" do not care for AC connection " is this statement correct ??

Maddy

In many cases it does not matter electrically which way you connect the two wires. examples
1. Incandescant light socket the hot goes to the center terminal and neut to the ring ie screw for the bulb. Either way the lite works BUT if you put the hot on the screwshell and someone contacts it (like I did once) they can get zapped - like I did.
2. Many DC motors will operate fine regardless of how you connect + and -. This is because you are not changing the connections of the fields when only connecting the DC line. Exception permanent magnet motors OR shunt motors that have the field separately powered.
3. You can put control switches in the neut on motor controls and they will work fine. However if you get a fault to ground on the neut between the relay and an open control switch the machine can start.

Being negligent about following convention, code, and good practice will at the least result in
"who is the dumbshit that hooked this up" to
"I'm gonna wring his neck"
after some guy grabs what he thought was a neut and was actually a hot because you did not follow color convention.

NEVER assume a white or green conductor has zero potential for three reasons
1. Last place I worked they stuck in any old wire that was handy.
2. The neut and the ground CAN have some potential on them. With current on them and long conductor length or a poor connection they can have an IR drop.
3. If and when you cut a neut on a multiwire circuit AND there is an energized load "downstream" of where you cut - one side of the neut is now hot. You also turned off the lites in that room by cutting the neut - course you may have found out that was not a good idea cause you burned a hole in your cutters.

Dan Bentler

thanks leitmotif



but i do not understand well how the ground may carry voltage , i know the netural may carry voltage specially for long distance and i know the ground terminal is a always safe terminal , if then the ground may also carry voltage it is not safe else


i agree with you the netural carries the same current pass through the hot line

also brigm said : " 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 "

but i do not understand how the Hot wire would be connected to the frame of the TV. and there is no problem for the customer ??

thanks again

i know the ground terminal is a always safe terminal

This isn't really true the true ground is there as a safety if the neutral
cannot carry all the voltage Bad connection etc then any stray voltage will use the true ground provided its the path of least resistance.

For example lets say you test on a 120/220 single phase circuit between
true ground and neutral ideally you should measure zero however yuo will probably be less than 1 volt with a poor neutral connection, undersized neutral or a harmonic inbalance you will get higher readings

I'm not sure about your TV question however if you have 120 volts on the chassis I would not consider that as safe

little off topic I mentioned Harmonics in regards to the above post so I thought I would provide a useful article I came across

thanks mordred

i agree with you if we have 120 volts on the chassis of any device it is not consider that as safe but you can see the post of brigm as he said : " 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 "

so i ask how then no problems for the customer ??


thanks

NO it is problem for the customer in that if that customer decides to change the plug himself or work on the TV himself (not being an electrician) he may or may not recognize the correct color code or mistaken wiring. However he does have a meter so he checks the + to the chassis sees no voltage and mistakenly thinks there is no power there BIG OOPS. Or he tries to discharge the capacitors to the N rather than to true ground again a big oops the Caps did not discharge. See the issue??

however will the customer get shocked by touching the chassis
when you have the leads reversed when you see 120 volts between neutral and chassis then the answer is no as thats only potential differents between a hot and a ground keep in mind leads are revered. A TV is a poor example of the dangers of this proactice as anyone working on it should be smart enough to unplug it first then discharge the caps A better way of thinking of the dangers is what if you need to change something while its still live? Ie a large machine with multiple circuits where you need to fix one small circuit without shutting down the entire system

Devices with 2 wires (appliance) have what we call "doable insulation).
That mean the chaise is out of the user hand.The user touch only insulated material.
In that case you allow to use 2 wire.
When you learn safety rules that one of them.
BTW on a TV or similar there is transformer one of the legs of the secondary is grounded.That is a different story.

Unfortunately I don't have any reading material in English about that issue.
It is too important to learn by corresponding.
I hope someone here can post a link to site which provide all that info.

Be careful.
Remember. accidents do not just happened they caused by.

When it comes to electricity you always have to care. This is the only sound advise I would give to anyone in any circumstance, period.

After being 28 years in the business, first as a machine builder, later as a designer and now as a trainer, I'm still 'afraid' of electricity and this keeps me on guard all the times.

Kind regards,

magdyfayad said:

thanks leitmotif

but i do not understand well how the ground may carry voltage , i know the netural may carry voltage specially for long distance and i know the ground terminal is a always safe terminal , if then the ground may also carry voltage it is not safe else


i agree with you the netural carries the same current pass through the hot line

also brigm said : " 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 "

but i do not understand how the Hot wire would be connected to the frame of the TV. and there is no problem for the customer ??

thanks again

Click to expand...

