Hello,

Is there a case for protecting the upstairs with an RCD ?
The follow-on question: what happens if you stand on a carpet (or wooden
floor) with an uninsulated live cable (and only this cable) in your hand --
(1) will it trip the RCD, and (2) will you feel anything ? I know what
happens if you stand on a wet lawn!

tia joe.

Joe Green wrote:

The follow-on question: what happens if you stand on a carpet (or wooden
floor) with an uninsulated live cable (and only this cable) in your hand --
(1) will it trip the RCD, and (2) will you feel anything ? I know what
happens if you stand on a wet lawn!

It all depends on the resistance between you and earth - which
depends on how insulating you carpet/wooden floor is.

If the resistance is more than 300k, you'll get less than a mA
through you, which will tingle but not do much harm. If the
resistance is more than a meg, you're unlikely to feel anything.

If the carpet/wood is dry, and you're wearing rubber soles, your
resistance is going to be pretty high. So holding the live wire
(just the live, not live + neutral/earth) will result in only a
few uA flowing through you, which you won't feel.

The RCD will only trip if you pass through a current greater
than it's trip current (e.g. 30mA).

--
Grunff

Thanks - and sorry to persist...
What about capacitance - what if I hold in the other hand a large metal
ladder standing (on the same carpet) on rubber feet, will current flow in
and out (at 50 Hz) of the ladder, and how much current ? And if it does
(and exceeds 30mA) will it trip the RCD ?
joe.

"Grunff" wrote in message
...
Joe Green wrote:

The follow-on question: what happens if you stand on a carpet (or wooden
floor) with an uninsulated live cable (and only this cable) in your
hand --
(1) will it trip the RCD, and (2) will you feel anything ? I know what
happens if you stand on a wet lawn!

It all depends on the resistance between you and earth - which
depends on how insulating you carpet/wooden floor is.

If the resistance is more than 300k, you'll get less than a mA
through you, which will tingle but not do much harm. If the
resistance is more than a meg, you're unlikely to feel anything.

If the carpet/wood is dry, and you're wearing rubber soles, your
resistance is going to be pretty high. So holding the live wire
(just the live, not live + neutral/earth) will result in only a
few uA flowing through you, which you won't feel.

The RCD will only trip if you pass through a current greater
than it's trip current (e.g. 30mA).

--
Grunff

Joe Green wrote:

Thanks - and sorry to persist...
What about capacitance - what if I hold in the other hand a large metal
ladder standing (on the same carpet) on rubber feet, will current flow in
and out (at 50 Hz) of the ladder, and how much current ? And if it does
(and exceeds 30mA) will it trip the RCD ?

The capcitance of the ladder will be way to low to support any
significant current flow - will be in nF.

So the reactance of the capacitor will be:

R = 1/(2Pi.F.C) (F = frequency, C = capacitance)

Let's assume 10nF (this is generous)

R = 1/(6.3x50x10E-9)
R = 317k

Which will only let say a mA through.

--
Grunff

If you have ever had a hairdryer or shaver 'blow up' during use, then you
will wish you had a protected circuit.

dg


"Joe Green" wrote in message
...
Hello,

Is there a case for protecting the upstairs with an RCD ?
The follow-on question: what happens if you stand on a carpet (or wooden
floor) with an uninsulated live cable (and only this cable) in your
hand --
(1) will it trip the RCD, and (2) will you feel anything ? I know what
happens if you stand on a wet lawn!

tia joe.

"Joe Green" wrote in message
...
Thanks - and sorry to persist...
What about capacitance - what if I hold in the other hand a large
metal
ladder standing (on the same carpet) on rubber feet, will current
flow in
and out (at 50 Hz) of the ladder, and how much current ? And if it
does
(and exceeds 30mA) will it trip the RCD ?
joe.


There are much easier ways of committing suicide, than grabbing hold
of a live wire, standing on a carpet, and holding a ladder in one
hand, but it might confuse the police when working out exactly what
happened, so best to leave a note. ;o)
--
Gavin Gillespie
Giltbrook
Nottingham UK

On Sun, 23 Nov 2003 14:17:54 +0000, Grunff wrote:

If the resistance is more than 300k, you'll get less than a mA
through you, which will tingle but not do much harm.

But it's more than enough to put your muscles into a 50Hz spasm and it
will fing hurt. Even it you don't come to any lasting harm from the
direct effects of the electric shock, the jolt may well make you
withdraw you arm rather rashly and bash your elbow or fall of the
ladder which can cause serious injury...

