(Q1)
Are 4160V direct-on-line vacuum contactor motor starters covered by IEEE C37.20.2? Or is the standard only covering medium voltage switcgear with circuit breakers.
The equipment concerned is SQUARE-D Iso-flex Model 4 Motor Control Centre using fused vacuum contactors only.
Which is the main standard(s) governing the design of such motor control centres?
(Q2)
What would be the "rated short time withstand current duration" required for a motor control centre designed in accordance with UL 845 and NEMA ICS1?
In my case the Isoflex Model 4 MCC main busbars is described as "braced to withstand 50kA rms symmetrical". Does this means 50kArms for 2sec duration?
Its main busbar is also described as capable of "withstanding the short circuit current (50kA) for 8.7 mili second duration as required for the starter to clear the fault downstream".
(Q3)
Is the following clause from IEEE C37.20.2 applicable for the MCC in (Q2)?
IEEE C37.20.2 section 5.4.5 defines "Rated short-time withstand current" of a metal clad switchgear as the following:
"The rated short-time withstand current of the MC switchgear assembly is the average rms symmetrical current that the bus and connections shall carry for 2 s."
Are 4160V direct-on-line vacuum contactor motor starters covered by IEEE C37.20.2? Or is the standard only covering medium voltage switcgear with circuit breakers.
The equipment concerned is SQUARE-D Iso-flex Model 4 Motor Control Centre using fused vacuum contactors only.
Which is the main standard(s) governing the design of such motor control centres?
(Q2)
What would be the "rated short time withstand current duration" required for a motor control centre designed in accordance with UL 845 and NEMA ICS1?
In my case the Isoflex Model 4 MCC main busbars is described as "braced to withstand 50kA rms symmetrical". Does this means 50kArms for 2sec duration?
Its main busbar is also described as capable of "withstanding the short circuit current (50kA) for 8.7 mili second duration as required for the starter to clear the fault downstream".
(Q3)
Is the following clause from IEEE C37.20.2 applicable for the MCC in (Q2)?
IEEE C37.20.2 section 5.4.5 defines "Rated short-time withstand current" of a metal clad switchgear as the following:
"The rated short-time withstand current of the MC switchgear assembly is the average rms symmetrical current that the bus and connections shall carry for 2 s."