The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

can i get electrocuted by holding the NEUTRAL ?

a circuit only needs two wires to be complete.

so how does the third wire - ground - fit in the circuit ?

"blackboab" wrote in message
oups.com...
The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second

yes

so that they swap over the roles of
positive and negative.

no

can i get electrocuted by holding the NEUTRAL ?


not if all is working properly (ie not wiring faults etc)

a circuit only needs two wires to be complete.

so how does the third wire - ground - fit in the circuit ?

it prevents dangerous voltages that might exist on metal parts of appliances
during fault conditions by connecting them to earth


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

if the nutral is carrying a current at the time of you holding it then yes
you can be electrocuted......nutral is the preferd method for a current to
make it's return. ground or earth is a protection circuit and back at the
generation site is connected to nutral.

"blackboab" wrote in message
oups.com...
The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

can i get electrocuted by holding the NEUTRAL ?

a circuit only needs two wires to be complete.

so how does the third wire - ground - fit in the circuit ?

Bob

AC current changes direction 50 times a second so the current must
first flow one way - live to neutral - and then the other way - neutral
to live.

no ?

On 5 Oct 2005 01:21:04 -0700, "blackboab" wrote:

The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

er..sort of.

can i get electrocuted by holding the NEUTRAL ?

Yes. See above.


a circuit only needs two wires to be complete.

?


so how does the third wire - ground - fit in the circuit ?

Electricity is generated three-phase:
http://en.wikipedia.org/wiki/Three_phase
(for various reasons including efficiency)

and then for domestic supply you get one of the three live conductors,
and the neutral:
http://en.wikipedia.org/wiki/Single-...electric_power

The ground connector is for safety only - it's carried round the house
and connected to various bits of exposed metal, including those that
are part of your electrical equipment. If then you have a fault in
some device where live becomes connected to these same bits of
exposed metal, a large current briefly flows to ground and your
fuse/MCB/whatever pops, cutting off the circuit.

C

"Charlie" wrote in message
...
On 5 Oct 2005 01:21:04 -0700, "blackboab" wrote:

The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

er..sort of.

can i get electrocuted by holding the NEUTRAL ?

Yes. See above.


a circuit only needs two wires to be complete.

?


so how does the third wire - ground - fit in the circuit ?

Electricity is generated three-phase:
http://en.wikipedia.org/wiki/Three_phase
(for various reasons including efficiency)

and then for domestic supply you get one of the three live conductors,
and the neutral:
http://en.wikipedia.org/wiki/Single-...electric_power

The ground connector is for safety only - it's carried round the house
and connected to various bits of exposed metal, including those that
are part of your electrical equipment. If then you have a fault in
some device where live becomes connected to these same bits of
exposed metal, a large current briefly flows to ground and your
fuse/MCB/whatever pops, cutting off the circuit.

C

If you disconnect the neutral of a circuit at any point then the neutral
will be at 230v with respect to earth as there is no volt drop across the
load. It could then kill you.

"blackboab" wrote in message
ups.com...
Bob

AC current changes direction 50 times a second so the current must
first flow one way - live to neutral - and then the other way - neutral
to live.

It changes direction because the live varies first positve with respect to
neutral and then negative with respect to neutral. The neutral wire is
(roughly) at earth potential and stays there (more or less - in practice
under no fault conditions, there may be a few tens of volts (ac) or so on
the neutral depending on the generating and distribution arrangements.

It's the size of the voltage with resepct to earth, not its sign that causes
the toucher problems.

I did say the neutral wont electrocute you under no fault conditions. It is
true, as another poster pointed out, that, if the neutral retrun becomes
disconnected in a circuit somewhere neutrals between there and an appliance
will rise to 240V if the appliance is on, giving, clearly, the risk of
electric shock - this is a fault condition though.

As a practical example, our incoming mains supply comes overhead in a
concentric cable. The centre inner core is the live. The outer sheath is the
neutral. They are insulated from each other (obviously) and insulated
overall, to guard against a) the outer becoming live under fault conditions
b) unwanted neutral leakage currents to earth (which can be quite high where
the impedance is very low and c) corrosion of the netral sheath. When my
meter was moved, they reconnected live. The outer insulation and neutral
sheath were removed/unwound and pulled back with no protective gear. The
inner was then cut with a pair of extremely insulated cutters!

