Sensing AC voltage by non-contact means.

[David Collier]

I need to detect live voltage in a mains cable, from outside the cable,
without electrical contact. The cable is the one INTO the main fusebox,
so no toucheee.

It's obviously possible - you can buy a pen-shaped thing in any hardware
shop which will do it.

After some web research I found that the standard circuit to do it is to
use an unloaded CMOS input, connected to a foil or wire, and pick up the
local electrical field.

I spend all my life avoiding unterminated CMOS inputs, and now I design
one in?

My question is - does anyone know of a ready-built sensor, maybe taking
in power, gnd, and outputting a yes/no flag, which I can go and buy,
rather than having to design, test and build my own?

Seems easy to buy a clamp-on device which will measure current... but I
can find nothing to detect just voltage.

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

 

[Phil Allison]

"David Collier"

I need to detect live voltage in a mains cable, from outside the cable,
without electrical contact. The cable is the one INTO the main fusebox,
so no toucheee.

** Stick a fine sewing needle through the insulation.

You can use any convenient AC voltmeter then.




......... Phil

 

[Pooh Bear]

I need to detect live voltage in a mains cable, from outside the cable,
without electrical contact. The cable is the one INTO the main fusebox,
so no toucheee.

It's obviously possible - you can buy a pen-shaped thing in any hardware
shop which will do it.

After some web research I found that the standard circuit to do it is to
use an unloaded CMOS input, connected to a foil or wire, and pick up the
local electrical field.

I spend all my life avoiding unterminated CMOS inputs, and now I design
one in?

Fit clamp diodes to Vdd and GND on the relevant pin plus a current limiting
resistor in series with the sensor.

Graham

 

[Rene Tschaggelar]

David Collier wrote:

After some web research I found that the standard circuit to do it is to
use an unloaded CMOS input, connected to a foil or wire, and pick up the
local electrical field.

Seems easy to buy a clamp-on device which will measure current... but I
can find nothing to detect just voltage.

What accuracy did you have in mind ?

Rene

 

[Pooh Bear]

What accuracy did you have in mind ?

I assumed he meant on - off. A cmos gate based sensor won't do better than
that for sure !

Graham

 

[Phil Allison]

"David Collier"

I need to detect live voltage in a mains cable, from outside the cable,
without electrical contact. The cable is the one INTO the main fusebox,
so no toucheee.

Seems easy to buy a clamp-on device which will measure current... but I
can find nothing to detect just voltage.

** Seems most unlikely there is ever zero current flow in a *live*
conductor feeding a main fuse box.

Nor any current whatever in a *dead* one.

So, in the absence of any need to get a voltage reading, a sensitive
current clamp will do for a live/dead descriminator .



........... Phil

 

[John Perry]

...
It's obviously possible - you can buy a pen-shaped thing in any hardware
shop which will do it.

After some web research I found that the standard circuit to do it is to
use an unloaded CMOS input, connected to a foil or wire, and pick up the
local electrical field.

I spend all my life avoiding unterminated CMOS inputs, and now I design
one in?

My question is - does anyone know of a ready-built sensor, maybe taking
in power, gnd, and outputting a yes/no flag, which I can go and buy,
rather than having to design, test and build my own?

Seems easy to buy a clamp-on device which will measure current... but I
can find nothing to detect just voltage.

You already have. The pen-shaped things do exactly what the CMOS
circuit does -- sense the electric fields around the conductors, which
propagate through the insulation just as well as magnetic fields from
current do. You don't need current flow.

So, attach a CMOS inverter to an insulated wire, which you'll then place
next to the AC input. DON'T LEAVE THE INPUT WIRE BARE -- the circuit
depends on capacitive coupling through the insulation. It should sense
any voltage through the insulation. You should get a 60Hz (50Hz?)
square wave out. Rectify the ouput of the input inverter, send the
rectified voltage to a second gate, attach an LED to the output of the
second gate, and you have a mains voltage sensor. I doubt that you
really need to protect the sensing input -- very little energy can get
through the insulation.

Note that this is not a measurement tool, it is a sensing tool.
Measurement depends on too many things to attempt it through two layers
of insulation. It may also be too sensitive, so you may have to try
some added grounding resistors (multimegohm, probably) to the sensing input.

Note also that the pen gadgets are intended for internal unshielded
wiring. At least where I live, the power company has individual
conductors anchored to the house up high, then a shielded 2-conductor
cable carrying the mains supply down to the meter. This circuit (or one
of the pens) is unlikely to work through the cable shield. But it'll
work fine on individual, insulated wires.

