 4mm (to offset the derating factor) and better still add a barrier between the cable and any insulation.

Something like, drop cable inside the void, cover cable with wood baton and then insulation is not in direct contact with the cable.
If the DPC is poor there is a danger of damp bridging the inner skin,

 

[shd1970]

Hi Chri5

Many thanks for your reply and apologies for the delay in responding.

Ok, i have just confirmed that "all" the electrics in the conservatory are supplied via 1 Volex VB32 (B32) fuse on the RCD. I presume this is a 32a fuse so it looks like its rated correctly.
The electrics in the conservatory consists of 3 x double sockets increasing to 4 x double sockets and it already has an existing fan/light in the roof.

The fan/light electrics are wired with a 5 amp fused spured off the conservatory electrics so again this all sounds honky dorey.

So, based on my req to have the 2 heaters (2 x 1250w) i believe everything is "in range" as the only other usage will be a small light and the xmas tree in a month or so's time.

Thanks for your advise also on the cavity / insulation / cabling dillema too.

Until i get the shelf off, i wont know exactly what i am up against, but understand your advise of basically dont imbed your cable and pack insulation tightly around it and use 4mm cable.

Give it some breathing space, yes ?

I have a mate who works at an electrical wholesalers.....i'll give him a shout too.

thanks again

 

[Chri5]

So are you saying that the conservatory is on a 32A fuse on it's OWN circuit or is it part of a circuit covering rooms aside from the conservatory ?

If it is just for the conservatory then it will be a 32A 2.5mm cabled ring or 32A 4mm cabled radial circuit.

I expect the former to be correct, and if so the circuit is designed for nealy 7kw of load.