Funny Incident

[gromit]

I thought you might like to share a funny incident that I encountered last week.I was with my son at the local college during an open day, looking at engineering courses, and the tutors in the electrical installation workshops had set up a small mock up practical session for the boys to do, which consisted of connecting two loose wires to a ceiling rose and a switch. The boys were paired up with one tutor and each given their own work area.

On completion the tutor checked their work, and then supplied power to the circuits.

The first one, did not light. "Oh you must have made a mistake" , is the reply from the tutor. Second boy Same as first, no illumination. "Oh, you seem to have a problem there as well", was the reply. Both boys look puzzled, and rechecked. Then I suddenly said "Have you checked the bulb?"

Yes, you guessed it a duff bulb!

It is always the simplest things that cause the biggest problems. Cheers have a good weekend!


Gromit

 

[andy]

college lecturers are useless. they once connected a ring main mock up to a 110V supply, supplied by a CTE transformer. he then couldnt understand why the 230V socket tester, clearly marked 200-250V didnt work... and still didnt understand the fact there was only 55V between phase and earth/neutral and earth. he insited my work was wrong. connected to a 230V supply and it worked. luck maybe?

 

[baldelectrician]

I must admit it's a different world at colleges, but I feel the lecturers get a bad press (electrical ones in particular)

I have met the bunch from my local (Ayr) college and they are all pretty clued up and approachable.

I may be getting old, but I think a lot of the youth nowadays seem only to think of themselves first, second and third, with a 'can't be bothered - too much hard work attitude.'

Some kids who want apprenticeships seem to think it will be a walk in the park, when they have to do a bit of work the enthusiasm goes out the window.

 

[Softus]

college lecturers are useless. they once connected a ring main mock up to a 110V supply, supplied by a CTE transformer.

Am I missing something? Does the fact that one lecturer made a human error mean that all "college lecturers are useless"? If so, then surely all college students are useless.

 

[andy]

Am I missing something? Does the fact that one lecturer made a human error mean that all "college lecturers are useless"? If so, then surely all college students are useless.

that was only 1 thing. theres a hell of a lot more. he once tried to tell us that is physically impossibly for a light to work if the switch goes in the neutral instead of live...

 

[Softus]

that was only 1 thing. theres a hell of a lot more. he once tried to tell us that is physically impossibly for a light to work if the switch goes in the neutral instead of live...

OK - I'm with you on that one andy - if he truly believed it then that's gross incompetence.

 

[ban-all-sheds]

he once tried to tell us that is physically impossibly for a light to work if the switch goes in the neutral instead of live...

How did that get resolved?

 

[breezer]

that was only 1 thing. theres a hell of a lot more. he once tried to tell us that is physically impossibly for a light to work if the switch goes in the neutral instead of live...

I hate to say this, but i think i see what the lecturer means

you have not quoted what he actualy said.

I cant put it exactly as he said but yes technicaly he is right (if you think about it)

look at it this way.


you have a lamp in a lamp holder

you connect it to a supply via 2 single wires, one red, one black
(the black is comming from the left, the red is coming from the right)
This is just so you can see where we are going with this expalnation.

at this point there is no switch only the connection to the supply

You connect the supply

the lamp comes on (no surprise there)

you remove the lamp (Lamp goes out)

you now get a meter set to ac voltage

you connect the black lead to the neutral supply (and it will now stay there for the purposes of this expalnation)

you now touch the red lead of the meter to the right lamp connection (thats the red wire, remember)

you get 240v (agreed?)