I have held neutrals many times under no fault conditions.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

"blackboab" wrote in message
oups.com...
The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

AC is usually regarded as not having positive and negative.


can i get electrocuted by holding the NEUTRAL ?

You can get electrocuted by holding any of the wires in a mains installation
(even if its only a fault that does it).
Treat all wires as though they could be live and you will survive for
longer.


a circuit only needs two wires to be complete.

Not strictly true as some circuits don't need wire to complete.


so how does the third wire - ground - fit in the circuit ?


Its the *most important* wire.
Its there to stop some common faults killing you.

On Wed, 5 Oct 2005 10:21:28 +0100, "Bob Watkinson"
wrote:


If you disconnect the neutral of a circuit at any point then the neutral
will be at 230v with respect to earth as there is no volt drop across the
load. It could then kill you.

indeed. If the circuit is all perfect though then the neutral *should*
be at the same potential as ground, so no current should flow. However
since the neutral is definitely a current carrying conductor you
shouldn't ever touch it in the first place, just in case.

C

"blackboab" wrote in message
oups.com...
The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

Yep

can i get electrocuted by holding the NEUTRAL ?

You shouldnt do, becasue back at the electrcity sub station the nuteral is
connected to the earth (and in the brown stuff outside) so everything is
connected to nutral all the time.

a circuit only needs two wires to be complete.

so how does the third wire - ground - fit in the circuit ?

The ground, or earth wire is only there for protection, if there was a fault
in an appliance where the live or the neutral wire somehow came into contact
with the metal casing of something, the current will travel down this wire
instead of down the neutral wire.
Now, if the wire that has become connected to the metal casing of the
appliance is the Live, this is effectively shorting the live to the neutral,
causing a lot of current to flow (because neutral is connected to the earth)
so your fuse or little MCB (Circuit breaker) will blow/trip.

Also, if you have an RCD, this checks the current going out of the Live, and
returning back via the Neutral, if there is an imbalance (because some is
going to earth, maybe through a person, or the earth wire etc.) then the RCD
trips.

Sparks...

Sparks

if the live wire comes loose and touches the metal case
of my toaster then the current flows from the generator down the live
wire , through the metal case, through the earth wire to ground,
through the ground back to the generator where it goes up the earth
wire there to neutral ?

when the neutral wire touches the metal case is the circuit simply
totally grounded with the neutral wire at the same potential as the
ground to which its connected ?

Charlie wrote:
On 5 Oct 2005 01:21:04 -0700, "blackboab" wrote:


The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.


er..sort of.

can i get electrocuted by holding the NEUTRAL ?


Yes. See above.


a circuit only needs two wires to be complete.


?


so how does the third wire - ground - fit in the circuit ?


Electricity is generated three-phase:
http://en.wikipedia.org/wiki/Three_phase
(for various reasons including efficiency)

and then for domestic supply you get one of the three live conductors,
and the neutral:
http://en.wikipedia.org/wiki/Single-...electric_power

The ground connector is for safety only - it's carried round the house
and connected to various bits of exposed metal, including those that
are part of your electrical equipment. If then you have a fault in
some device where live becomes connected to these same bits of
exposed metal, a large current briefly flows to ground and your
fuse/MCB/whatever pops, cutting off the circuit.

C

Arggh, whenever people post wikipedia links I always waste hours
clicking on hyperlinks and end up learning bizarre things.

On that topic, I have a theory that in order to create the ultimate AI
computer, all that is needed it to write a program that allows the
machine to cross reference unknown words in text files. Then simply
feed the entire contents of the OED into it and let it site there for a
bit while it cross references every word in it. It will then be able to
reccursively cross-reference every word and gain total and utter
comprehension of the English language.

"blackboab" wrote in message
oups.com...
Sparks

if the live wire comes loose and touches the metal case
of my toaster then the current flows from the generator down the live
wire , through the metal case, through the earth wire to ground,
through the ground back to the generator where it goes up the earth
wire there to neutral ?

