Is it safe to use 10mm flexi conduit for single circuit cable run, less than 3m, mounted in ceiling, 2 LED domestic lighting points?

[Dave Gething]

Trying to replace a single run, approx 3M with no bends, of a single 1.5mm twin & earth cable between 2 lighting points in a domestic space. Cable to be mounted IN the ceiling & plastered over. Both points to carry an LED light fitting so minimal current. Is it safe to use 10mm conduit? BS7671 doesn't go lower than 16mm for calculating capacity factor unless I'm missing another table. I foolishly lent my regs book to a colleague & doubt I'll ever see it again.

I'm trying to avoid chasing out big channels for 20mm conduit & the client definitely doesn't want surface mounted.

I see 10mm conduit available but no idea whether it's safe to use. Space is in a tower block too so safety is, you know, paramount.

 

[telectrix]

what is the ceiling made from, and is there a void above it?

 

[Dave Gething]

what is the ceiling made from, and is there a void above it?

This is part of the issue as it's unclear exactly what the composition is. There is definitely no void above it. A bit of plasterboard, maybe some kind of insulation above that. Then concrete.