Maddy
I think there a couple hurdles that must be addressed.
1. Language barrier.
2. Terminology problems - what they call stuff in Egypt may be different than what we call it here in USA.
3. You really need to go to class and learn from a qualified instructor. You are smart enough to get huge gains and knowledge this way. This long distance learning you are doing and the long distance instructing we are doing is not efficient nor in your best interest. Dont worry about what we call stuff in USA nor how we do it - you are not in USA and you need to learn how to do it in Egypt.

I think I have already defined the different conductors for you as used in residential and commercial wiring here in USA.

GROUNDING CONDUCTOR is a conductor (green or green w/ yellow stripe or bare in USA) It is BONDED to the ground grid at the service entrance in a residence or commercial occuptancy. It normally carries no current. Its purpose is two fold
A to ensure that non energized parts are maintained at ground potential.
B IF there is a fault it serves as an additional path for fault current to flow back to circuit breaker to trip it.

GROUNDED conductor (neutral, common, center tap etc etc) in USA a white or gray conductor that is BONDED to ground at the service entrance. It carries current but should stay near ground potential. The current will be the same as the phase conductor if 120V and will be the difference in teh currents of the TWO phase (ie HOTS or black and red commonly) conductors ie 240.

There are three ways to screw up a 120 VAC single phase plug where you have a phase conductor ie HOT a neutral (GROUNDED) and a ground (GROUNDING green).

Connect the phase (HOT) to where the neut should go and the neut to where the hot should go. The internals will not care about this. All they see is the potential difference between the hot and neut.

Connect the hot to the frame of an appliance and the neut to the hot terminal and the ground to the neut termianal
OR neut to neut and ground to the hot. You will likely shock someone UNLESS you are in a house with wood floors which may provide enough insulation UNTIL they touch another properly grounded appliance or "source" of ground. Course the wrongly wired appliance will not work.

REverse the neut and the ground. Now the GROUNDING (green) is the current carrying GROUNDED conductor and the neut is the GROUNDING conductor. In a single panel residence this may not be a problem because the neut and the ground both tie to the same bus. With multiple panels where the downstream panel has the neut floated (not bonded to ground in THAT panel) and the GROUNDING conductor on a separate bus you will get current flow in the GROUNDING conductor between the two panels. While incorrect this may not cause a problem UNLESS you have ground protection for the second panel. This situation will trip the ground protection.

Now on TVs and other old appliances especially tube types where they grounded the internal circuits (that is where the terms B+ and B- -- uh were they DC ?? came from I think) to the chassis which was inside the case. The chassis was tied to the neut. If you reverse the HOT and neut I think you would (may ??) screw up the tubes and the TV or radio would not work. In addition the chassis (NOT the CASE) would be energized and there would be a tech that would be awful irritated with you if he touched the chassis and ground.

In USA ranges and dryers bonded the external metal to the neutral
it worked OK and was done for years.
UNTIL NEC changed and required a four conductor 240 a neut (GROUNDED) and a ground (GROUNDING) conductor and plug - much better and safer.

Dan Bentler

Dan

I don't think in old TVs and other old appliances.switching between the hot and neutral can make any damage.
Old systems ware not grounded or use transformer with secondary leg grounded.

I think we do bad service to the original poster.
Your explanation about grounding for someone who do not understand it.make it more confusing.
To understand what behind you need to learn in certain order to build up your knowledge base.
In US there was different ruse then here and Europe.but in the last few years things changed.but still you do some thing which here they would be forbidden.Like grounding secondary leg of Delta\Delta transformer(grounding hot point).

To the original poster.
It is not rocket since.Find someone who understand all of that and ask him to teach you.It would not work by corresponding.

thanks for this information leitmotif


thanks

ArikBY said:

Dan

I don't think in old TVs and other old appliances.switching between the hot and neutral can make any damage.
Old systems ware not grounded or use transformer with secondary leg grounded.

I think we do bad service to the original poster.
Your explanation about grounding for someone who do not understand it.make it more confusing.
To understand what behind you need to learn in certain order to build up your knowledge base.
In US there was different ruse then here and Europe.but in the last few years things changed.but still you do some thing which here they would be forbidden.Like grounding secondary leg of Delta\Delta transformer(grounding hot point).

To the original poster.
It is not rocket since.Find someone who understand all of that and ask him to teach you.It would not work by corresponding.

Click to expand...

Arik
Think I already covered that:
2. Terminology problems - what they call stuff in Egypt may be different than what we call it here in USA.
3. You really need to go to class and learn from a qualified instructor. You are smart enough to get huge gains and knowledge this way. This long distance learning you are doing and the long distance instructing we are doing is not efficient nor in your best interest. Dont worry about what we call stuff in USA nor how we do it - you are not in USA and you need to learn how to do it in Egypt.

Dan