You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old October 2nd, 2008, 12:44 AM   #1
magdyfayad
Member
Egypt

magdyfayad is offline
 
Join Date: Aug 2007
Location: cairo
Posts: 245
Question " do not care for AC connection " is this statement correct ??

frequently , i hear this statement " do not care for AC connection but must care for DC connection "

who say this statement wants to connect " L " terminal and " N" terminal any connection for AC connection , but for DC it must connect the positive terminal to a certain terminal and the negative terminal to a certain terminal

but i have some questions :

1- if this statement is correct , why the devices which worked by AC marked their terminal by " L" & " N " ??

2- what happen for AC devices if i reverse the connection for " L" & " N " ?? I know if the ground is connected to the nuteral and when i reverse the plarity , then the body of this device will be have a voltage , is there any thing more ?? i.e : if i reverse the polarity for AC devices , they also work , or not work , or damage ?? or different from some devices to another and what is the difference ??

3- the contactors either operate by AC or DC , we do not care for their connection , as if i reverse the connection for " L " & " N " or for " +ve " & " -ve " the contactors will also work , which means the statement is not always right , am i correct ??

4- when i must care for the connection for both AC & DC devices ?? what is the theory for this ??




thanks in advance
  Reply With Quote
Old October 2nd, 2008, 01:40 AM   #2
HJTRBO
Member
New Zealand

HJTRBO is offline
 
HJTRBO's Avatar
 
Join Date: Jul 2008
Location: Melbourne
Posts: 592
if you are going to do the job properly then you would wire correctly to the terminals as marked.

AC can be switched around, use the bridge rectifier as a good example of this. Should your component have its ground linked to nuetral, (unlikely) you reverse the connection then bang!

The polarity of DC will effect your LEDS and solenoids relays etc.

Nothing worse than grabbing a supposed nuetral and getting a belt cause some a hole was rough. Prove test prove I know, but come on
  Reply With Quote
Old October 2nd, 2008, 01:59 AM   #3
magdyfayad
Member
Egypt

magdyfayad is offline
 
Join Date: Aug 2007
Location: cairo
Posts: 245
thanks


i know i must connect correctly , but i want to konw if any one revercse the polarity what haappen ?? what happen for AC device which does not contain bridge rectifer , or any AC device must contain bridge rectifer ??

thanks
  Reply With Quote
Old October 2nd, 2008, 02:48 AM   #4
ArikBY
Member
Israel

ArikBY is offline
 
ArikBY's Avatar
 
Join Date: Oct 2003
Location: Oranit Israel
Posts: 1,434
Hi

This statement is not correct.
In some cases it might be true.
For DC. some DC devices MUST be connected in right direction.Other wise they would damage or not work.
Some devices like contractors or relays lamps,can work anyhow.
My conclusion.You better understand what you have in hand before you power it.
For AC.My rule of thumb.If you have 2 wires(without ground)device it is not important.
If you have 3 wires.Open your eyes.
In some cases you might connect the HOT(220V Phase)to the body of the device and kill someone.See my conclusion.

The theory behind it sometime it simple sometime its not.
There is different rules in different country's.
What excepted in US is not excepted in Europe or over here.
The problem is where you ground the center of the feed transformer.At that point you get the ground point and the neutral point.Grounding the center its like grounding the minus of power supply.
To be on the safe side you have to pull 3 wire from that point to your device(trough the panels CB etc).Any short cut might hurt someone.Some places you can pull the ground from local point,like water pipe.in that case you might get bed quality of grounding.
You have to learn the safety rule of the your place.Before you play with AC/DC over 50V.
__________________
Arik

Barak Control Israel
  Reply With Quote
Old October 2nd, 2008, 02:54 AM   #5
ArikBY
Member
Israel

ArikBY is offline
 
ArikBY's Avatar
 
Join Date: Oct 2003
Location: Oranit Israel
Posts: 1,434
AC Device don't need any rectifier there is not polarity in AC.

