Determining the Short Circuit Current Rating (SCCR) of an unrated panel that has power and control

[bdn2004]

I'm asked to determine the SCCR of what's been deemed an "Industrial Control Panel" and must meet the qualifications of NEC 409. I understand to use the "weakest link method" UL508A to do this. But in NEC 409 there is this exception to 409.110 (4): "Short-circuit current ratings are not required for industrial control panels containing only control circuit components".

My question then is this:

The box I'm looking at is a custom built heat tracing panel. It has contactors and a panelboard that's connected to the heat tracing circuits. And it has bunch of 120VAC hard-wired control relays that interact with the external thermostats, the pushbuttons, indicating lights, etc and the contactors that power the heat trace circuits.

If this were just a control panel - no rating is needed. Can I assume then that the 120VAC control portion of this panel is ok and doesn't figure into the "weakest link" ?

 

[LionelHutz]

You can't just look at the breaker and first component to determine the fault rating. Appearing to not fully understand this is why the panel should remain rated as it is.

Sure UL508A exists, but you can't use UL508A unless you have a UL508A file open with UL. UL508A is for manufacturers of control panels to use, not the end users.

I think a P.Eng signed modification or calling in a field inspector and get them to agree to the change with a new label are the only ways to get a re-rating.

 

[jraef]

The 5kA SCCR label on the panel is what I call the "lazy" method. The panel builder said to themselves;
[ol 1]
[li]"I have to put an SCCR label on the panel."[/li]
[li]"Nobody specified what it needed to be."[/li]
[li]"I can put 5kA on it without coordinating my components or expending even a minimal amount of extra effort to check the data sheets."[/li]
[li]"So I can mix manufacturers to get the lowest cost of each individual component part, even though they will not be tested for higher SCCR levels together, but I don't care because I need to be the lowest cost to get this order."[/li]
[/ol]
So the REAL issue here (i.e. what you can learn from this for future projects) is Item #2;
Do NOT give the panel builder the option to take the lazy/cheapest route, make sure your tender specifications state a reasonable SCCR requirement.

As to what you can do now, that's tough. Article 409 requires the panel to be LABELED in an approved method, so that panel ALREADY has a label that says 5kA and then UL does not permit alteration of labels in the field. The only way that could change is for that panel shop, or another, to take possession of that panel in their shop and rebuild it with the properly coordinated components (as you correctly laid out as the options). You cannot do this in the field without violating the UL listing and thereby labeling of that panel.

Now TECHNICALLY, Article 409 of the NEC states that the label may be applied based on an "approved method", then has a footnote showing UL508A as the only EXAMPLE of an approved method. But if you look up "approved" in article 100 definitions, it states that it can be “Acceptable to the authority having jurisdiction” (the inspector). I have heard that some AHJs will accept, as an alternative, that you could get a registered PE to design a protection scheme and sign and stamp plans to make the alterations in the field by adding equipment (usually CL fuses) ahead of the panel and making you a new label for the panel under his auspices. Finding a PE willing to do that and getting that accepted by the AHJ might be more of a challenge than just sending the panel to a panel builder though.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[bdn2004]

These are custom built panels at a very large well known industrial facility. They are new but they are operating right now in a critical part of the process - you can’t let your cooling water freeze.

As far as a AHJ ... I guess that would be the local inspector - but they don’t inspect anything inside a facility like this. I was told before they know that qualified union electrical contractors are doing the work. And they have competent engineers overseeing and auditing their installations. That’s who identified this issue.

I think what I’ve identified is that the original design is flawed. I’ve presented them a few options. I suspect our Client will present this info to them and they will come out and fix it at their expense.

Or

This is a big company that made these panels. It wouldn’t surprise me that they could get documentation from Sq D that the ABB contactor is indeed series rated, amend their drawings and send us a new label and be done with it.

 

[jraef]

No, the Sq.D and ABB components will not be series listed together. To attain that, they must be tested and the test for each line item costs about $25,000. So who would pay for that, SChneider or ABB? And why? So they could NOT get the order for the other component? Nope.

The only time it happens is if one or the other of the components is actually brand labeled by the other company, and that is NOT happening between those two bitter rivals. You would need to change one or the other brand.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[bdn2004]

I was speculating, I stand corrected. I know I've seen mixed brands in the series coordination databases before for some things. Maybe that is what you are referring to and made me think of that. If it truly does cost $25K per test that's good info to know. Thanks.

 

[jraef]

The only time I have seen what appeared to be "mixed brands" in a series rating is when one of the components is actually a brand-label agreement with the other mfr. An example of that was that at one time, Allen Bradley used to brand-label their circuit breakers from Eaton (actually Westinghouse, but Eaton inherited that arrangement). So when A-B did series listing of devices with breakers, they were the Eaton breakers with A-B labels on them, so in reality the same breakers with Eaton labels on them were series listed as well. I knew some integrators that would take advantage of that by buying their breakers in bulk from Eaton to get the best deal, then use them in building A-B assemblies. The hard part is, you don't know who is brand labeling what from whom without some inside knowledge.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden