I have encountered a 1200A MCCB in a facility with the instantaneous trip elements removed. The breaker is a Westinghouse NB style. My question: is this an NEC violation?
Depends on if the CB was designed for such a field modification and the equipment it is installed in was designed for such.
You can buy CB's with the instantaneous portion of the curve disabled for better selective coordination of downstream trip curves, but you need to be sure you are feeding equipment that have 30 cycle ratings such as UL 1558 Switchgear.
Agreed. Common for us to see new installs where the mains and large feeders only have short-time protection to allow for easier coordination of the downstream instantaneous breakers.
And while there's the equipment short circuit current rating issue, there's also the personal safety issue: Instantaneous is usually a critical part of reducing incident energy if arc flash is a concern.
Thank you for your replies. I should clarify that this is the main breaker in a switchboard type assembly so since it is in the same physical enclosure with no real separation from the feeder breakers, it cannot be used to reduce the incident energy (arc flash) for the switchboard. This is based on the premise that an arcing fault on the bus or load side or a failure of a breaker would engulf the main breaker unless it is suitably separated from the rest of the enclosure.
My thoughts were that the breaker had been modified from its original design and is no longer of the configuration that was used for UL testing and approval. It is more like a molded case switch versus a breaker.
I know there are cases were a main breaker has no instantaneous function to allow for coordination with the feeder breakers. However that switchgear which that type of breaker is installed must be able to withstand a fault on the bus for a greater period of time. I believe 3 cycles and the rating should be listed.
Switchboards listed to UL 891 "generally" are not listed for use when protected by an upstream breaker without instantaneous protection. 891 equipment is 3 cycle rated and no instantaneous protection requires 30 cycle ratings, similar to 1558 SWGR.
I have encountered a 1200A MCCB in a facility with the instantaneous trip elements removed. The breaker is a Westinghouse NB style. My question: is this an NEC violation?
Was this a factory mo dr I fixation? Probably not as the trip unit would have to be removed and the factory sealed remove in order to access and defeat the instantaneous elements. Also, the MB breaker never had a short time delay. A model was available as a molded case switch with a dummy trip unit until the mid '80s or do the it was not allowed as the device could be destroyed should it's withstand be exceeded. As such high mag only trip units were required after that which included the modification suffix 'K". There is no option to remove the instantaneous trip.
But it is interesting the the OP omitted and part or style numbers to varify his assertions with. A simple call to Eaton with reference to those numbers requesting a description of the device would remove all of the intregue.
The MB breaker is a molded case breaker as opposed to an insulated case , power breaker, for air ciruiit breaker.
I am assuming that you made the call the Eaton directly for their description as I just don't have the time to do it. But, S/N 4997D20G02 appears to be just the frame only, NB31200F. If it has a non mag trip it would have a molded case switch label over the trip unit covering the holes tht the inst adjustments would have been.
Otherwise the trip would have a small window woth a number showing the trip rating and three red msg adustments unless it has a dummy trip unit which is requiretod latch a nonauto breakerand someone removed the molded case trip label exposing 3 empty round holes where the mag adjustments would have been.