John Perry

 

[Fred Bloggs]

I need to detect live voltage in a mains cable, from outside the cable,

without electrical contact.

For what purpose- to locate the cable or verify voltage presence.

The cable is the one INTO the main fusebox,
so no toucheee.

Makes no sense, it is only a cb away from being an interior cable.

 

[Ken Smith]

After some web research I found that the standard circuit to do it is to
use an unloaded CMOS input, connected to a foil or wire, and pick up the
local electrical field.

This is not a "standard circuit". It is a "substandard circuit". It will
detect the AC or perhaps the static build up in your clothes until the
CMOS gate gets zapped.

Those things that use a Neon bulb are most likely what you really want.
They will tell you that there is AC voltage there.

If you want to actually measure the voltage, that's another matter all
together. You can measure AC voltages with a fair accuracy without making
electrical contact. The design of such things in not a prject for the
beginner because it involves mains voltage.

 

[Sjouke Burry]

"David Collier"




** Stick a fine sewing needle through the insulation.

You can use any convenient AC voltmeter then.




........ Phil

If it is an incoming cable,it should have a steel
wire mantle(in my house it has),so any voltage
will be shielded from you,and you may measure
anything between zero and full voltage.

 

[[email protected]]

This is not a "standard circuit". It is a "substandard circuit". It will
detect the AC or perhaps the static build up in your clothes until the
CMOS gate gets zapped.

2 diodes take care of that.

Those things that use a Neon bulb are most likely what you really want.
They will tell you that there is AC voltage there.

they wont work with no contact

If you want to actually measure the voltage, that's another matter all
together. You can measure AC voltages with a fair accuracy without making
electrical contact. The design of such things in not a prject for the
beginner because it involves mains voltage.

I doubt that stopped many folk on this ng


NT

 

[Joseph2k]

I need to detect live voltage in a mains cable, from outside the cable,
without electrical contact. The cable is the one INTO the main fusebox,
so no toucheee.

It's obviously possible - you can buy a pen-shaped thing in any hardware
shop which will do it.

After some web research I found that the standard circuit to do it is to
use an unloaded CMOS input, connected to a foil or wire, and pick up the
local electrical field.

I spend all my life avoiding unterminated CMOS inputs, and now I design
one in?

My question is - does anyone know of a ready-built sensor, maybe taking
in power, gnd, and outputting a yes/no flag, which I can go and buy,
rather than having to design, test and build my own?

Seems easy to buy a clamp-on device which will measure current... but I
can find nothing to detect just voltage.

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

Assuming that you live in North America call your local IBEW office and ask
them where to purchase this very common device. Electricians use them all
the time, and i bought mine from a local store (several carried them) (Los
Angeles area) some time ago. Also try ham radio shops. If you still
cannot find them, repost, i may send you mine. I am sure that i can
replace it easily. (us$10-20).

 

[David Collier]

** Seems most unlikely there is ever zero current flow in a *live*
conductor feeding a main fuse box.

Nor any current whatever in a *dead* one.

DONG - wrong answer.

We have

board fuse ( may trip )
meter ( may go faulty , though unlikely )
first consumer unit ( may trip )
second consumer unit ( may trip )

I'm not allowed to connect to the wires before the exit from the 1st
consumer unit, ( safety rules ), but I must diagnose any of the above
faults, as most of them need to call out a different engineer :-(

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

 

[David Collier]

You already have. The pen-shaped things do exactly what the CMOS
circuit does -- sense the electric fields around the conductors,
which propagate through the insulation just as well as magnetic
fields from current do. You don't need current flow.

So, attach a CMOS inverter to an insulated wire, which you'll then
place next to the AC input. DON'T LEAVE THE INPUT WIRE BARE -- the
circuit depends on capacitive coupling through the insulation. It
should sense any voltage through the insulation. You should get a
60Hz (50Hz?) square wave out. Rectify the ouput of the input
inverter, send the rectified voltage to a second gate, attach an LED
to the output of the second gate, and you have a mains voltage
sensor. I doubt that you really need to protect the sensing input --
very little energy can get through the insulation.

Note that this is not a measurement tool, it is a sensing tool.
Measurement depends on too many things to attempt it through two
layers of insulation. It may also be too sensitive, so you may have
to try some added grounding resistors (multimegohm, probably) to the
sensing input.

Note also that the pen gadgets are intended for internal unshielded
wiring. At least where I live, the power company has individual
conductors anchored to the house up high, then a shielded 2-conductor
cable carrying the mains supply down to the meter. This circuit (or
one of the pens) is unlikely to work through the cable shield. But
it'll work fine on individual, insulated wires.

