2 circuits down one 4core and earth cable

[mo23449]

hello there!!

does anyone know if it is within the regs to run 2 seperate circuits down one 4 core and earth cable woth both sharing the cpc?


I.E

Run a lenghth of 2.5mm 4core & earth FP200

- Use one pair as live and neutral for a 16A circuit and the other pair as live and neutral for a 6A circuit both using the same single 2.5mm cpc?

 

[Qedelec]

No this is not allowed in the regs. Each final circuit must have its own cpc sized in accordance with the live conductors.

 

[Adam_151]

No this is not allowed in the regs. Each final circuit must have its own cpc sized in accordance with the live conductors.

You sure about that QED?

543-01-02 Where a protective conductor is common to several circuits, the cross-sectional area of the protective conductor shall be:

(i) Calculated in accordance with Regulation 543-01-03 for the most onerous of the values of fault current and operating time encountered in each of the various circuits, or

(ii) Selected in accorance with Regulation 543-01-04 as to correspond to the cross-sectional area of the largest phase conductor of the circuits.

 

[Qedelec]

If the op is using 2.5 for the live conductors for two circuits then 1.5 is not going to be adequate as a combined cpc for both finals.

Correct me if I'm wrong but doesn't FP200 use an aluminium cpc? So add that into the equation.

 

[Spark123]

Isn't it tinned copper

 

[securespark]

Think so...

 

[RF Lighting]

Yup

 

[Qedelec]

I stand corrected it is tinned copper. but its still 1.5mm and that don't sound adequate.

 

[securespark]

Does 2.5 as the main earthing conductor for a TT supply sound adequate?

 

[Taylortwocities]

But in a TT system the earth current is limited by the trip current of the incomer |(RCD 100ma). I think 2.5mm will be OK to carry that...

TTC

 

[securespark]

Depends on whether these two circuits are RCD protected or not.

 

[Lectrician]

You can do this with no problems. You must label accessories where two protective devices independently feed it though.

QED - It is common practice to share CPC's in conduit/trunk wiring. If you ran a 2.5mm socket radial circuit, a 1.5mm lighting circuit, and a 2.5mm radial to a water heater, you could happily use a 2.5mm earth.

You could even use a 1.5mm earth, but it is common practice with singles to size LNE the same sizes.

 

[ColJack]

think of it this way..

in a 3 phase circuit you only have 1 earth.. not one for each phase..

the logic is that in the event of a fault, it is extremely unlikely that 2 or more phases would come into contact with the earth at exactly the same time..

since they are obviously going to the same place though, can you not just fit a 4mm² 20A radial and fuse down for the lights? saves expensive cable too...

 

[securespark]

You must label accessories where two protective devices independently feed it though.

Like hall/landing switches?

Is that a regulation?

 

[Spark123]

I stand corrected it is tinned copper. but its still 1.5mm and that don't sound adequate.

A 1.5mm² CPC is OK in most instances when used in 2.5mm² twin and earth fed from a 32A MCB i.e. in a spur on a ring final circuit. As long as it passes the adiabatic equation it is fine.

You must label accessories where two protective devices independently feed it though.

Like hall/landing switches?

Is that a regulation?

Possibly 461-01-03, although it may be argued that turning off the main switch isolates both supplies.