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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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    how the UPS system can recover from this

    And that can be "interesting" at times. I had one situation where a fault in a server PSU triggered the UPS into by-pass, which allowed the 3.15A fuse in the PDU to blow to isolate the faulty equipment, but also tripped out the C16 MCB that was feeding mains into the UPS. Nett result was that the faulty server went off immediately, then about 3 hours later all the other equipment fed from the same UPS went down, despite mains being present (because the UPS batteries had discharged).

    (and no, having an MCB feeding the UPS wasn't my design - just what was there originally)

       - Andy.

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  • 0

    how the UPS system can recover from this

    And that can be "interesting" at times. I had one situation where a fault in a server PSU triggered the UPS into by-pass, which allowed the 3.15A fuse in the PDU to blow to isolate the faulty equipment, but also tripped out the C16 MCB that was feeding mains into the UPS. Nett result was that the faulty server went off immediately, then about 3 hours later all the other equipment fed from the same UPS went down, despite mains being present (because the UPS batteries had discharged).

    (and no, having an MCB feeding the UPS wasn't my design - just what was there originally)

       - Andy.

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