Earth in EU/USA plug sockets

[themadhippy]

Where are you going to find a two pin socket with no earth in the EU?

In the bathroom normally

[mzzj]

Where are you going to find a two pin socket with no earth in the EU?

They're everywhere. Not every house was built within the last 10 years. You'll still find 1920s installations around.

Here in Finland two pin sockets were banned in 1997 for new construction and 2022 in expansions to existing installations. Still commonly available on market and allowed for replacement for broken units.

[Benta]

In the bathroom normally

Those are for shavers and contain a 20 VA isolation transformer.

[tooki]

Thanks,
We want to produce a (400W peak) offline power supply for a product in EU. (+ elsewhere)

OK.

Thing is, power supplies for household items must be in totally enclosed plastic cases for safety reasons.........

Says who?

There are plenty of metal-housed devices, including ones with power supplies inside, with or without an earth pin.

if you have that, then you need to have an internal metal foil  inside the plastic enclosure, otherwise you will not pass radiated EMC regulatory compliance testing.

Says who? There are plenty of plastic-housed devices, including ones with power supplies inside, which do not use internal shielding. (What I mean is that internal shielding isn't a requirement per se. It is, however, often a sensible way to achieve EMC compliance.)

...And if you have a metal foil surrounding the SMPS, then its best to connect it to earth...

Not necessarily. (Bearing in mind that I'm at the limits of my knowledge on this point -- I just know there are name-brand devices out there that have completely floating shields.)

but if the two pin socket doesnt have an earth, then how can this be done?

Obviously it can't -- sorta.

Look at what SMPSs do to reduce EMI. EMI noise is AC, mostly at frequencies well above 50/60Hz. So what you do is to capacitively couple the secondary-side ground to the AC input using a small Class Y safety cap. The small value of the cap makes it high-impedance at 50/60Hz, but low-impedance at the high frequencies you want to arrest. Since the neutral side of mains is tied to earth somewhere, that's your path to earth. Since you don't know which AC wire will be neutral, you use another safety capacitor between secondary-side ground and the other AC wire. (This is why devices with unearthed SMPSs often tingle when you touch them: their ground is floating at 1/2 mains voltage, albeit at minuscule current.)

The end result is that no matter which way the plug is inserted, the secondary ground, to which your shielding is tied, is tied to earth as far as high frequency AC is concerned.

Lots of AC-powered home AV gear is Class II, with the double square symbol, but is in a metal case with ventilation slits, using no earth

Thanks, may i ask what this metal case is connected to....or is it just "floating"?

It's either truly floating or (often) connected to secondary ground.


With all this said, I'm no expert on this, and you would be remiss to not engage the services of an EMC consultant.


Also, when you say "offline", do you mean non-isolated? (There seem to be multiple competing meanings of what the term indicates...) Or what exactly do you mean?

[IanB]

Where are you going to find a two pin socket with no earth in the EU?

They're everywhere. Not every house was built within the last 10 years. You'll still find 1920s installations around.

So what do you do if you live in one of those houses and you buy an appliance that requires an earth connection? Do you use it (unsafely) without an earth, or do you simply not use such appliances?

In the UK, houses that pre-date modern standards were generally re-wired long ago. Not least because wiring that had rubber insulation (rather than PVC) became dangerous and had to be replaced.

[Benta]

Where are you going to find a two pin socket with no earth in the EU?

They're everywhere. Not every house was built within the last 10 years. You'll still find 1920s installations around.

So what do you do if you live in one of those houses and you buy an appliance that requires an earth connection? Do you use it (unsafely) without an earth, or do you simply not use such appliances?

In the UK, houses that pre-date modern standards were generally re-wired long ago. Not least because wiring that had rubber insulation (rather than PVC) became dangerous and had to be replaced.

I dunno where you've been in your life. Flag says US...

In a house without receptacles with earth, you just plug in the two-prong plug. Works fine in most EU countries. Otherwise adapters are available. Consumers are not electrical engineers. Whatever works, works.
And regarding the UK: I've been there often, and the electrics (not to mention plumbing) is a nightmare. Your "replacement" scenario must have been in a dream... or some luxury hotel.

[tooki]

I dunno where you've been in your life. Flag says US...

In a house without receptacles with earth, you just plug in the two-prong plug. Works fine in most EU countries.

FYI, that is a peculiarity of the Schuko and type F sockets (the only ones in use where the earth isn't implemented as a male pin on the plug).*

Everywhere else, earthed plugs are mechanically incapable of fitting into a 2-pin socket, e.g. USA, UK, Australia, or Switzerland.



*OK, fine: and the Japanese, with their weird earthed plugs that are just the 2-pin plug with a flying earth wire coming out the side!

[IanB]

I dunno where you've been in your life. Flag says US...

Britain. The USA is where I live, not where I'm from.

In a house without receptacles with earth, you just plug in the two-prong plug. Works fine in most EU countries. Otherwise adapters are available. Consumers are not electrical engineers. Whatever works, works.

