UL vs NEC

[Dale Hayes]

To establish UL component SCCR ratings, UL uses the chart examples listed on the Peak Let-thru values (Ipeak) charts ... whereas NEC uses the chart examples taken from the Available Fault Current Symmetrical (R.M.S.) chart values. Will someone please tell me why?

 

[jim dungar]

To establish UL component SCCR ratings, UL uses the chart examples listed on the Peak Let-thru values (Ipeak) charts ... whereas NEC uses the chart examples taken from the Available Fault Current Symmetrical (R.M.S.) chart values. Will someone please tell me why?

Two similar but not directly related methodologies.

UL 508A effectively says to use the published SCCR of each device. Based on the way UL tests a device's SCCR, they have developed a Peak Let-Thru chart that can be used when the published SCCR is not appropriate. This methodology relies heavily on UL's testing standards. For all intents these charts are for 'series rating'.