Earth conductor size

[recre8]

I'm swapping out some 2.5mm2 twin and earth with house wire in a 20mm conduit. The purpose being to add an additional circuit in the conduit and stuffing two T+E's in a 20mm conduit is almost impossible. With a 2.5mm2 twin and earth, the earth conductor is usually only 1.5mm2.
Do the same rules apply for single conductor (house wire)? Can the earth conductor size be reduced to 1.5mm2 or must it stay the same as the phase conductor size?

[GCE]

I'm swapping out some 2.5mm2 twin and earth with house wire in a 20mm conduit. The purpose being to add an additional circuit in the conduit and stuffing two T+E's in a 20mm conduit is almost impossible. With a 2.5mm2 twin and earth, the earth conductor is usually only 1.5mm2.
Do the same rules apply for single conductor (house wire)? Can the earth conductor size be reduced to 1.5mm2 or must it stay the same as the phase conductor size?

If you look at 6.12.1.1c - It explains why the earth can be smaller - The cable has been designed around certain parameters like max current - When the earth does not form part of the cable , single house wires , then you need to use table 6.28 - If I read it correctly then you would need to use 2,5sqmm earth

[recre8]

If you look at 6.12.1.1c - It explains why the earth can be smaller - The cable has been designed around certain parameters like max current - When the earth does not form part of the cable , single house wires , then you need to use table 6.28 - If I read it correctly then you would need to use 2,5sqmm earth

Thanks very much! 2.5mm green house wire it is then.