I bought some old 5 amp plugs and adaptors just yesterday they all date back to the 1950s at a guess the one that got my curiosity is a Bakelite adaptor with a BC lightsocket for a standard British incandescent bulbs the other end is a 2 pin plug that don't fit any of the standard British sockets of 2 5 or 15 amp the pin spacing is slightly wider than 5 amp and a bit narrower than 15 amp also the pin diameter is slightly narrower than 5 amp plug pins does anyone have any thoughts on this curiose device?

Are those by any chance plain normal European pins ? (centers 19mm apart, thickness about 5mm)

UK had some mess of plug types in the past. The plug could be some early 2 pin thing, or one made for 3 pin sockets (for what i knwo not all of them were compatible with the 2 pin ones). There were all sorts of 3 pin sockets too. like the one with the fuse as the Phase pin

Hi Ash after I posted this I went back into the shack and tried it with a euro adaptor and it fitted perfectly and it works when I put a bulb in. However the plug was originally intended for a 10 amp socket which did exist in some areas  although no new ones were installed after the 1950s. The plugs with the live pin as a fuse were I think made by DORMAN SMITH the idea never really caught on for some reason

The one with the fuse is quite badly flawed :

The fuse is made of porcelain, so can crack. Imagine drpping the plug on the floor and the fuse cracking, but still holding together. Next time you plug it in, the fuse breaks off inside the socket. You remove the plug and part of the fuse remains stuck in the socket, so at the very least the socket is left unusable, at the worst the ripped out fuse wire sticks out from the hole and poses shock hazard

I know it wasn't a brilliant design I imagine that these days such a design wouldn't be allowed all the safety nuts would go mad!

I think I've found out what my adaptor was for its as french device the plug pins are a perfect fit for a euro plug adaptor I've got and I've been told that the french used BC bulbs as well as ES types years ago I had better be careful as the adaptor might not be designed for 240 volts mains I believe France used to use 110 volts

All the safety nuts better worry about Chinese products floding the market. As recent as today's morning computer speakers smoked up in my face when i plugged them in.... Opened them, not even a fuse inside. One of the wires of the 240V input just blew itself off and thats how the short stopped

As long as the adapter isolating surfaces are clean and the distances between conductors are not tiny (order of 1mm), it will hold 240V and more without trouble, whether it was made for 110V or not

That's good to know it is clean and seems in good condition so I should be OK. I don't leave it running unattended any time just when I'm in the shack. I run any vintage equipment from a vintage plugboard fed from an RCD protected supply.

The not running it unattended part is over the top....

Same with some computer power cables. We get them occasionally with USA plugs, rated at 125V, and containing the USA standard Black/White/Green colored wires. As long as the cable is of good quality, you can cut off the plug and put on the normal 240V one, and it is as safe as any 240V cable. I would take one of those any day over some "proper" 240V cables we have...

RCD won't do anything to protect an unearthed & floating device (where no Earth is present at any shape - not from the plug, not from you touching it, and no from outgoing cables like communication cables). This applies to the socket adapter as long as you dont touch it (and provide Earth through yourself)

The RCD protected supply is used for testing any vintage or unknown gear just in case there's a problem. It's not harming anything so il just continue as I am. I think it's best to prove vintage fittings are definitely OK before really trusting them although I think ide rather trust a 50 year old US or European made fitting than a new Chinese one. Ash are you in the UK? I'm just curiose

It does not harm to have RCD on top of RCD, but one thing is, the ones used for homes are not really meant to be installed in cascade (one downstream from the other). So when something goes wrong, you cannot guarantee which one will trip - It is possible that the faster one to react is the main of the home or circuit, and it will trip before your test bench one does

The only real way to prevent the tripping of an upstream RCD of this type is use of isolation transformer. But the transformer output is floating, so just placing an RCD on it won't do anything at all - it will never trip, no matter what (unless there is a short to Earth inside the transformer itself at the same time as a short in the cnnected load)

To use an RCD after the transformer, you have to relate its output to Earth - connect one of the output wires to the Earth from the input side. By doing this you define the wire as the Neutral, then the other one becomes the Phase

In safety isolation transformers the output Earth is disconnected from the input Earth, this is intentional to render the output safe against voltages present on the input side Earthing. But if you use the transformer as an RCD trip zone boundary and not as a safety isolation transformer, you have to reconnect the Earth

There is one neat hack with RCDs : You can use a 3 phase RCD as a 1 phase RCD, at double the sensitivity (so, a 30mA leakage RCD will work as a 15mA leakage RCD). Just loop the circuit twice through the RCD, in the same direction



I dont have an isolation transformer, so no way to really predict which RCD will trip - So i dont bother with a test bench RCD. I let the main one in the panel deal with leakage currents, and test it to ensure that it is working

Eventually i may wire a separate circuit from the panel just for the testing of stuff, which is not on the main RCD, then it can be protected by really separate RCD without tripping the entire home when something goes

The old one is usually better, but i really dont trust stuff like this before i opened and looked in. Either one may be a shock waiting to happen, whether from age and abuse or from manufacturing quality.....

I am from Israel

Yes I understand what you are saying and I totally agree with you I have my own RCD because our house only recently had RCDs installed in the mains DB before that it was a row of China fuse carriers mostly  15 amp for sockets. I also don't have an isolating transformer I can use so an RCD is best it definitely has saved me a couple of times