You can't do that in the UK. All appliances are sold (by law) with a BS1363 plug attached to the cord, and any dwelling you can reasonably live in has BS1363 sockets on the walls. There is one single device you can buy in the UK that has a two pin plug, and that is an electric shaver. It will not plug into a BS1363 socket without an adapter, but that's fine because it's non-earthed device to earthed socket. There is no case in the UK of earthed device to non-earthed socket.

And regarding the UK: I've been there often, and the electrics (not to mention plumbing) is a nightmare. Your "replacement" scenario must have been in a dream... or some luxury hotel.

You can't live in a home in the UK that does not have BS1363 sockets installed, because no electrical devices you buy will be usable without.

[Monkeh]

And regarding the UK: I've been there often, and the electrics (not to mention plumbing) is a nightmare. Your "replacement" scenario must have been in a dream... or some luxury hotel.

Regarding the UK: I live here. I have done for quite some time. You perhaps want to wind your neck in, or redefine 'nightmare' not to include 'oh dear god two taps' and 'that socket isn't what I'm used to'.

[themadhippy]

There is one single device you can buy in the UK that has a two pin plug

you forgot the rechargeable toothbrush

You can't live in a home in the UK that does not have BS1363 sockets installed, because no electrical devices you buy will be usable without.

not even the old couple,still living in the house they moved into back in the 50's that hasn't had the wiring touched since and apart  from the new tv  ,all the appliances pre date the 1992 legislation?

[IanB]

You can't live in a home in the UK that does not have BS1363 sockets installed, because no electrical devices you buy will be usable without.

not even the old couple,still living in the house they moved into back in the 50's that hasn't had the wiring touched since and apart  from the new tv  ,all the appliances pre date the 1992 legislation?

That old couple is not me or you. And you cannot tell me that people are still using appliances bought in the 50's?

If you try to move into a house that has not been touched since the 50's, isn't it going to have trouble with the EICR?

[IanB]

I grew up in a house that was built in 1960, and the electrical system was fine but for two things: there were not enough sockets (e.g. one socket per bedroom was considered adequate), and the lighting circuits had no earth (was OK at the time with lamps and shades hanging from a ceiling rose). But all the sockets even then were BS1363 three-pin and earth.

[themadhippy]

And you cannot tell me that people are still using appliances bought in the 50's?

i didnt say 50s,i said pre 1992

isn't it going to have trouble with the EICR?

  on the first page of our  regs is states

Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading.

Welcome to the one of the many grey areas within the regs

[IanB]

i didnt say 50s,i said pre 1992

Yes, but 1992 is modern times. I bought a flat built in 1986 and the electrical installation was basically the same as today.

[Monkeh]

i didnt say 50s,i said pre 1992

Yes, but 1992 is modern times. I bought a flat built in 1986 and the electrical installation was basically the same as today.

He's obtusely referring to The Plugs and Sockets etc. (Safety) Regulations 1994 (I'm not sure why 1992 keeps coming up), which is when it became a requirement for products to have a BS1363 plug fitted at sale.

[IanB]

He's obtusely referring to The Plugs and Sockets etc. (Safety) Regulations 1994 (I'm not sure why 1992 keeps coming up), which is when it became a requirement for products to have a BS1363 plug fitted at sale.

Yes, I lived through it. All the product packaging had to change, because now they had to find space for a giant plug to fit inside the box without scratching anything, whereas before they could just have the loose end of the power cord tucked away and a card telling you how to fit a plug to it 

[Nusa]

Thanks,
We want to produce a (400W peak) offline power supply for a product in EU. (+ elsewhere)
Thing is, power supplies for household items must be in totally enclosed plastic cases for safety reasons.........if you have that, then you need to have an internal metal foil  inside the plastic enclosure, otherwise you will not pass radiated EMC regulatory compliance testing.
...And if you have a metal foil surrounding the SMPS, then its best to connect it to earth...but if the two pin socket doesnt have an earth, then how can this be done?

You're confusing product legal requirements with stuff that's never going to be under your control. If you provide the appropriate safety ground and advise using the appropriate grounded outlet, you've likely done your due diligence. If the user plugs it into his ungrounded house anyway, that's not your responsibility.

In the case of the US, residences only have to meet the codes as of the day of install, unless modifications trigger updated code requirements. Which is why there are still ungrounded houses out there, with people using all the usual things without an actual safety ground connected to the appliance. We are talking about places 50+ years old that haven't had major electrical updates, but there are quite a lot of those. I grew up in a 1925 house, and am currently in a 1955 house. The only outlets that have safety ground are the ones on the shop circuit I added and a handful of other outlets I've updated (my computer setup and the kitchen counter).

[themadhippy]

I'm not sure why 1992 keeps coming up),

old memory aint wot it used to be

Yes, but 1992 is modern times. I bought a flat built in 1986 and the electrical installation was basically the same as today.

