Re: [PSES] High Touch Current and GFCIs

Fri, 26 Aug 2022 09:54:10 -0700 

Good point.

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Best wishes John Woodgate OOO-Own Opinions Only
www.woodjohn.uk
Rayleigh, Essex UK
It all depends



On 2022-08-26 17:02, Don Gies wrote:
The cancellation that Mr. Woodgate points out could occur with industrial equipment that was powered from North American  120/240 V ac, 3-wire single phase or 240 Vac, single phase circuits (where there are two line conductors separated in phase by 180 degrees on a center-tapped, single-phase distribution transformer) or from 208 Vac, single-phase equipment  (where the two line conductors are separated in phase by 120 degrees on a 3-phase distribution transformer).
If your market was strictly North America, you might use this to your advantage.  It is likely, though, that such equipment is sold on the global market, so you might test for touch current with a 230 V, single phase input (that is, 230V to earthed neutral).  Then, no such cancellation of touch current. 

Best regards,

*Don Gies*


Internal

*From:*John Woodgate <j...@woodjohn.uk>
*Sent:* Thursday, August 25, 2022 3:32 PM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* Re: [PSES] High Touch Current and GFCIs

[External email: Use caution with links and attachments]

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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. 

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Best wishes John Woodgate OOO-Own Opinions Only
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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
    <000000734758d943-dmarc-requ...@listserv.ieee.org>
    <mailto: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.

    Sent from my iPad



        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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