No need to fuse it down, if the supply circuit is already of a suitable rating.
There was an hospital plug system, where a round pin plug/socket was used which had a screw in fuse as the live pin, maximum 13amps. The sockets were wired as per a normal 30amp ring main circuit, but using a different style of fused plug.
It detered people from stealing the appliances and people plugging normal rectangular 13amp plugs into the hospitals supplies.
I'm pretty sure a relative who had a house built to his specification has some sockets which are like that. The lighting (and other 'electrics' are computer controlled. There are several small switch pads in each room and you can control most, if not all, the light etc in the room from them. Some have remote control. All a bit complicated if you are a visitor ;-)
It all works very well and is quite impressive but he did comment that the system was already obsolete (it was installed 15+ years ago) and, if anything failed, he may have issues replacing modules. I was curious how it was configured but didn't get the opportunity to discuss it in detail.
Sounds like a Dorman & Smith style plug.
It's also got a nasty design fault. If the fuse comes out of the plug when it's removed from the socket, you've got a live metal pin sticking out.
But if it's a lighting circuit it may only be capable of 6A.
Those were made by D&S. A contender for the ring main system (there were others). Some blocks of flats in central London used them and you could buy spare fuses in Selfridges! BBC TV Centre also used them for technical supplies until somebody discovered that you could leave the fused leg in the socket when removing the plug.
Not really as those D&S plugs were used in some domestic premises.
is a more likely reason. The BBC used those horrid D&S plugs for technical mains.
Yup.
Yes - I've seen that happen. They also had dreadful cord grips. Just a rubber grommet.
A bit like this then ... just skip to the last couple of minutes.
Some Mothers Do 'Ave 'Em
:-)
I grew up in the 60s / 70s when round pin BS 546 plugs and sockets were the norm and the live pin on the plug was a screw in fuse.
As you suggested, the fuses had a tendency to work loose after the plug have been plugged in and taken out a number of times and, as a five year old who wasn't totally aware of the dangers of electricity, I noticed there was a pin missing from the plug and tried to pull the fuse out of the socket with my fingers ...
No harm done but, needless to say, I didn't try it again!
Thankfully the house was rewired in 1972 / 73 with the 'new' BS 1363 shuttered sockets and all appliances fitted with new plugs with internal fuses
We were on DC until ~1950 and my experiments resulted in welding a pair of pliers to a solid hot plate on the cooker.
On Tue, 18 Jul 2023 07:59:37 -0000 (UTC), jon snipped-for-privacy@nospam.cn wrote: [snip]
As a matter of interest, what appliances or equipment could not be used with DC?
I assume all heating equipment (cookers, radiators, kettles, irons etc) would be okay but with heavier duty switches.
I believe radios could be AC, DC or dual standard. Gramophones I assume were similar.
Were incandescent lightbulbs the same or were the DC ones different because the current would be continuous and not alternating? No fluorescent lighting, I assume.
Were different motors needed for vacuum cleaners, washing machines, fridges etc? Could they be dual standard?
Was rewiring needed or could it be assumed if the cables were suitable for DC they would be equally suitable for AC? Did DC have an earth cable?
Did the Electricity Board pay for the change?
...
...
An ancient radio I had was AC/DC and used a voltage-dropping mains cable, one normal wire, one resistance wire, to adapt it to 240V (it got warm - warning not to shorten it!). Inside I think it had special valves to get the series heater circuit to add up to 120V AC/DC and the HT ran directly off the mains through a half-wave rectifier.
The same applied to old TVs, no mains transformer, live chassis, and various different valve heater voltages but all 300 mA in series. Half- wave valve rectifier direct off live.
I've run fluorescents off DC!
(It was an optical experiment and I didn't want the flicker. Electronic current control and custom starter. Recommended to reverse the tube after each use to even out the "wear" between the ends.)
nib
I have heard about live chassis (radios too, I believe) but I never understood it. Why was it not negative earth like cars?
I did not realise this could be done.
Am 18/07/2023 um 09:26 schrieb Scott:
Because connecting the chassis to the electrical earth (as opposed to RF earth) was not safe back in the day. It is safe now because you have circuits breakers.
OV (zero volt) is not the same thing as earth, especially in tube circuits.
Never connect an old radio or TV chassis to the electrical earth and never mix RF earth with electrical earth.
I installed 5A unstitched sockets controlled by a light switch in my lounge when we extended the house around 2003. One morning I went to bed leaving brother in law watching some tripe on TV. The following day I discovered the switch was "on" but lights not. It transpired he'd gone round all the lamps turning them off individually then blundered around finding the exit.
"Live chassis" simply meant directly coupled to the mains, but with 2 pin reversable plugs the chassis could be at either potential. Anyway, my first cars were positive earth
Probably electronics would be OK on DC. Most things rectify the mains then use a switch-mode regulator for the required voltages. Peak voltage from the rectifier would be only 240V rather than the 340V-ish from rectified 240V AC, but most equipment such as wall warts are specified to work from 90V to 250V, to allow international use.
The switch may have to be a different design to break more quickly. AC switches rely partly on the zero crossing to quench the arc.
Yes, in my youth radios and TVs were often AC/DC, often 200-240V. There was a large power resistor with taps to adjust to the local mains voltage. I can remember when some of the major items in the Radiospares catalogue were replacement mains droppers for popular TV models. You could also buy low-value cylindrical ceramic resistors which could be stacked on a metal rod, if the right dropper was not available.
The AC mains voltage is quoted as an RMS value, meaning exactly the same heating effect as the equivalent DC into a resistive load. A light bulb isn't a linear load but it is resistive.
Yes, the motors were usually AC/DC, called 'universal'. Many of the motors in use now probably would not work on DC.
Yes, with no transformer there was no isolation, so the whole circuit floated on the mains. As the metal chassis was used as one side of the electronic circuit, it was inevitably connected to one side of the mains or the other. Repair shops often had 1:1 isolating transformers so could ground the chassis for safety when working inside.
Note that meant that poking a knitting needle through the cardboard back panel, which obviously needed lots of ventilation slots, could easily touch live. And also the knobs on the front were often just fitted to possibly live metal shafts, relying on just the bakelite knob for insulation. Sometimes they were even just clipped onto the shaft so you could pull them off and touch live metal. The other external touchable metal, the aerial socket, was isolated by capacitors.
Good old days, hey! Electrical safety has come a long way.
nib
Was there an earth with DC? How could it be safer to connect the chassis to the live?
Surely neither is safe but it must be safer than the live?
I have seen shuttered round pin sockets, but none with a fuse in the plug, particularly the two smaller sizes, None had shrouded mains and neutral either, though I do wonder really how much difference this really makes. Brian
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