One of the big "selling points" of current limiting fuses and circuit breakers is that when properly applied, they can dramatically reduce the prospective incident energy.

Here is this week's question:

Have you/clients ever ADDED/SPECIFIED current limiting devices to reduce incident energy?
Yes
No
Not part of my job

When this technique is used, you must be sure that the arcing fault current reaches the level where the device is capable of reacting and limiting the fault current. Many times high IE levels are due to low arcing fault current and slow overcurrent protective device response times.

Yes, we have had success limiting incident energy at the equipment our techs are working on by replacing upstream protective devices. We understand the IE is still high on those devices, but chances of our techs working on them is slim.

Adding CL fuses are a great way to reduce the incident energy and isolate protective devices from the equipment you are protecting. Fuses are considerably cheaper than breakers. I just recently priced a 400A breaker and it was over $8k.

I answered no because I have rarely found any value in doing so. I'm specifically talking about fuses. I'm aware of but haven't seen any of the "current limiters" that are being developed that are essentially a parallel combination of a current limiter (inductor) and a vacuum interrupter. I haven't had much experience with current limiting circuit breakers either because they are generally very expensive and very limited in the size ranges that they are available in, and they seem to be limited to only a couple of the manufacturers out there.

I think part of the problem is that the IEEE 1584 empirical equation is not separable on arcing current. By this I mean there are not separate equations so that we can compute F(X1, X2, X3, X4) = F1(X1, X2) * F2(X3, X4). The fuse equations in IEEE 1584 show dramatic improvement (not to mention that they are trivially easy to use). But I don't know of any of the commercial software packages that support them and considering that they are only available based on fuses from a single manufacturer using a single (unspecified) fuse product line, and even though it is pretty clear that the manufacturer is Mersen, without knowing the specific product name, I can't use them.

I haven't because I haven't happened to find an instance where this would help enough to justify the cost and inconvenience of installation.

Yes, and at the same time reduce the fuse size. I work for a Division 1 MAC conference university. We have and have had metering on all our buildings since 1999 so we have 17 years of historical data. Most of our building "services" (actually technically feeders) have oil filled pad mounted transformers and main switchboards that are much larger than need be based upon years of metering data. As a result we have higher available fault currents and incident energies than we should have.

I've found that changing out the pad mount primary side fuses can sometimes reduce the incident energy on the secondary side (depends on several factors) and for our buildings that have fusible main switches we can and have often reduced the fuse size/type. Say, going from 2500A down to 800A or sometimes lower.

On the pad mounts you have to look at the manufacturer tables to see what bayonet fuses you can install and not go lower than the transformer inrush. There are also current sensing, current limiting, dual sensing etc. types. Need to look at the curves for all of these and the tables and also make sure they coordinate with low voltage side main CB or fuses of course.