How to certify a ring main with lighting circuit taken of a fused spur???

[newbie111]

just wondering how i would certify this type of installation, would i take the highest resistance value of r1+r2 of the lighting circuit and use this to add to ze? would i also have seperate values for the two circuits recorded on the EIC. any help eould be very welcome

 

[marcusone]

Hi Newbie

I would record the lighting circuit separately on the EIC but make it clear that it is a spur off the ring main. The lighting circuit has its own protective device and Ze for the lighting circuit will be measured at the fused spur.

Cheers

Mark.

 

[newbie111]

thanks for your prompt reply, so the fuse will be the protective device for the lighting spur and not the mcb at the distribution board? so the lighting circuit is tested as a completely seperate circuit and recorded assuch. thanks again
also if the ring trips and the lights also go out.As they are feed from the ring,does it comply to 17th as we must minimise inconvinence to users?

 

[malcolmsanford]

Well you answered your own question, it's not a great design to take a lighting circuit of a ring final circuit, which is why you don't often see it. There is nothing in the regs to stop you doing it, as whoever did it thought that was the best design for the circumstances, and who can say he/she was wrong, as we don't know what the circumstances were.

 

[newbie111]

where would i find the zs for a 3amp fuse,if that is the protective device and would i do pfc and pefc at that point too,thanks again.

 

[chiplard]

Hi Newbie

I would record the lighting circuit separately on the EIC but make it clear that it is a spur off the ring main. The lighting circuit has its own protective device and Ze for the lighting circuit will be measured at the fused spur.

Cheers

Mark.

The Ze is ONLY measured at the Supply. A Zs figure should be measured at the furthest point of the lighting circuit to ensure it meets the tabulated values for the MCB.

 

[newbie111]

so the circuit would be measured for zs at the furthest lighting point and should not be done seperately for the ring final and lighting circuit,sorry getting a bit confused on how i should complete an EIC with this circuit?

 

[DurhamSparky]

do the test as usuall!!

include the spur as part of the ring! as effectively thats what it is..! go to th furthest light and get a zs..! if your ZS is Higher that the ring ZS note that one down! but make sure the cert is naoted that its a socket / light circuit!

 

[newbie111]

thank you

 

[DurhamSparky]

welcome

 

[gamblor6]

agreed durham. its never its own circuit if its spurred off a ring.

 

[gamblor6]

ze from the fcu ive heard it all now lol

 

[DurhamSparky]

creating a new circuit with in a circuit on its own protective device as well!! ermmmm!! wtf! surely at some point ALL the circuits will be on a 32 unless its a magic FCU that stays on when the MCB trips!

 

[Deleted member 19807]

I have started to record spurs with an "a" after the circuit number with the details of the fuse in the fcu as the over current device, so if the ring is on circuit 3, the spur will be 3a, I just think that anyone looking at it later when trying to sort out a problem will then know there is an fcu controling " outside lights" as an example.

May be a bit ott but not a lot of extra work.

 

[newbie111]

just trying to get this correct( which for my small brain is something), zs is taken from the furthest lighting point and is the zs for the ring final and lights combined. The 5amp fused spur which feeds the lights will have a zs value for the fuse disconection time and this will be recorded on a seperate line and noted as a spur.
The recorded value(R1+R2 )for the lights is 1.27 ohms at the furthest point,but this is to high for a type b 32 A circuit breaker i believe. So the lighting circuit needs to be re-routed or cable csa increased?
Also the installation is a TNS, the main earth connection to the MET is 10 mm,but then has been increased to 16 mm from the met to the consumer unit. Is that acceptable? thanks in advance