86 was the 15th edition were some really stupid bonding rules were introduced ,rcd's wernt required  everywere,spd's were unheard off,plastic dis boards were considered modern and  the wires were prettier colours,just a  few  things that wouldnt meet  todays regs

[IanB]

86 was the 15th edition were some really stupid bonding rules were introduced ,rcd's wernt required  everywere,spd's were unheard off,plastic dis boards were considered modern and  the wires were prettier colours,just a  few  things that wouldnt meet  todays regs

Perhaps, but none of that affects the basic functionality of the electrical system. I don't know anything about the bonding rules, but the other stuff is just designed to make installations more expensive. People keep updating the regs because they have nothing better to do with their time (yes, I'm cynical).

[ejeffrey]

Where are you going to find a two pin socket with no earth in the EU?

They're everywhere. Not every house was built within the last 10 years. You'll still find 1920s installations around.

So what do you do if you live in one of those houses and you buy an appliance that requires an earth connection? Do you use it (unsafely) without an earth, or do you simply not use such appliances?

Yes. When I lived in the Netherlands I never saw a grounded socket in a residential setting except in the kitchen and bathroom.  It was all type C / CEE 7/1 outlets.  If you bought something with a shucko plug it would just get used ungrounded.  Not only that, but since it isn't recessed the pins would be slightly exposed during insertion.

[themadhippy]

but the other stuff is just designed to make installations more expensive

we came to the conclusion the regs were sponsored by the equipment manufacturers

People keep updating the regs because they have nothing better to do with their time

No No  No,its all for our safety.It also has nothing to do with them fleecing us every 2 or 3 years for a new set of books (around £100 for the regs and guides) or  the fees  every 10 or so years for taking another     how to read a book regs course and exam

[Faringdon]

Look at what SMPSs do to reduce EMI. EMI noise is AC, mostly at frequencies well above 50/60Hz. So what you do is to capacitively couple the secondary-side ground to the AC input using a small Class Y safety cap. The small value of the cap makes it high-impedance at 50/60Hz, but low-impedance at the high frequencies you want to arrest. Since the neutral side of mains is tied to earth somewhere, that's your path to earth. Since you don't know which AC wire will be neutral, you use another safety capacitor between secondary-side ground and the other AC wire. (This is why devices with unearthed SMPSs often tingle when you touch them: their ground is floating at 1/2 mains voltage, albeit at minuscule current.)

The end result is that no matter which way the plug is inserted, the secondary ground, to which your shielding is tied, is tied to earth as far as high frequency AC is concerned.

Thanks very much ....this sounds like the right way to do the secondary grounding when the product has no mains earth connection.
As you know, for some reason, it often doesnt get done...often, only one Y cap is used, and it is placed from the primary DC bus ground to the secondary ground. As you know, "primary dc bus ground" is alternately line then neutral, due to the Full wave bridge....and between "primary dc bus ground", and the incoming AC L or N wire, there are usually filter inductors, which would impeded the HF emission on its way back into the L and/or N wire....though maybe thats OK?...because it "filters" the emission?

There are plenty of plastic-housed devices, including ones with power supplies inside, which do not use internal shielding. (What I mean is that internal shielding isn't a requirement per se. It is, however, often a sensible way to achieve EMC compliance.)

Thanks, thats right...and  if they are more than about 30W, then they will not pass Radiated EMC to EN55032.
They get away with it because nobody checks them.
I actually worked in a place where their offline SMPS in plastic-with-no-metal-shielding failed Radiated EMC......and they just kept selling it.

[Siwastaja]

Where are you going to find a two pin socket with no earth in the EU?

They're everywhere. Not every house was built within the last 10 years. You'll still find 1920s installations around.

Here in Finland two pin sockets were banned in 1997 for new construction and 2022 in expansions to existing installations. Still commonly available on market and allowed for replacement for broken units.

And note this is about large round 2-pin sockets that can accept either an Europlug or an earthed Schuko plug (so that earthing would be lost).

It is not illegal at all to install 2-pin sockets, if they are europlug sockets. This is because you can only connect Europlug devices, which by definition are double insulated.

[Faringdon]

Thanks, yes, i think we all agree that there are loads of things that have no earth connection, and loads of mains sockets that give no earth connection.

It would be impractical to ensure that every socket in the EU had an earth connection...so the authorities simply  let that one slip.

But to pass radiated EMC to EN55032, any plastic enclosed offline SMPS of >75W, must comprise metal foil, or metal plate, or "metal net" lining, otherwise it simply wont pass Radiated EMC compliance testing to EN55032......i say >75W, because they contain a hard switching PFC stage.....some <75W smps are resonant, and can pass radiated EMC even if no metal lining.

The best way to get through EN55032 radiated EMC, is to have that metal lining connected to earth ground...but if no earth is presented, then as IanB [EDIT....sorry, Tooki]  puts it......there would hopefully be Y caps strategically placed connected to secondary ground, and these would effectively kind of connect the metal shield to earth ground.
If even y caps arent present, then the metal shield would hopefully be connected to some "quiet" node on the PCB...ie not a switching node....that would increase its chance of passing EN55032 radiated EMC.

As you know, in the testing house, they will have a socket available with an earth wire.

[IanB]

then as IanB puts it

That was not me. I think it was tooki?