The importance of polarity in AC is which point will be referenced to the ground, if existing or needed.
__________________
Arik

Barak Control Israel
  Reply With Quote
Old October 2nd, 2008, 03:30 AM   #6
magdyfayad
Member
Egypt

magdyfayad is offline
 
Join Date: Aug 2007
Location: cairo
Posts: 245
Hi


thanks


you said : " For DC. some DC devices MUST be connected in right direction.Other wise they would damage or not work"

i know that but when theses devices donot work only and not damaged , and when donot work and also damaged ??



you said : " For AC.My rule of thumb.If you have 2 wires(without ground)device it is not important "

why then marked the two terminals by " L " & " N " if it is not important ?? or it is marked terminals by " L " & " N " for only three wires i.e : contain ground ??


you said : " To be on the safe side you have to pull 3 wire from that point to your device(trough the panels CB etc)."

do you want to say if the nuteral is sepatred to the ground is more safe as if the nuteral for any reason carry some voltage the body of the dvice is still zero voltage as the ground is insulated to the nuteral , do you want to say that ??

but i ask , cannot the ground wire carry some voltage also as the nuteral or not ??
  Reply With Quote
Old October 2nd, 2008, 04:02 AM   #7
nightex
Member
Lithuania

nightex is offline
 
Join Date: Jun 2007
Location: Šiauliai
Posts: 34
Quote:
Originally Posted by magdyfayad
Hi


thanks


you said : " For DC. some DC devices MUST be connected in right direction.Other wise they would damage or not work"

i know that but when theses devices donot work only and not damaged , and when donot work and also damaged ??



you said : " For AC.My rule of thumb.If you have 2 wires(without ground)device it is not important "

why then marked the two terminals by " L " & " N " if it is not important ?? or it is marked terminals by " L " & " N " for only three wires i.e : contain ground ??


you said : " To be on the safe side you have to pull 3 wire from that point to your device(trough the panels CB etc)."

do you want to say if the nuteral is sepatred to the ground is more safe as if the nuteral for any reason carry some voltage the body of the dvice is still zero voltage as the ground is insulated to the nuteral , do you want to say that ??

but i ask , cannot the ground wire carry some voltage also as the nuteral or not ??
for exemple if device has switches wich obviously operates in L wire it is important when u switch it off all circuits have 0 potencial. Also some circuit elements operates as switches if they go ofline maybe they protect circuit in some cases. For exemple if u have device witch is not stationary then it is uninportant if u change L with N, if it is constructed properly and can be pluged everywhere.
  Reply With Quote
Old October 2nd, 2008, 04:38 AM   #8
ArikBY
Member
Israel

ArikBY is offline
 
ArikBY's Avatar
 
Join Date: Oct 2003
Location: Oranit Israel
Posts: 1,434
Some DC component would not work if they connected in wrong way.and some would damage.It depend on quality of the component and manufacturer wish.
There is no rule for that.The only rule I know is if the voltage is high or not stable the component might damaged.

When I wrote " For AC.My rule of thumb.If you have 2 wires(without ground)device it is not important "

I mean from the point of electricity it is not important.
If you take lamp it will work either way .
From the point of safety you need to connect in the right way.
L&N cam to indicate the hot and the neutral for safety reason.

To clear the issue.
I think it more safe to use separated conductors for ground and neutral(Even they cumming from the same point).Ground conductor should not carry any voltage.

You Wrote "but i ask , cannot the ground wire carry some voltage also as the nuteral or not ??"
Defiantly NOT.
All the safety system base on the ground cannot use the ground as conductor.
__________________
Arik

Barak Control Israel
  Reply With Quote
Old October 2nd, 2008, 04:44 AM   #9
HJTRBO
Member
New Zealand

HJTRBO is offline
 
HJTRBO's Avatar
 
Join Date: Jul 2008
Location: Melbourne
Posts: 592
do an apprentiship or read a book.

Just connect to as marked and you cant go wrong, and when you know enough by experience then connect how you see fit.

