Non Polarity Contingent Appliances

[Chetlaham]

Does anyone else have a "thing" or like the way non polarity contingent wiring looks? By non polarity dependent I mean electrical designs where the neutral side of the line is switch internally as much as the hot side of the mains.

 

 

 

 

Here is a nice example I fell in love with on reddit.

 

 

<span style="font-size: 18pt;">The Live Side:</span>

 

The live mains hot wire hits the fuse, where it leaves the other side as a brown wire, hitting one terminal of the cavity lamp socket, transitioning to black going down to hit the primary interlock terminal, transition back to brown providing power to the electronic control. Going through the primary interlock itself onto the other terminal, one yellow wire then heads over to the fan motor, a black wire heads down to the monitor switch transitioning to red which heads over to the turn table motor. Going through the monitor switch (acting as dual secondary switch and short switch) a red wire emerges going down to one terminal of the magnetron's step up transformer. A white wire emerges from the other terminal of the step up transformer heading over to the normally open cook relay.  

 

The cavity lamp always remains live, and with the door closed the turn table motor, fan motor and magnetron step up transformer are always at 120 volt potential.   

 

 

<span style="font-size: 18pt;">The Neutral Side:</span>

 

White mains side comes in and hits the MOT thermostat, going through it, transitioning to blue, hitting the cavity thermostat. Going through the cavity thermostat, a white wire emerges where it goes down to the shorting terminal of the monitor switch, transitioning to blue going to the cook relay, from there heading over to the neutral side of the 3 terminal Molex connector for the electronic control. On the electronic control there is relay which connects the 3 terminal Molex connector yellow wire to the blue neutral wire to complete the circuit for the cavity lamp, stirrer and fan motor. The yellow wire emerging from the 3 terminal Molex connector heads over to the other terminal of the cavity lamp, where it splits into two blue wires, one heading to the other terminal of the fan motor, the other heading down to the turn table motor. 

 

What is so fascinating about this design is how so much of the safety, functional and cycle switching is done through the neutral wire. Where as only fusing and the door is done through the hot wire.

 

I'm guessing who ever engineered this was used to 230 volt 50Hz Schuko appliances where the plug can typically be inserted any way and polarity does not matter. I kind of like it in a strange way as both legs are switched internally.

 

 

More pictures can be found in the Reddit link.

 

 

 

[cfz2882]

I don't think polarized plugs were used in the US until about 1979 or 80-and that is with some radios from the 1930s-50s one side of line connected to a metal chassis and live knob shafts-no wonder people were warned in the '50s about the shock hazard of a radio or TV close to the bathtub

 

[me]

I've needed to trace the wiring on one or two washing machines we've had over the years when they have developed faults, and I recall at least one of them and probably both were wired so that opening the door isolated just the neutral wire which went via the door latch to the heating element, motor, solenoid valves and I think possibly also the drain pump, plus I think one had a microswitch on the dispenser draw that just cut the neutral to all the valves. If that's the sort of thing you mean, but as it makes sense to do it that way, I'd assume it's just normal practice.

The live legs to the motor etc was switched by the electronics on the control board.

 

[mattl]

I have a few older appliances I use, a Singer Rocketere sewing machine and a Sunbeam waffle iron, that have non polarized plugs. If I don't plug it in properly when I run my hand over the metal portions I feel a slight charge. I've put a bit of red duct tape on the side that is live, problem solved.

 

[fan-of-fans]

Seems like though there didn’t seem to be any appliances with polarized plugs before the late 70s/early 80s, the receptacles themselves have been at least since the 1940s, or at latest the early 1950s(?) I wonder why that was.

 

[Chetlaham]

@me: Yes, you got it! Switching the neutral instead of the live. None existent in some appliances, common in others.

 

@Fans of Fans: I'm wondering the same thing. I'm guessing to deal with older homes from the 40s and earlier that may not have had polarized outlets.

 

@cfz2882: I remember that! One side was referenced to the chassis, latter models used a high impedance resistor in series with the incoming neutral before connecting to the chassis. Thankfully that to went away latter on.  

 

 

[novum]

Continental European plugs are mostly not polarised. The ‘Schuko’ system allows both grounded and non-grounded plugs to be inserted in either polarity, and it’s the de facto European standard.

The Belgian/French variant is polarised when wired correctly, as the grounding pin only functions in one orientation.

This Wikipedia image explains both

https://upload.wikimedia.org/wikipe...g_diagram,_schuko,_french_socket,_cee_7-7.jpg

(UK/Ireland plugs are the only European system that is fully polarise - they have no two-pin option. Even non-grounded appliances include a surplus pin ground pin, sometimes its plastic. It’s required to open the socket safety shutters.)

https://upload.wikimedia.org/wikipe...x-UK_BS_1363_plug_and_socket_(IEC_Type_G).png

 

[gelaundry4ever]

american lines

What about the American lines? Aren't they polarized or not?

 

[novum]

Modern outlets and circuits are polarised in the US and grounded 3 pin plugs always were, as they only go in one way and were the norm for grounded major appliances for a very long time.

In general polarity isn’t that big a deal for AC appliances. The issue only comes up with on-board fusing or switching. Any appliance using a figure of 8 connector for example is non polarised, regardless of what type of plug is on the other end of the cable.

In European appliances (including in the UK) they mandate that they have to be safe in either polarity. So main switches that are controlling any exposed parts cut both line and neutral etc and both sides might be fused

You should never assume any appliance is completely dead and work on a repair unless it’s fully unplugged or you can otherwise guarantee it’s isolated. You can’t be entirely certain that there isn’t a polarity reversal.

The single biggest risk is Edison screw type bulb holder on lamps. If the outer ring is live, you can potentially get a shock while handling a bulb on a lamp that’s switched off. European designs use a deeper socket with a cuff and minimal contact to avoid that. British light bulbs didn’t have the issue in the past as they used bayonet connectors, but have live spring loaded pins.

You’re very unlikely to encounter appliances that use chassis as neutral etc unless you’re working with old antiques.