(also for the pedantic among you the supply is 240v ac for the purposes of this explanation))

you remove meter lead (0v on meter)

you put lamp back in (lamp comes on)

with insulated side cutters you cut the black wire (the black wire, jones)

the lamp goes out

you now remove supply and fit a switch in the black wire where you just cut it

now unless you are thinking ahead of me, you should be thinking the lamp went out becuse the neutral was cut so i too am wrong.

no, please carry on reading

what you have just done is not cut the neutral wire (yes i did say cut the black)

all you have done is to cut the black wire
(the electricity doesnt know / care what colour the wire is)

"but that is neutral" you should be saying

you turn the switch over so its button is face down, and terminals are face up

you now reconnect the supply

(the switch is in the on position)

the lamp comes on

you now flip the switch and the lamp goes out

(you say "there you are, you have switched the neutral again!")

no i havent, i have swithced the black wire (its not the same, read on)

with the supply on, and the switch off the lamp is off (we all know that)

now here is the interesting bit

(the lamp is sitting above the switch, the supply connections are below the switch, sorry i didn't mention it earlier)

so the top black wire from the switch goes to the lamp, the bottom wire from the switch goes to the supply

you connect your red meter lead to the bottom switch terminal

(remember the meter black lead is still connected to the neutral supply)

your meter will show 0v (no potential difference between neutral and neutral)

are you with me so far?

(if not go back and start again)

you now put the meter red lead on the top switch terminal

(which is the black wire going to the lamp)

you get a potential difference of 240v showing on the meter

so that means this black wire is live doesnt it, because it has 240v showing

the live current is flowing from the live supply, up the red wire, through the lamp down the black wire and stops at the swicth

so as the lecturer said no matter where the swicth goes you are still switching the live, even though the switch is in the black wire , because the voltage is running through the lamp down the black wire.

as you have proved by putting the meter red lead on the top wire on the switch, which although it is black, is actually live

this is true no matter where you put the switch so lomg as the lamp is a working lamp

so the lecturer really is right, what he didn't say or was miss quoted / miss understood is that ..............................

well you figure it out, as i said when i started i cant put it into the right words

 

[Softus]

If I've understood you correctly (which involves pretending that you connected the switch before using it), then you've simply renamed the neutral on the 'return' from the lamp and called it a live on the grounds that your meter measures a PD across the open switch when it is connected on that neutral path.

There's no point in having a nomenclature unless you stick with it, so renaming the lead is (a) confusing, and (b) pointless.

Nothing you've written changes the basic physics of how the circuit works - you're just messing with the words to make it look as though the lecturer could have been right.

 

[breezer]

we are all entitled to an opinion, mine was as i wrote, ( I recall a similar point being raised, donkeys years ago when i was at college) not messing with words, your opinion is that i messed with words, lets leave it at that

virtual pints ore on me. cheers!

 

[Softus]

we are all entitled to an opinion, mine was as i wrote, ( I recall a similar point being raised, donkeys years ago when i was at college) not messing with words, your opinion is that i messed with words, lets leave it at that

virtual pints ore on me. cheers!

breezer, I take your point, about opinions, and I greatly respect the civilised flavour of your response, but not all opinions are equal just because they are opinions. For example, you and the lecturer are currently in a minority of two, which has to count for something.

And it isn't my opinion that you messed with the words - you called a neutral "live", just because it had a potential relative to an unconnected neutral.

If you can't stick with the accepted nomenclature to explain your point, what hope do you have of your opinion being accepted? Perhaps you had no hope or expectation of it being accepted, in which case then fair enough, but why post it?

 

[breezer]

i posted it because if you actually read all of what i had written

the first line i wrote said

I hate to say this, but i think i see what the lecturer means

optimum word being "think", so to me you did not read / understand all of what i had written, this then brings into question your understanding of the complete post, also you say myself and the lecturer are in a minority, you are the only one who has "read / replied" to my post, so that makes YOU the one in the minority

come, lets have a beer

 

[Softus]

i posted it because if you actually read all of what i had written

It is because I read all of what you wrote that I was able to point out to you that you hadn't connected the switch, viz:

you turn the switch over so its button is face down, and terminals are face up

you now reconnect the supply

(the switch is in the on position)

the lamp comes on

the first line i wrote said

I hate to say this, but i think i see what the lecturer means

optimum word being "think"

Oh, trust me, I knew it was something you thought and did not know.

