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Pin

01/07/2012 7:34 AM

i have a ? that why we r indicate the earth pin as big compared to reamaining....but dont say that it is for identification .

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Guru

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#1

Re: pin

01/07/2012 7:41 AM

Please restate this jibberish in other words...

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Guru
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#2

Re: pin

01/07/2012 7:42 AM

So that if you try to plug it in the wrong way, it won't fit.

(In future, please try to compose literately; txtspk is reviled here.)

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Guru
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#3

Re: pin

01/07/2012 7:50 AM

Earth pin is usually longer so that the earth connection is made before the others. Larger area is to ensure sufficiently low contact resistance.

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Guru

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#21
In reply to #3

Re: pin

01/09/2012 9:55 AM

Then what about the contact area required for the phase pin, thro which also the fault current would flow? Need it not have a larger contact area too? Your answer as regards the larger cross section is incorrect.

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Guru
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#22
In reply to #21

Re: pin

01/10/2012 3:10 AM

I'm not interested in fault current here, rather in protection against electrocution.

Here's a scenario:

A student gets back to his cluttered bedsit after walking through the wet grass on campus, and wants to grab a couple of slices of toast before dashing out to the pub to meet his mates. He starts washing up a plate left over from the previous meal, then thinks it'd be a good idea to put the toast on while he's finishing the washing up. He gives his hands a perfunctory wipe, and grabs the bread.

Little does he know that a wire has come adrift between the lever-operated switch and the heater element, and is resting against the inside of the metal case of the toaster ...

He shoves the bread in the slots, steadies the toaster body with one hand and pushes the lever down …

The contact resistance of the phase pin is totally irrelevant here - provided it will carry at least an amp or so. If the resistance from the case to earth via the protective conductor is not sufficiently low (compared with the soggy student), he is, sadly, the one who's toasted.

I stand by my answer.

[Edit - this is probably more important in Europe and other regions using 230Vac than in the USA, but the principle still applies]

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Guru

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#23
In reply to #22

Re: pin

01/10/2012 4:18 AM

Again, even for protection against electrocution, isn't it necessary that the entire current path must be of low resistance?

Alteranately, during electrocution, if the the higher resistive path offered by a thinner phase pin is OK from a protection perspective, why then, the same thickness is not sufficient for the earth pin too?

Moreover, it can even be proved by calculations that even an earth pin of the cross section of the phase pin would offer sufficiently low resistance during an earth leakage, to offer protection to a person from electrocution.

When compared with the human body resistance (bare foot, wet floor), a few milli meter reduction in thickness for the earth pin wouldn't matter much as the plug top pin is made up of Copper or a better conductive material than a wet human body.

I still stand unconvinced by your answer. And, I do still stnad by my answer posted earlier (as quoted by KVS) and which had got me a good 6 GAs.

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#24
In reply to #23

Re: pin

01/10/2012 5:03 AM

"... even for protection against electrocution, isn't it necessary that the entire current path must be of low resistance?" No. Why should the resistance at the phase pin matter?

When I spoke of area, I was referring to the area available to make a sufficiently low resistance contact. Although I didn't specifically state it, surface area is the important factor - I did specify "contact resistance", not "conductor resistance". It was you who introduced cross sectional area in post #21.

For portable appliance testing (PAT testing) in the UK the earth bond test must give a figure of less than or equal to 0.1Ω + the lead resistance (at a current of 1.5 x the fuse rating). Every little reduction in contact resistance at the plug-top earth pin helps.

And isn't bragging about GAs rather childish? What were the qualifications of the people who awarded them? I suggest you just don't go there.

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#25
In reply to #24

Re: pin

01/10/2012 5:33 AM

Er, JohnDG and EE65, having learnt a lot from both of you, i think the electrical engineering community would be benefited considerably if both of you can critique the earth-pin systems prevalent in other countries.

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#27
In reply to #25

Re: pin

01/10/2012 7:43 AM

That looks like patent #7,521,738, by Rube Goldberg. How long will it take for the flex wires or slip rings to wear out?

