you can do whatever you want. but when you ask for advice it would seem to be reasonable to at least listen to what is said.
you cannot use the rating of the OCPD found there as a means of determining the available short circuit current. the device rating is not meaningful.
you need to know what the real number actually is.
then you need to figure out what the short circuit current will be at the new devices. this is relatively simple Ohms law work.
you also need to know what the SCCR of the new equipment is.
if the SCCR of the new equipment exceeds the available SCC, you are fine. if not, you have to deal with it in some way.
one way of dealing with such things is to reduce the available SCC. It might be as simple as adding some extra wire. or maybe some reactors. just depends on what you find in your specific case.
another way of dealing with the problem is to raise the SCCR of the equipment you are installing. sometimes this is pretty simple. a lot of industrial control devices have series ratings with certain CL fuses. Add a CL fuse to the circuit and your 5kA SCCR magically becomes 65kA. But, this is not something that is universal. You have to actually take a look at all the power components in the new gear. The lowest rated component is the SCCR for that piece of gear.
Say the lowest rated component is a motor starter and overload. They may be rated at 5kA SCCR on their own. With the additional of a Class J fuse, the rating may be 65Ka SCCR. So if you add a class J fuse somewhere upstream (usually the rating is limited to a certain range), you have solved the problem for this piece of equipment. Again, this is not universal. You actually have to go check it out for each power component. It is not especially hard to do, but it is the only way to do it right.
Just adding a CL fuse to the circuit does NOTHING for you without doing the rest of the work.
Thank you for the help!
The reason I am avoiding the measuring is:
The service has multiple disconnects fed from a wire way so to be precise, I would have to take at least 2 enclosures apart to check wire size. It is all gear running at 480 volts in a dusty machine plant. I avoid risk when I can and do not see the reward.
The equipment is fundamental to the plant operation and shutting it down for even a minute to poke around is not allowed. This goes for the service as well as the compressor. The place runs 3 shifts.
I can appreciate your wanting to be exact but is there really any harm in assuming the worst?
Can we not assume the SCCR of the lowest component is 5K and therefore the unit is 5K. That does not seem unreasonable to me.
I can call the power co and get the transformer info to then get a guess of what is at the diso terminals. Point to point with
estimated wire sizes used for the feeders. (In your opinion should I up size the wire to the next size in case the previous contractor did so for safety?)
I do not see how adding wire can help because the runs are short and in a tight area.
I have never worked with inductors so I am lost as to how to size, order or install them.
I seems to me that you have respectable knowledge in this but I simply can not understand why the fuses will not work. The fuse manufacturer, an engineer friend and a few other posters here have indicated they will. (
This is one of your posts "My understanding is that, at least in general, the idea of using current limiting fuses to protect devices other than overcurrent protection devices is pretty sound.")
Are they not produced solely to limit current. I reread the littlefuse white pages on how to raise SCCR of a panel and all they do is add fuses. Yes they find the lowest SCCR of the parts but the end result is the same. ( the link is in another of my posts if you care)
Is this a matter of paperwork and certification rather then real safety?
Lastly, I thought class J fuses are for non motor (single element fast acting)
