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  • UPS Neutral/Earth Short

    From Huge@21:1/5 to All on Thu Jan 12 17:27:13 2017
    XPost: uk.d-i-y

    Much investigation of the intermittent RCD trips this afternoon (I'm
    shattered after spending all afternoon unplugging things and plugging them
    in again.

    One thing we discovered, which may well be a red herring, was that my
    APC UPS, when switched off, with no power being fed to it, exhibits a Neutral/Earth near short circuit on its input. (0.4 Mohm)

    Is this normal? It cannot be permanent, else the RCD would trip the
    moment the UPS input was powered on. Does the UPS perhaps strap the earth
    and neutral together when there is no input power to provide a false earth
    to the hardware being protected? Or is it just faulty?

    (Looks like the trips are, as expected, N/E leakage on the external feed to
    the Klargester and workshop. [Forsees large bill for replacing the workshop supply. Sigh.])


    --
    Today is Boomtime, the 12th day of Chaos in the YOLD 3183
    I don't have an attitude problem.
    If you have a problem with my attitude, that's your problem.

    --- SoupGate-Win32 v1.05
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  • From Caecilius@21:1/5 to Huge on Thu Jan 12 17:57:37 2017
    XPost: uk.d-i-y

    On 12 Jan 2017 17:27:13 GMT, Huge <Huge@nowhere.much.invalid> wrote:

    Much investigation of the intermittent RCD trips this afternoon (I'm >shattered after spending all afternoon unplugging things and plugging them
    in again.

    One thing we discovered, which may well be a red herring, was that my
    APC UPS, when switched off, with no power being fed to it, exhibits a >Neutral/Earth near short circuit on its input. (0.4 Mohm)

    400K ohm is not a near short circuit. Even between live and earth
    that wouldn't trip an RCD on its own as it would only pass 0.6mA at
    240V.

    But did you check that with a multimeter? I had nucience trips a few
    years ago, and found there was sometimes a big difference between the
    N-E resistance shown by a multimeter (which uses a few volts) and a
    megger (which uses a few hundred volts).

    Is this normal? It cannot be permanent, else the RCD would trip the
    moment the UPS input was powered on. Does the UPS perhaps strap the earth
    and neutral together when there is no input power to provide a false earth
    to the hardware being protected? Or is it just faulty?

    (Looks like the trips are, as expected, N/E leakage on the external feed to >the Klargester and workshop. [Forsees large bill for replacing the workshop >supply. Sigh.])

    When I had a similar problem, I found a few problems with a megger and
    sorted them out. But I only cured the problem for good when I changed
    out all the RCDs for RCBOs.

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  • From Bob Minchin@21:1/5 to Huge on Thu Jan 12 18:00:19 2017
    XPost: uk.d-i-y

    Huge wrote:
    Much investigation of the intermittent RCD trips this afternoon (I'm shattered after spending all afternoon unplugging things and plugging them
    in again.

    One thing we discovered, which may well be a red herring, was that my
    APC UPS, when switched off, with no power being fed to it, exhibits a Neutral/Earth near short circuit on its input. (0.4 Mohm)

    Is this normal? It cannot be permanent, else the RCD would trip the
    moment the UPS input was powered on. Does the UPS perhaps strap the earth
    and neutral together when there is no input power to provide a false earth
    to the hardware being protected? Or is it just faulty?

    (Looks like the trips are, as expected, N/E leakage on the external feed to the Klargester and workshop. [Forsees large bill for replacing the workshop supply. Sigh.])


    I recently posted on a related topic where the UPS I purchased to run my
    gas boiler did NOT have any connection between the power output and
    earth which meant the flame detector failed as it expects the neutral to
    be at or around earth potential.
    The manufacturer finally admitted that this was the case but would not
    give me the circuit so I could devise the connection of a relay to
    effect an earth neutral short when the mains failed.
    In the end I fitted a resistor of a suitable value in situ all the time
    what kept the flame detector happy and yet did not trip the RCD.

    Maybe APC have included the relay that I would have liked to add to mine?
    I would suggest that you could fit a double pole switch on the power
    input to fix your problem maybe?

    Bob

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  • From Dave Liquorice@21:1/5 to Huge on Thu Jan 12 17:43:06 2017
    XPost: uk.d-i-y

    On 12 Jan 2017 17:27:13 GMT, Huge wrote:

    One thing we discovered, which may well be a red herring, was that my
    APC UPS, when switched off, with no power being fed to it, exhibits a Neutral/Earth near short circuit on its input. (0.4 Mohm)

    Is this normal? It cannot be permanent, else the RCD would trip the
    moment the UPS input was powered on.

    A 30 mA RCD won't trip with 0.4 M ohm (400 k ohm) neutral earth. The
    earth loop has to be around 7 k ohm or lower (do the maths...)

    You haven't mixed up your M's and m's have you?

    --
    Cheers
    Dave.

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  • From John Rumm@21:1/5 to Huge on Thu Jan 12 19:45:24 2017
    XPost: uk.d-i-y

    On 12/01/2017 17:27, Huge wrote:

    (Looks like the trips are, as expected, N/E leakage on the external feed to the Klargester and workshop. [Forsees large bill for replacing the workshop supply. Sigh.])

    For starters could you separate the workshop/klargester feed off on to
    its own RCD separate from the house?

    (I have a dedicated CU here with its own RCD for all the outbuilding
    stuff. At least that way if there is a fault I do not import the
    consequences back into the house)


    --
    Cheers,

    John.

    /=================================================================\
    | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------|
    | John Rumm - john(at)internode(dot)co(dot)uk | \=================================================================/

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  • From Andy Burns@21:1/5 to Huge on Thu Jan 12 19:05:23 2017
    XPost: uk.d-i-y

    Huge wrote:

    One thing we discovered, which may well be a red herring, was that my
    APC UPS, when switched off, with no power being fed to it, exhibits a Neutral/Earth near short circuit on its input. (0.4 Mohm)

    Is that mega or milli?
    I've got a couple of spare APC units kicking around I could compare ...

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  • From Andy Burns@21:1/5 to Andy Burns on Thu Jan 12 22:53:44 2017
    XPost: uk.d-i-y

    Andy Burns wrote:

    I've got a couple of spare APC units kicking around I could compare ...

    With an ordinary multimeter on 200 MOhm range, E->N reads as infinity.

    With a hand-cranked analogue "megger" it wobbles about somewhere between infinity and 100 MOhms, the wobbling is more likely from the action of
    cranking it while trying to hold two probes in contact with the plug and avoiding zapping myself with 500V.

    See, I knew that schuko to C19 cable I didn't throw away the other week
    would come in handy!

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  • From Andy Burns@21:1/5 to Andy Burns on Fri Jan 13 13:19:30 2017
    XPost: uk.d-i-y

    Andy Burns wrote:

    See, I knew that schuko to C19 cable I didn't throw away the other week
    would come in handy!

    But perhaps having so many C14->C13 cables which strung nose-to-tail
    they reach over 95m, is a couple too many?

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  • From Mike Tomlinson@21:1/5 to All on Fri Jan 13 13:32:55 2017
    XPost: uk.d-i-y

    En el artículo <eds2dgFjccpU1@mid.individual.net>, Andy Burns <usenet@andyburns.uk> escribió:

    But perhaps having so many C14->C13 cables which strung nose-to-tail
    they reach over 95m, is a couple too many?

    I've seen it, believe me. One reason not to leave boxes of C13-C14
    cables where the lusers can get at them.

    --
    (\_/)
    (='.'=) systemd: the Linux version of Windows 10
    (")_(")

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