adding to a mcb

[amckay]

Is there anything wrong with this scenario.
Customer wants two extra socket about 2m from each other, first one being 400mm from consumer unit.
No spare ways on CU, nearest outlet on rfc is 5m away.
Is it possible to just add a radial fed from the MCB which feeds the rfc for that floor?
I'm thinking its just bad practice to do so but can find info in osg.
MCB rated at 32A and protected by 30mA RCD.

 

[telectrix]

you can add a single outlet as a spur from the CU, but if you want 2 outlets, the either fuse down with a FCU or divert the RFC through your 2 new sockets, thus maintaining the RFC.

 

[Octopus]

Simple answer is yes BUT, MCB to 13A FCU, then the customer can have as many sockets as they like.

 

[amlu]

use 4mm cable you can have a radial.

 

[VoltzElectrical]

Shouldn't this be in the trainee section?

 

[amckay]

Cheers chaps

 

[Octopus]

use 4mm cable you can have a radial.

Are you advocating a 4mm radial off the same 32A MCB as the RFC?

Not sure I'd do that!

 

[Pete999]

use 4mm cable you can have a radial.

Pardon, are you sure?

 

[Silly Sausage]

use 4mm cable you can have a radial.

Are you advocating a 4mm radial off the same 32A MCB as the RFC?

Not sure I'd do that!

Pardon, are you sure?

Alright then, give us valid reasons as to why not?

 

[D Skelton]

Popcorn at the ready! :1eye:

 

[Paul.M]

Shouldn't this be in the trainee section?

No mate, Amckay can handle himself in the main forum, good sparky.

Tel has already given answer, extend the ring. If these two sockets are that close to the CU (400mm & 2m), extend the T&E in the CU to the two new sockets. Simples.

 

[Deleted member 26818]

No reason why 4mm cable to 2 new sockets can't be done.
If it's added to the present socket circuit, there would not even be a requirement to notify under Part P.

 

[Pete999]

No reason why 4mm cable to 2 new sockets can't be done.
If it's added to the present socket circuit, there would not even be a requirement to notify under Part P.

Can you point me in the right direction where it says your idea is OK please spinlondon.

 

[telectrix]

can you point to the reg. that says it's not OK?

 

[stevethesparks]

Everyone becoming frightened of the electrical bible rather than thinking for themselves and applying their knowledge to think outside the box. As long as all safety aspects and calcs are met, not a problem.

 

[Pete999]

can you point to the reg. that says it's not OK?

Well I can only quote app 15 Tel now iut's someone elses turn

 

[Octopus]

I'm not sure there is a reg but good practice suggests have a RFC of 2.5mm and a radial of 4mm in the same MCB isn't a good idea.

Effectively, by description, they are 2 circuits yet you should only have 1 circuit per MCB.

 

[Plonker 3]

Why is it " 2 circuits" by description? Its no different to putting a FCU and several sockets off that is it.

 

[ImpededLoop]

What are the potential consequences of a fault on the existing ring final or a fault on the new 4mm?

I can't think of any that would cause any problems. Both circuits (ring and 4mm radial) are usually ok on a 32A mcb, so I can't see that sharing the same mcb presents any additional risk.

 

[Flanders]

The only thing that may course an issue is with the 4mm cable in the MCB is not allowing the clamp connection of the mcb tightening onto the 2.5mm cables giving a good firm connection but as long as this is checked at the install stage by the good old give it tug test! I cant see problem

 

[Prat P]

It would be a first for me to see on a schedule of test results ph conductor 4mm/2.5 neutral 4mm/2.5mm....
plus when testing the ring for end to end continuity,the readings would not be accurate with the presence of 2 different diameter cables,so unless you can get carol vorderman helping you work it out its probably not a great idea mixing 4 mm with 2.5.

 

[Octopus]

It would be a first for me to see on a schedule of test results ph conductor 4mm/2.5 neutral 4mm/2.5mm....
plus when testing the ring for end to end continuity,the readings would not be accurate with the presence of 2 different diameter cables,so unless you can get carol vorderman helping you work it out its probably not a great idea mixing 4 mm with 2.5.

To do it thoroughly, you would need 2 lines of results on the schedule of test results - anything else would not make any sense.

 

[Deleted member 26818]

Nothing in the Regs prohibiting it.
Yes we would all look at it and say that it's two circuits off of one MCB, but according to the definition of a circuit, it's not.
At the end of the day you have to balance whether you want or need the extra work that replacing the CU, or adding an extra CU would generate, against the cost for the customer.
Obviously spurring off the RFC at the CU would be cheaper for the customer, but it won't pay you as much.

 

[Flanders]

To do it thoroughly, you would need 2 lines of results on the schedule of test results - anything else would not make any sense.

That how I do it when I come across it during an EICR , I come across it quite a lot

 

[SPARTYKUS]

In an ideal world they would be separate.

but the thread presents a less than ideal world.

it would be the first time I had seen a 4.0mm2 radial circuit sharing the same 32A MCB as a 2.5mm2 ring. That said I do not think it is unsafe. Given all the points mentioned so far.

I prefer the "extending the ring" suggestion though

 

[7029 dave]

Would you get one 4mm in, with two 2.5mm, these new CU's (all modular) are not up to it me thinks.?

 

[SPARTYKUS]

Would you get one 4mm in, with two 2.5mm, these new CU's (all modular) are not up to it me thinks.?

Not ideal thats for sure

 

[amckay]

Just to clarify in the op scenario, the rfc in the 32A MCB is 2.5mm and new radial fed from existing rfc MCB will be 2.5mm also (bearing in mind its only feeding two dbl skt outlets).

4mm radials are common practice mainland Europe. Ask them what an rfc is and they look at you like you've got two heads!

 

[Guest55]

absolutely nothing wrong with adding 2 sockets wired in 4mm to an existing 32A ring mcb.

the only limiting factors would be

a. can the cable carry full circuit load - yes it can

b. will the ELI at the furthest new socket be within limits - almost certainly as its only a few mtrs from the cu.


and a single circuit can still have multiple cables originating from source.

 

[Andy78]

Just to clarify in the op scenario, the rfc in the 32A MCB is 2.5mm and new radial fed from existing rfc MCB will be 2.5mm also (bearing in mind its only feeding two dbl skt outlets).

4mm radials are common practice mainland Europe. Ask them what an rfc is and they look at you like you've got two heads!

2 double sockets on a 2.5mm radial from the 32A MCB ? assuming method C, the cable CCC is 27A so clearly the OCPD at 32A is not sufficient with a potential draw on the radial of 52A. You could take a 2.5mm spur from the MCB with a maximum of one double outlet.
Just break into and extend the ring as has already been suggested.