On Sunday, 26 July 2020 01:39:42 UTC+1, Paul wrote:
tabbypurr wrote:

The underwriter's knot doesn't stop wires moving, that's why it's never used here. I gather it's something from US history where effective cordgrips have not been adopted to the same extent.


NT

For the lamp project, the base is solid pine, with holes
provided for running the wire. And shop class had no
assortment of fixings, so you basically wire up the
light socket, then place a knot to prevent the cord
from being pulled out (hot).

If it had started as a commercial item, the fittings
would be different.

When you repair an electric kettle here, it already
has the correct restraint on the base, and after you
remove a piece of cord to get rid of the cord break,
the cord is placed back inside the restraint. And the
cord won't move through one of those.

Something like this, for three conductor flat cord.
These can be recycled, so you don't need a new one.

http://heyco.com/blog/strain-relief-...s-life-easier/

Paul

I'm not overly fond of those things, but they work more or less.

Here when the concept of cordgrip was on its way in there were 2 types mainly used. One was to tie the strings in the flex together, the other was to put a simple knot in the whole cord. Both stopped the thing being pulled out of the appliance, but neither immobilised the wires at their connections.

Nowadays it's either a screwed down plastic strip, a serpentine groove for the cord or a moulded on bushing. Less often it's those things above. All immobilise the final joints.

Up to the 1950s there were various wacky schemes that didn't work well, especially on mains plugs, but they're all long gone thankfully. The worst one I saw was an IDC mains plug: a prong on each pin pierced the unstripped mains wire, and was held together with horrifyingly low force - a fire waiting to happen. IIRC the prongs doubled as a cordgrip of sorts.


NT