# Re: [PSES] High Touch Current and GFCIs

```

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 <j...@woodjohn.uk>
Sent: Thursday, August 25, 2022 12:32 PM
To: ri...@ieee.org; EMC-PSTC@LISTSERV.IEEE.ORG
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
<mailto:000000734758d943-dmarc-requ...@listserv.ieee.org>
<000000734758d943-dmarc-requ...@listserv.ieee.org>
Sent: Wednesday, August 24, 2022 1:44 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
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.

On Aug 24, 2022, at 3:27 PM, Brian Kunde <bkundew...@gmail.com
<mailto:bkundew...@gmail.com> > 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

-
----------------------------------------------------------------

This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<emc-p...@ieee.org <mailto:emc-p...@ieee.org> >

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Website: http://www.ieee-pses.org/
Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)
<http://www.ieee-pses.org/list.html>
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> >

For policy questions, send mail to:
Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> >
David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> >

_____

To unsubscribe from the EMC-PSTC list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC
<https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1> &A=1

-
----------------------------------------------------------------

This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<emc-p...@ieee.org <mailto:emc-p...@ieee.org> >

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Website: http://www.ieee-pses.org/
Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)
<http://www.ieee-pses.org/list.html>
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> >

For policy questions, send mail to:
Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> >
David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> >

_____

To unsubscribe from the EMC-PSTC list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC
<https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1> &A=1

-
----------------------------------------------------------------

This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<emc-p...@ieee.org <mailto:emc-p...@ieee.org> >

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Website: http://www.ieee-pses.org/
Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)
<http://www.ieee-pses.org/list.html>
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Mike Cantwell <mcantw...@ieee.org <mailto:mcantw...@ieee.org> >

For policy questions, send mail to:
Jim Bacher <j.bac...@ieee.org <mailto:j.bac...@ieee.org> >
David Heald <dhe...@gmail.com <mailto:dhe...@gmail.com> >

_____

To unsubscribe from the EMC-PSTC list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC
<https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1> &A=1

-
----------------------------------------------------------------
This message is from the IEEE Product Safety Engineering Society emc-pstc
discussion list. To post a message to the list, send your e-mail to
<emc-p...@ieee.org>

All emc-pstc postings are archived and searchable on the web at:
http://www.ieee-pses.org/emc-pstc.html

Website:  http://www.ieee-pses.org/
Instructions:  http://www.ieee-pses.org/list.html (including how to unsubscribe)
List rules: http://www.ieee-pses.org/listrules.html

For help, send mail to the list administrators:
Mike Cantwell <mcantw...@ieee.org>

For policy questions, send mail to:
Jim Bacher:  <j.bac...@ieee.org>
David Heald: <dhe...@gmail.com>
_________________________________________________
To unsubscribe from the EMC-PSTC list, click the following link:
https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
```