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

 

[dimspark]

I'm no expert but I think changing an MCB from 30 to 20 is notifiable wirepuller

 

[Jimmy Boy]

I still think it's notifiable..

because... Work NOT in a special location or Kitchen is NOT notifiable unless you satisfy note (f) page 21 Electricians guide to Building regs I don't believe it is in it's present form, and by changing the protective device at source I think it's on thin ice. Just my opinion.

ATB Steve

 

[Deleted member 9648]

Apologies,I think you are correct on changing the protective device requiring notification....although as it is being downgraded it is a slightly grey area.

 

[WayneL]

........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.

Don't agree with this bit, either, Wirepuller - are you having a bad day??

If the OP had done what he originally planned (extended ring by 8 socket outlets), or added the radial to the existing ring, then of course he would be required to do a full set of tests - all the parameters will have changed: Zs, R1 + R2.....and he'd have to IR test.

And you couldn't call it 'minor works' - that would be a stretch of anyones imagination - so would require an EIC, Schedule of Inspections and a Schedule of Test results.......regardless of whether it's 'notifiable' or not.

 

[ian.settle1]

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

Bit late asking now isn't it.

 

[Jimmy Boy]

1.4 of Electricians guide to Building Regs clearly states..The technical requirements of Part P shall apply to all electrical installation work in dwellings whether the work is notifiable or not.

So seeing as the regs book is the substance of the Part P work that clearly means a full EIC. I agree with Wayne.

 

[Deleted member 9648]

Don't agree with this bit, either, Wirepuller - are you having a bad day??

If the OP had done what he originally planned (extended ring by 8 socket outlets), or added the radial to the existing ring, then of course he would be required to do a full set of tests - all the parameters will have changed: Zs, R1 + R2.....and he'd have to IR test.If he is an electrician,yes....if he is not...no.

And you couldn't call it 'minor works' - that would be a stretch of anyones imagination - so would require an EIC, Schedule of Inspections and a Schedule of Test results.......regardless of whether it's 'notifiable' or not.Incorrect....a minor works will cover an alteration or addition to one existing circuit,no matter how extensive

If an existing circuit is extended...even considerably by 8 sockets then that is minor works,and a minor works cert would suffice,although I accept I was incorrect in that if the protective device was changed then the work would be notifyable. Even if the protective device was changed as long as the alteration was to an existing circuit that would still be covered by a minor works cert,an EIC would not be required.
If the work is not notifyable anyone can do it in any way they please and not carry out any tests or provide any certs....Bs 7671 is not statutory and and part P does not apply to many installs.
If the OP was a qualified electrician then he would be negligent not carrying out a full test,if he is a DIYer he can do whatever he likes.

 

[WayneL]

If an existing circuit is extended...even considerably by 8 sockets then that is minor works,and a minor works cert would suffice,although I accept I was incorrect in that if the protective device was changed then the work would be notifyable. Even if the protective device was changed as long as the alteration was to an existing circuit that would still be covered by a minor works cert,an EIC would not be required.
If the work is not notifyable anyone can do it in any way they please and not carry out any tests or provide any certs....Bs 7671 is not statutory and and part P does not apply to many installs.
If the OP was a qualified electrician then he would be negligent not carrying out a full test,if he is a DIYer he can do whatever he likes.

Sorry, Wirepuller, cannot accept this statement - and very misleading for others reading this thread.

A MEIWC is for the addition of a socket outlet, or a lighting point, to an existing circuit, or similar works - not to extend a 'Ring Final' to encompass a new room with 8 socket outlets.

Tell me, where on the Minor Works Certificate would you fill in your 'Ring Final' test results?

And what is the 'tick-box' on an EIC for that says 'Alteration to an Existing Installation', if not for a job like this one?


GN3, Pg 96 - MEIWC Scope

The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not extend to the provision of a new circuit. Examples include the addition of a socket outlet or a lighting point to an existing circuit, the relocation of a light switch etc. This certificate may also be used for the replacement of equipment such as accessories or luminaires, but not for the replacement of distribution boards or similar items. Appropriate inspection and testing, however, should always be carried out, irrespective of the extent of the work undertaken.

Also,

GN3, Pg 98 Guidance For Recipients

A seperate Certificate should have been received for each existing circuit on which the minor works have been caried out.
This certificate is not appropriate if you requested the contractor to undertake more extensive installation work, for which you should have received an Electrical Installation Certificate.

So I think a MEIWC is not appropriate in this instance and all rellevant tests should be carried out and recorded on the 'Schedule of Test Results'

 

[Deleted member 9648]

"The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not extend to the provision of a new circuit. Examples include the addition of a socket outlet or a lighting point to an existing circuit, the relocation of a light switch etc. This certificate may also be used for the replacement of equipment such as accessories or luminaires, but not for the replacement of distribution boards or similar items. Appropriate inspection and testing, however, should always be carried out, irrespective of the extent of the work undertaken"

The section of your quote I have highlighted is relevant in this instance.....For alterations to an existing circuit an EIC is a sledgehammer to crack a nut. You state that where is the provision for recording ring continuity results?...well the same applies if you add one socket to a ring as well as eight...are you going to do an EIC for one socket which you have extended the ring to install?I If you wish to record ring continuity results you can use the comments box.
Let me make it clear that I am NOT advocating that tests on this sort of install need not be carried out,of course they should and an appropriate cert completed,,(minor works)....The point I was making is that legally,anyone can do this sort of install with no tests or certs,because very often it does not come under part P.
I will state catagorically that I have been using minor works forms for just this sort of install for the 15 odd years we have been NIC,,,and on our yearly inspection this has never been queried.
Minor works is relative anyway....8 sockets added to an existing circuit in a one bed flat may seem major....but in a large commercial premises 8 additional sockets added to a legnth of dado trunking is minor.Do an EIC for a minor job on such premises and you will have to carry out inspections and tests to verify supply characteristics at the intake/main switch type/main fuse type/Ze/psc/....if the DB serving the circuit is a sub board you will need the same for that as well......ridiculous for a simple addition to an existing circuit......a sledgehammer to crack a nut.