Cable Derating

Status
Not open for further replies.
H

harritr1

Member
Location
Houston, TX
I am working with a manufacturing site trying to replace some 480V cable, we are planning on putting in 5 new 3/C 350kcmil cable (about 2 inch outer diameter each) but the site is pushing back on installing new cable tray. Right now they have 12in ladder type cable tray out there and I am trying to find in the code where it can guide me into proving to them that there isn't enough space in the tray and to show them how much ampacity the cable will lose. Can someone maybe point me towards an article or section? I have already looked at 392.80, 392.22 and 310.15 of NFPA 70 2017.

Thanks
 
You looked correct. 322(A)(1)(a) says single layer in tray. Then 392.80(A)(1) says as long as you aren’t covered you get same as in conduit, if you maintain (1) cable diameter you can have free air ampacity, and if more than (3) CCC apply derate.

So your (5) 2” diameter is less than 12” tray. Single layer and same ampacity as in conduit. Were they getting more ampacity in the previous configuration?
 
publicgood said:
You looked correct. 322(A)(1)(a) says single layer in tray. Then 392.80(A)(1) says as long as you aren’t covered you get same as in conduit, if you maintain (1) cable diameter you can have free air ampacity, and if more than (3) CCC apply derate.

So your (5) 2” diameter is less than 12” tray. Single layer and same ampacity as in conduit. Were they getting more ampacity in the previous configuration?
Click to expand...

Right now they are trying to say that these 5 350kcmil cables currently in the 12" tray are rated to cover 1600A....
 
harritr1 said:
Right now they are trying to say that these 5 350kcmil cables currently in the 12" tray are rated to cover 1600A....
Click to expand...
They are probably basing their statement on 240.91(B)

Roger
 
Status
Not open for further replies.
Top