If the carpet/wood is dry, and you're wearing rubber soles, your
resistance is going to be pretty high. So holding the live wire
(just the live, not live + neutral/earth) will result in only a
few uA flowing through you, which you won't feel.

Do you volunteer to have the mains applied to your anatomy to prove
your hypothesis?

--
Cheers
Dave. pam is missing e-mail

Thanks for your replies, do I take it that the opinion is that if you touch
the live only, possibly while standing on, and holding on to, a large
A-frame metal ladder, but otherwise (you AND the ladder) insulated from
earth and neutral, that:

- it will hurt somewhat, but the RCD will not trip (30mA)

Dave Liquorice wrote:

Do you volunteer to have the mains applied to your anatomy to prove
your hypothesis?

Hey, the number of shocks I've had anyone would think I do it
recreationally :-(

--
Grunff

In uk.d-i-y, Joe Green wrote:
Thanks for your replies, do I take it that the opinion is that if you touch
the live only, possibly while standing on, and holding on to, a large
A-frame metal ladder, but otherwise (you AND the ladder) insulated from
earth and neutral, that:

- it will hurt somewhat, but the RCD will not trip (30mA)

Roughly, yes. The reason that RCDs for personal shock protection are
rated at a nominal 30mA (and in fact required (a) not to trip below
15mA, and (b) required fer-sure to trip by the time the current imbalance
is 30mA, within 0.2seconds, and (c) to trip within 0.04seconds with a
current imbalance of 150mA) is that this figure is chosen to balance a
low probability of serious injury against nuisance tripping.

So, if the path to earth is high resistance enough not to trip it, your
experience will be of discomfort and a feeling of stupidity (including the
particularly galling feeling that there's no-one else to blame. Unless the
cat happens to be passing, of course ;-). If the path to earth is of low
enough resistance to trip the breaker, your experience will be of greater
discomfort, some pain, but little likelihood of your beneficiaries collecting
on the life or disability insurance!

Obviously, only the teenaged lads among us will be daft enough to do the
trial "for real", 'cos it's a dumb idea to play games with mains electricity.
And whole-house 100mA RCDs will let significantly more damaging currents
through for longer before tripping, if at all.

HTH - Skefet

Joe Green wrote:
Thanks for your replies, do I take it that the opinion is that if you
touch the live only, possibly while standing on, and holding on to, a
large A-frame metal ladder, but otherwise (you AND the ladder)
insulated from earth and neutral, that:

- it will hurt somewhat, but the RCD will not trip (30mA)

Are you that Joe Green who wrote all those splendid operas?
If so, I saw some of your stuff in Verona and it was excellent.

On Sun, 23 Nov 2003 18:57:09 -0000, "Joe Green"
wrote:

Thanks for your replies, do I take it that the opinion is that if you touch
the live only, possibly while standing on, and holding on to, a large
A-frame metal ladder, but otherwise (you AND the ladder) insulated from
earth and neutral, that:

- it will hurt somewhat, but the RCD will not trip (30mA)

No. Does this count as the most idiotic question of the year or the
decade?

May I suggest you try the experiment whilst sitting in a bath of
water containing 2.667 kg of NaCl and a zinc plate firmly attached by
means of a 4mm sq wire to mains earth?


--
Peter Parry.
http://www.wpp.ltd.uk/

On Sun, 23 Nov 2003 19:40:29 +0000, Grunff wrote:

Do you volunteer to have the mains applied to your anatomy to prove
your hypothesis?

Hey, the number of shocks I've had anyone would think I do it
recreationally :-(

How do you know you've had 'em if the don't hurt? B-)

I've lost count but I know damn well that they all hurt! The worst
having pain/stiffness at the elbow for the following 8hrs combined
with viral type ache in the muscles from the shoulder down. The point
of contact was the hand somewhere. That must have been an up the arm
and out somewhere else jobbie most others have been across parts of a
hand and no were near as nasty.

--
Cheers
Dave. pam is missing e-mail

Dave Liquorice wrote:

How do you know you've had 'em if the don't hurt? B-)

There's a big difference between the ones that tingle and the
ones that really bite. ;-)

--
Grunff

wrote:

In uk.d-i-y, Joe Green wrote:
Thanks for your replies, do I take it that the opinion is that if you touch
the live only, possibly while standing on, and holding on to, a large
A-frame metal ladder, but otherwise (you AND the ladder) insulated from
earth and neutral, that:

- it will hurt somewhat, but the RCD will not trip (30mA)

Roughly, yes. The reason that RCDs for personal shock protection are
rated at a nominal 30mA (and in fact required (a) not to trip below
15mA, and (b) required fer-sure to trip by the time the current imbalance
is 30mA, within 0.2seconds, and (c) to trip within 0.04seconds with a
current imbalance of 150mA) is that this figure is chosen to balance a
low probability of serious injury against nuisance tripping.

