Mains Cable retention.

[G6Tanuki]

In olden times methods used to secure mains-cables to radios were often distinctly questionable - I'm sure we've all seen examples of the [single-insulated] flex being threaded through an ungrommeted hole in the rear of the chassis and simply tied in a knot to stop it pulling-out!

Clearly unacceptable these days! So - what is your preferred method for securing a replacement flex?

Mine is to fit a screw-down cable-gland to the chassis-hole in order to clamp the flex [I generally use the circular 2-core or 3-core flex of the type typically sold for lamp pendants] but remembering a requirement in some British Standard or other for "two means of retention" I put a couple of cable-ties round the flex immediately inboard of the gland so if the gland loosens its grip on the flex there's still something to stop it being pulled out.

What do you do?

[Paul JD]

I also usually use some form of cable clamp gland and if practical fit a P clip somewhere convenient in the chassis as a secondary measure

https://www.ebay.co.uk/itm/Plastic-P..._5Jrw38U2P8okQ

I often find there is a suitable bolt or hole to mount it to without having to drill.

In addition if the chassis is earthed I make sure the earth wire is longer than the live and neutral wires, that way if the cable does pull out and the live contacts the chassis it should blow the fuse before the earth wire gets pulled out.

[Boulevardier]

The size of those cable glands can be a problem. I recently built a Band II FM pantry transmitter, and went to a lot of trouble to fit it into as small as possible a metal case (such are the requirements of "domestic management" around here). I also scavenged some thinnish mains cable (remember that?) from a 60-year-old 25W Henley's Solon iron. Putting a large cable gland on that would have looked ridiculous. I have to admit that I just used a long-sleeved entry grommet, and put a tight fibre washer on the cable inside the sleeve, with a tight cable-tie around the cable after that to prevent the cable pulling through the washer. Also, a 1 Amp fuse in the plug. That seemed a reasonable safety approach in the circumstances.

Mike

[G6Tanuki]

The "industrial" IP68 cable-glands [M20] are indeed bulky - but there's a range of them available for smaller diameter cables.

These litle ones are more what I'm thinking of for domestic radios:

https://uk.rs-online.com/web/p/cable-glands/3620045/

I use them too for running 'thin' coax into waterproof boxes for ATUs etc; just don't tighten the gland up too much or it can deform the inner dielectric of the coax.

[Bobdger]

Lapp pg7 glands are small. I use a lot of these for small signal cables from sensors and flow meters.
Bob.

[dglcomp]

The option is to use a mains rated plug and socket, plenty of relatively compact options on the market.

[paulsherwin]

I don't think it's particularly appalling to use a knot to retain the cable if that was how it was done originally and the appliance is low current. Obviously the cable shouldn't come into contact with any sharp edges, and any missing or deteriorated grommets should be replaced.

[Boulevardier]

I agree, and have often done this. It's a much safer way of doing things than, e.g, some of those old clunky Bulgin plugs where you have to thread the internal cores around an insulating washer inside the plug body. I always thought they were distinctly dodgy and unsafe.

[Refugee]

Light pendants were in old times often retained by a knot and held up by the screw on part of the ceiling rose.
I was in a room where one eventually cut through the rubber insulation and fell to the floor after detaching from the bottom of the knot with a loud "pop".
I am pretty sure it was just shortened and retained with a new knot.

[Terry_VK5TM]

Not one for throwing things out that have been salvaged from other equipment, I use those cable retainers that have both a clamp and posts so the cable has to snake around the "s bend" as well as being clamped.

The styles vary, but most of them have the clamp part also cover the "s bend" so the cable can't pop up out of it. Some also contain the chassis entry point or I'll recycle something else appropriate.

More modern equipment doesn't seem to use these anymore, unfortunately, they usually have some form of connector as mentioned above.

[G6Tanuki]

Originally Posted by dglcomp

The option is to use a mains rated plug and socket, plenty of relatively compact options on the market.

Yes, I'll use an IEC309 if there's room: I particularly like the IEC-inlets that include a 20mm fuse, an on/off switch and a RFI-filter.

https://uk.rs-online.com/web/p/iec-filters/8826213/

They do require quite a bit of space behind the panel though.

I've also got some circular chassis-mount inlets that take a 3-pin US-style line-socket. But again they're bulky. A small gland-clamp will often fit the original cable-hole with minimal enlargement.

[David Simpson]

As Terry says - be careful what you throw out. Always retain decent grommets, P-clips, cable clamps etc. Above all else - mains cables from old test equipment. In my experience they were of a higher quality than normal vintage domestic radios. Particularly Marconi, Tek, HP.
I remember, several years back, in a thread about snipping off mains plugs & cables of equipment being auctioned at BVWS Swapmeets, I pleaded with Mike Barker just to do the snipping very close to the three pin mains plug. As particularly those lovely greyish/blueish Marconi cables are as rare as rocking horse manure. And Marconi, in their wisdom, often just left the smallest of small grommet holes & sometimes had the tail to the internal termination fed through the tightest of space. I.e. the TF995A/5 Sig Gen.
Often, the modern flex sold by B & Q and other DIY outlets is of a larger(0.75mm sq. or 1mm sq.) cross sectional area than required for vintage radios & T/Eq. I've said this often enough - using a 13A plug doesn't mean you have to insert a 13A fuse. Most of the time just a 1A fuse will suffice, as only the low hundreds of mA is being drawn. Yep, some items do experience a bit of a surge upon initially switching-on, so perhaps occasionally a 2A fuse can be used.

Regards, David