How do you guys normally do cable strain relief on entry into a project box? I’m specifically concerned about twin and earth mains cable, which is not cylindrical, but flat edged oval in shape. Normally these are strain relieved by cable clamps inside the device, does anyone have a source of such clamps and suggestions as to how they can be securely mounted inside a plastic project box?
how about running through a hole in the box an twisting it into a knot?
There is a time-honored tradition of tying what is called the Underwriter’s Knot but I really cannot recommend it for anything other than a lamp.
I have used C14 IEC connectors like the ones found on most PCs and laptop power supplies. C14 is the common shape for two conductors and a safety ground–a rectangle with the corners cut off. This allows you to just buy a cord that works, particularly if the gizmo is used in more than one country.
The cable you mentioned “twin and earth mains” is called NMB here in the USA and is solid copper wire used for in-the-wall wiring. Here I would just go to any hardware store and buy either plastic or metal strain relief like this:
Sometimes a strain relief clamp is built into the work box in the wall instead, particularly for what are called old-work boxes for retrofitting something.
In the USA for things like extension cords and device cords, we use what is called SJ cable which is a round flexible stranded cable with a vinyl or rubber cover. The strain relief clamps for that are the little black plastic circular parts that go around the cable and then get pushed and locked into a hole in panel. Here is a link to one at Jameco:
So are you building something to go into the walls? If not, I would look for the simpler solutions of SJ cable and bushings or IEC connectors.
Hope this helps! I realize things are different all over the world.
Yes, this is yet another great idea @bko. Given the box will be fixed permanently in my roof space I’m wondering if I’m just causing problems for myself. I have a junction box designed for a parallel lighting circuit (radiates lamps in a star arrangement). This has strain relief, but no mounting holes. My box will be mounted and given the cable is also meant for permanent installation with cable clips externally, maybe I don’t need to get hung up on it.
I have enough trouble getting to grips with coding the Core itself, never mind the intricacies of mounting it