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

   
Topic Options
Rate This Topic
#11385 - 07/11/02 01:26 PM Sizing HVAC circuits.
master66 Offline
Member
Registered: 04/18/02
Posts: 260
Loc: Masontown, PA, USA
Other than calling the HVAC contractor for a cut sheet, is there a way to calculate breaker sizes and wire sizes for HVAC units such as roof top units?

Example: 20 ton RTU 480V 3 Phase
(Gas heat)

What should the breaker size be and what should the wire size be? Also, what will the running amps be? (I do realize that it may vary slightly from brand to brand.)
Top
Work Gear for Electricians and the Trades
#11386 - 07/11/02 04:40 PM Re: Sizing HVAC circuits.
George Corron Offline
Member
Registered: 05/16/01
Posts: 728
Loc: Lorton, Va USA
M-66,
Don't do it. There are a dozen calcs you can use, none of which will match the nameplate. The only time I'd feel comfortable with this is if their package stores, or something similar, and they use the same thing over and over.

OR.......you could run parallel 500s over to it......that oughta do it.

Now ya gotta decide to use fuses, or take a chance it'll accept an hacr breaker, ah go ahead and use fuses, their always accepted.
Top
#11387 - 07/11/02 07:03 PM Re: Sizing HVAC circuits.
master66 Offline
Member
Registered: 04/18/02
Posts: 260
Loc: Masontown, PA, USA
I know that this is going to sound wierd but, I don't like to see fuses on 3-Phase units for fear of "single-phasing"

As for the 500's, aluminum or copper?
Top

Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box

Recent Posts
Forum Styles
by sparkyinak
01/24/17 02:04 PM
License exam
by TRUE POWER
01/23/17 09:16 PM
Looking for older post
by sparkyinak
01/23/17 12:27 AM
Members: Non-Members: Did you know?
by Admin
01/22/17 02:34 PM
Safety at heights?
by HotLine1
01/21/17 08:51 PM

Who's Online
3 registered (Admin, sparkyinak, Ruben Rocha), 119 Guests and 16 Spiders online.
Key: Admin, Global Mod, Mod
New in the Gallery:
Desk-mounted "power-board"
Top Posters
gfretwell 9066
Trumpy 8560
pauluk 7693
HotLine1 6833
sparky 5545
Member Spotlight
Tom
Tom
Member Since: 01/01/01
Posts: 1069

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