Connecting an Industrial Control Panel with a Low SCCR

[richwaskowitz]

Let me stop being general and spell it out.

We are a controls systems integrator and we design industrial control panels. We are also a UL panel shop so we put UL labels on our panels. We, the designers, utilize the methods found in UL508A SB to determine the SCCR of our panels. We take advantage of the provisions in part SB to improve what would otherwise be a low rating when we can. Sometimes however, at the customer's insistence, we have had to include in a panel a VFD which has no published SCCR. That means it defaults to the value in table SB4.1. For a drive up to 50 hp, that means 5 kA. This can bring the entire assembly (panel) down to 5 kA. So, we do our due diligence and put a label on the panel indicating the 5 kA SCCR. What do you guys do with it when it shows up on the floor and you know the bus can deliver 45 or 65 or more kA?

I guess what I am getting at is that I believe that I need to advise our management against this practice and set some minimum rating or target such as 45 or 100 kA for our designs in cases where the end-user does not specify a minimum. In the case of the VFD with the low rating, I suppose we will have to decline the job.

 

[mkgrady]

Let me stop being general and spell it out.

I guess what I am getting at is that I believe that I need to advise our management against this practice and set some minimum rating or target such as 45 or 100 kA for our designs in cases where the end-user does not specify a minimum. In the case of the VFD with the low rating, I suppose we will have to decline the job.

Won't that make your company less competitive and less successful?

I don't know much about your issue but I'm wondering why this is your problem? Is your company responsibe to coordinate your product with the available fault current on this job? If yes, then what is the problem? If no, then why are you concerned?

Products are misapplied all the time. I would think your SCCR label and instasllation instructions would cover your liability, and would cause the customer to be responsible for any coordination issues.

 

[augie47]

I would be afraid to guess what percentage of equipment is installed with no regard to the SCCR
I commend you for your efforts and reluctantly agree with mkgrady.
A disclaimer on your company's part might be the best path
I think it evidenced for the post here that the problem is often ignored or addressed improperly.
Fuse let-thru ratings are improperly accepted in many jurisdiction with which I have familiarity.

 

[benaround]

Jim's statement works if the research to get this listing occurs at the UL panel builders facility and comes on the equipment label. You cannot perform this analysis in the field.
I make the installing folks run additional length of wire, that almost always works.

Ron, Who figures out what size wire and how long the additional length should be ? I have

done this several times as an installer. Most of the time it has been " just add 20' to what

you have", does that sound right ?

 

[ron]

Frank,
It is a calculation based on the fault current calculated without the additional length, the wire size, and the new wire length. I keep adding length until I get below the rating of the equipment.
Additional wire is more impedance, so the fault current will reduce at the end of the longer wire.