ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Calling all Non-US members!! (Non-US only)
by HotLine1. 06/13/18 01:50 PM
GE Lighting Recalls LED Tube Lamps
by Admin. 06/12/18 09:32 PM
Ketra Recalls Recessed Downlights
by Admin. 06/12/18 09:17 PM
diazed fuses
by Texas_Ranger. 06/11/18 07:31 AM
soda can fuse from UK, facebook
by wa2ise. 06/06/18 11:02 PM
New in the Gallery:
Plug terminals
Housebilding DIY wiring
Who's Online Now
0 registered members (), 31 guests, and 7 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
A/C Feeder #94734
08/10/05 11:32 PM
08/10/05 11:32 PM
G
George Little  Offline OP
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
If I have 3 air conditioning condensers on a feeder and the info on the name plates say Minimum circuit 36a. - What minimum size feeder conductor should I install and how should it be fused?

Each condensing unit has 2 motors and a crankcase heater.


George Little
2017 / 2014 NEC & Related Books and Study Guides
Re: A/C Feeder #94735
08/11/05 12:00 AM
08/11/05 12:00 AM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,227
Estero,Fl,usa
Interesting question ... again. ;-)
Does voltage drop figure in here?
Are you going for the minimum that is legal (2 ga with 125 O/C) or what would give better reliability (1 ga and 150) both using 240.4(B).
I would want to use staggered timeouts on the compressor time delays so you wouldn't have 3 liquid slugged compressors in locked rotor at the same time on a power hit.


Greg Fretwell
Re: A/C Feeder #94736
08/11/05 08:53 AM
08/11/05 08:53 AM
G
George Little  Offline OP
Member
Joined: Jan 2004
Posts: 1,489
Michigan USA
Greg- I would say that #2 and 125a OC Minimum.

Some would say #1 and it probably would be a better design choice for the reasons you stated. Some inspectors maintain that you add an extra 25% of the largest motor. Some inspectors will take the largest motor of an individual A/C unit and add up all the other motors and come up with a smaller conductor yet.


George Little
Re: A/C Feeder #94737
08/11/05 12:07 PM
08/11/05 12:07 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,227
Estero,Fl,usa
I think we already covered that ground last time. Some might even argue that the 125% thing has been done 3 times in that engineered number on the HVAC label.
If the run is not excessive the #2 should be OK. The only caveat I would have is staggering the time out relays and that is really a design issue.


Greg Fretwell
Re: A/C Feeder #94738
08/11/05 07:38 PM
08/11/05 07:38 PM
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Every A/C I've seen also state, on the nameplate, "minimum circuit ampacity."

Since this is one of the "exceptions" to generalbranch circuit sizing rules, an example would be a specification of "25 amp" minimum ampacity being provided by #12 conductors.

Now, if you were to use a single feeder, and tap off it to all three condensers, I would forget the "minimum circuit ampacity" and size the feeder according to "full load amps" and motor feed rules.


Featured:

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

 

Member Spotlight
Tom
Tom
Shinnston, WV USA
Posts: 1,044
Joined: January 2001
Show All Member Profiles 
Top Posters(30 Days)
twh 5
Popular Topics(Views)
247,581 Are you busy
184,910 Re: Forum
174,136 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.016s Queries: 14 (0.004s) Memory: 0.9684 MB (Peak: 1.1060 MB) Zlib enabled. Server Time: 2018-06-19 04:30:36 UTC