Author Topic: Grounded device case causes frequent ESD  (Read 12333 times)

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Offline Monkeh

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Re: Grounded device case causes frequent ESD
« Reply #25 on: December 15, 2014, 01:01:31 am »
In the US most appliances are light loads so that's why we do fine with lower voltage, also neutral is grounded somewhere (but don't go touching it)

But enjoy eating your steaks with butter knifes, because you know that will be next :)

Show me statistics that show the contrary and how unsafe the US system really is:
http://www.esfi.org/index.cfm/page/Injury-and-Fatality-Statistics/pid/12015
http://www.electricalsafetyfirst.org.uk/news-and-campaigns/policies-and-research/statistics/

Oh, btw take if from some UK EE guy:
http://boards.straightdope.com/sdmb/showpost.php?p=4535712&postcount=5

Forgive me if I don't listen to someone who thinks our supply voltage is 220V.
 

Offline Galaxyrise

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Re: Grounded device case causes frequent ESD
« Reply #26 on: December 15, 2014, 01:13:06 am »
When I travel in cars with seat covers made with some woven fabric, I get this thing where when I get out of the car and go to close the door, the door "bites" me with a snap and a static discharge. It really puts me on edge, and I have lately resorted to gingerly closing car doors by pushing against the non-conductive window glass to avoid the jolt.
If the car door has a metal frame (like most/all non-convertibles), then the trick to this is:
  • open the door
  • grab the top of the door with your bare hand
  • then step out of the door (still holding on to the car door.)
Side benefit: if you happen to step out onto ice, you're already holding onto something ;)
I am but an egg
 

Offline timb

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Re: Grounded device case causes frequent ESD
« Reply #27 on: December 15, 2014, 01:28:56 am »

Thats the american incomprehension of safety. In EU, safety rules are very strict and only a few, hardly chinese crap products aren't compliant to these safety rules.
When you need a unearthed device, it must comply to even stricter rules of double insulation, and so. Switchmode PSU is hard to get designed right for the class II rules, no manufacturer woud not do that for fun. The insulation of class II devices must withstand 4kV~ pri-to-sec for 60 seconds. Someone having link to english version of the standards for class II devices in EU?

Yes, I also have an old Compaq laptop computer here with only two wire unearthed psu. But these things are no longer made for EU region and I suspect, that the computer wasn't made for EU either, because these earthing safety rules for electrical engineering are there for quite some time. I suspect, the computer problably has been imported from outside EU. I have got that from a local junk store.

See the PELV:
http://en.wikipedia.org/w/index.php?title=Extra-low_voltage&redirect=no

Huh, it must be certified to those strict rules then!




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Any sufficiently advanced technology is indistinguishable from magic; e.g., Cheez Whiz, Hot Dogs and RF.
 

Offline IanB

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Re: Grounded device case causes frequent ESD
« Reply #28 on: December 15, 2014, 01:39:16 am »
Just slightly OT, but Apple makes these modular power adapters with nice interchangeable mains plugs, but can you buy a genuine Apple plug adapter for a different country? Can you heck! There are times when I think Apple has completely lost the plot.
 

Offline Yansi

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Re: Grounded device case causes frequent ESD
« Reply #29 on: December 16, 2014, 01:24:01 am »
Don't those adaptors have only two wires in and two out? Nothing strange at all then, huh?

But one of your colleagues here mentioned, that some products in USA  come with an adaptor, which allows you to plug threewire (separate earth) device into two wire installation. Which is wrong, in EU it is forbidden. Any of our inspection technician would likely want to kill ya, If he would see you doing such a thing.  >:D

Summary: In EU, there is no way you can plug a device with threee wires (Class I, L N PE) to a two wire socket. 

Threewire EU plug simply does not fit into two wire socket (we have almost none twowire sockets, 99% of them are like german Schuko type, finding a socket for 3w plug is not a problem at all). And any power adaptors from 2 to 3 wires are forbidden, illegal and brutal safety risk.

On the other hand, 3 to 2 wires adaptors exist. The 2w plug fits into 3w, but these 3-to-2 adaptors are made with more than one output sockets. They allow you to connect more 2w (Class II) devices into 3w socket. Which is right, because 2w (Class II) device are made safer than safe, they don't need to be earthed.

See? The 2w plug fits there: http://i3.cn.cz/1131518818_zasuvka.jpg
But here you just can't fit the 3w plug.  Impossible. Simply no way. Any attempt of that is illegal and safety risk. http://www.elektrahk.cz/gif/e030200.gif

Or did I understood the american adaptors wrongly? I think that it is obvious, why trying to plug 3w device into 2w socket is a safety risk.


It is a little more complicated, it would be a nice discussion, but it doesn't fit here, I don't like making mess in threads :-)
 

Offline Jeroen3

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Re: Grounded device case causes frequent ESD
« Reply #30 on: December 16, 2014, 06:24:46 am »
Summary: In EU, there is no way you can plug a device with threee wires (Class I, L N PE) to a two wire socket. 
Not true. Houses are equipped with these in the walls: http://static.webshopapp.com/shops/004230/files/001612800/gira-079803-2-voudige-stopcontact-zwg.jpg
And you can buy those at your local diy shop. They'll fit all plug.
 

Tac Eht Xilef

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Re: Grounded device case causes frequent ESD
« Reply #31 on: December 16, 2014, 08:37:15 am »
Just slightly OT, but Apple makes these modular power adapters with nice interchangeable mains plugs, but can you buy a genuine Apple plug adapter for a different country? Can you heck! There are times when I think Apple has completely lost the plot.
Like this kit that contains them all + a USB charger?

FWIW I've bought the individual heads for US & UK plugs too - they're not listed online & probably aren't in stores, but they were available as spare parts (or were a few years ago) from a local Apple business/edu dealer.
 

Offline mikerj

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Re: Grounded device case causes frequent ESD
« Reply #32 on: December 16, 2014, 01:23:31 pm »
So far as I know, the US is the only market in which a device designed for a 3-pin supply comes with an adapter allowing you to connect it improperly.

The genuine Apple (iPod/Iphone) chargers I own don't have a grounded output, and the output floats at a pretty high voltage (90v or so measured to ground) which you can definitely feel (as someone else mentioned, it feels like the surface is vibrating).

Apple isn't the only one though, many (probably most) "wall wart" chargers/adapters have a plastic earth pin with class Y caps across the transformer to reduce EMI, and yet they invariably have the "double isolated" symbol on them.  AFAIK an appliance could only be rated as double isolated if failure of a single component couldn't expose the user the dangerous voltages, but if the EMI cap shorted this would be dangerous.
 

Online wraper

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Re: Grounded device case causes frequent ESD
« Reply #33 on: December 16, 2014, 01:33:07 pm »
So far as I know, the US is the only market in which a device designed for a 3-pin supply comes with an adapter allowing you to connect it improperly.
AFAIK an appliance could only be rated as double isolated if failure of a single component couldn't expose the user the dangerous voltages, but if the EMI cap shorted this would be dangerous.
It means what it says, double insulated, not double component. By single component you can call optocoupler and transformer too.
Quote
These products are required to prevent any failure from resulting in dangerous voltage levels becoming exposed causing a shock etc. This must be done without the aid of an earthed metal casing. Ways of achieving this include double layers of insulating material or reinforced insulation protecting any live parts of the fitting.

There are also strict requirements relating to the maximum insulation resistance and leakage to any functional earth or signal connections of such appliances.
 

Offline Yansi

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Re: Grounded device case causes frequent ESD
« Reply #34 on: December 16, 2014, 05:58:35 pm »
Summary: In EU, there is no way you can plug a device with threee wires (Class I, L N PE) to a two wire socket. 
Not true. Houses are equipped with these in the walls: http://static.webshopapp.com/shops/004230/files/001612800/gira-079803-2-voudige-stopcontact-zwg.jpg
And you can buy those at your local diy shop. They'll fit all plug.

This is type C socket, prohibited in most countries which have people with at least some intelligence. Sweden prohivited them in 1994, so did other countries. Usage possible only up to 2.5 Amps IT (isolated) mains. If you use them, poor you, poor your country. I've never seen these suckers anywhere. Maybe countries using Schuko/French type sockets (as does our country) have a little bit more sense for safety, not allowing any so dumb things like not using mains earth. So I think I was wrong, not the whole EU is so smart, so I will modify that statement to "some smarter EU countries".  >:D
 

Offline Ether

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Re: Grounded device case causes frequent ESD
« Reply #35 on: December 16, 2014, 05:59:12 pm »
I don't want to sound like an idiot but I have been experiencing this too because when I touched the screws of my grounded power supply, I got a shock. The problem persists even after I've worn an anti-static strap. Does anybody know what's the problem?
 

