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Puzzled about Online UPS + GFCI Behavior

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Bratster:

--- Quote from: Jeroen3 on October 01, 2018, 05:38:37 pm ---The mains not being present doesn't inhibit the operation of most GFCI/RCD switches.

--- End quote ---
How so?
if there is no Mains, then there is no power for the circuitry to detect a ground fault as well as being no power to actuate the trigger mechanism to trip it.


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DrDeke:

--- Quote from: Bratster on October 01, 2018, 05:22:10 pm ---Perhaps this conversation should get moved to its own thread so we can better help the heater OP instead of polluting this thread?
Not sure what proper etiquette would be.

--- End quote ---

I'm not sure what general etiquette here is either, but as the OP of the UPS+GFCI question, I am also pretty interested in the heater person's question and do not mind reading about it in the thread.

Jeroen3:

--- Quote from: Bratster on October 01, 2018, 06:03:26 pm ---
--- Quote from: Jeroen3 on October 01, 2018, 05:38:37 pm ---The mains not being present doesn't inhibit the operation of most GFCI/RCD switches.

--- End quote ---
How so?
if there is no Mains, then there is no power for the circuitry to detect a ground fault as well as being no power to actuate the trigger mechanism to trip it.

--- End quote ---
There is not active circuitry in a A or AC type GFCI/RCD. Yes, some expensive variants will have digital indicators. (Eaton dRCM)
F or B type GFCI/RCD will have active circuitry since they are also sensitive to DC or high frequency currents.
But cheap GFCI/RCD will use the fault current to trip. Some rare parts do use mains to energise the trip coil.
This means an earth fault after the UPS, when the UPS does not connect neutral and earth, can trip them.

You can even trip an RCD on your desk with an AA battery. Try it.

Bratster:

--- Quote from: Jeroen3 on October 02, 2018, 06:09:42 am ---
--- Quote from: Bratster on October 01, 2018, 06:03:26 pm ---
--- Quote from: Jeroen3 on October 01, 2018, 05:38:37 pm ---The mains not being present doesn't inhibit the operation of most GFCI/RCD switches.

--- End quote ---
How so?
if there is no Mains, then there is no power for the circuitry to detect a ground fault as well as being no power to actuate the trigger mechanism to trip it.

--- End quote ---
There is not active circuitry in a A or AC type GFCI/RCD. Yes, some expensive variants will have digital indicators. (Eaton dRCM)
F or B type GFCI/RCD will have active circuitry since they are also sensitive to DC or high frequency currents.
But cheap GFCI/RCD will use the fault current to trip. Some rare parts do use mains to energise the trip coil.
This means an earth fault after the UPS, when the UPS does not connect neutral and earth, can trip them.

You can even trip an RCD on your desk with an AA battery. Try it.

--- End quote ---
That's all news to me, I will definitely be checking out some of the GFCI Outlets we use here in the US.

Curiosity has been piqued, thank you.

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Messtechniker:
After carefully reading the ideas presented in this thread,
I have come up with the following circuit for UPSsing a
central gas heater requiring a mandatory neutral connection for its
ionization flame detector/sensor to operate.

Note: this is just an idea. Do not implement it without
advice from a professional electrician!

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