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Slide 1
https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/training-presentations/bus-ele-tr-component-protection.pptx
The top design meets 110.10 of the NEC because a 65kA fault would be cleared in ½ cycle or less and the MCC is rated for 3 cycles. The bottom design violates 110.10 because a 65kA fault could continue for 6 cycles, but the MCC is only rated for 3 cycles. 800A Power CB w/STD = 6 cycles 65,000A RMS Sym. Available 800A MCC with 3 cycle 65kA Bracing
Simplified Guide To Understanding Short-Circuit Current Rating
http://www.aic-controls.com/fullpanel/uploads/files/guide-to-understanding-sccr-v2-00002.pdf
higher ratings— A 65kA circuit breaker will more than double your cost compared to a 14kA circuit breaker. The fusible solution provides an interrupting rating as high as 200kA, at a comparable cost to your existing design, making it the most economical solution. …
Bracing of Conductors in Switchboards
https://www.dli.mn.gov/sites/default/files/pdf/eli_bulletin_bracing.pdf
The purpose of bracing is to restrain the conductors from violent movement during fault conditions. Conductors ... For conductor lashing instructions on switchboards marked 65kA, 100kA or 200kA short circuit current ratings, refer to the following instructions: 4.15.1. Switchboards with a single fusible main switch rated 4000A or less do not ...
65kA at 240V AC Circuit Breakers - Grainger Industrial …
https://www.grainger.com/category/electrical/fuses-circuit-breakers-safety-switches/circuit-breakers-panelboards-load-centers/circuit-breakers-accessories?attrs=Max.+AIR+Rating%7C65kA+at+240V+AC&filters=attrs
Hazardous location enclosed circuit breakers are used where hazardous materials are handled or stored and are fully enclosed to prevent sparking or water damage. Circuit breaker accessories are used to mount, protect, or enhance the functionality of circuit breakers. Max. AIR Rating 65kA at 240V AC Hazardous Location Enclosed Circuit Breakers
MCC Bus Bar Bracing - Electric power & transmission
https://www.eng-tips.com/viewthread.cfm?qid=339789
The reason is that the 65kA fault rating is achieved by taking the incoming test cables and shorting them then adjusting the power source until 65kA flows. Then, the cables are connected to the MCCB and the MCC is tested with a short. Well, 65kA won't flow any longer since the impedance of the MCC components will lower the fault current.
SCCR for existing installation - Mike Holt's Forum
https://forums.mikeholt.com/threads/sccr-for-existing-installation.2557493/
We had an interesting situation where we had a number of MCCs that were rated 42kA (due to bus bracing), while all of the buckets had a 65kA rating (the MCC as a whole is a UL 508 assembly). SCCA at the MCC was ~55kA.
SCCR for existing installation | Page 2 | Mike Holt's Forum
https://forums.mikeholt.com/threads/sccr-for-existing-installation.2557493/page-2
Word to the wise on MCC bus bracing: I made that same mistake once, it was a PITA to fix. The difference between 42kA and 65kA bracing on most brands of MCCs is very very little, in one case I know of, it is one extra sheet metal screw per section, but it cannot be changed in the field, the UL label on the MCC states the bracing and that is that.
Pow-R-Line switchboard catalog - Eaton
https://www.eaton.com/content/dam/eaton/products/low-voltage-power-distribution-controls-systems/switchboards/pow-r-line-distribution-switchboards-vol02.pdf
65 kAIC bus bracing standard; optional 100 or 200 kAIC Standard tin-plated aluminum bus; optional copper- or silver-plated copper bus Standard bus ampacities based on UL® heat test ratings. Optional density rated bus systems are also available Main and Individually Mounted Devices Magnum® SB insulated case circuit breakers, 800–
Who Cares? - EC&M
https://www.ecmweb.com/content/article/20893216/who-cares
Bus bracing on 480V MCCs, as an example, comes in standard large increments of 42kA, 65kA, and 100kA. With a 2500kVA transformer and a typical 6% impedance, your plant s.c. value (using infinite bus near the transformer) will be about 50kA. Purchase MCCs with 65kA bracing. If you want to reduce these values so you can buy the 42kA MCCs, use fused
What Is Short Circuit Current Rating? - Control Concepts, Inc.
https://ccipower.com/content/what-short-circuit-current-rating
Typically, this is 65kA or greater. The intent of this is for personnel protection, lowering insurance rates, and meeting specific codes such as NFPA 70E and UL 508A Supplement SB. This is becoming more and more common, and unfortunately all too often, people are finding out about it at time of installation.
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