# Re: [PSES] High Touch Current and GFCIs

```If I have EE or a rake of equipment or several pieces of equipment plugged
into a power strip that has a combined touch current that trips a GFCI,
what can be done about that?  Will an isolation transformer solve the
problem?```
```
Thanks,
The Other Brian

On Sat, Aug 27, 2022 at 6:38 PM Richard Nute <ri...@ieee.org> 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 <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
> 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.
>
>
>
>    1. 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 <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
> *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> 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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