That's right - but as there isnt much resistance in this circuit, lots and
lots of current flows (as it is effectivly a short circuit) so the fuse or
circuit breaker will brlow/trip

when the neutral wire touches the metal case is the circuit simply
totally grounded with the neutral wire at the same potential as the
ground to which its connected ?

yes - if you dont have an RCD, then this fault will remain undetected, but
as long as the earth is all connected properly, then the toaster will still
finction and you shouldnt get a shock.

If you did not have an RCD, and you connected somthing to Live and Earth,
the appliace should work and nothing should blow or trip

If the circuit has an RCD, then some of the current will return via the
nutral wire, but some will return through the earth. The RCD will see that
there is an inbalance between the current flowing from the live and
returning via the nutral (It doesnt care where it has gone, it just knows it
is missing!), and it will trip.
Sockets will usually have a 30mA RCD - this will trip if the inbalanace is
30mA or greater.

This means, if there was a fault with your toaster where either the live or
the neutral was in contact with the metal casing, but the earth wire was not
connected, if you touch the metal casing, some current will be conducted
through you to earth - the RCD will spot this missing current, and trip,
hopefully saving your life :-)

Sparks...

In article , Richard Conway
wrote:
On that topic, I have a theory that in order to create the ultimate AI
computer, all that is needed it to write a program that allows the machine
to cross reference unknown words in text files. Then simply feed the
entire contents of the OED into it and let it site there for a bit while
it cross references every word in it. It will then be able to
reccursively cross-reference every word and gain total and utter
comprehension of the English language.

30 years ago that's what we thought. Then computers started to get fast enough
to do a very small amount of that task and we realised that each word didn't
need simple hooks to other words but a whole word-specific program of their
own. AI (true AI) is now further away than it was in the late seventies. ;-(

I don't know how she worked it out - or how much it was deliberate - but my 14
month old granddaughter calls our small dogs 'dog' and her own (much larger)
dog 'dog-dog'. One of us swears that, on seeing a horse, she called it
'dog-dog-dog'. Now tell me how you'd program a computer to produce the
possible grammar behind that!

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing

John Cartmell wrote:
In article , Richard Conway
wrote:

On that topic, I have a theory that in order to create the ultimate AI
computer, all that is needed it to write a program that allows the machine
to cross reference unknown words in text files. Then simply feed the
entire contents of the OED into it and let it site there for a bit while
it cross references every word in it. It will then be able to
reccursively cross-reference every word and gain total and utter
comprehension of the English language.


30 years ago that's what we thought. Then computers started to get fast enough
to do a very small amount of that task and we realised that each word didn't
need simple hooks to other words but a whole word-specific program of their
own. AI (true AI) is now further away than it was in the late seventies. ;-(

I suppose the problem is that even if it could cross reference all the
words, it still wouldn't actually know what any of them mean.

I don't know how she worked it out - or how much it was deliberate - but my 14
month old granddaughter calls our small dogs 'dog' and her own (much larger)
dog 'dog-dog'. One of us swears that, on seeing a horse, she called it
'dog-dog-dog'. Now tell me how you'd program a computer to produce the
possible grammar behind that!

You'd have to create an algorithm that took factors such as the
dimensions and mass of an animal and output the word dog x number of
times as a result!

On Wed, 5 Oct 2005 08:39:23 +0000 (UTC), "pat"
wrote:

| if the nutral is carrying a current at the time of you holding it then yes
| you can be electrocuted......nutral is the preferd method for a current to
| make it's return. ground or earth is a protection circuit and back at the
| generation site is connected to nutral.

Assuming proper wiring, there will only be a *small* voltage on the neutral
wire, whatever current is being carried. IIRC it needs more than 30 volts
to kill someone, I have personally touched 30 volt supplies more times than
I care to remember without ill effects, apart from a tingle. Mind you it
is a practice best avoided ;-)

--
Dave Fawthrop dave hyphenologist co uk
The London suicide bombers killed innocent commuters.
Animal rights terrorists and activists kill innocent patients.

