Neutral Shocksssssss

[paulcopeman]

How come I have got a shock off a neutral before.

I never normally get anything from neutral. But I'm sure I got neutral shock onetime.

It was a commercial installation and I was working on emergency lighting CCT. Light was turned off via key swiitch if I remember correctly. I was certainly surprised especially as I was standing around 25ft up in the air on one of those sky winders. Lol

I've been a sparks for twelve years but never understood why u can get a shock off a neutral....

 

[binky]

Happens all the time, either via induced voltages, or some arse badly modifying circuits. Neutral isn't a dead circuit, and should always be treated as LIVE, circuit dead or not.

 

[apprentice87]

If you have been a spark for 12 years but cannot figure out how you can get a shock off neutral, it is time to retire...

john...

 

[binky]

all right enough abuse, he may never get to retirement unless we educate him, for which he will be eternally grateful, maybe :^O

one of my guys got well and truly belted of a neutral a couple of weeks ago......serves him right for ignoring the first tingle :slap

I hasten to add I didn't train him.

 

[SPECIAL LOCATION]

How come I have got a shock off a neutral before.

I've been a sparks for twelve years but never understood why u can get a shock off a neutral....

  headbang

:shakehead

Sorry..  but there's a contradiction in your above statement......

If you Cannot understand how any conductor can give a shock then you have Not yet become an electrician...

nor are you competent......

You may have been an electricians mate for 12 years ...

But clearly if you don't understand the basics of electrical science and how different potentials between conductive parts cause a current to flow...... 

You probably cant get your head around the dangers of "borrowed" / "shared" neutrals either...??? 

:C

:coat

 

[steptoe]

I was thinking maybe a switched neutral would be my first check,  :C

 

[Chewbacca]

Enough stormtrooper behaviour, educate the daft ******.

 

[kerching]

You can only get a shock when current flows

Current can only flow when there is a difference in potential

A neutral is only a neutral when it is referenced to earth, if you cut a neutral when the cable is on supply AND there is a load connected, the current cannot go anywhere. BUT, and it is f big BUT, it WILL flow through you IF you are providing a path for it.

THIS. Scenario can seriously ruin your day

Well that is how electricity used to work BUT mr Merlot has been around this evening, so it may all be different now

Just saying

 

[SPECIAL LOCATION]

have a look at Definitions...  page 30 of BS7671

top of the page...

LIVE PART:-  a conductor or conductive part intended to be energised in normal use; INCLUDING A NEUTRAL CONDUCTOR..

and I am guessing we all know that any LIVE part can give an electric shock if not correctly...

insulated, isolated, enclosed, placed out of reach..  etc...   etc...   etc... 

Try thinking of a typical circuit supplying a load...

{Supply#1}---{Cable}---{Protective device}---{Cable}---{Isolating/Functional switch}---{Cable}---{Load}---{Cable}---{Supply#2}

Break the circuit at ANY point between Supply#1 & Supply#2..

and you will have the FULL supply voltage between the two points where you break the circuit...

even if the cable happens to be called a neutral conductor!!!!!

opcorn

 

[SLIPSHOD & SLAPDASH]

In addition to all that has been said above, in your case, the most likely reason you got a shock was the emergency lights were only part of that circuit and when you touched the neutral you completed  a circuit to earth for other 'normal' lights that were still switched on.

 

[ProDave]

What the OP seems to have missed is "test for dead"

You should properly isolate a circuit (NOT just turn off the EM light test key) and test for dead with a proper tester.  As already noted, there were almost certainly other lights still operating on that circuit.  The ONLY way is to identify the mcb that feeds the whole light circuit and turn that off.  If someone taught you that it's okay to change a light fitting just by turning it off at a switch then they taught you wrong.

I would suggest the OP gets a neon screwdriver.  Before anyone slaps me for suggesting that, I am NOT suggesting using a neon as your primary means of "test for dead"  But I work on the principle that I never touch anything that my neon has not touched first.  In this case it would have light up and you would know you have a problem and not to touch anything until you have investigated and properly isolated.

If you really dislike the thought of a neon, then a volt stick is a poor, less reliable second best tool to have always in your pocket.

