Just noticed there are changes, among many others, to the definition of arc flash boundary in the upcoming NFPA 70E Standard for Electrical Safety in the Workplace (see http://www.ecmag.com/section/safety/whats-new-whats-changed-2018-nfpa-70e-update for the comprehensive list of changes)...
You wouldn't expect someone staying and frying in front of the arc for 136 seconds waiting until the arc is cleared by a protection device, would you? It's usually assumed that the outer limit for the arcing time is no more than 2 seconds. Although this is not a hard and fast rule, it accounts...
If the ARCPRO assumption (the arcing current is equivalent to the bolted current) was right, than the arc voltage and impedance would be equal to zero and there would be no power released in the arc in the first place. Hence, it would be safe to assume there is is no hazard associated with the...
Regarding Stephen's comment that On medium voltage systems it is reasonable to assume that this is equivalent to the bolted current. What may seem reasonable to some is not necessarily seemingly reasonable to others. If the ARCPRO developer is so confident about the assumption, why does the...
Could you please quantify the difference? If difference was really small and negligible, why doesn't ARCPRO require bolted fault current on its input instead of arcing current?
I would have reservations against using ARCPRO for arc flash calculations. As an example, the program requires arcing current value on its input. You have to calculate the value somehow before running analysis or make up and justify the number. IEEE 1584 provides formulae for arcing current...
The modified NFPA 70E 2015 table method is not fit to be used in the first place. Why? The fault clearing time is required in order for the method to be used. The time cannot be determined unless the arcing fault current is known. Although the NFPA 70E incident method provides formula from the...
Have a look at arcadvisor.com for a variety of online resources, PC software and mobile apps for short circuit fault current, arc flash hazard analysis and labeling. All the programs and apps are available in free trial versions.
In my understanding, minimum available fault current is the amount of short circuit current coming from service entrance only while all the other sources and/or inductive loads are turned off. Alternatively, maximum available fault current assumes all motor loads and generators are running and...
1. I see no problems applying the formulae to 50Hz system. Please consider IEEE 1584 empirical model suitable for frequencies of 50 Hz and 60 Hz when in doubt. Note also that the IEEE 1584 fuse equations were developed based upon testing at 600V. I would not take liberty applying them at...
The infamous 1.2 cal/cm^2 threshold incident energy for a 2nd degree burn on bare skin cited in NFPA 70E and widely accepted in arc flash industry actually comes from misinterpretation of Alan Privettes' "Progress Report for ASTM Burn Study". As a matter of fact, Privettes' work is based upon...
The IEEE 1584 4.6 Step 5 reads "For fuses, the manufacturer's time-current curves may include both melting and clearing time. If so, use the clearing time. If they show only the average melt time, add to that time 15%, up to 0.03 seconds, and 10% above 0.03 seconds to determine total clearing...
According to IEEE 1584 and NFPA 70E line of reasoning, indeed there is no difference between the 1MVA 2 sec fault and the 20MVA fault lasting 0.1 sec only. The issue of using incident energy as a measure of arc flash danger without taking into consideration the rate the energy was delivered (aka...