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Guru
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#26
In reply to #23

Re: pin

01/10/2012 7:36 AM

Alternately, during electrocution, if the the higher resistive path offered by a thinner phase pin is OK from a protection perspective, why then, the same thickness is not sufficient for the earth pin too?

Earth pin is sink so lower is resistance of earth pin means lesser is potential gradient at the point of contact of person which is good,on other side Phase pin is source pin so higher is Resistance of it, means better is for person,because it will reduce potential at contact point with ref to earth.doesn't it look logical?

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Guru
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#4

Re: pin

01/07/2012 8:24 AM

An excellent explanation has been provided in another thread by electricalexpert65

http://cr4.globalspec.com/comment/719459

You really need to learn how to search.

You also need to learn written English.

You also need to learn manners ('dont say ...')

Oh...what's the use.

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Guru

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#20
In reply to #4

Re: pin

01/09/2012 7:21 AM

Oh! Thanks KVS! for remembering that post. I was about to post my answer now. Let the OP search for himself.

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#5

Re: pin

01/07/2012 10:04 AM

I'm finding this guy's language really annoying!

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Guru

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#6
In reply to #5

Re: pin

01/07/2012 10:58 AM

No more annoying that some coward who won't even take the time to register and come out from behind the cloak of anonymity such as yourself!

You said in the OP's only other post, "Before asking a damn question in this forum, first get your English at least to an understandable level. I didn't get a slight drop of logic out of your thread. Did you flunk your English exams in your school days?"

Now that's really constructive, isn't it?

Why not go find an insect and pull its wings off.

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Guru
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#7
In reply to #6

Re: pin

01/07/2012 11:59 AM

Calm down please, you'll be having a seizure over something not worth the effort.

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Guru

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#8
In reply to #7

Re: pin

01/07/2012 12:08 PM

Don't worry.

Just honing the tongue a little. I like to keep it sharp in case I really need it.

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#9
In reply to #8

Re: pin

01/07/2012 12:23 PM

sorry sir i did"nt expect these much of reaction with my language, i realy dnt know sir i will try to improve thanks for encourage ..i never forget these day sir

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Guru

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#10
In reply to #9

Re: pin

01/07/2012 12:29 PM

Please, no apologies are necessary, especially to me. I understood both your posts.

I pay no attention to anonymous posters anyway. They're just a nuisance, sorta like flies.

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Guru
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#11
In reply to #9

Re: pin

01/07/2012 12:36 PM

"txt spk" and similar styles are not appreciated here. Using "?" instead of spelling the word "question", and "r" instead of "are" only make your presentation even less readable. We understand that English is not your first language, but using such lazy abbreviations just makes things worse. Many around here (myself included) find it very irritating.

You'd also benefit from using the spell-checker before posting.

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#18
In reply to #9

Re: pin

01/08/2012 12:07 AM

If you really want to be a long runner of this forum you should show some continuous improvement in your posts, which is not evident in this Post, though its your third post, You could have calm down those reactions by-

Using I instead of i, Don't instead of dnt, Sorry Instead of sorry, etc.

People here want you to improve, No one expect you to be perfect, which is impossible for anyone anyway, I am sure members will help you to forget these days if you come up with some sincerity and improvements in your next post.

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Guru
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#19
In reply to #6

Re: pin

01/09/2012 3:25 AM

Try switching to decaf.

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#12

Re: pin

01/07/2012 1:44 PM

Lyn

I thought there was a requirement to be registered before you could post. if not, we should ask the site administrator to make that a rule.

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Guru
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#13
In reply to #12

Re: pin

01/07/2012 1:57 PM

You are correct. No more "Guests" posting. Been the case for a while now.

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#15
In reply to #12

Re: pin

01/07/2012 2:36 PM

I'll defer to Admin.

I'm just a user.

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Guru
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#14

Re: pin

01/07/2012 2:33 PM

Then how does AS#1 and AS#2 post?

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Anonymous Poster #2
#16
In reply to #14

Re: pin

01/07/2012 4:24 PM

When you post there's a checkbox (top lhs) "I want to post anonymously". JohnDG.

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Guru
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#17
In reply to #16

Re: pin

01/07/2012 4:28 PM

Sorry top rhs. Trouble with posting anon is you can't edit.

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