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polarized mains plugs - do we really need them?

I remember reading a few years back that it was illegal to design a product that relied on the polarized nature of its plug for electrical safety (not sure if that was just for the US, or a european country, or where..). Such a regulation would make sense, what with "cheater" plugs and outlets that might be wired wrong in the first place.

So do we really need them? It seems that most appliances and devices that still use polarized (but not three-prong grounded) plugs are internally "double insulated" or completely isolated via step-down xformers.

Reply to
NG Neer
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"NG Neer"

** Before posting any more of your dumb trolls - at least check out Wiki on the topic.

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The Australian / NZ / Chinese domestic power outlet has a switch plus is inherently polarised with 2 pin plugs.

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BTW

Being " double insulated " is no guarantee of appliance safety as the insulation gap can be bridged by a component failures or water ingress while so called "isolation" transformers can suffer insulation failure too.

Many SMPS wall wart adaptors pay notional lip service only to the requirements of Class 2 ( ie double insulation) and are seriously unsafe designs.

..... Phil

Reply to
Phil Allison

If a product has no exposed metal or connectors on it, you really don't need the grounding. If the product does have exposed metal, it is far better for that metal to have its own ground return.

You really want the chassis ground connection to be the first to make contact and last to break. This suggests a longer pin be used as is the case for the 3 prong plug I pluuged in a few hours ago.

Many products have an EMI filter that places a capacitor between the mains connection and the chassis. This adds a single point failure that can lead to the chassis being hot.

Reply to
MooseFET

The UK plug is made like that.

Leon

Reply to
Leon

Moons ago, one of the techs had a plastic clock hanging on the wall=20 in the lab. The industrial safety guy gigged him for not having a=20 three-prong plug on it, so he wired in a three-wire line cord. What=20 really made the safety guy happy is when the tech showed him how he=20 connected the ground wire to the case - star washer and all.

They also alarmed the second door of the lab because having two=20 doors with locks made it half as secure, even though the two doors=20 opened to the same hall, twenty feet from each other.

Yep. That's a tough one.

--=20 Keith

Reply to
krw

If you use semiconductor to switch, not paying attention can turn a high side switch into a low side switch with un intended consequences! Some thinking about the total environment and system is required to make a circuit idiot proof to ac mains "polarization".

Marc

Reply to
LVMarc

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