ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
VDE 0100 to introduce AFCIs
by sparky. 01/20/18 05:09 PM
MRI LED lights dimmer control replacement - wow!
by Potseal. 01/19/18 08:52 PM
Video: Inventor of the GFCI self-testing shocks
by Bill Addiss. 01/17/18 11:11 PM
FPE in Germany
by HotLine1. 01/17/18 07:07 PM
Fujifilm Recalls Power Adapter Wall Plugs
by Admin. 01/16/18 07:04 PM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
0 registered members (), 3 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
1200 amp sevice conductor sizing #170419
11/02/07 05:38 PM
11/02/07 05:38 PM
T
trekkie76  Offline OP
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
I have a question about conductor sizing.
I have a 1200 amp main breaker on a 120/208Y service feeding a grocery store.
I came up with (4) 500 MCM per phase.
380A x4= 1520amps.
1520A x .80(T310.15(b)(2)(a)4-6 conductors in a raceway.=1216 A
1216A Round down to next standard= 1200A.

Have I gone astray somewhere? With all the lights, computers, etc. I would consider the neutral a current carrying conductor. I have seen other topics on here and none had mentioned the wire size I came up with.

As always thanks for the help gentlemen!
Gary

Work Gear for Electricians and the Trades
Re: 1200 amp sevice conductor sizing [Re: trekkie76] #170420
11/02/07 06:22 PM
11/02/07 06:22 PM
M
mahlere  Offline
Member
Joined: Nov 2005
Posts: 507
New Jersey
I would run 4 conduits, each containing 4 400MCM...A,B,C,N

For derating purposes, you use the 90deg column...so 400MCM is 380A x 4 = 1520A * 0.8 = 1216A

However, whether the Neutral is actually a CCC can be disputed. If not, then you can get away with 350MCM




Re: 1200 amp sevice conductor sizing [Re: mahlere] #170421
11/02/07 06:39 PM
11/02/07 06:39 PM
T
trekkie76  Offline OP
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
I thought you could only use the column that corresponded to the temperature rating or the terminations?

Re: 1200 amp sevice conductor sizing [Re: trekkie76] #170422
11/02/07 06:40 PM
11/02/07 06:40 PM
M
mahlere  Offline
Member
Joined: Nov 2005
Posts: 507
New Jersey
for sizing...for derating you can use the 90deg column..

Re: 1200 amp sevice conductor sizing [Re: mahlere] #170429
11/02/07 07:15 PM
11/02/07 07:15 PM
T
trekkie76  Offline OP
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
I dont understand what you mean. I thought you sized the conductor according to ampacity required, then adjusted the selected conductor according to ambient temp, # of conductors in conduit, etc. I am not trying to sound obtuse, but I guess I was tuaght differently.

Re: 1200 amp sevice conductor sizing [Re: trekkie76] #170430
11/02/07 07:22 PM
11/02/07 07:22 PM
M
mahlere  Offline
Member
Joined: Nov 2005
Posts: 507
New Jersey
Originally Posted by trekkie76
I dont understand what you mean. I thought you sized the conductor according to ampacity required, then adjusted the selected conductor according to ambient temp, # of conductors in conduit, etc. I am not trying to sound obtuse, but I guess I was tuaght differently.


nope...you size the conductors based on the terminal temp rating...but for derating purposes only, you can use the 90deg column. because you are worried about the insulation rating, not the connection rating.

without derating, 4-350's or 4-400's have enough ampacity in the the 75deg table to carry the load. but for derating only, you can use the 90deg table.

maybe someone else can explain it better.

Re: 1200 amp sevice conductor sizing [Re: mahlere] #170431
11/02/07 07:31 PM
11/02/07 07:31 PM
T
trekkie76  Offline OP
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
but wouldnt that result in a conductor sized below the ampacity of the 75 degree column?

Re: 1200 amp sevice conductor sizing [Re: trekkie76] #170432
11/02/07 07:32 PM
11/02/07 07:32 PM
T
trekkie76  Offline OP
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
i am going to look at this tommorrow morning and laugh im sure!

Re: 1200 amp sevice conductor sizing [Re: trekkie76] #170433
11/02/07 07:37 PM
11/02/07 07:37 PM
M
mahlere  Offline
Member
Joined: Nov 2005
Posts: 507
New Jersey
nope...not in this case...

I will say this though...find out if the inspector wants you to consider the neutral as a CCC...if not, no derating necessary...then you can run 350's...

Re: 1200 amp sevice conductor sizing [Re: mahlere] #170464
11/03/07 05:34 PM
11/03/07 05:34 PM
G
gibbonsseabee80  Offline
Member
Joined: Oct 2005
Posts: 40
Chesapeake, VA
I am thinking the same as Mahlere. I was taught you size your conductors to the terminal ratings of the equipment you are hooking up, which most of the time is the 75 deg C colum. You use that colum for your basic calculation for ampacity, then if you derate due to conduit fill or a change in ambient temperature..you look right to the 90deg colum. So rather than changing wire gauge you change insulation type by looking at the 90 deg colum only for conduit fill or ambient temp derating. This was explained to me in the Mike Holt exam book. Good luck, Brian


Brian Gibbons
Page 1 of 2 1 2

Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
The_Lightman
The_Lightman
Orlando, Fl, USA
Posts: 49
Joined: August 2001
Show All Member Profiles 
Top Posters(30 Days)
Admin 20
sparky 16
Potseal 15
Popular Topics(Views)
243,573 Are you busy
180,372 Re: Forum
170,846 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.020s Queries: 16 (0.003s) Memory: 1.0232 MB (Peak: 1.2026 MB) Zlib enabled. Server Time: 2018-01-21 06:51:24 UTC