Are you licensed to be working with electricity??? Doesn't sound like you are?
  Reply With Quote
Old October 2nd, 2008, 05:09 AM   #10
tragically1969
Member
United Kingdom

tragically1969 is offline
 
Join Date: Jun 2007
Location: uk
Posts: 1,232
Quote:
Originally Posted by HJTRBO
do an apprentiship or read a book.

Just connect to as marked and you cant go wrong, and when you know enough by experience then connect how you see fit.

Are you licensed to be working with electricity??? Doesn't sound like you are?
Well said, but look up his other posts, there is history with this one !!
  Reply With Quote
Old October 2nd, 2008, 06:09 AM   #11
Brijm
Lifetime Supporting Member
United States

Brijm is offline
 
Brijm's Avatar
 
Join Date: May 2006
Location: St. Marys, PA
Posts: 640
As others have said, the concern with AC is safety, not function. I remember back in the school days, the instructors telling us about working on TV's with non-polar plugs. Some TV's had grounded frames, that if someone had changed a plug, and not paid attention to L / N, then the Hot wire would be connected to the frame of the TV. No problem for the customer, the TV worked fine.... but not good, for the Tech, who may be taking the insulated cover off.

-Mur
  Reply With Quote
Old October 2nd, 2008, 06:14 AM   #12
magdyfayad
Member
Egypt

magdyfayad is offline
 
Join Date: Aug 2007
Location: cairo
Posts: 245
thanks who answer me !!

this site for interactive questions and answers only , not for ironic !!!

i ask here and all can ask and any one can answer but by polite method only !!

if any one speak with me by impolite method and i can also speak by the same method but i do not do that because i am polite and i want to learn only !!

i say again i entered this site for learning only not for unuseful speaking
  Reply With Quote
Old October 2nd, 2008, 06:29 AM   #13
ArikBY
Member
Israel

ArikBY is offline
 
ArikBY's Avatar
 
Join Date: Oct 2003
Location: Oranit Israel
Posts: 1,434
magdyfayad

I would suggest you to learn the AC issue very carefully.
WE can help but not give you the foundation.
Pay attention to the safety rules.
Mistake might be disaster.
In most of the country's you need a license to work with more then 50V.
__________________
Arik

Barak Control Israel
  Reply With Quote
Old October 2nd, 2008, 07:05 AM   #14
tragically1969
Member
United Kingdom

tragically1969 is offline
 
Join Date: Jun 2007
Location: uk
Posts: 1,232
Ironic ?

You can take this as Ironic or however you want BUT:

You show such little understanding of the principals that you are dealing with its hard to believe that somebody lets you loose on any equipment that they own.

Do you realise if you do some of the things you show your apparent lack of understanding of you may actually kill somebody ?

This is not really the place for learning such basic electrical principals however, college, university or an appenticeship is.

There are thousands of superb text books which will explain all you need to know about your many questions, of course people here will help you where they can but you may get several different answers, no of which would be admissable in court if you do injure somebody !!

I urge you to stop playing with different theories of L&N connections, questioning reverse polarity, worrying about single phase vs three phase terminology and actually go and learn the basics !!
  Reply With Quote
Old October 2nd, 2008, 07:26 AM   #15
magdyfayad
Member
Egypt

magdyfayad is offline
 
Join Date: Aug 2007
Location: cairo
Posts: 245
i am very careful for the connection for both ac & DC drvices but i asked only to know what happen if any one reverse the polarity for the device ?? and also i asked why i hear this statement frequently " do not care for AC connection " although we have marked " L " & " N "

I reapeat again i am very careful when i connect the power supply for any device !!
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
CIP over Ethernet/IP on VMS -- 0x6a error when writing to a tag? vorfeed LIVE PLC Questions And Answers 10 August 20th, 2010 05:41 PM
ControlNet Connection Count? kdcui LIVE PLC Questions And Answers 5 June 26th, 2008 09:33 AM
Help with Profibus CPU315-2 DP Rafael Guedes LIVE PLC Questions And Answers 5 September 3rd, 2007 06:44 AM


All times are GMT -5. The time now is 10:16 AM.


.