i. XXX was assumed to have a short circuit rating of XXkA. This is typical for a XXXXXX of this type. 4. Protective Devices a. XXXX BREAKER/FUSE which was found to be a XXXX BREAKER/FUSE was assumed as an XXXX BREAKER/FUSE. This was assumed because the actual BREAKER/FUSE was not available in the modeling software and the trip characteristics of the assumed BREAKER/FUSE closely match that of the one found on site. WHY WAS THE ASSUMPTION MADE? b. In instances of obsolete or unmarked molded case circuit breakers of 225A or less, breakers were estimated as closely as possible to the actual breaker type based on the manufacturer, frame size
and short circuit ratings as available in modeling software and data collected. c. XXX Feeder circuit breaker was assumed to have a TYPE setting at XXXX. 5. Cable Size
a. In the case of installations where equipment could not be opened either due to inaccessible or faulty defeat mechanisms and plant operation, cables were assumed to have been installed in a manner consistent with the rest of the site’s installation. Assumptions on the cable size were made according to the size of the breaker or equipment rating that the assumed cables feed based on standard practices. 6. Single-Phase Equipment a. Single-phase equipment is not accounted for in IEEE 1584-2018 as no conclusive research has been done to establish a consistent calculation method. Therefore, all single-phase equipment in this report has been run using the 3-phase calculation methodology. 7. Motor Groups a. For the motor loads, the motors of 50HP or less were grouped together and modeled as one group motor load in the model. The single motor group shown contains the number of motors in the equipment and with the HP taken as the average HP of the motors. In most cases grouped motors will not be included on TCCs for motor starting. This assumption has been made as motors of 50 HP or less are not commonly a problem for motor starting and grouping of motors in this way remains accurate for the calculations involving motor loading. 8. XFMR Impedances a. XFMR-XXX had an impedance estimated at XX%. WHY WAS THE ASSUMPTION MADE?
This information was necessary for creating a model of the electrical system but was not available or accessible at the time of the audit. These assumptions were made to model the system as accurately as possible while still providing the worst-case arc flash value for the equipment.
SITE NAME ARC FLASH STUDY
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INTERSTATES DATE
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