Also be aware, particularly in old houses, that you may also encounter a borrowed neutral situation. So even if you have isolated the lighting circuit you are working on, you may find splitting the neutral results in one leg becoming live via a different circuit. So a tip for working in older houses is turn of ALL the lighting circuits, not just the one you are working on. And keep that neon handy.

 

[Steve3948]

Called to a fault late yesterday, old cottage rented and a right sh*t hole stuff everywhere, not all lights working and on those that don't just a couple CFL's flickering or pulsing if switched on.

Checked random switch where lights don't work and voltage present testing L-E 230V, checking L-N 178V, N-E 178V.

Find one lighting fuse with three circuits connected, find cable feeding faulty circuit, IR tests ok.

Start tracing circuit and find cable from fuseboard to first light which runs upstairs is the problem, however its through a flat roof section that was replaced 6 months ago.

So this is the first light fed from the fuseboard and it has 230V L-E, 178V L-N and N-E when connected at the board, Its a TT Install with front end RCD with no tripping issues.

Disconnect supply from fuseboard to first light of the problem circuit both ends, feed first light with temp supply on plug top to get lights on as its now table lamp and torch time. All problem lights now working fine, check if this affects the remaining lights of the other two circuits if the fuse is pulled at the fuseboard, other lights go out, 

It's looking like a damaged neutral/cable and or a borrowed neutral, or another light between the fuseboard at what we think is the first light with a lamp in and on, although no lights were on anywhere we could see, and as it was dark so should not be hard.

Need to get back now today or early next week, more testing, more investigation and find out what the hell is going on.

With regard to the OP we have a situation where we have 178V on the Neutral.

 

[ProDave]

Nail through cable when flat roof was replaced is my bet.  Might be a PITA to pull a new cable through.

Continuity check end to end on each conductor of the suspect leg will prove that fault.

 

[paulcopeman]

Thanks for your replies .

I thought it might be because of the other lights on same circuit wer still being used.

As usual for this site I should have explained myself fully to let certain people know that I thought I already knew the answer but was just querying it, but I can't be bothered to spend loads of time writing an essay when I just want a quick reply.

Why do u always get people with their noses stuck in the air making comments.

Thanks again to everyone except aprentice87 and special location.

 

[ProDave]

Thanks for your replies .

I thought it might be because of the other lights on same circuit wer still being used.

As usual for this site I should have explained myself fully to let certain people know that I thought I already knew the answer but was just querying it, but I can't be bothered to spend loads of time writing an essay when I just want a quick reply.

Why do u always get people with their noses stuck in the air making comments.

Thanks again to everyone except aprentice87 and special location.

So you admit you didn't isolate the circuit, just turned off the EM lights.

I wonder what training you have done, because clearly you missed the bit about safe isolation, test for dead etc.

 

[binky]

Thanks for your replies .

I thought it might be because of the other lights on same circuit wer still being used.

As usual for this site I should have explained myself fully to let certain people know that I thought I already knew the answer but was just querying it, but I can't be bothered to spend loads of time writing an essay when I just want a quick reply.

Why do u always get people with their noses stuck in the air making comments.

Thanks again to everyone except aprentice87 and special location.

post in the right way and you will find these guys are very, very helpful, like all professions we get fed up with semi-trained people, hence some members on this site can be a bit pointy at times, especially if you post somthing that makes you look like a muppet  :shakehead   . I, and many other members believe in-reducating people as part of a drive to improve standards and get our profession recognised as the dangerous, technical discipline that it is. Hence I try to promote tolerance to posts, and I dare say some members think I'm a pillock for doing so  :slap    Hang around a bit longer and you will see what I mean.

 

[apprentice87]

Yes, i agree, i should not have said what i did. Sorry about that......

john...

 

[apprentice87]

Look at it like this; As has been pointed out, Neutral is a live conductor, but it SHOULD be at earth potential because it is tied to earth at the star point of the transformer that supplies the installation. Now, so how do you get a shock???

Well, i will take liberties with terminology here for the sake of simplicity. Neutral is connected to the star point of the transformer that supplies you. To stop the neutral floating about at all funny voltages, [as a result of differing loads on each phase, [and so causing any single phase supplies to have some very strange phase to neutral voltages] the neutral is tied to earth at that, and at several other points too.

