The requirement to fuse is found in the manufacturer's instructions for that specific piece of equipment. Still, that only means that there has to be a fuse somewhere in the circuit. If the nameplate reads "fuse," rather than "overload device (or some such), then a fuse is needed; a breaker is not sufficient.
Otherwise, the disconnect has to be mounted as the code calls. There is no rule against having more than one disconnect; many times I have seen the fused disconnects at the control center, while there was a second disconnect mounted right at the equipment.
As I remember, it must be within 3 feet of the device.
And usually the panel board will contain the air compressors "Primary Protection" rated at 125% of the FLA and the fused disconnect, "Secondary Protection" will be rated anywhere from 175% to 250% or higher per NEC 430 something depending on the fuse characteristics.
I'd like to add that using a MCCB as the primary protection with a fuse (in place of another MCCB) for the secondary protection offers the best combination of protection against both short circuit and arc flash serneros.
Well, I was working off of memory...and I'm an engineer...
Wow, I really fell into this one.
I guess that you should also clarify "insight" as being no more than 50 feet. (oops - I re-read your post and noticed that you had already stated this - sorry).
And...being from the industrial world for almost 30 years, if it isn't close to the machine most maintainence personal will try to work without disconnecting the machine. That's why we always try to maintain the distance to around 3 feet or a step or two away.
Considering the code reads like it was written by a bunch of lawyers and gets re-written every few years by industry insiders it no surprise that we all miss a subtlety of the code every now and then. My favorite debate is the whole “minimum voltage drop is not a code requirement, it’s just a recommendation”.
Sure 3ft is a good design and as an engineer you can put that on the plans as part of the scope, the code should be read as a minimum requirement for a reasonably safe installation, and why design to minimum requirements?
101° Rx = + /_\
#163622 - 05/12/0703:04 PMRe: Fusible safety switch for Air Compressor
I wouldn't want to see any short distance, like 3', we have enough trouble keeping disconnects 110.26 compliant as it is. As long as they are truly within site and convenient for the maintainer so they will actually get used, I am happy.
I can't think of a better example of where the NEC is a 'safety minimum,' rather than a design manual, instruction manual, etc. This topic also highlights the trouble with 'one size fits all' solutions.
When it comes to disconnects, I like to begin with "forget about the code..."
Under what circumstances will you want to disconnect the thing? And, where will you be when that happens?
It makes sense to be able to disconnect something from the control room. It makes sense for things that need checking ... such as fuses ... to be placed where they are easily accessible. It also makes sense that the guy working on the thing be able to surely disconnect it, right there ... and that there be no possibility of grabbing the wrong disconnect.
If I was changing a motor, I'd want a switch right at the end of the flex that feeds it. Indeed, a cord & plug would be even better.
If I were needing to disconnect the next Chernobyl, I'd want the disco located somewhere, say, 25 miles upwind.
I sure an heck don't want to have to climb on a roof, in the rain, to check the fuses, or push the starter reset. Yet, few things are more discouraging than a wall of unmarked switches, with everything disappearing into a gutter.
I know what you mean Reno. One of my few red tags was a 2000 sqft equipment rooms with all the disconnects neatly grouped by the door. I told the installer to go take the covers off one of the 480v air handlers at the far end, start poking around in the wiring box and I will call "maintenance" to complain about my AC not working. Maintenance man opens the door and says "here's your problem".
They got the point. In fact what we got was an additional disconnect at each machine. They were thinking the disconnect was for firemen entering the room to fight a fire. I pointed out you are also protecting the people who maintain the boxes. I also got another entrance to the room. (actually a tall attic) It is amazing what engineers can come up with when they get on board. They found a "pull down" attic ladder that was class 1 and handled a 14' ceiling. It may have actually been custom built. Very slick.
From experience, many service calls, callbacks, and even a few consulting gigs, I feel very comfortable saying that maintenance men are dangerous and we professionals should make damn sure they know how to turn it off before they start beating it with a hammer.
Fuses are a good thing, they cost money and even the dumbest of maintenace men will think twice after burning up the second set...