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UPS Fault Level Calculation

Semaj

Does anyone know if there is a standardised way of calculating fault levels at the output of a large UPS like IEC60909 does for transformer and generator supplied faults?

I imagine things will change between manufacturers but a good rule of thumb would be very useful as it seems that no matter the installation, downstream of the UPS the breaker settings have been poorly thought out and my concern is that these downstream circuits will not actually acheive ADS due to the fault level being too low to trip the downstream breaker because the trip settings are too high.

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    I've only ever dealt with smaller UPS units but yes, ADS can be a challenge especially for submains. I would go to the manufacturer for their data. Note that unless they're specifically designed for it, you'll only get perhaps something of the order 10-50% over full load current as an overload with a specified time limit before the units shut down, but not in a controlled way.

    Earth faults can be detected with RCDs etc set sensitively, but another gotcha to be wary of will be how the earth is derived: On principle you might not be able to rely on any upstream N and E link so do check what the UPS does.

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    I've only ever dealt with smaller UPS units but yes, ADS can be a challenge especially for submains. I would go to the manufacturer for their data. Note that unless they're specifically designed for it, you'll only get perhaps something of the order 10-50% over full load current as an overload with a specified time limit before the units shut down, but not in a controlled way.

    Earth faults can be detected with RCDs etc set sensitively, but another gotcha to be wary of will be how the earth is derived: On principle you might not be able to rely on any upstream N and E link so do check what the UPS does.

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