John Perry

I'd give that answer an A*

I am simply looking for a go/no-go so I can call out the right engineer,
( off a list of 3 ). It all saves money, and improves time - to - resume
- service. I've got 8 hours of back-up battery to get it fixed, and I
can't afford to call out all 3 engineers in succession, apart from the
cost. This lot could be 50 miles from the nearest house, let alone depot.

My only point is that I'd like to be able to BUY one of these things,
rather than make one. Why can't I ( pout ).

I am hoping that I can access the live tail just where it enters the
board fuse - I appreciate it will be well shielded all the way to there,
but I'm hoping the shielding stops short enough for my purposes.

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

 

[David Collier]

This is not a "standard circuit". It is a "substandard circuit". It
will detect the AC or perhaps the static build up in your clothes
until the CMOS gate gets zapped.

Agreed, which is why I'd like to buy it in with the bugs taken out. I'll
pot the thing or stick it in a biro tube or something, which should
avoid too much risk of static....

Those things that use a Neon bulb are most likely what you really
want. They will tell you that there is AC voltage there.

Gadzooks, a new idea. Do we really reckon a neon bulb with one end free
will detect electricity from a mains cable enough to light up?
I could make an opto-coupler up with it, and that would be really sexy,
and, as you say, actually robust and safe.

If you want to actually measure the voltage, that's another matter
all together. You can measure AC voltages with a fair accuracy
without making electrical contact. The design of such things in not
a prject for the beginner because it involves mains voltage.

ain't a beginner

and anyway I have no intention of going inside the cable insulation,
that's the whole point!

but I don't want to measure, just detect presence.

TVM.

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

 

[Phil Allison]

"David Collier"

DONG - wrong answer.

** My comments are fine.

YOU failed to explain your wacky application !!!!

We have

board fuse ( may trip )
meter ( may go faulty , though unlikely )
first consumer unit ( may trip )
second consumer unit ( may trip )

I'm not allowed to connect to the wires before the exit from the 1st
consumer unit, ( safety rules ), but I must diagnose any of the above
faults, as most of them need to call out a different engineer :-(

** Then you need to sense ALL the cables concerned to see if they are
live.

NOT just the incoming supply as you FALSELY posted !!!


" I need to detect live voltage in a mains cable, from outside the cable,
without electrical contact. The cable is the one INTO the main fusebox,
so no toucheee. "




.......... Phil

 

[David Collier]

** My comments are fine.

YOU failed to explain your wacky application !!!!

What is it about Aussies that makes them so easy to start an argument
with?

actually no....


** Seems most unlikely there is ever zero current flow in a *live*
conductor feeding a main fuse box.

I have a consumer unit with a single cct breaker running a single load.
Either the RCD, or the cct breaker can trip, and give me zero current
each side of the board fuse, while it's all still live.

Even in a domestic situation tripping the RCD would contradict you.

But let's not start a flame war about it.

Thanks for caring enough to answer!

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

 

[David Collier]

Assuming that you live in North America call your local IBEW office
and ask them where to purchase this very common device.

Yup. Absolutely - but I want that device with a computer interface. Or
more exactly a gnd,+5V in, and an o/c drive out, all packaged up into
something I can cable-tie onto the wire.

Sorry I should have been more exact in my question

JosephKK

David Collier

email can be sent to Dexdyne.com , under name from_usenet@

 

[Phil Allison]

"David Collier"

What is it about Aussies that makes them so easy to start an argument
with?

** What is it that makes pommy pricks into such pig arrogant cunts ??

All bastard sons of trollops and vile pommy bitches - I suppose.

** Seems most unlikely there is ever zero current flow in a *live*
conductor feeding a main fuse box.

I have a consumer unit with a single cct breaker running a single load.

** Was a " main fusebox " in your OP.

Be a fucking pink elephant next.

Even in a domestic situation tripping the RCD would contradict you.

** Shame how several major household appliances are *NOT* fed from an
CD - plus all the lighting circuits etc

But let's not start a flame war about it.

** Never need to throw flames at a complete FOOL who would not know if
his arse was on fire.

Like it is right now.

Thanks for caring enough to answer!

** Drop dead.

David Collier = another trolling dickwad.

.......... Phil

 

[Jim Thompson]

On Mon, 23 Jan 2006 11:44 +0000 (GMT Standard Time),

What is it about Aussies that makes them so easy to start an argument
with?

[snip]

Fortunately Phil is NOT your typical Aussie. I've found the
Australians to be marvelously friendly people (Phil and Bill excepted
;-)

...Jim Thompson