withstand rating

[lquadros1]

How do we assign or find out withstand rating of say 48VAC switch mode power supplies? The manufacturer supplies only di-electric strength data.
Will a catastrophic failure at main 480VAC bus within the device can safely trip the circuit ?

 

[jim dungar]

are you going from 480V down to your 48VAC power supply, or are you stepping up from 48V?

 

[Jraef]

Withstand ratings have been supplanted by "SCCR" (Short Circuit Current Ratings), because there is more to it than the old "withstand ratings". But you do not need an SCCR for a 48VDC power supply, even if it is connected direct to the 480V line, because inside, it is essentially just a transformer on the 480V side.

SCCR, and for that matter withstand ratings, had no relation to "will it safely trip the circuit", it was/is only about "will it cause collateral damage if it tries to rapidly disassemble itself during a short circuit fault".

 

[lquadros1]

Sorry. 48VAC was a typo. We have 3 phase 480VAC Omron switch mode power supplies that does not have withstand/SC rating marked. S8VK series. It is used as 24VDC power supply.

Just found out from AI, that if there is no info, Based on UL 508A (Supplement SB), which is commonly used to comply with NEC requirements for Industrial Control Panels, the default short-circuit current rating (SCCR) for an unmarked Switch Mode Power Supply (SMPS) or other power components is 5 kA (5,000 amperes).

Do you agree? Or any other options are available?

 

[EngineeredElectric]

If it's not published from the manufacture, I'd assume what the UL listing guarantees.

 

[Jraef]

Read Supplement SB again, you don’t have to include power supplies and control transformers, just the circuit protection feeding them.