The Electrical Contractor Network

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

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Industrail Control Panel bonding per 409.108
by sparkyinak
Yesterday at 06:29 PM
Calling all Non-US members!! (Non-US only)
by aussie240
12/07/16 02:39 AM
Photo Upload Tutorial
by DanK
12/06/16 11:35 PM
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 13
HotLine1 10
sparkyinak 9
Texas_Ranger 8
Potseal 6
Who's Online
1 registered (Tjia1981), 219 Guests and 5 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#94734 - 08/10/05 08:32 PM A/C Feeder
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: 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

Top
2014 / 2011 NEC & Related Books and Study Guides
#94735 - 08/10/05 09:00 PM Re: A/C Feeder
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: 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

Top
#94736 - 08/11/05 05:53 AM Re: A/C Feeder
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: 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

Top
#94737 - 08/11/05 09:07 AM Re: A/C Feeder
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: 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

Top
#94738 - 08/11/05 04:38 PM Re: A/C Feeder
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: 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.

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals