Machine Nameplate Data. NFPA79-E (16.4) 1

[Roboteck]

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

 

[davidbeach]

Continuous and fault currents.

 

[CJCPE]

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.

 

[waross]

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