UL891 vs UL1558 Gear
- Thread starter anbm
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- Wisconsin
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- PE (Retired) - Power Systems
This is like asking for information on the differences between a 4x4 and a full size pick-up. Just because there are differences, it does not mean one is necessarily better than the other, it all depends on your application.
Do you have a specific reason for asking?
Do you have a specific reason for asking?
Someone said if we used UL1558, it will helps to meet selective fully coordination as required by NEC article 700 on emergency distribution system, can't do this with UL891 gear because of CB characteristic. The cost difference between these two gear will be a significant number. The owner is looking for more specific reasons that can convince them to go with UL1558 gear construction.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
This is not absolutely not true. We regularly selectively coordinate, to 700 and 701, using UL891 gear and UL489 circuit breakers. Several manufacturers have tested combinations of breakers for selective coordination and publish them in tables similar to fuse ratio tables.
In your specific case the difference would be, that breakers in UL1558 gear are allowed to be provided without an instantaneous trip function.
Pay for the coordination study to be performed first, then buy your gear. A large component of coordination is the amount of available fault current
Wish this was always the case however in a design - bid - build envireoment it's tough to provide an accurate arc flash / coordination study until the equipment is purchased and the TCC and settings are known and the feeder lenghts are known, and in a design - bid - build design with competivie bids this can be tough. however as stated earlier the major difference besids price is size clearances, typically 1588 gear utilizes 1066 style breakers and is tested to handle fault currents for up to 30 cycles and allow you to disable the instantenous of the breaker allowing for instaneous to remain on on the secondary breakers allowing for better coordination, but resulting in higher arc-flash ratings (typically) unless something like an ARMS (arc reduction maintenances switch) is utilized when working on energized switchgear, where UL891 is only tested to withstand a 3cycle bracing, and the associated breakers also, but you have to be careful because in 891 gear you could still get breakers with electronic trip charasterstics and you have to be sure not to set the instantenous so high it pretty much disables it because it is dialed up higher than the availabel fault current then there might be a problem, (henc the corrdination study an important factor) and there are ways to coordinate breakers / breakers based on manufacturer tested data as others have indicated also be aware of x/r ratios as 489 breakers are testes at (i am trying to remeber from memory 4.9 where 1066 berakers are at 6.5) and if you are feeding a ATS directly this can come into play, one last item is space requirements typically 1588 switchgear will require front and rear access and is deeper than most switchboards and some switchboards can even be front access only, last but not least if you choose to go with a 1588 construction and 1066 style breakers be aware of "square rated breakers" newer breakers are built with plastic frames inleau of odler sytle iron frames (still avaliable) however the plastic frames will have a "slash" or "square rating" where the 30cycle withstand will be different with the instaneous turned on vs off on it might be a 100ka breaker but with the instaneous off may only be a 30ka breaker something else to keep in mind, all that being said I will get off my soapbox now.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
One way to get the higher AIC rating for power breakers is to have them begin to open faster so that an arc is created (adding impedance) prior to the fault reaching the full available value. I have performed several studies where the 65KAIC breakers opened too fast to coordinate, but their 50kAIC relatives were not a problem.
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