Sccr

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CEDEng

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Alright, I surrender, I've googled this to death...there should be a dedicated website for this issue!

My latest Q's: Are components after a Drive counted? (For instance, terminal blocks between the Drive and the Motor - let's not discuss the sense of the design for now!) What about downstream of a Motor Starter / Overload, and before the Motor? (again TBs would apply.) Is the motor always excluded? (For instance - a fan inside the panel.)

[Please forgive my confusion. The Suppl. SB is clear on certain issues - but gray on others.]
 
Try to re-state your question. It may make a lot of sense to you since you are familiar with the situation. Maybe we can help you then. From your post, I don't know what you are counting or trying to count.
 
Ah, you're absolutely right - my apologies - my ongoing frustration has led to some fast typing and slow thinking!

Replace "count" with "consider" (roughly!)

For instance, wire size is not considered (or counted!) in the SCCR calculation. What about devices between the drive and the motor? Between the OverLoad and the motor? The motor itself, if it's in the panel?

Hope this makes a little more sense...thanks!
 
It makes perhaps a little more sense, but not enough for me to be able to offer any help. I don't know what "SCCR" means, and I don't know what sort of calculation you are talking about. Let's hope there are other members who are familiar with this topic.
 
SCCR - Short Circuit Current Rating. More relevant to panel builders than anyone else. I've posted it here in "NEC" as that's where the trouble all started (as per the code change) but it may be better suited in the UL area - as UL is defining how to perform this calculation.
 
CEDEng said:
Ah, you're absolutely right - my apologies - my ongoing frustration has led to some fast typing and slow thinking!

Replace "count" with "consider" (roughly!)

For instance, wire size is not considered (or counted!) in the SCCR calculation. What about devices between the drive and the motor? Between the OverLoad and the motor? The motor itself, if it's in the panel?

Hope this makes a little more sense...thanks!
Click to expand...

The power circuit (i.e. power distribution) components are counted. UL508A Table SB4.1 provides a list of the components, as does paragraph SB4.2.1. Wire is not included. A motor is not a power distribution component, and is also not included. To get to your question, I would think that the components between a drive and motor, or an overload and motor, would be limited to terminal blocks. Terminal blocks are included.
 
kc8dxx said:
... A motor is not a power distribution component, and is also not included. ...
Click to expand...

I believe that for large systems, connected motors are to be counted as they can contribute to the fault current.
 
A short circuit current analysis will use motor currents to determine what kind of short circuit currents are available in the system. Motors cause additional short circuit currents to be developed, but they do not affect the SCCR rating of an Industrial Control Panel.

The rating of what a panel can withstand is different than the short circuit current that a system can develop. One would hope that the designer would ensure that the panel ratings are adequate to account for the short circuit currents that can be developed.
 
Thanks, all of you, for your input.

As we've discovered, terminal blocks, even downstream of a VFD, need to be considered. Motors, pumps, or fans, never.

An additional note: While it's true you would want the panel designed to withstand a (for instance) max. short circuit situation like a motor, the point of the SCCR is to notify the installer of the maximum available short-circuit current that may be made available to that particular panel. The installer is responsible for making sure the limit is met, as I understand it.
 
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