500 kcm

[mcelweec@gmail.com]

Nearly every drawing i've been getting showing multiple sets of 500's,has been counting 500's as 400a e.g. 1200a = 3 sets of 500kcm.I know up to 800a provided load calcs workout you may fuse 2 sets at 800a.I have been getting these drawings from different engineering companies which makes me wonder ,were 500's ever counted as 400a?

 

[Dennis Alwon]

Nearly every drawing i've been getting showing multiple sets of 500's,has been counting 500's as 400a e.g. 1200a = 3 sets of 500kcm.I know up to 800a provided load calcs workout you may fuse 2 sets at 800a.I have been getting these drawings from different engineering companies which makes me wonder ,were 500's ever counted as 400a?

I believe they may be using 240.4(B) but that is incorrect since the multiple sets would make it larger than 800 amps.

 

[480sparky]

.......,were 500's ever counted as 400a?

From 1965, 500 in the 85-90?C column is listed as 405 amps. In 1985, 85? and 90? were in seperate columns, with both being 405.

In 1981, they went to 415 and 430 amps, respectively. The 85? colum was dropped in 1993, and 500 was in the 90? column as 430amps as it is today.

 

[bob]

Nearly every drawing i've been getting showing multiple sets of 500's,has been counting 500's as 400a e.g. 1200a = 3 sets of 500kcm.I know up to 800a provided load calcs workout you may fuse 2 sets at 800a.I have been getting these drawings from different engineering companies which makes me wonder ,were 500's ever counted as 400a?

You are allowed to go to the next size fuse, 800 amps, if the calculated load is not greater that 760 amps(2 x 380). Since the 1200 amps exceeds the 800 amp rule, you would need 3 600 kcm(3 x 420) to match the 1200 amp main.

 

[augie47]

If they happen to be terminating in a MLO panel using the 6 disconnect rule then as long as the calculated load is less than 1140 they are fine.
That's pretty common here.

 

[jim dungar]

I have been getting these drawings from different engineering companies which makes me wonder ,were 500's ever counted as 400a?

Up to the mid 80's it was common, in industrial facilities, to see 500MCM considered as 400A conductor, especially up to 1200A.