This means, if there was a fault with your toaster where either the live
or
the neutral was in contact with the metal casing, but the earth wire was
not
connected, if you touch the metal casing, some current will be conducted
through you to earth - the RCD will spot this missing current, and trip,
hopefully saving your life :-)

Sparks...

Just curious. How safe is an RCD. If I stood bare footed on a damp concrete
floor and grabbed the Live wire, would it still be a nasty shock but not
kill me, or does it switch off so quick that I would not even notice it.

Simon

In article , Huge wrote:
30 years ago that's what we thought. Then computers started to get fast
enough to do a very small amount of that task and we realised that each
word didn't need simple hooks to other words but a whole word-specific
program of their own. AI (true AI) is now further away than it was in the
late seventies. ;-(

W-e-e-e-e-e-e-llll. Have a look at the CYC project, now at
http://www.opencyc.org/

Thanks for that. I'm *very* rusty with my AI reading but I know when I start
I'll want to contribute - and that will be a full-time project!
When I retire ...

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing

In article , Richard Conway
wrote:
I don't know how she worked it out - or how much it was deliberate - but
my 14 month old granddaughter calls our small dogs 'dog' and her own
(much larger) dog 'dog-dog'. One of us swears that, on seeing a horse,
she called it 'dog-dog-dog'. Now tell me how you'd program a computer to
produce the possible grammar behind that!

You'd have to create an algorithm that took factors such as the dimensions
and mass of an animal and output the word dog x number of times as a
result!

That's easy enough. The problem is how the easily-communicated idea developed
in the first place. No one has taught her the concept of multiple words =
bigger and, at the stage of hardly even having a communicable vocabulary
(whilst she talks plenty I don't pretend to understand any of it - except to
her!) she appears to have generated a grammar of her own. This isn't a new
observation: very young children brought up in a family using (deaf) sign
language will probably acquire a formal, slow, limited, grammar but - where
able to converse with other, similar kids at a young enough age, develop a
natural fast, open-ended grammar of their own making.
this is uk.d-i-y.grammar isnt it?
Organic life is far more proficient than any artificial equivalent that we can
(yet) design.

--
John Cartmell john@ followed by finnybank.com 0845 006 8822
Qercus magazine FAX +44 (0)8700-519-527 www.finnybank.com
Qercus - the best guide to RISC OS computing

On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:

AC current changes direction 50 times a second

No, it doesn't.

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

Bob Eager wrote:
On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:


AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.

Alex.

"Simon" wrote in message
...

This means, if there was a fault with your toaster where either the live
or
the neutral was in contact with the metal casing, but the earth wire was
not
connected, if you touch the metal casing, some current will be conducted
through you to earth - the RCD will spot this missing current, and trip,
hopefully saving your life :-)

Sparks...

Just curious. How safe is an RCD. If I stood bare footed on a damp
concrete
floor and grabbed the Live wire, would it still be a nasty shock but not
kill me, or does it switch off so quick that I would not even notice it.

Simon

Assuming the RCD is working correctly it would trip between 10 and 20
milliseconds while carrying 30mA (depending on type). To quick for you to
feel it I would think but as they say 'Don't try this at home folks'.

"Simon" wrote in message
...

This means, if there was a fault with your toaster where either the live
or
the neutral was in contact with the metal casing, but the earth wire was
not
connected, if you touch the metal casing, some current will be conducted
through you to earth - the RCD will spot this missing current, and trip,
hopefully saving your life :-)

Sparks...

Just curious. How safe is an RCD. If I stood bare footed on a damp
concrete
floor and grabbed the Live wire, would it still be a nasty shock but not
kill me, or does it switch off so quick that I would not even notice it.

It depends on your heart really, if you were in good health, then I expect
you would be OK, but dont try it!! You would feel it for sure.
The RCD should trip extremly fast (I think it has to be at most .04 of a
second)

Sparks...

"AlexW" wrote in message
...
Bob Eager wrote:
On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab" wrote:


AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential wrt
the neutral.

You fell into his little trap! It changes direction 100 times per second,
having a burst in both directions 50 times a second.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

On 5 Oct 2005 01:21:04 -0700, "blackboab"
scrawled:

The LIVE and NEUTRAL wires are both passing current and the current is
reversing at 50 times a second so that they swap over the roles of
positive and negative.

