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.

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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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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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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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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 | |-----------------------------------------------------------------|
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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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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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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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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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