...so to me you did not read / understand all of what i had written, this then brings into question your understanding of the complete post, also you say myself and the lecturer are in a minority, you are the only one who has "read / replied" to my post, so that makes YOU the one in the minority

Well I'm glad it amuses you, but my point, repeatedly, has been that the lecturer was wrong, and, if you think that he's right, then you are wrong too. You can dress up your answer, and/or attempt to distract me from my points by claiming that I didn't understand your post, but nothing you've written has changed the laws of electrical physics. And if you really really think that other forum members will agree with you on this, then I'm happy to wait and see. BTW, opinions from joe-90, GTM and TGM do not count on this subject.

come, lets have a beer

Sure - I'm happy to have a beer with you

 

[ban-all-sheds]

Breezer, you're a clown - I don't know what the point of all that was, if it was not to make us all laugh.

you connect the black lead to the neutral supply (and it will now stay there for the purposes of this expalnation)

you now touch the red lead of the meter to the right lamp connection (thats the red wire, remember)

you get 240v (agreed?)

So in other words, you have connected the red lamp conductor to the supply live, and the black lamp conductor to the supply neutral (you hadn't said, but your description of what the meter shows means that this is what you did.)

Do you really think that in that case the conductor connected to the supply neutral would ever be called by anybody with any common sense, anything but the "neutral wire", or just "the neutral"?

with insulated side cutters you cut the black wire (the black wire, jones)

Working on an energised LV supply. Tut tut...

now unless you are thinking ahead of me, you should be thinking the lamp went out becuse the neutral was cut so i too am wrong.

Yes, you are wrong, because as I said, nobody would ever sensibly call that black wire anything but the neutral wire.

what you have just done is not cut the neutral wire (yes i did say cut the black)

Yes you have, because as I said, nobody would ever sensibly call that black wire anything but the neutral wire.

you now reconnect the supply

I don't recall disconnecting it, but there ya go..

(the switch is in the on position)
the lamp comes on
you now flip the switch and the lamp goes out
(you say "there you are, you have switched the neutral again!")

no i havent, i have swithced the black wire (its not the same, read on)

Yes it is the same, because as I said, nobody would ever sensibly call that black wire anything but the neutral wire.

You aren't Big_Spark in disguise, are you?

you connect your red meter lead to the bottom switch terminal

(remember the meter black lead is still connected to the neutral supply)

your meter will show 0v (no potential difference between neutral and neutral)

are you with me so far?

Yes I am - it seems that the black wire is the one connected to the supply neutral, i.e. it is the neutral wire.

you now put the meter red lead on the top switch terminal

(which is the black wire going to the lamp)

you get a potential difference of 240v showing on the meter

Depends on how accurate your meter is, doesn't it.

I tell you something else, too - if you used an analogue meter, and had a good enough detector, you'd find some heat coming off the lamp, as it wouldn't be entirely off...

so that means this black wire is live doesnt it, because it has 240v showing

No. Surely a pedant like you are pretending to be would argue that it is no longer a neutral conductor because it is no longer connected to the supply neutral.

the live current is flowing from the live supply, up the red wire, through the lamp down the black wire and stops at the swicth

Current can't stop like that. In the absence of anything to complete the circuit (switch or meter) no current will flow at all.

so as the lecturer said no matter where the swicth goes you are still switching the live, even though the switch is in the black wire , because the voltage is running through the lamp down the black wire.

If your permanent meter connection was to the supply live, then exactly the same argument as this twaddle could be turned round to "prove" that there is no live wire, only neutral ones...

so the lecturer really is right, what he didn't say or was miss quoted / miss understood is that ..............................

No he's not - nobody would ever sensibly call that black wire anything but the neutral wire.

. . . . .

But what I don't understand is why, if you wanted to get all pedantic to prove that the switch is actually in a live conductor, you didn't simply point out that a neutral conductor is a live conductor, and that the distinction should be between phase and neutral, not live and neutral....

 

[ban-all-sheds]

you are the only one who has "read / replied" to my post, so that makes YOU the one in the minority

Not any more