No, it's live and neutral you're after. Positive and negative are for
DC. I'd forget about the swapping over bit, it sort of isn't relevant.

can i get electrocuted by holding the NEUTRAL ?

Yes

a circuit only needs two wires to be complete.

Technically.

so how does the third wire - ground - fit in the circuit ?

There for protection, as others have explained.
--
Stuart @ SJW Electrical

Please Reply to group

In article ,
says...
Bob Eager wrote:
On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:


AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

It changes direction twice on each cycle.

"Bob Watkinson" wrote in message
...

"Simon" wrote in message
...

This means, if there was a fault with your toaster where either the
live
or
the neutral was in contact with the metal casing, but the earth wire
was
not
connected, if you touch the metal casing, some current will be
conducted
through you to earth - the RCD will spot this missing current, and
trip,
hopefully saving your life :-)

Sparks...

Just curious. How safe is an RCD. If I stood bare footed on a damp
concrete
floor and grabbed the Live wire, would it still be a nasty shock but not
kill me, or does it switch off so quick that I would not even notice it.

Simon

Assuming the RCD is working correctly it would trip between 10 and 20
milliseconds while carrying 30mA (depending on type). To quick for you to
feel it I would think but as they say 'Don't try this at home folks'.



Thanks. Quite a useful thing to have then. Why don't they build one into the
electricity meter and then all homes would automatically have one? An even
better design would be to have a small light on the meter that came on when
the RCD trips, then you would be able to see to turn it back on again.

Simon

Bob Mannix wrote:
"AlexW" wrote in message
...

Bob Eager wrote:

On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab" wrote:



AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential wrt
the neutral.


You fell into his little trap! It changes direction 100 times per second,
having a burst in both directions 50 times a second.



Trap?

It still changes 50 times second though for the UK supply, the limits
would be a minimum of 99 to 101 times. AC current could actually change
at any frequency.

Rob Morley wrote:
In article ,
says...

Bob Eager wrote:

On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:



AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.


It changes direction twice on each cycle.

Yes.

"AlexW" wrote in message
...
Bob Mannix wrote:
"AlexW" wrote in message
...

Bob Eager wrote:

On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:



AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.


You fell into his little trap! It changes direction 100 times per second,
having a burst in both directions 50 times a second.



Trap?

It still changes 50 times second though for the UK supply, the limits
would be a minimum of 99 to 101 times.

So that would be 100, not 50

AC current could actually change at any frequency.

Well so it could but it *could* also be a 330,000 V AC supply, in which case
I wouldn't touch the neutral!
The context of the question implied a UK domestic supply of 24V 50Hz, where
the current changes direction 100 times per second and the neutral isn't
that dangerous.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Assuming the RCD is working correctly it would trip between 10 and 20
milliseconds while carrying 30mA (depending on type). To quick for you to
feel it I would think but as they say 'Don't try this at home folks'.



Thanks. Quite a useful thing to have then. Why don't they build one into
the
electricity meter and then all homes would automatically have one? An even
better design would be to have a small light on the meter that came on
when
the RCD trips, then you would be able to see to turn it back on again.

This isn't done because a whole house RCD is not a good idea...

Say you were working in your workshop at night and you tripped it, what
would happen?
(All the lights would go out too!)

Sparks...

Simon wrote:

Thanks. Quite a useful thing to have then. Why don't they build one into the
electricity meter and then all homes would automatically have one? An even

On a modern install they almost do. The RCD will usually be present in
the consumer unit where it protects *some* of the circuits (typically
socket circuits where there is a good chance that the socket may be used
to power and appliance used outside, or where there is another
particular risk factor)

People used to install RCDs such that they protected the whole house
(i.e. in the meter tails that fed the CU). The danger here is that you a
swapping one hazard for another. You reduce the risk of death by
electrocution, but *increase* the risk of death by trip or fall. (e.g.
you are drilling into the wall at the top of the stairs on a ladder -
hit a cable in the wall, and trip the whole house RCD which plunges you
into darkness!).

