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Best wishes John Woodgate OOO-Own Opinions Only
www.woodjohn.uk
Rayleigh, Essex UK
It all depends
-------- Forwarded Message --------
Subject: Re: [PSES] High Touch Current and GFCIs
Date: Mon, 29 Aug 2022 14:07:46 +0100
From: John Woodgate <[email protected]>
Organisation: J M Woodgate and Associates
To: Brian Kunde <[email protected]>
In all such cases, the best approach is to draw the schematic. You can
usually see the current paths quite clearly then. I can't answer your
question because I can't visualise the schematic of your set-up. It may
be that you are measuring the total current in the PEC somehow. What is
the current rating of the fuse?
======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only
www.woodjohn.uk
Rayleigh, Essex UK
It all depends
On 2022-08-29 13:41, Brian Kunde wrote:
When I run the Touch Current test and the EUT is not isolated from PE
when I press the Test Button that opens the PE conductor, the meter on
the test will max out. Sometimes it will even blow the fuse. What is
happening at that point? Am I reading the Touch Current from every
piece of equipment in the building?
Thanks,
The Other Brian
On Sat, Aug 27, 2022 at 6:38 PM Richard Nute <[email protected]> wrote:
I wouldn’t describe the phenomenon as “cancellation.” The touch
current is always present and must have a path to earth/ground.
The equivalent equipment circuit:
Y1 capacitor L-(line)-to-PE.
Y2 capacitor N-(neutral)-to-PE. Capacitor value is 25x Y1
capacitor value.
4.6 volts N-to-(grounded)-PE.
In the USA, N is connected to a ground rod at the building service
entrance. PE is connected to N at the breaker box. In the
building, PE is parallel to N, but is a non-current-carrying
conductor except in the case of a fault.
The Y1 and Y2 capacitors are in series and comprise a voltage
divider to an open PE. Because the Y2 capacitor is 25x the Y1
capacitor, the open-circuit voltage at the PE connection is very
low compared the line voltage (instead of the usual half the line
voltage).
Normal condition touch current path is from L to Y1 to PE (open)
to a 2,000-ohm resistor to ground, Touch current is calculated
using Ohm’s Law from the measured voltage across the 2,000-ohm
resistor. The 2,000-ohm resistor is (in essence) parallel to the
Y2 capacitor. Some of the L-to-Y1 current (not touch current!)
returns to ground through the Y2-N-ground circuit, depending on
the parallel network of capacitance reactance and the 2,000-ohm
resistor.
Reverse polarity (L and N reversed in the supply to the equipment)
current path is N to Y2 to PE (open) to the 2,000-ohm resistor to
ground. Because Y2 is 25x Y1, the touch current is much higher
than normal polarity. As in the normal polarity condition, some
of the current (very small) returns to ground through the Y1
capacitor.
If the Y1 and Y2 capacitors are of equal value, the supply voltage
is 120 volts, and the touch current limit is 0.5 mA, the Y1 and Y2
capacitance reactance is 238,000 ohms each. The Y2 capacitance is
shunted by the 2,000-ohm resistor and can be ignored as the
voltage across the Y2 and 2,000-ohm resistor is 1 volt. (The
current through the 238,000-ohm reactance is 4.2 microamps.)
We have a parallel circuit to ground from the junction of Y1 and
Y2 when the PE is open and when touch current is being measured.
One circuit to ground is through the touch current measuring
circuit. The other circuit to ground (via the N) is through the
Y2 capacitor. If the Y2 reactance is small, a significant N
current can be in that path to ground thereby reducing the touch
current, not a partial cancel of the touch current.
Best regards,
Rich
*From:*John Woodgate <[email protected]>
*Sent:* Thursday, August 25, 2022 12:32 PM
*To:* [email protected]; [email protected]
*Subject:* Re: [PSES] High Touch Current and GFCIs
There is also a question in my mind as to whether there can be
partial cancellation of touch current. I suspect this is highly
improbable in the US, due to the distribution system ensuring that
the neutral has a very low voltage difference from the PEC. But in
Europe, it's not inconceivable that the neutral could be, say, 4.6
V relative to PEC and the neutral-to-PEC capacitance 25 times that
of L to PEC, so that half the L-to-PEC leakage current is
cancelled by the N to PEC current.
======================================================================================
Best wishes John Woodgate OOO-Own Opinions Only
www.woodjohn.uk <http://www.woodjohn.uk>
Rayleigh, Essex UK
It all depends
On 2022-08-25 19:12, Richard Nute wrote:
I wish to make two points:
1. Kirchoff’s Current Law states that the sum of currents
entering a node equals the sum of currents leaving the
node. The Law applies to summation of leakage (touch)
currents (e.g., through a 2,000-ohm resistor) and to
summation of protective conductor currents (through 0
ohms). In a power strip protective grounding conductor,
I’m assuming 0 ohms to ground, so the current is slightly
higher (1 to 10 % depending on the leakage current limit
and the voltage you are using) in the protective grounding
conductor than leakage (touch) current.
See IEC 60990 for touch (leakage) current and protective
conductor current measurement procedures.
2. A GFCI measures the current difference between line and
neutral conductors, not current in the protective
conductor. It nominally operates at 5 mA. We assume
(with a reasonable degree of accuracy) that leakage
(touch) current is 100% of the differential current
measured by the GFCI. It is possible, although unlikely,
for some of the GFCI differential current to find another
return path than the protective grounding conductor.
Best regards,
Rich
*From:* Lfresearch Jose
<[email protected]>
<mailto:[email protected]>
*Sent:* Wednesday, August 24, 2022 1:44 PM
*To:* [email protected]
*Subject:* Re: [PSES] High Touch Current and GFCIs
I have wondered about something similar.
If I use a 6 way power strip, I’m assuming all the leakage
currents for anything plugged in sum. Is that correct? I
recall getting a few trips when I used a power strip and It’s
only just twigged that might be why.
Cheers,
Derek.
Sent from my iPad
On Aug 24, 2022, at 3:27 PM, Brian Kunde
<[email protected]> wrote:
If I have a rake of electrical equipment with a
single power cord and a combined touch current exceeding
6mA, and I plug the rake into a circuit with a GFCI, will
it trip?
Thanks.
The Other Brian
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