ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
Where is Everyone?
by gfretwell - 04/09/21 01:08 AM
HI gang, long time since I was here...
by gfretwell - 04/09/21 01:02 AM
Lock-down Thread
by gfretwell - 04/06/21 09:30 PM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
0 registered members (), 3 guests, and 19 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Cable Tray Derateing Of Parallel 500 kcmil conduc #175951 03/15/08 07:31 PM
Joined: Mar 2003
Posts: 849
Y
Yoopersup Offline OP
Member
392.8 (d) conductors in cable tay Paralleled Shall be Grouped.
392.11 (B)(2) single conductors 1/0 to 500 kcmil grouped shall be derated at 65% per tables 310.17 -310.18 .
tray no cover free air copper 500 kcmil=(700amp at 90%c) (for derateing only)x 65% = 455 amps per group.

Unless installed with free air space per 392.11 (b)(4)then table 310.20 (500 kcmil=580amps at 90c )

Wanna check my work guys ???
YoopersUp




2017 / 2014 NEC & Related Books and Study Guides
Re: Cable Tray Derateing Of Parallel 500 kcmil conduc [Re: Yoopersup] #176283 03/28/08 10:04 AM
Joined: Mar 2003
Posts: 849
Y
Yoopersup Offline OP
Member
??????????
Nobody does this type of work???

Re: Cable Tray Derateing Of Parallel 500 kcmil conduc [Re: Yoopersup] #176285 03/28/08 01:25 PM
Joined: Mar 2005
Posts: 1,213
S
SteveFehr Offline
Member
Just use a bigger tray laugh Grouping doesn't mean they have to be bundled, you just need to run the whole group together in a single tray (or parallel trays are OK too, I believe). If you can leave a cable diameter between the 500kcmil cables, you don't need to derate at all. I've often seen them tie-wrap cables to the trays to maintain spacing. Looks cheap with all the tie-wraps (IMHO), but very clean, and is very effective at maintaining spacing.

I really don't see why NEC would specifically disapply 310.15(B)(2) though, it doesn't make sense, and 65% is a HARSH derating. Ask your AHJ, they may be lenient about minimum cable space to avoid derating- I know I sure am on cable spacing in venetilated trays.

Alas, I won't have to worry about this anymore- as of 2008, 708.10(C) specifically prohibits it for my sites, even when the EMI environment will allow open tray. All RMC from now on, I suppose. Maybe the occassionally SCH80 duct bank...

Last edited by SteveFehr; 03/28/08 01:35 PM.

Featured:

2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
JoeKP
JoeKP
Berkley, MA
Posts: 144
Joined: March 2008
Show All Member Profiles 
Top Posters(30 Days)
BigB 1
Popular Topics(Views)
277,512 Are you busy
211,221 Re: Forum
198,244 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3