Timeismoney08
Member
Does anyone have any recommendations on how to calculate this and possibly any standards that show this formula or method?
Thank you!
Thank you!
Originally posted by Rson:
Unless you have a very complicated panel - basically find the SCCR ratings (listed by manufacturer) of the protective devices on your power feed.
That's kind of the way it was BEFORE SCCR came into the picture. We don't design particularly complicated panels and it is very seldom the OCPDs that are the limiting devices for SCCR.
Do you have a power distribution block? Those are often no better than 100kA even if you have Class J or better fuses in front of them. Depending on the size of conductors you connect to them the SCCR can be significantly lower.
Is your contactor actually a listed combination with the OCPD in front of it? That will drop the branch to the contactor's default SCCR.
You are unconditionally correct with the power supply branch in your example but only because power supplies are consider exempt from SCCR consideration.
You really need to go through the whole exercise using an accepted evaluation method to know where you sit.
Keith
Transformers, PLCs etc don’t count. Only devices on the POWER circuit that could open or operate during a fault will count. So the protective device FOR the transformer would count, but not the transformer itself nor anything down stream of it, like a power supply, control components etc.I’m a recently retired controls engineer who took several SCCR classes and have the examples put out by Siemens and Bussman but I could never get the hang of doing it to my satisfaction.
All of our panels were quite different with transformers, PLC’s, 480V components, etc. I could never get a straight answer to my questions. Glad that I’m out of it now.
Calculation is kind of pointless unless you are a registered PE willing to stake your livelihood on the results. The SCCR you can apply to a panel is basically going to be determined by the lowest rated device OR SERIES COMBINATION of devices used in the power circuit of your panel. So you can either use all components that have series listings at higher values (attained via testing that is too expensive to do for anyone other than the manufacturers), accept the lowest level of any device in the panel, or accept the "courtesy" 5kA SCCR for untested components. Doing so of course puts a major burden on the installer to limit their available fault current to 5kA, which is very very difficult in an industrial facility.
That's kind of the way it was BEFORE SCCR came into the picture. We don't design particularly complicated panels and it is very seldom the OCPDs that are the limiting devices for SCCR.
Do you have a power distribution block? Those are often no better than 100kA even if you have Class J or better fuses in front of them. Depending on the size of conductors you connect to them the SCCR can be significantly lower.
Is your contactor actually a listed combination with the OCPD in front of it? That will drop the branch to the contactor's default SCCR.
You are unconditionally correct with the power supply branch in your example but only because power supplies are consider exempt from SCCR consideration.
You really need to go through the whole exercise using an accepted evaluation method to know where you sit.
Keith