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Machine Nameplate Data. NFPA79-E (16.4)

Machine Nameplate Data. NFPA79-E (16.4)

Machine Nameplate Data. NFPA79-E (16.4)

(OP)
The NFPA79-E chapter 16.4.1
lists the 7 items to be included in the "Machine Nameplate Data".
What is the difference between:
item #5 ("Maximum ampere rating of the short circuit and ground-fault protective device, where provided")
and item #6 ("short-circuit current rating of the control panel")

Thanks

RE: Machine Nameplate Data. NFPA79-E (16.4)

Continuous and fault currents.

RE: Machine Nameplate Data. NFPA79-E (16.4)

Item #5 is the actual current that the fuse, circuit breaker or whatever is rated to carry without tripping.

Item #6 is the short circuit current that the panel and the components in it can withstand without damage or with damage not exceeding certain limits or not extending outside of the enclosure.

RE: Machine Nameplate Data. NFPA79-E (16.4)

For example a 15 amp circuit breaker may have a 10,000 amp short circuit rating. It will trip at 15 amps and will safely interupt a current of 10,000 amps. If a breaker rated for 10,000 amps is used on a system cappable of supplying 25,000 amps, it may explode when it tries to interupt a fault current.
Some other factors that are encountered when considering short circuit ratings are symetrical and asymetrical currents, feeder impedance, KVA, percent impedance voltage, and the X/R ratio of the supply transformer.
Fault currents may be asymetrical. Short circuit ratings are based on symetrical current ratings with a safety factor.
A relay engineer working on utility protection must use asymetrical currents.
A design engineer selecting switchgear for a building may use the easier symetrical calculations, but he will check the X/R ratio on larger transformers. If the X/R ratio on a large transformer is too high, he may not use the simple calculations. This is probably more than you wanted to know.
respectfully

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