(Note that installs with what is known as TT earthing (commonly found
with overhead power wires) are usually covered by different requirements)

Since many many more deaths occur each year as a result of trips and
falls than by electrocution, the regs were changed to require better
discrimination between faults. Such that completely unrelated circuits
(i.e. lights etc) should not be de-energised when a fault causes a trip
on another circuit

better design would be to have a small light on the meter that came on when
the RCD trips, then you would be able to see to turn it back on again.

This is worth doing anyway. What you require is an "emergency light"
(cost about 20 to 30 pounds). These react to loss of power by turning on
the lamp powered from internal batteries. I added one to my meter
cupboard powered from the downstairs lighting circuit. That way if that
MCB trips the light comes on.

Something like:

http://www.tlc-direct.co.uk/Products/EMWP3NM.html

or if you want to use it as an ordinary light controlled from a switch
as well then:

http://www.tlc-direct.co.uk/Products/EMWP3M.html

See also:

http://www.tlc-direct.co.uk/Technica...ting_Guide.pdf


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Simon" wrote in message
...

"Bob Watkinson" wrote in message
...

"Simon" wrote in message
...

This means, if there was a fault with your toaster where either the
live
or
the neutral was in contact with the metal casing, but the earth wire
was
not
connected, if you touch the metal casing, some current will be
conducted
through you to earth - the RCD will spot this missing current, and
trip,
hopefully saving your life :-)

Sparks...

Just curious. How safe is an RCD. If I stood bare footed on a damp
concrete
floor and grabbed the Live wire, would it still be a nasty shock but
not
kill me, or does it switch off so quick that I would not even notice
it.

Simon

Assuming the RCD is working correctly it would trip between 10 and 20
milliseconds while carrying 30mA (depending on type). To quick for you to
feel it I would think but as they say 'Don't try this at home folks'.



Thanks. Quite a useful thing to have then. Why don't they build one into
the
electricity meter and then all homes would automatically have one? An even
better design would be to have a small light on the meter that came on
when
the RCD trips, then you would be able to see to turn it back on again.

Simon

The thing is you don't want to put everything on an RCD. For example if you
had a fault on your lights you wouldn't want the power to be disconnected to
your freezer. Better to have stuff like the immersion heater and shower etc
on an RCD and other stuff not. That's why we have split CU's

Bob Mannix wrote:
"AlexW" wrote in message
...

Bob Mannix wrote:

"AlexW" wrote in message
. ..


Bob Eager wrote:


On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:




AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or the
current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.


You fell into his little trap! It changes direction 100 times per second,
having a burst in both directions 50 times a second.



Trap?

It still changes 50 times second though for the UK supply, the limits
would be a minimum of 99 to 101 times.


So that would be 100, not 50


AC current could actually change at any frequency.


Well so it could but it *could* also be a 330,000 V AC supply, in which case

Yes, it could.

You snipped the context of the (rest of) the question though and the
response did not really clarify things for the OP.

I wouldn't touch the neutral!

Why not assuming its at the same/similar potential as you?

The context of the question implied a UK domestic supply of 24V 50Hz, where
the current changes direction 100 times per second and the neutral isn't
that dangerous.



In this context I agree that touching neutral should not be deadly or
whatever unless part of you is touching something else at significantly
potential to neutral.

Alex

"AlexW" wrote in message
...
Bob Mannix wrote:
"AlexW" wrote in message
...

Bob Mannix wrote:

"AlexW" wrote in message
...


Bob Eager wrote:


On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:




AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or
the current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.


You fell into his little trap! It changes direction 100 times per
second, having a burst in both directions 50 times a second.



Trap?

It still changes 50 times second though for the UK supply, the limits
would be a minimum of 99 to 101 times.


So that would be 100, not 50


AC current could actually change at any frequency.


Well so it could but it *could* also be a 330,000 V AC supply, in which
case

Yes, it could.

You snipped the context of the (rest of) the question though and the
response did not really clarify things for the OP.

I responded to the OP question in another posting which was crystal clear.
In this posting I was responding to your assertion that "it did actually"
change direction 50 times per second (which it doesn't)


I wouldn't touch the neutral!

Why not assuming its at the same/similar potential as you?