So, if the path to earth is high resistance enough not to trip it, your
experience will be of discomfort and a feeling of stupidity (including the
particularly galling feeling that there's no-one else to blame. Unless the
cat happens to be passing, of course ;-). If the path to earth is of low
enough resistance to trip the breaker, your experience will be of greater
discomfort, some pain, but little likelihood of your beneficiaries collecting
on the life or disability insurance!

Obviously, only the teenaged lads among us will be daft enough to do the
trial "for real", 'cos it's a dumb idea to play games with mains electricity.
And whole-house 100mA RCDs will let significantly more damaging currents
through for longer before tripping, if at all.

HTH - Skefet

I think but am not sure that Stefaks post (above) has explained
my question.
Cos I've been looking for the term 'imbalance' in previous posts
about RCDs.
I thought I understood that these operate on an 'IMBALANCE' of
current between the live wire and the neutral wire?
So may I ask, as follows?
Let's suppose an electrical appliance is drawing, say, 10 amps
(2300 watts) through a circuit equipped with an RCD.
Suppose then an imbalance occurs, for some reason, whereby the
current between live and neutral differs by more than 15
milliamps, somewhere say around a 30 m/a 'difference'. That
imbalance will cause the RCD to trip the circuit within 0.2
seconds (12 cycles); yes?
Then, supposing the same circuit is not supplying any load
current to an appliance at all; somebody gets onto a ladder and
what with body capacitance, damp slippers on a metal ladder,
holding onto an uninsulated live wire in their teeth etc. or
other nonsense, a current greater than 15 milliamps, say around
30 m/a flows in the live conductor only. Again we have an
imbalance. The RCD will again trip the circuit within 0.2
seconds; yes?
Or have I missed something? Cheers. Terry.
PS. At low DC voltages holding say test probes in my calloused
(read 'hard working, son of the soil' etc.) my skin resistance is
around 100,000 ohms. however at higher voltages and or with minor
cuts there could easily be a break down of that figure. Got a few
scars to prove it. Worst was discharging a 2000 volt DC medium
size capacitor across my knuckles about year 1950. Yup. small
scar still there!

In uk.d-i-y, Terry wrote:

I thought I understood that these operate on an 'IMBALANCE' of
current between the live wire and the neutral wire?

Exactly so.

So may I ask, as follows?
Let's suppose an electrical appliance is drawing, say, 10 amps
(2300 watts) through a circuit equipped with an RCD.
Suppose then an imbalance occurs, for some reason, whereby the
current between live and neutral differs by more than 15
milliamps, somewhere say around a 30 m/a 'difference'. That
imbalance will cause the RCD to trip the circuit within 0.2
seconds (12 cycles); yes?

For sure.

Then, supposing the same circuit is not supplying any load
current to an appliance at all; somebody gets onto a ladder and
what with body capacitance, damp slippers on a metal ladder,
holding onto an uninsulated live wire in their teeth etc. or
other nonsense, a current greater than 15 milliamps, say around
30 m/a flows in the live conductor only. Again we have an
imbalance. The RCD will again trip the circuit within 0.2
seconds; yes?

Right on the money, again. An RCCD (of the currently-available current-
operated sort) doesn't care whether the circuit it's controlling has
40A flowing round it or 0.4A; what it cares about is that "what goes out
comes back" - i.e. that the current flowing out through the Live terminal
is within a gnat's whisker of the current coming back to its Neutral
terminal. Though more recent ones use electronics for this differential
sensing, the classic construction method is to use two coils with the
same number of turns but wound in opposite directions around an iron toroid
(doughnut-shape) - these are the "sense coils". When the currents are
in balance, there's no nett magnetic field set up in the toroid, as the
sense coils are wound in opposite directions. But if some of the current
going out of the live terminal finds a different way back to earth, the
two fields no longer cancel, and the nett field is used by another coil
- the "search" coil - to pull back a solenoid which is all that's stopping
the breaker spring from disconnecting the circuit. Pop.

So, back to your two scenarios: both result in an imbalance in the
currents in the two sense coils, so both create a magnetic field, which
the search coil turns back into electrickery to operate the disconnection
mechanism.