Now; The power comes to your CU yes??? you have isolated the power to the circuit you want to work on by means of the MCB yes??? BUT, the MCB is only a single pole device, the neutral of your circuit is connected to ALL the other neutrals in the neutral bar. Let us imagine one of the other circuits is "on" If there is any resistance [even that caused by the volt drop of the cables], or even a break in the neutral upstream. what is going to happen???

Remembering that the neutral is tied to earth at the star point, the current will flow round the "other" circuit to the neutral bar, then back up "your" neutral, through you, and hence to earth and back to the star point thus completeing the circuit. Result; You feel anything from a tingle, to a huge 400V shock.....

This is before you have even touched on borrowed neutrals and the like.

So always isolate the lot, not just the circuit you are working on, and test ALL conductors for dead....

The reason for isolating the lot, is that in the case of a borrowed neutral, it may all test dead ok, you are then working on the thing, someone switches on a load on an entirely different circuit fed by an entirely different MCB, and your "dead" neutral, now becomes very live!!!

Always remember too, that a result of a wiring fault, ]whether deiliberate or otherwise], You can test your neutral and find it dead. [while it is still connected to the neutral block that is] but you disconnect it, and you can sometimes find that it is VERY live all of a sudden!!! [do not ask me how i know that!!!]

john...

 

[ProDave]

Look at it like this; As has been pointed out, Neutral is a live conductor, but it SHOULD be at earth potential because it is tied to earth at the star point of the transformer that supplies the installation. Now, so how do you get a shock???

Well, i will take liberties with terminology here for the sake of simplicity. Neutral is connected to the star point of the transformer that supplies you. To stop the neutral floating about at all funny voltages, [as a result of differing loads on each phase, [and so causing any single phase supplies to have some very strange phase to neutral voltages] the neutral is tied to earth at that, and at several other points too.

Now; The power comes to your CU yes??? you have isolated the power to the circuit you want to work on by means of the MCB yes??? BUT, the MCB is only a single pole device, the neutral of your circuit is connected to ALL the other neutrals in the neutral bar. Let us imagine one of the other circuits is "on" If there is any resistance [even that caused by the volt drop of the cables], or even a break in the neutral upstream. what is going to happen???

Remembering that the neutral is tied to earth at the star point, the current will flow round the "other" circuit to the neutral bar, then back up "your" neutral, through you, and hence to earth and back to the star point thus completeing the circuit. Result; You feel anything from a tingle, to a huge 400V shock.....

This is before you have even touched on borrowed neutrals and the like.

So always isolate the lot, not just the circuit you are working on, and test ALL conductors for dead....

The reason for isolating the lot, is that in the case of a borrowed neutral, it may all test dead ok, you are then working on the thing, someone switches on a load on an entirely different circuit fed by an entirely different MCB, and your "dead" neutral, now becomes very live!!!

Always remember too, that a result of a wiring fault, ]whether deiliberate or otherwise], You can test your neutral and find it dead. [while it is still connected to the neutral block that is] but you disconnect it, and you can sometimes find that it is VERY live all of a sudden!!! [do not ask me how i know that!!!]

john...

Neutral IS bonded to earth in normal circumstances. But may still be at a different potential to your local earth, particularly on a TT install.

So baring a fault neutral will be at or very close to earth and you won't get a shock.

BUT you were working on a LIVE circuit.  By your own admission, the circuit was still energised, other lights on that circuit were on, it was just the emergency lights turned off.

So the other working lights will have been drawing current which was returned via the neutral connection.

With lighting it's common for the neutral connections to be daisy chained often looping in and out at a light fitting.

So if you remove a light fitting from a LIVE circuit, you break the neutral connection where it is looped through.

So one of your lights that is ON will no longer have a return path as you have broken it's neutral connection.  that open connection will now be connected via the light fitting to LIVE

Now do you understand why you can get a shock from it and you MUST isolate the whole circuit AND TEST FOR DEAD, not just turn off some of the lights?

It always astounds me that people take up a trade as an electrician, just by learning the regulations, but have little or no understanding of how electrical circuits work  how current flows, and how dangerous voltages can be present under "fault" conditions (in this case the "faulr" was a broken neutral connection at the light fitting)

 

[apprentice87]

Hi Dave, It is easy to say that neutral is bonded to earth, but as i said, it SHOULD be, BUT as you point out in the next sentence, it may very well not be if there is a fault..

john...