It was necessary with DC mains. As I have previously recounted, when I was a child I pulled out a 15A plug that was feeding a 2 bar electric fire. The arc set light to newspaper and thence an armchair. I remember being excited to see a fire engine up close.
We had 2A, 5A and 15A plugs/sockets on our DC mains. All 3 pin. But we also had 2 pin 2A ones for lamps etc.
What was the third pin connected to? I didn't think DC supply had an earth. Was it bonded to the plumbing?
Did AC require an earth from the start? Does this mean when a property was converted from DC to AC it would need to be rewired?
Was it also necessary for DC switches to have a spring to prevent arcing? I remember in our house some of the sockets and light switches were far more substantial than the newer ones.
I think light switches of back then had this mechanism, to prevent the arc in cases where they were used for DC. SWMBO's parents' house still had them until the house was sold after FiL's demise last year. Hadn't been rewired for 50 years. Nice postive feel to them and a characteristic sound as they were switched.
"Live chassis" is a bit misleading. You endeavoured to connect the neutral side of the mains to the chassis, but with unpolarised plugs & sockets in use it became a lottery if the chassis was live or not.
Many UK colour TV sets of the 1980s were worse, they used similar techniques but with full-wave rectification, with the chassis ending up at "half mains", irrespective of the mains plug orientation.
Scott:
etc) would be okay but with heavier duty switches.
Grams usually used a synchronoous motor, so no dc. Some old ones used a motor with centrifugal governor, ok on ac or dc, but less accurate speed
Universal or live chassis radios were fine on dc, if the plug was in the right way. Transformer sets not.
because the current would be continuous and not alternating?
same. The filament is just a heating wire.
fluorescent lighting, I assume.
Flourescents were run on a resistor ballast on dc, less efficient.
fridges etc? Could they be dual standard?
Universal motors worked on either. Induction motors, typical of fridges, didn't. Gas fridges were one option, ammonia cycle fridges another, many of course had no fridge.
for DC they would be equally suitable for AC? Did DC have an earth cable?
no major difference in spec
nib:
the worst were knobs with grub screws. Some were recessed, some not. The 'not' grub screws often came close to the knob surface & were insulated with a bit of wax. Time & inevitable repairs meant the wax was lost, and any slight wetness of hand would connect you to the often live grub screw. Ditto if the grub was replaced with one slightly longer, and that happened often enough.
Brian Gaff:
curtain burners
Brian Gaff:
dc supplies were in reality rectified multiphase ac
of course they thought about it, fluorescent lighting was a thoroughly studied subject by the 1940s
charles:
IIRC there were actually 3 standards created in the 1940s: BS1363 that we still use, D&S & I think the 3rd was Wylex.
Joe:
legal to sell now.
they are. Good option for freezers etc.
Max Demian:
The Sonys used a small audio transformer just for the earphone socket
Max Demian:
50% of customers got grounded -ve, 50% got grounded +ve. 3 wire split phase transmission is cheaper.Scott
little or no load on the secondary causes high voltages on the anode, as the transformer acts as a choke. It can cause failures.
Bob Eager
2 pin 5A were common, both for wall sockets & appliance leads. Was it BS372? There was also a 2 pin 15A in the standards, though I don't remember seeing one. I think kettle leads were a derivative of it, adding side contact earthing.Scott:
yes
switches were far more substantial than the newer ones.
I don't remember any live chassis set making any attempt to have it neutral. Lots had one mains wire go through the switch then to chassis, so it was inevitably live either when on or when off.
They were hefty foot operated switches with a strong spring. Too strong for me to operate, which is why I just pulled the plug out.
Early? ALL 13A plugs had all metal pins until extremely recently
I don't suppose any insulated pins existed before 1990
"August 1984: BS 1363:1984 "Specification for 13 A fused plugs switched and unswitched socket-outlets" published. This standard superseded BS
1363:1967. Changes include the introduction of sleeved pins on Line and Neutral, metric dimensions replacing inches, specifications added for non-rewirable plugs and portable socket-outlets. The standard was aligned, where possible, with the proposed IEC standard for domestic plugs and socket-outlets. "So there you go. Hardly 'early' for a specification that goes back to 1947.
Not 'inevitably' surely - 50/50 depending on the polarisation at the plug.
I don't remember foot operated ones. Were they intended to be foot operated or was this merely custom and practice in some households? I remember the ones with a slightly cone shaped bar sticking out that required quite a lot of force to operate.
Well yes, if it was wired as suggested above with the switch in the chassis side, then with the plug one way round the chassis would be live when switched on, and with the plug the other way round the chassis would be live when switched off - via the circuit.
nib
Having no loudspeaker loading was a known cause of output stage failure in valve amplifiers. I'm not sure which component(s) failed. I saw a radio where the internal loudspeaker switch was combined with the external speaker plug so at least something would be plugged into the amplifier output. If you have extension speakers (popular in the past) you might well want to switch the speaker off in the room where the radio was.
Sorry, I must be missing something here. If we are talking DC, if the switch is on the positive side, when the switch is off nothing should be live. If the switch is on the negative side, then I assume the chassis would remain live.
In the face of such obvious danger, why did they not fit a two pole switch? With two pin plugs, was there a convention that the positive/live should always be on the right?
In essence this can (theoretically) place very high voltages on the output transformer primary risking flashover there and in the output valve(s).
I've never seen or heard of it actually happening though. Normally feedback will stop it.
It didn't work if the plug was in the wrong way round. The half wave rectifier would stop any current getting in and damaging the electrolytics.
With a DC supply the chassis will always be negative and therefore safe (I think).
I always blamed Mr McLaughlin - a true historical injustice.
I may have been slightly wrong!
1) If the equipment had the switch in the hot side then: a) plug one way round all is safe b) plug the other way round, chassis is always live 2) If the equipment had the switch in the chassis side then: a) plug one way round, chassis live when switched on (via switch) b) plug the other way round, chassis live when switched off (via the rest of the circuit)Yes, double-pole would be better! Switch in the hot side and polarised plug is almost as good.
As to why, I think almost all early domestic electrical equipment never went beyond the most basic safety precautions.
nib
Wait a minute - why would a DC circuit have a rectifier?
Unless the plug is rotated 180 degrees?
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