3036 rewirable rcd protection

[ianphilip007]

have a customer with a 3036 rewireable board. i Need to provide rcd protection for 1x30a ring circuit and 1x5a lighting circuit for additions. my plan is to remove the ring main and lighting circuit from existing fuse board.

From one of the now spare ways run a 6mm2 t+e fused at 40a to a new 2way 63a 30ma C.U. the ring main now on 32a mcb and lighting 6a mcb both circuits now rcd protected.

anyone see any issues ??

 

[Darkwood]

is not replacing the D.B. a better option? for a few quid more than you are already spending on the additional 2way board complete you could get a full 17th edition board, im sure a chat with your customer is what you need to do, spend now save later and flexibility to expand.

 

[ianphilip007]

yes darkwood i agree and will be my prefered option just wanted to check if my plan was a suitable alternative if they dont want to pay for a new cu, to provide the rcd protection.

 

[ianphilip007]

just done a quick cable calc re correction factor for a 3036 fuse.

6mm2 rated current 45Amps 45x0.725 = 32.625 (In Max)
10mm2 rated current 65Amps 65x0,725 = 47.125 (In Max)

it = in/Cc 40/0.725 = 55.17

ib=38<In=40<Iz=65

so my original plan to use 6mm no good will have to be 10mm feed to 2nd cu.

 

[Guest55]

Current rating of 6mm T&E in free air is 51A ,

 

[Guest55]

But is still not enough unfortunately.

 

[ianphilip007]

51 a ? for 6mm2 its 47a for 70'c clipped direct as per osg , but yes 6mm2 not big enough ill need to use 10mm2.

 

[ianphilip007]

apart from a new dual rcd main C.U any other options for providing rcd protection to both circuits.

just thought only one lighting circuit/ ringmain my oriiginal plan would put both on single rcd which i want to avoid. Im hoping they will opt for a complete new main cu.

 

[rich.250]

just out of interest, is it the older 1mm cpc in the RFC? if so i think your option of new door separate db is best. as 2.5/1mm will not meet disconnection time for 30a 3036

 

[rich.250]

door... edit. DB or

 

[ianphilip007]

not sure as to 1mm or 1.5mm cpc or current zs for ring final circuit.

 

[rich.250]

1mm more than likely cannot take the fault current to operate the OCPD in the required time.
If it is 1.5 there is the option of fitting a rcd after the consumer unit, in a 2w enclosure for each cct.
Although i personally think your options are the way to go

 

[Guest55]

Connect the new circuits into a small enclosure containing 2 RCBO's for lights / sockets.
Feed this unit with 6mm T&E using one of the spare fuseways fitted with a wylex
plug-in 40A mcb , saves having to derate due to rewirable

 

[rich.250]

Plan
What short cct rating have plug in mcbs got??

 

[Strima]

Henley block, new box with suitable RCCB and breakers.