This same current-imbalance sensing is what causes multi-circuit RCDs
to trip when you short a neutral to earth on a circuit you've "disconnected",
i.e. pulled-the-fuse/manually-tripped-the-MCB on. The other circuits
are still live, and the sum of current being drawn by them is neatly
balanced on the way out and on the way back. Then you - to take a purely
hypothetical example - let the neutral wire of the immersion-heater cable
you're working on brush against the (uninsulated) copper tank. Pop, whole
house in darkness (yes, this place had a single whole-house RCD; no longer
Regs-compliant, but given the crappy state the electrics were in, a Win
for safety on balance!). That's because you've just given all those
eager electrons coming down the neutrals a second way back to Earth than
through the N terminal of the RCD - enough of them like this New Way back
that the RCD is unbalanced, and pops. (Remember all the Ns are commoned
up together back at the consumer unit, right? And pulling the fuse only
breaks the N connection on the circuit you're working on.)

We had a related case just the other day on this group - someone had
wired their new circuit so it took a live feed from the RCD-protected side
of their CU, but had connected the return N back to the non-RCD side.
Unsurprisingly, the moment the load was switched on, the imbalance made
the RCD trip.

HTH - Setfek [determined to keep up the inner anagramming, while keeping
the "Two Es" feature of the name unchanged and thus subliminally reinforcing
the most-frequently-gashed feature of his moniker :-]

wrote in message
...
. (Remember all the Ns are commoned
up together back at the consumer unit, right? And pulling the fuse only
breaks the N connection on the circuit you're working on.)

you might want to rephrase that

wrote:

In uk.d-i-y, Terry wrote:

I thought I understood that these operate on an 'IMBALANCE' of
current between the live wire and the neutral wire?

Exactly so.

Thanks Stefak for a very complete reply. Also you mentioned that
whole house tripping RCD question and explained it for me.
Yes here too we have the earth/ground supposedly connected to the
neutral once only; at the main circuit breaker panel (CU). In
older homes RCD type breakers are not yet commonly in use AFIK.
But outlets so equipped are now common and required for all
'damp' locations e.g. a bathroom and/or for use of 'outside'
appliances such as an electric mower, hedge clipper etc. and are
called GFCI (Ground fault circuit interrupter is, I think, the
right term?)
There are two basic types of GFCI duplex outlet; one type
'protects' itself and any other outlets downstream of it. The
other only protects itself and anything plugged into it.
For example we have a GFCI in the garage which also 'protects'
one downstream outlet on an outside wall. Out thre we have
plugged AC mains to our slide into truck camper unit. Every so
often there is some kind of imbalance that trips the GFCI; it's
probably the old fridge in the camper! Although the camper unit
is not grounded (oops, sorrry, earthed!) Doesn't matter because
the camper is only stored there for the winter with power used
occasionally.
The major difference is that we have a 115-0-115 volts, three
wires; with 230 volts across the two outside wires (hence two
pole breakers for 230 volt circuits). Typical house service is
200 amps (230 x 200 = 46 kVA). especailly if electric heating
(Cost equiv. to about 3.5 to 4.0 pence per unit). The
earth/ground is provided by an earth rod connected to both the
ground bar and the incoming power utility neutral only once at
the incoming electrical service and incidental connection to any
available metallic water supply etc. back at the transformer tha
middle 'zero' potential wire neutral is also connected to earth
and via what is called a multi grounded neutral MGN to everything
else in sight, including guy wires telephone company cable
sheaths etc.
Your info/discussion much appreciated. My regards. Terry.

In uk.d-i-y, Chris Oates none wrote:

up together back at the consumer unit, right? And pulling the fuse only
breaks the N connection on the circuit you're working on.)

you might want to rephrase that

(blush) yeah well, the intelligent reader knows I *ought* to have written
"breaks only the L connection" instead; the unintelligent will believe
the literal stuff as written and select themselves out of the gene pool
soon enough ;-)

Skefet

Peter Parry wrote in message . ..

May I suggest you try the experiment whilst sitting in a bath of
water containing 2.667 kg of NaCl and a zinc plate firmly attached by
means of a 4mm sq wire to mains earth?


What would happen if someone went out and did that? Would you be
criminally liable in any way? Where is the line drawn?

Regards, NT

What would happen if someone went out and did that?

They would win a Darwin award.

Christian.

"Peter Parry" wrote
| May I suggest you try the experiment whilst sitting in a bath of
| water containing 2.667 kg of NaCl and a zinc plate firmly attached by
| means of a 4mm sq wire to mains earth?

Shouldn't that be 6mm, or 10mm if not mechanically protected or a PME
installation?

Owain

On 24 Nov 2003 01:31:52 -0800, (N. Thornton)
wrote:

Peter Parry wrote in message . ..

