SCCR NEC409

[milmat1]

I have a question about calculating the SCCR for a panel I am designing for a machine.
In my MCC panel I have a circuit breaker that is feeding a separate hoist control panel, separately from my panel.
That panel comes prebuilt as part of a hoist assembly and it has an SCCR rating of 5ka.
Since technically I am only calculating my SCCR to the line side of the branch circuit OCD can I ignore the 5ka rating of the hoist control box
while calculating my cabinets SCCR ?

The separate hoist control panel contains the starters and O.L.'s for the hoist motor.
I will try to attach a drawing of the 480 dist page..

 

[jim dungar]

I have a question about calculating the SCCR for a panel I am designing for a machine.

Is this panel going to be listed/labeled as meeting 'standards'? If so follow their procedures.
If not, I do not see how you can rate the panel SCCR as being any higher than its lowest component.

 

[milmat1]

Is this panel going to be listed/labeled as meeting 'standards'? If so follow their procedures.
If not, I do not see how you can rate the panel SCCR as being any higher than its lowest component.

That is sort of my question. Since the panel I'm feeding is a separate panel with its own SCCR rating. And will be non compliant because my panel will have an AFC (going to that panel) much higher than the 5ka rating of the sub. And the sub panel being supplied by a different manufacturer.

 

[jim dungar]

That is sort of my question. Since the panel I'm feeding is a separate panel with its own SCCR rating. And will be non compliant because my panel will have an AFC (going to that panel) much higher than the 5ka rating of the sub. And the sub panel being supplied by a different manufacturer.

Your panel rating is independent of the sub-panel's rating, unless your contract says otherwise. It is up to the installer to follow NEC 110.10 - a common methods is to add enough impedance (e.g. long lengths of small conductors) to lower the available Short Circuit Amps.

Has anyone calculated what fault current is likely to exist at both panels?

 

[Jraef]

"Panel" is being used a little flippantly for my taste here, I'm not sure which "panel" you are referring to and where the "MCC" is in all of this. Nor am I clear on your role here; are you the installing contractor, a panel builder, the end user?

Assuming you are a panel builder, if the "panel" in your drawing, let's call it "7549", is the one YOU are building, the "hoist panel" is external and is essentially a load fed FROM this panel. So you do not need to account for the SCCR of that remote device in THIS panel's listing, that's their problem. You can list 7549 at a level commensurate with the SCCR of the devices inside of it. Per the SCCR tables from AB, you can ALMOST list that panel at 65kA SCCR. The problem is, you are apparently attempting to use that last MPCB as a "feeder" breaker, and it is not UL listed for that purpose. The 140M devices are only listed as "Branch" protection, meaning it is the last protective device before the end use unit, i.e. a motor. You are "feeding" another panel, so the device in 7549 must be UL 489 listed as a "Feeder" and per the NEC and UL, that means it must have fixed trips, i.e. a "Molded Case Circuit Breaker" (MCCB).

There is a version of those little IEC devices that IS listed under UL 489 as an MCCB that looks essentially the same, albeit the next frame size up.
It would be a 140U-D6D3-C25 (with 25A trips) and is listed at 100kAIC. So with that change, you could apply an SCCR of 65kA on that panel.

The 5kA listing of the hoist panel is probably going to be a problem for someone though. For that to be connected, whomever makes that connection will have to show an AFC of 5kA or less at it's terminals, and that is extremely unlikely on a 480V system. It's a problem people have in allowing vendors to sell them panels without making this issue part of the purchase specifications. Some OEMs will take advantage of it because anyone can get a 5kA "courtesy" listing of a panel without testing or paying attention to the component selection, meaning they can buy mis-matched components as cheaply as they can find them. The problem is passed down to the installer, and IMHO that's not right, because it's EXTREMELY difficult to deal with in the field.

 

[milmat1]

Your panel rating is independent of the sub-panel's rating, unless your contract says otherwise. It is up to the installer to follow NEC 110.10 - a common methods is to add enough impedance (e.g. long lengths of small conductors) to lower the available Short Circuit Amps.

Has anyone calculated what fault current is likely to exist at both panels?

I should have been more clear, the sub panel is still part of our original machine. It just happens to be a prebuilt part of a hpist assembly that we mount onto our machinery. So does your statement about still hold ?

 

[GoldDigger]

I should have been more clear, the sub panel is still part of our original machine. It just happens to be a prebuilt part of a hpist assembly that we mount onto our machinery. So does your statement about still hold ?

I would still say that it does not affect the rating of your panel, but that you may not be allowed to install it in the machine in the first place because of its own rating.

If it is part of a (UL listed?) assembly, I am not sure whether Jraef's concern about a feeder breaker still applies though.

