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