May I suggest you try the experiment whilst sitting in a bath of
water containing 2.667 kg of NaCl and a zinc plate firmly attached by
means of a 4mm sq wire to mains earth?


What would happen if someone went out and did that?

There would be a lot of fizzing and some weak meat soup would be
manufactured.

Would you be criminally liable in any way?

No. Stupidity at a certain well developed level always has been and
always will be a fatal affliction. (See www.darwinawards.com/ for
many examples).

Where is the line drawn?

A very long way from this.

--
Peter Parry.
http://www.wpp.ltd.uk/

wrote in message
...

When the currents are in balance, there's no nett magnetic field set
up in the toroid, as the sense coils are wound in opposite
directions.

Point of detail, Mr. Z: the coils are wound in the same direction, it's the
currents that go in opposite directions - like this:

. i1
L --------UUUUU---------- L
supply .- - - load
N --------UUUUU---------- N
- - - i2
sense- uuuuu
wind'g | | (residual current = |i1-i2|)
| |
o o
trip


HTH - Setfek [determined to keep up the inner anagramming

Hmm, basket faze, bakez feast: ze fab skate... (s'pose you've seen em all
though).

--
Andy

Joe Green wrote:

Hello,

Is there a case for protecting the upstairs with an RCD ?
The follow-on question: what happens if you stand on a carpet (or wooden
floor) with an uninsulated live cable (and only this cable) in your hand --
(1) will it trip the RCD, and (2) will you feel anything ? I know what
happens if you stand on a wet lawn!



The answer is probably not in both cases, but I would not recommend it.

I am not going to comment on teh whole RCD issue.

There are arguments for and against, and personally I am somewhere in the middle...



tia joe.

Joe Green wrote:

Thanks - and sorry to persist...
What about capacitance - what if I hold in the other hand a large metal
ladder standing (on the same carpet) on rubber feet, will current flow in
and out (at 50 Hz) of the ladder, and how much current ?


Yes,

Very little.

And if it does
(and exceeds 30mA) will it trip the RCD ?


Yes, but its unlikley that it will.


joe.

"Grunff" wrote in message
...

Joe Green wrote:


The follow-on question: what happens if you stand on a carpet (or wooden
floor) with an uninsulated live cable (and only this cable) in your

hand --

(1) will it trip the RCD, and (2) will you feel anything ? I know what
happens if you stand on a wet lawn!

It all depends on the resistance between you and earth - which
depends on how insulating you carpet/wooden floor is.

If the resistance is more than 300k, you'll get less than a mA
through you, which will tingle but not do much harm. If the
resistance is more than a meg, you're unlikely to feel anything.

If the carpet/wood is dry, and you're wearing rubber soles, your
resistance is going to be pretty high. So holding the live wire
(just the live, not live + neutral/earth) will result in only a
few uA flowing through you, which you won't feel.

The RCD will only trip if you pass through a current greater
than it's trip current (e.g. 30mA).

--
Grunff

In uk.d-i-y, Andy Wade wrote:

Point of detail, Mr. Z: the coils are wound in the same direction, it's the
currents that go in opposite directions - like this:

. i1
L --------UUUUU---------- L
supply .- - - load
N --------UUUUU---------- N
- - - i2
sense- uuuuu
wind'g | | (residual current = |i1-i2|)
| |
o o
trip

D'oh! Totally bleedin' obvious now you point it out. That'll teach me
to engage brain (and perhaps make the Maxwell three-finger-gesture ;-)
before posting.

HTH - Setfek [determined to keep up the inner anagramming

Hmm, basket faze, bakez feast: ze fab skate... (s'pose you've seen em all
though).

One of the better ones an obviously-underemployed colleague at previous
employer (s/w house just south of Oxford; hello any Joint European
Tourist types ;-) came up with in a fit of story-writing in which he
insisted on anagramming all our names was that arabic variant, Fez Atabesk.

Must get myself a new Blunkett made out in that moniker ;-)

wrote in message
...

D'oh! Totally bleedin' obvious now you point it out. That'll teach
me to engage brain (and perhaps make the Maxwell three-finger-
gesture ;-) before posting.

Err, did Maxwell have a three-finger salute? The left-hand (motor) rule is
Fleming's; the RH (dynamo) one - wasn't that Faraday's?

[...] that arabic variant, Fez Atabesk.

Good one. I knew my efforts were sub-optimal :-(

Must get myself a new Blunkett made out in that moniker ;-)

A Blunkett(n.)? - a reference to ID cards, perhaps?

--
Andy