ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

ECN Shout Chat
Top Posters(30 Days)
Admin 19
Recent Posts
Anyone hiring inspectors?
by HotLine1. 03/27/17 08:03 AM
Old decora style outlets
by Admin. 03/25/17 11:40 AM
ESA Arc flash course
by TheShockDoctors. 03/24/17 10:15 AM
fuse rejectors
by HotLine1. 03/24/17 07:53 AM
Another Forum Update
by Admin. 03/22/17 03:04 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
231,647 Are you busy
166,544 Re: Forum
160,728 Need opinion
Who's Online Now
0 registered members (), 68 guests, and 12 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#169961 - 10/21/07 09:03 PM Service Calculation  
Sparky_1  Offline
Member
Joined: Nov 2004
Posts: 14
Hello,

On a residential service calculation, can the main breaker be calculated at 100% or does it have to be 80%?, code ref. please.



2017 / 2014 NEC & Related Books and Study Guides

#169964 - 10/21/07 10:31 PM Re: Service Calculation [Re: Sparky_1]  
Sparky_1  Offline
Member
Joined: Nov 2004
Posts: 14

The reason I ask about the main, is because I'm installing a hot tub that has dual ratings, 30 amp and 50 amp circuit. The service size is 150 Amps, with a electric range, dryer and AC for major appliances. If I do a service calculation with the added hot tub load, I get 120 amps with the 30 amp hot tub load and 132 amp with the 50 amp hot tub load, so by using the service calculations, can I put the hot tub on the 50 amp circuit or does it have to go on the 30 amp circuit?

My inspector is telling me that the calculated load can't be more than 80 % of the main breaker, 120 Amps.

I see in the code book, on page 718 example D2c that the calculated load is 144.96 with a service
size of 150 amp.

I believe that I can add to this service as long as my service calculation are 150 amp or less.


Thanks George


Last edited by Sparky_1; 10/21/07 10:42 PM.

#169965 - 10/21/07 10:31 PM Re: Service Calculation [Re: Sparky_1]  
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
And the answer is 100% The code references are: 230.42, 215.2, 210.19
The issue is "continuous load". Since residential loads are not considered to be continuous you can load a branch circit, feeder or Service to it's actual rating which is 100%. I don't think it's a good idea but the code allows it. Most inspectors would recommend a little head room and most contractors agree and provide this head room.


George Little

#169966 - 10/22/07 12:44 AM Re: Service Calculation [Re: George Little]  
gfretwell  Online Content


Member
Joined: Jul 2004
Posts: 9,059
Estero,Fl,usa
Dwelling loads better be "diverse" or we will have to repeal 310.15(B)(6) wink


Greg Fretwell


Member Spotlight
Niko
Niko
Campbell, CA
Posts: 356
Joined: August 2006
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.016s Queries: 15 (0.004s) Memory: 0.7583 MB (Peak: 0.8899 MB) Zlib enabled. Server Time: 2017-03-28 17:45:45 UTC