Connecting Wires

[HavntaClue]

Hi,

I have a 2.5mm PVC mains cable which i want to use as the feed to run outside for power to my shed. I do understand about Part P regs and notifiable work etc... but can you connect to this 2.5mm then run a larger size armoured cable from this, say a 4mm or 6mm or is there no point and you have to keep it at 2.5mm ?

Regards
HaC

 

[Aragorn84]

Cant you run the armour right back to the CU?

Where does this existing 2.5mm cable come from?

How much power do you need in the garage?

 

[ricicle]

The cable might have to be bigger if the distance is an issue

 

[HavntaClue]

Hi,
Cant run direct from Cu, decoration, logistical and maybe capacity issues. There are no fuse slots loft for another cable.
The only accessible power would be from the loft, which i think is a 2.5mm cable which is taken (is it called a spur) off the upstairs main. The shed would be a run of 36m to the bottom of the garden.

I want to power my main shed with One(1) Flures 5f to 6f Light with a switch and a power socket. The second shed has an aviary inside and i need the lighting for the birds. I want two (2) flures 3 foot lights and standard light socket (to use as a night light with a low watt bulb) and a power socket. I want to put the lights on timers in the bird shed, so they will need to be plugged into a socket (ifs thats the case then i'll need three power sockets, with two being used for the lights).
If push comes to shove, i can do without the power sockets as the lighting is the most important thing.

Obviously i could connect a 2.5mm Armoured to my existing 2.5mm PVC but to increase capacity could i connect a 6mm Armoured instead ?

HaC

 

[londonboy]

Obviously i could connect a 2.5mm Armoured to my existing 2.5mm PVC but to increase capacity could i connect a 6mm Armoured instead ?

No you cant do this. Cant you cleat armoured around house and drill into back of the cu? Or go up into the loft and back down again?
36 metres is a long way.

 

[RF Lighting]

No.

You are limited to 13A to all the sheds if you try and reuse your bit of 2.5mm² in the loft.

Probably the best soloution would be to ask an electrician to call round and see how this installation should actually be wired.

 

[Aragorn84]

Theres nothing wrong with using the 6mm cable, you just wont gain anything from it, you'll still be limited by the 13A your allowed to spur from a ring main.

If you do use the ring feed, you'll need to run the spur to something like this:

http://www.screwfix.com/prods/83049...eed-_-Electrical Supplies-_-Volex 13A RCD FCU

Its not ideal though.

You really should be aiming to run a cable from the CU itself.

 

[HavntaClue]

Thanks for your help.

So, if i ran it from the cable in the loft then i might aswell use the 2.5mm armoured as i wouldnt gain anything from the 6mm.

I cant use the Cu. As i said, all the 'slots' are taken. Even if it wasnt, it would me drilling a hole in my new PVC door or side panels to get access, then running unsightly cable up the wall of the hall and into the unit.

Will the voltage drop then due to the lengh of the cable ? What ampage do lights work from ? I do have another light cable in the loft which is a direct feed to the Cu. I think its either 1 or 1.5mm. Could i run two cables from the loft ? One from the lights for the lights in shed and another from the Ring Main for the power sockets ?Would that help ?
I do realise i will have to have added RCD protection at the point of these connections in the loft aswell. Thanks for the link.

HaC

 

[flameport]

2.5mm will limit you to around 2kW before volt drop becomes an issue.
No problem for a few lights, but sockets are out of the question.
4mm would allow the full 13A to be used.

2 separate cables would be a shoddy mess, and probably cost more than one larger cable.

Connecting it - unless your house is only made from PVC doors and panels, there must be some solid wall to get the cable through?
Even if the existing CU is full, you could have an additional small one fitted?
A picture of the CU and surrounding area will help.

 

[HavntaClue]

Hi there,

I'll try and get a picture of my Cu. Its in the hall so the only access to the outside is the front door which is uPVC. Otherwise to get out through a solid wall would meen drilling through to the lounge then out through the front or side. That would look crap, even it it were boxed in.

Can you tell me why running two cables would be a shoddy mess ?
They would run together both be the armoured types. Would this work. Spur off the light in the loft with a 1.5mm armoured and also spur off the 2.5mm mains with the same size but armoured ? Would that allow me to have sockets ?

Regards
HaC

 

[Aragorn84]

If you spurred it from a 13A FCU (with suitable RCD protection) then you can have sockets, you'll just be limited to what you can plug in before the 13A fuse blows. Plus, when it does blow (or the RCD trips etc) you then have to climb up into the attic to fix it...

Cant you go up from the CU? Thru the ceiling and into the attic that way?

Incidentally, at 36M the voltage drop on 2.5mm SWA at 13A would be 4%, which i think is acceptable?

I'd always consider using a larger cable than just scraping it in on a thinner one, but the whole proposal is entirely shonky, even to my untrained eyes.

IMO, if you do a job like this, you should aim to do it once and do it properly, and that means a properly sized cable run back to the CU on its own MCB/RCBO.

 

[HavntaClue]

I totally agree, but if you cant do a 'proper' job then whats the alternatives ? I need to try and explore all avenues hence all the questions. If the Fuse/RCD was in the shed rather that the loft then would that be acceptable rather that an RCD at the spur ? It will be armoured cable i will be using. The whole house is RCD protected anyway at the Cu.

You say a 4% drop in voltage on armoured cable at that lengh on 2.5mm. That sounds easily sufficient for lighting. I take it things like Lawn Mowers which are 13A and such like would cause it to trip due to the loss of voltage ?

HaC

 

[Aragorn84]

If the Fuse is in the shed, then whats protecting the 2.5mm SWA thats connected to the spur from the ring main?

The lawn mower wont bother about the voltage drop. The main issue is that the combined draw from everything out there cant exceed 13A, so depending on what your doing out there means you might exceed it and blow the fuse...

Theres always a way to do a proper job. The usual issue is making that proper job aesthetically pleasing. But form over function is a no-no with things like this.

Why cant you take some trunking up the wall from the CU, thru the ceiling and up into the loft that way?

 

[flameport]

Lighting circuits are limited to a maximum volt drop of 3%, and that is the total drop from the CU in the house to the furthest extent of the circuit.

As for alternatives - there are 2. Do the job properly, or don't do the job at all.

I hope those fluorescent lights you are getting will be high frequency types?

 

[mikhailfaradayski]

I totally agree, but if you cant do a 'proper' job then whats the alternatives ?

Alternatives to a proper job
1, Don't do it.
2, do something dangerous/non-compliant

Option 1 would be the only acceptable solution IMO.

I need to try and explore all avenues hence all the questions. If the Fuse/RCD was in the shed rather that the loft then would that be acceptable rather that an RCD at the spur ? It will be armoured cable i will be using. The whole house is RCD protected anyway at the Cu.

You say that you are aware of Part P requirements, so im assuming that you want to avoid the cost of LABC pre-notification fees and are therfore getting a sparky in to do this.
If this is the case, why not get the spark round to look at the job and then suggest various possibilities?

You say a 4% drop in voltage on armoured cable at that lengh on 2.5mm. That sounds easily sufficient for lighting. I take it things like Lawn Mowers which are 13A and such like would cause it to trip due to the loss of voltage ?
HaC

Not really, but if you are getting a spark in, why worry? He will be able to advise you on a solution which will be compliant (and safe)