Yes, it's going to take a lot of painful experiences before specifications and purchase order processes change. Cheapest usually has a reason behind it, yet often that's the primary decision criteria.
The other issue is that the electrical and mechanical engineers at the design firms don't always talk to each other about these issues.
Exactly. What I told the customer I mentioned above was to send it back to the supplier and insist that they do a better job of paying attention to that. Almost all of the parts inside were from the same mfr, so it really was just a process of looking up the UL SCCR file data on them to get a higher value, they were just being too lazy about it. But it was THEIR UL label, so they had to be the ones to change it, and UL doesn't let you change labels in the field. They came back and insisted on $1,000 plus shipping both ways to do this. Total ripoff if you ask me...
The solution is what it's always been. The request for quote and the purchase order specifies what the short circuit rating actually needs to be.
I think that technically the current limiting fuses do not let you increase the SCCR of the device. They let you decrease the available fault current to the device.
Not the way it works. If you add current limiting fuses in the ul508a feeder circuit, you get to use the let thru current as the maximum available scc for most components and can label the panel sccr as such.
What I was trying to say was exactly that the CL fuse does not change the SCCR of the panel, it changes the current that the panel is required to withstand at its input to be less than the upstream available fault current and within the existing SCCR of the panel.
Yes. That is the way it works. It is not a universal thing. You have to follow the rules found in ul508a to do so, but it can be done. You can also add other current limiting devices in the feeder circuit such as current limiting circuit breakers or transformers and use them to increase the sccr of the panel. CL fuses are the most common because they are relatively inexpensive.
How does that change the rating on the control panel itself ? I though the upstream current limiting device, reduced the available fault current at the panel to a value this is equal to or lower than the marked SCCR rating.
The way it works is sort of screwy. You have to start with the sccr you want. Let's call it 65ka.
I understand that you can use the current limiting device to lower the available fault current at the control panel, but hat has no effect on the SCCR rating of the control panel. You have simply made it compliant by reducing the available fault current at the panel to a level below its marked rating.
Not according to ul508a. Read thru the supplement on sccr, especially the part on current limiting devices in the feeder circuit.
UL508A has nothing to do with what I do in the field...it is not a legally adopted code or standard.
But ul508a is the std by which sccr is determined for control panels.
But that does not help the installing electrician...I have to find a way that the available current at the control panel is less than the SCCR marked on the panel.