 

[milmat1]

I can change the hoist feeder breaker to a 489 breaker, no problem there. If I do that, and then I rate my 7549 panel at 65ka. Now the hoist panel is at 5ka SCCR.
If I calculate the AFC to the hoist panel (via the 489 MCCB), and it is much higher than 5ka. Then that panel becomes the problem. Are you starting to see my dilemma here, I might have to rate my 7549 panel at 5ka, just so I remain compliant with feeding the 5ka hoist.

I know this is very confusing and I appreciate everyone trying to help..

 

[GoldDigger]

I can change the hoist feeder breaker to a 489 breaker, no problem there. If I do that, and then I rate my 7549 panel at 65ka. Now the hoist panel is at 5ka SCCR.
If I calculate the AFC to the hoist panel (via the 489 MCCB), and it is much higher than 5ka. Then that panel becomes the problem. Are you starting to see my dilemma here, I might have to rate my 7549 panel at 5ka, just so I remain compliant with feeding the 5ka hoist.

I know this is very confusing and I appreciate everyone trying to help..

Based on Jraef's earlier comments, making your panel 5kA SCCR would just be kicking the can back down the road to the customer at install time for your equipment and may very well, in practice, make your equipment unusable.
Changing your panel SCCR rating to 5kA is not what would make the sub panel legal. It would be configuring the installation environment to be less than 5kA available fault current that would do that.

The whole assembly would technically conform to code and UL requirements, but likely be impossible (or at least very difficult and expensive to install. Is that the kind of behavior that would give you a competitive advantage? I suspect not.

 

[milmat1]

Based on Jraef's earlier comments, making your panel 5kA SCCR would just be kicking the can back down the road to the customer at install time for your equipment and may very well, in practice, make your equipment unusable.
Changing your panel SCCR rating to 5kA is not what would make the sub panel legal. It would be configuring the installation environment to be less than 5kA available fault current that would do that.

The whole assembly would technically conform to code and UL requirements, but likely be impossible (or at least very difficult and expensive to install. Is that the kind of behavior that would give you a competitive advantage? I suspect not.

I think this might be the silver bullet..

 

[petersonra]

The scope of UL508a specifically excludes things that are not part of the control panel.

1.4 An industrial control panel does not include an evaluation of the controlled equipment such as motors,
heaters, lighting, and other loads connected to power circuits. Unless specifically noted on the wiring
diagram of the industrial control panel, an industrial control panel does not include equipment mounted
remotely from the panel and connected via a wiring systems or equipment field installed on or within the
industrial control panel.

There are times you might want to make it part of your control panel, such as if you have a disconnecting means that is separate but is required by the standard.

 

[Jraef]

If it were me, and I am responsible for the entire assembly, I would rebuild the hoist panel and make it compatible with a reasonable AFC. Its not really that difficult if you know what to do. I can see you might not want to change any control systems and maybe drives if there are any in there, but if you look up the drives or starters, chances are that they can have a higher SCCR when used in conjunction with a specific protection device. So all you need do is use that specific protective device, not the cheapest piece of junk the OEM could find. If they used some bizarre piece of equipment that has no SCCR rating available, it might be worth investigating changing it out for something that does. Control components don't count, only devices in the power circuits.

 

[milmat1]

The scope of UL508a specifically excludes things that are not part of the control panel.




There are times you might want to make it part of your control panel, such as if you have a disconnecting means that is separate but is required by the standard.

Thank You !

If it were me, and I am responsible for the entire assembly, I would rebuild the hoist panel and make it compatible with a reasonable AFC. Its not really that difficult if you know what to do. I can see you might not want to change any control systems and maybe drives if there are any in there, but if you look up the drives or starters, chances are that they can have a higher SCCR when used in conjunction with a specific protection device. So all you need do is use that specific protective device, not the cheapest piece of junk the OEM could find. If they used some bizarre piece of equipment that has no SCCR rating available, it might be worth investigating changing it out for something that does. Control components don't count, only devices in the power circuits.

Exactly,
I should mention this hoist control panel (sub) Contains the starters and OL's for the hoist motor. it'll wait until the hoist gets here and look at the components and see how I can best marry them to my system. I don't want to just default my panel to 5ka (As the hoist company seems to have done!)
then I can evaluate what I need to do to maintain a higher SCCR.

Great discussion guys ! I Thank you for all the great replies, there is a lot of talent and knowledge on this forum and it is always very helpful..

 

[Jraef]

Something worth noting that I just read yesterday: in the 2017 NEC changes, they have apparently added a rule that a "machine" that has multiple control panels on it must now be labeled with an overall SCCR for the system as a whole. So that becomes pertinent to your exact situation. If you have 5 different panels on the machine and just one of them is defaulted to 5kA, the label for the entire machine must now say 5kA even if the other 4 are 65kA. So it's becoming even more important for OEMs to address this up front and for users to specify what kind of SCCR they require for anything they buy that has controls (for line power) on it.

Whether or not your state has adopted the 2017 code yet or not is relevant, at least for now. Here in CA we just recently finally adopted the 2014 code, so it's not going to hit here for a while.

 

[dkidd]

I haven't really checked this out, but it looks like a good resource.

http://lvpinfo.com/319/Copied/ea83f...9e/ELDID/0580364d-d23e-4e64-84f6-8cf1ff463d10

To make improving your control panel design easier, our experts have designed this toolkit take the work out of SCCR calculations so you can stay focused on the bigger picture. Click on the link in our Resource Center below to get your FREE pocket-sized slide rule to assist you with on-the-spot calculations. Our 3-step training module walks you through real-life examples of calculations. Our white paper gives an overview of the process. Be sure to stay up to date with the latest solutions and technology by subscribing to our newsletter. In addition, the published system ratings of tested and certified motor controllers are listed on the UL website, providing you another information time-saver to make control panel design even simpler.

 

[petersonra]

Something worth noting that I just read yesterday: in the 2017 NEC changes, they have apparently added a rule that a "machine" that has multiple control panels on it must now be labeled with an overall SCCR for the system as a whole. So that becomes pertinent to your exact situation. If you have 5 different panels on the machine and just one of them is defaulted to 5kA, the label for the entire machine must now say 5kA even if the other 4 are 65kA. So it's becoming even more important for OEMs to address this up front and for users to specify what kind of SCCR they require for anything they buy that has controls (for line power) on it.

Whether or not your state has adopted the 2017 code yet or not is relevant, at least for now. Here in CA we just recently finally adopted the 2014 code, so it's not going to hit here for a while.

I don't see that in article 409. Where is this new rule to be found?

 

[Jraef]

I don't see that in article 409. Where is this new rule to be found?

I read it in the course of looking for something else, I can't find it now. I just remember seeing it and that it pertained to the 2017 NEC, but since we just recently accepted 2014, I didn't pay a lot of attention. I'll have to go through my browser history I guess, but I tend to get lost in it again when I do that....

 

[drktmplr12]

The overcurrent fuses FU1, FU2, FU3 you have selected are current limiting type. You can take the available fault current and find out from the fuse mfg how much "peak let through current" those fuses will allow. Read this from Littelfuse, it provides information on improving SCCR with current limiting fuses. I used to design panels for a 508 shop and we used this method time and time again when certain distribution blocks didn't have combination ratings with the circuit breakers.

I have a hard time believing that the available fault current at the hoist is higher than 5kAIC. What size conductors (#10 AWG) and what length are feeding the hoist? What is the available fault current at the 7549 bus? How much fault current is "let through" when the 7549 panel is subjected to 65 KAIC, and how much of this reaches the hoist considering the impedance of the conductors connecting the hoist to 7549?

 

[milmat1]

The overcurrent fuses FU1, FU2, FU3 you have selected are current limiting type. You can take the available fault current and find out from the fuse mfg how much "peak let through current" those fuses will allow. Read this from Littelfuse, it provides information on improving SCCR with current limiting fuses. I used to design panels for a 508 shop and we used this method time and time again when certain distribution blocks didn't have combination ratings with the circuit breakers.

I have a hard time believing that the available fault current at the hoist is higher than 5kAIC. What size conductors (#10 AWG) and what length are feeding the hoist? What is the available fault current at the 7549 bus? How much fault current is "let through" when the 7549 panel is subjected to 65 KAIC, and how much of this reaches the hoist considering the impedance of the conductors connecting the hoist to 7549?

I think the hoist manufacturer (as many people do) took the easy road and just defaulted their cabinet to 5KA.
And I could easily do the same. But as someone mentioned I would doing to my customer what Saturn done to me..

The fuses have a 200KA ip rating !

 

[milmat1]

Something worth noting that I just read yesterday: in the 2017 NEC changes, they have apparently added a rule that a "machine" that has multiple control panels on it must now be labeled with an overall SCCR for the system as a whole. So that becomes pertinent to your exact situation. If you have 5 different panels on the machine and just one of them is defaulted to 5kA, the label for the entire machine must now say 5kA even if the other 4 are 65kA. So it's becoming even more important for OEMs to address this up front and for users to specify what kind of SCCR they require for anything they buy that has controls (for line power) on it.

Whether or not your state has adopted the 2017 code yet or not is relevant, at least for now. Here in CA we just recently finally adopted the 2014 code, so it's not going to hit here for a while.

I don't see that in article 409. Where is this new rule to be found?

Yeah ME Too !
I don't have a 2017 here, only my 2014 copy..
That would make sense in a situation such as mine where a machine could have separate cabinets all fed from a common panel.

Just since I came to work here have I started pushing to properly label the cabinets. They have never labeled them at all here..