Use of RJ11 for mains !!

Thanks, but you and others don't need to tell me not to do this. As an engineering grad with considerable experience I would not do it, or have allowed it to be done by staff, in the proverbial month of Sundays.

The cable might rated at 300V to enable use in shared ducting/trunking with mains cables, and not require a separate compartment?

When I think what I've got away with in the past, it does make you think what level of safety is it you need. I have wired old 8 watt l fluorescents up with three core cable bought from Tandy. Solid core, sleeved and outer sleeved but with very inappropriate colouring and the wire was really very thin. No issues at all for many many years, but it would confuse the heck out of the next person to come along of course. I fused it at 5 amp. I did try a live test on an offcut. If a live cable was cut,then nothing really happened but the fuse blowing. Brian

there's been way worse out there