Griff8966 wrote:
This label is being utilized through out our company on equipment that is being utilized and interacted with on a day to day basis's. I have one location that had 777 label placed on equipment. It is causing a HUGE misconception of how the equipment will react if operated. I have reviewed the studies and some equipment is underrated and we identify those device's and remediate ASAP. A lot of the equipment has marginal results, IF conductor impedance is utilized and motor contributions along with realistic settings in the model the equipment becomes cat 4 or in some cases lower.
In a nut shell this type of sticker is crippling the facilities from a operations stand point, even if the equipment is underrated it can be interacted with safely.
Example: MCC has bus that is underrated BUT the buckets are not and are cat 2 or lower, the buckets can be opened and motor overloads reset with proper PPE. The bus is not going to explode if you turn a bucket off and open the door to reset an overload. If you have to remove the bucket from the MCC that is a whole different scenario! I appreciate all of the responses...This is huge topic right now for us!
This is a complete but common misunderstanding. You are mixing apples, oranges, and everything else.
In an overload and indeed most of the time during switching we are at most at 2-7 times FLA at most.
In an arcing fault the current is 40-85% of the bolted fault current. Typically again it's not a problem. There is also the principal of dynamic impedance which current limits even that but I'm digressing into details here. Suffice to say that arc flash has absolutely NOTHING to do with "underrated" equipment.
Bolted faults are what this problem is...during a short circuit the possibility of things flying apart. This is where we get to 10-100 times the normal operating current or more. Since magnetic force is porportional to the square of current, even modest underratings are really, really bad. You won't get much of an arc flash with these...just a boom and everything is torn to shreds. Biggest danger is shrapnel as things come flying apart under extremely high force, or the tendency for breakers to NOT open or explode if they do.