Offline Yansi

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Re: Grounded device case causes frequent ESD
« Reply #36 on: December 16, 2014, 06:17:34 pm »
I really don't know what to say, after reading about so much confusion and safety risking in many countries, including USA and possibly Netherlands.
This would not just happen to you here. Safety regulations on electrical installations are tight here. Almost zero possibility you could get here live screwhead even whole metal case of an appliance.

By the way, do our american and dutch colleagues know what  RCD is? I don't know, if they use it, possibly not. Just another interresting safety device, required (in our country and I think all neighbouring countries such as Germany, Austria, Poland, Slovakia...) in all new installations and all places with increased safety risk, such as wet rooms, sockets outside of ur house, installations in wood structures and for appliances submerged in water (water pumps)...

And sure enough, RCD can work only in TN-S mains, so we have here no room for such shits as type C wall sockets.
 

Offline Monkeh

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Re: Grounded device case causes frequent ESD
« Reply #37 on: December 16, 2014, 07:44:50 pm »
I don't want to sound like an idiot but I have been experiencing this too because when I touched the screws of my grounded power supply, I got a shock. The problem persists even after I've worn an anti-static strap. Does anybody know what's the problem?

Yes, you probably don't have an earth at all.
 

Offline Jeroen3

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Re: Grounded device case causes frequent ESD
« Reply #38 on: December 16, 2014, 08:12:54 pm »
By the way, do our american and dutch colleagues know what  RCD is?
Yes, they are mandatory since forever. One 30 mA RCD every 4 x 16 Amp breaker.
We call them Aardlekschakelaar, which translates to "earth leakage switch".

Unfortunately our house build somewhere 198x is completely fitted with IEC Type C. Except for kitchen, garage and attic with central heater/washer/dryer. They are still sold around here, bought one two weeks ago to repair a damaged switch-socket combi.
I've exceeded that 2.5 Amp limit a lot. Probably exceeding it now, since that is only 600 Watts. And my entire desk is on it.

Earth for my desk is coming from the copper* central heating pipes. Yes I know I shouldn't. Do as he says right?
Some intelligence you say?

*They are plastic nowadays.
 

Offline Richard Crowley

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Re: Grounded device case causes frequent ESD
« Reply #39 on: December 16, 2014, 08:28:31 pm »
I don't want to sound like an idiot but I have been experiencing this too because when I touched the screws of my grounded power supply, I got a shock. The problem persists even after I've worn an anti-static strap. Does anybody know what's the problem?
Current must have a complete circuit to flow. Since you have not revealed the REST of the circuit, no, nobody knows what your problem is.
If you want to fill in some details, maybe we can try to offer some suggestions.
Consider details like:
What does "shock" mean?  Are you talking about a momentary discharge?  Or a continuous "tingling"? or what exactly?
When you say "my grounded power supply", is this a commercial unit, or a home-made gadget?
How do you know your power supply is "grounded"?  How do you know it isn't broken?
Do you get the same "shock" (however you are defining it?) from other things that are "grounded"?
Do you have a meter that you can use to test things with?
 

Offline Richard Crowley

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Re: Grounded device case causes frequent ESD
« Reply #40 on: December 16, 2014, 08:30:06 pm »
I have to laugh every time I read the subject line of this thread.   :-DD

It is like saying that guard rails cause car crashes.
 

Offline miguelvp

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Re: Grounded device case causes frequent ESD
« Reply #41 on: December 17, 2014, 12:17:03 am »
By the way, do our american and dutch colleagues know what  RCD is?

No we don't but do you know what GFCI is? ;)
 

Offline Monkeh

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Re: Grounded device case causes frequent ESD
« Reply #42 on: December 17, 2014, 12:21:05 am »
By the way, do our american and dutch colleagues know what  RCD is?

No we don't but do you know what GFCI is? ;)

A letter too far.
 

Offline mikerj

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Re: Grounded device case causes frequent ESD
« Reply #43 on: December 17, 2014, 12:18:48 pm »
It means what it says, double insulated, not double component. By single component you can call optocoupler and transformer too.
Quote
These products are required to prevent any failure from resulting in dangerous voltage levels becoming exposed causing a shock etc. This must be done without the aid of an earthed metal casing. Ways of achieving this include double layers of insulating material or reinforced insulation protecting any live parts of the fitting.

There are also strict requirements relating to the maximum insulation resistance and leakage to any functional earth or signal connections of such appliances.


In which case no charger/adapter that exposes the output connections (e.g. with a DC power plug or 3.5mm jack plug) should be able to be rated as Class 2 ("Double isolated"), since a single failure could result in dangerous voltages on the output.  However, I have a couple of brick chargers in front of me that have the double isolated icon on them.
 


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