ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Prototype production service needed
by carmend12345. 09/24/18 04:40 AM
220/230/240V 60Hz Systems
by gfretwell. 09/23/18 02:50 PM
Inspection camera help
by petey_c. 09/22/18 07:52 AM
Motion detectors and dimmers
by gfretwell. 09/20/18 04:02 PM
Extension cords
by annemarie1. 09/20/18 08:54 AM
New in the Gallery:
Plug terminals
Housebilding DIY wiring
Who's Online Now
0 registered members (), 39 guests, and 23 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Derating and adjustment factors #77308
05/20/01 12:24 AM
05/20/01 12:24 AM
D
doc  Offline OP
Member
Joined: Nov 2000
Posts: 123
Texas
lets say u are running 440 volt 3 phase equipment.now inside conduit u run 21 wires all thhn #12 stranded these wires are going to 440 volt 3 phase motors do they get derated just like any other wire and if you get to a j-box and cut them into u now have 42 wires in that box would u then use a different derating # or would u still stay with 21 article 310-8{a} hope this makes since to u guys


MAY THE SUN SHINE ON YOUR FACE IN THE MORNING AND YOU AWAKE WITH A SMILE
2017 / 2014 NEC & Related Books and Study Guides
Re: Derating and adjustment factors #77309
05/20/01 05:14 PM
05/20/01 05:14 PM
S
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,360
doc,
is there a NEC reason to not derate? and why 310-8(a) , i'm a little slow, sorry..... [Linked Image]

Re: Derating and adjustment factors #77310
05/20/01 09:16 PM
05/20/01 09:16 PM
D
doc  Offline OP
Member
Joined: Nov 2000
Posts: 123
Texas
SORRY FOR THE MIX UP I am looking in article 310 and in the 96 code book on page 196 u have 8 Adjustment factors then u have {a} at that point it shows 21-30 wires if I have 21 then I would derate them to 45 percent.Now i go to a junction box i cut them into at that point I now hve 42 wires in the j-box would I derate those wires using 41 or more which would be 35 percent or even though I did cut them in the j-box it would still be 21 wires hope this helps


MAY THE SUN SHINE ON YOUR FACE IN THE MORNING AND YOU AWAKE WITH A SMILE
Re: Derating and adjustment factors #77311
05/20/01 09:42 PM
05/20/01 09:42 PM
S
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,360
oh, ok,,,
the 'pipe fill' bears derating,
30A(T310-16) x 45%(T310-15(b)(2))= 13.5A,
so next 240-6 would be 15A

the 'jb' needs only to meet fill requirements. As the wires have been cut, instead of passing thru, i beleive your fill requirements are doubled.
21 x 2.25= 47+ cubes
42 x 2.25= 94.5 cubes

ok doc?
[Linked Image]

Re: Derating and adjustment factors #77312
05/21/01 01:15 AM
05/21/01 01:15 AM
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
doc,
Derate like this:

Table 310-16: #12 THHN cu @ 90 degrees = 30 amps.
Table 310-15(b)(2)(a): Number of current carrying conductors: 21-30 = 45%
Multiply 30 amps x .45 = 13.5 Amps

This is for 30 degrees C Ambient Temperature. If higher than 30 C, adjust maximum amperage of 310-16 [30 amps for #12 THHN cu] by the corection factor, then derate for 21-30 conductors.
If the loads are LCL, then derate the maximum amperage [30 amps for #12 THHN cu] by 80%, making it 24 amps - then apply temperature corrections [if any], then finally derate for 21-30 current carrying conductors.

The conductors in the raceway [conduit] are the ones being derated. Box fill is another area.

Steve had already pointed out the corrected value of 13.5 amps - using 15 amp OCPD, so this message is just to explain how he came up with that figure.

Scott SET


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Re: Derating and adjustment factors #77313
05/21/01 06:52 AM
05/21/01 06:52 AM
S
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,360
ok guys...
that's the normal routine.
doc's got motor circuits here, so let's apply 430, part D if branch circuits, part F if control circuits [Linked Image]

which have you doc?

Re: Derating and adjustment factors #77314
05/21/01 08:49 AM
05/21/01 08:49 AM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
Guys,
Remember that with motor circuits the dreated ampacity of the conductors only has to equal 125% of the motor current as shown in Tables 430-147 through 430-150. It does not have to equal the rating of the branch circuit short-circuit and ground fault protection device.
Don(resqcapt19)


Don(resqcapt19)
Re: Derating and adjustment factors #77315
05/21/01 05:18 PM
05/21/01 05:18 PM
Tom  Offline
Member
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA
Another reminder that doesn't apply to this post, but seems to be a common oversight, you cannot round up to 15 amps if the conductors are part of a multi-outlet branch circuit that supplies receptacles for cord and plug connected portable loads.

Tom


Few things are harder to put up with than the annoyance of a good example.

Featured:

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

 

Member Spotlight
dougwells
dougwells
kamloops BC Canada
Posts: 1,149
Joined: May 2003
Show All Member Profiles 
Top Posters(30 Days)
Admin 13
Trumpy 9
Popular Topics(Views)
249,438 Are you busy
187,353 Re: Forum
176,695 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.020s Queries: 15 (0.004s) Memory: 0.9942 MB (Peak: 1.1540 MB) Zlib enabled. Server Time: 2018-09-24 19:22:46 UTC