2.5mm radial

[gos]

I have a basement that has 2 rooms. 1 has power and the other has not. I installed a 2.5mm ring in the room with no power, comprising of 8 double sockets. When I went to add these to the ring in the other room I discovered that there is no ring, it is actually a 4mm radial circuit on a 30 amp breaker.

My solution is to turn the new 2.5mm ring in to a radial circuit and join it on the the existing 4mm radial and drop the breaker down to 20 amps. Is this an acceptable and safe solution?

Thank you.

Graham

 

[telectrix]

what kind of load willyou have on the 8 new sockets?

 

[gos]

It's going to be for a home cinema. Projector, AV amp, DVD Player, PS3, SKY box

 

[telectrix]

suggetion. make your new 2.5 into 2 radials, say 4 sockets apiece, feed each with a fused 13A spur off the 4mm radial. then you,ve still got 32A cct. in first room

 

[gos]

Ah not possible now as it's been plastered and I removed the last cable so it's now 2.5mm radial. Any other suggestions Telectrix

 

[adavis]

Why not wire you new 2.5 ring direct to the CU?

 

[telectrix]

could fit FCU to radial but that will only give you 13A max. or, fit enclosure with 1 16A MCB.... BTW, i am assuming that your original circuit is RCD protected. if not, fit one, or RCBO.

 

[gos]

It is RCD protected. Is dropping the breaker down to 20amp not an acceptable solution then?

 

[davelerave]

some guys would've made a 'lassoo' out of the 4mm radial+2.5 ring and left the 30amp -not me anyhow

 

[Jimmy Boy]

Without trying to be too overly critical as you are installing new circuits you should have established the the condition of and circuit arrangements of the existing installation (s) before undertaking alterations or additions to the installation which sorry to be blunt begs the question do you have the necessary competence and compliance to carry out the work to BS 7671 and comply with Part P regs ?

ATB S

 

[troonboy]

20amp is borderline on a 2.5 ( depending on de-rating factors) also different sized circuit conductors should not be mixed on the same circuit. someone could come along after you and uprate the breaker to a 32amp assuming that the circuit is a continuous 4mm.

 

[Jimmy Boy]

MAX CCC of 2.5 is 27A under perfect install conditions I agree I never go with more than 20A I prefer to stick to 16A unless I can clearly see it will never be buried under a ton of insulation

 

[gos]

Steve I agree I should have checked, I assumed it would be a ring. I trained as a sparks about 15 years ago, before part P, changed careers since and forgotten a lot of it. As I'm now stuck with what I have and the room has been plastered, I just want to make sure it's safe. The wiring is behind 50mm insulated plasterboard, so you reckon dropping the breaker down to 16A will protect the circuit?

 

[nickblake]

Tend to agree with steve on this one how do you know how large the existing ring you wanted to connect to was it could well have 20 sockets on it , as for you radial with 8 socket outlets although this would be better as a ring , you can use a 20 amp MCB on this circuit provided that the maximum Zs can be reached and that de rating factors have been met also if there is no risk of overload which could cause unacceptable inconvieniant tripping

 

[IQ Electrical]

also different sized circuit conductors should not be mixed on the same circuit. someone could come along after you and uprate the breaker to a 32amp assuming that the circuit is a continuous 4mm.

Absolutely incorrect, as long as the overcurrent protective device affords protection for the lowest CSA cable then of course you can reduce CSA as a circuit progresses (a common way of avoiding volt drop issues with economics in mind).

Another one for the myths thread!

 

[Paul.M]

IQ spot on again. Oh and another thing, don't have a ring fed by a radial.

 

[Sintra]

Reducing cable csa through a circuit is common practice on lighting radial circuits.

 

[Jimmy Boy]

suggetion. make your new 2.5 into 2 radials, say 4 sockets apiece, feed each with a fused 13A spur off the 4mm radial. then you,ve still got 32A cct. in first room

That's what I would do but I should advise you that if this is a dwelling you need to be registered under a competence person scheme or you need to notify building control to get them sign to it off, dwelling or not I would seriously suggest you get a the on-site guide and familiarise yourself with the current regs especially those regarding earthing and bonding, have you even establihed the supply characteristics ? Not to mention you will need test instruments to measure Ze,PFC, and Zs for your final circuits as well as all the other verification tests required..Good luck dude

 

[Deleted member 9648]

That's what I would do but I should advise you that if this is a dwelling you need to be registered under a competence person scheme or you need to notify building control to get them sign to it off, dwelling or not I would seriously suggest you get a the on-site guide and familiarise yourself with the current regs especially those regarding earthing and bonding, have you even establihed the supply characteristics ? Not to mention you will need test instruments to measure Ze,PFC, and Zs for your final circuits as well as all the other verification tests required..Good luck dude

As long as the anticipated load is within the limits of the protective device there is no reason why the circuit cant be a 20a radial,although it may exceed the recommended floor area of 50sqm...this is a recommendation not a requirement.
If the alteration to an existing circuit does not involve alterations in a kitchen or bathroom it does not come under part P and so no requirement to register with BC......and you do not need to be registered with a competant person scheme,any Tom,Dick or Abdul can legally extend or alter an existing circuit not in a kitchen or bathroom, or outside without carrying out any tests or inspections,they can wire it in a bit of wet string if they want.....doesnt make it right but thats the way it is.

 

[telectrix]

another myth bites the dust