Well I would make the assumption (for my own safety) that given a 240V
supply might generate stray neutral voltages of up to 30V, a 330kv one
*might* generate neutral voltages of up to 30kv. Of course it might not, as
such supplies would be three phase and arranged differently, but I wouldn't
take the chance myself!


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

In article ,
says...

"AlexW" wrote in message
...
Bob Mannix wrote:
"AlexW" wrote in message
...

Bob Mannix wrote:

"AlexW" wrote in message
...


Bob Eager wrote:


On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:




AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or
the current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.


You fell into his little trap! It changes direction 100 times per
second, having a burst in both directions 50 times a second.



Trap?

It still changes 50 times second though for the UK supply, the limits
would be a minimum of 99 to 101 times.


So that would be 100, not 50


AC current could actually change at any frequency.


Well so it could but it *could* also be a 330,000 V AC supply, in which
case

Yes, it could.

You snipped the context of the (rest of) the question though and the
response did not really clarify things for the OP.

I responded to the OP question in another posting which was crystal clear.
In this posting I was responding to your assertion that "it did actually"
change direction 50 times per second (which it doesn't)

It does in a way - given that it changes 50 times in half a second it
must change 50 times in a second (then another fifty times as well), but
I think he's just wriggling.

AlexW wrote:

snip


You snipped the context of the (rest of) the question though and the
response did not really clarify things for the OP.


Sorry Bob E snipped.
snip

Everyone seems to be saying tripping out the lights is a bad Idea as you may
fall over in the dark, so why not have two RCDs, one for lights and one for
everything else. I must admit ours is old and protects everything. I have
never found it turning the lights off a problem. I have only ever tripped it
by accidentally touching the neutral, I never had the nerve to touch the
live to see if it hurt. I have always liked the idea that everything in the
house was protected so that I have to do something very foolish before I can
electrocute myself. Just wish that there was one light in the garage that
came on so that I could climb across all the junk in the garage to reset it.

"Simon" wrote in message
...
Everyone seems to be saying tripping out the lights is a bad Idea as you
may
fall over in the dark, so why not have two RCDs, one for lights and one
for
everything else. I must admit ours is old and protects everything. I have
never found it turning the lights off a problem. I have only ever tripped
it
by accidentally touching the neutral, I never had the nerve to touch the
live to see if it hurt. I have always liked the idea that everything in
the
house was protected so that I have to do something very foolish before I
can
electrocute myself. Just wish that there was one light in the garage that
came on so that I could climb across all the junk in the garage to reset
it.

Thats exactly what I have - and have never managed to trip the lights!

Sparks...

Rob Morley wrote:
In article ,
says...

"AlexW" wrote in message
.. .

Bob Mannix wrote:

"AlexW" wrote in message
...


Bob Mannix wrote:


"AlexW" wrote in message
. dk...



Bob Eager wrote:



On Wed, 5 Oct 2005 08:53:23 UTC, "blackboab"
wrote:





AC current changes direction 50 times a second


No, it doesn't.


I thought it did actually as Electrons flow from -ve to +ve IIRC, or
the current flows from +ve to -ve in conventional notation.

The live is always energised though with either a +ve or -ve potential
wrt the neutral.


You fell into his little trap! It changes direction 100 times per
second, having a burst in both directions 50 times a second.



Trap?

It still changes 50 times second though for the UK supply, the limits
would be a minimum of 99 to 101 times.


So that would be 100, not 50



AC current could actually change at any frequency.


Well so it could but it *could* also be a 330,000 V AC supply, in which
case

Yes, it could.

You snipped the context of the (rest of) the question though and the
response did not really clarify things for the OP.

I responded to the OP question in another posting which was crystal clear.
In this posting I was responding to your assertion that "it did actually"
change direction 50 times per second (which it doesn't)


It does in a way - given that it changes 50 times in half a second it
must change 50 times in a second (then another fifty times as well), but
I think he's just wriggling.

My original response was to Bob Eager's point blank "no it doesn't"
which is not specific at all as to why it "doesn't". I inadvertantly
accused Bob Mannix snipping here and lack of clarity ... apologies, I
mis-read the sender in the thread.

Alex