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Air Con/HVAC systems #134636
11/23/02 11:11 PM
11/23/02 11:11 PM
Trumpy  Offline
OP
Member
Joined: Jul 2002
Posts: 8,231
SI,New Zealand
Anyone need any advice about air-conditioning systems and general HVAC systems?.
My company installs these systems all the time and I normally end up wiring them,
any questions on how these systems actually work?. [Linked Image]

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Re: Air Con/HVAC systems #134637
11/24/02 07:59 AM
11/24/02 07:59 AM
S
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,342
I am often confused about proper OCPD sizing

Re: Air Con/HVAC systems #134638
11/24/02 11:44 AM
11/24/02 11:44 AM
G
golf junkie  Offline
Member
Joined: Apr 2001
Posts: 507
York, NE
Sparky,
We always size the feeder and OCPD by the max. fuse/breaker rating on the nameplate. That insures plenty of ampacity for startup.

Where it gets more difficult is on remodels where older HVAC units without the nameplate info are being reused. Then it often becomes a guessing game.

GJ

Re: Air Con/HVAC systems #134639
11/24/02 10:13 PM
11/24/02 10:13 PM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Trumpy — In your region, what is the unusual breakpoint in rating for 1ø versus 3ø hermetic compressors in residential and light commercial facilities? 1ø is typical for up to 5 tons [60,000 Btuh] in the western US, although 3ø hermetic compressors are readily available in 2-or-3-ton up.

Re: Air Con/HVAC systems #134640
11/26/02 01:53 AM
11/26/02 01:53 AM
Trumpy  Offline
OP
Member
Joined: Jul 2002
Posts: 8,231
SI,New Zealand
BJ, what do these Dots, indicate?.
Only after I find out this, can I give you a
real sort of answer?. [Linked Image]

Re: Air Con/HVAC systems #134641
11/26/02 10:54 AM
11/26/02 10:54 AM
C
CTwireman  Offline
Member
Joined: Feb 2002
Posts: 840
Connecticut, USA
Trumpy,

I'm guessing you mean the circles with the lines through them. That's a symbol we use for convenience to say "phase."

So, it means "single phase" or "three phase."


Peter
Re: Air Con/HVAC systems #134642
11/26/02 02:24 PM
11/26/02 02:24 PM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Sorry Trumpy. Apparently something didn't translate correctly. {Used Alt-0248 for a lower-case phi from Windows 2000 "Character Map."}

"Trumpy — In your region, what is the unusual breakpoint in rating for 1-phase versus 3-phase hermetic compressors in residential and light commercial facilities? Single-phase is typical for up to 5 tons [60,000 Btuh] in the western US, although 3-phase hermetic compressors are readily available in 2-or-3-ton and up."

Re: Air Con/HVAC systems #134643
11/27/02 01:03 AM
11/27/02 01:03 AM
Trumpy  Offline
OP
Member
Joined: Jul 2002
Posts: 8,231
SI,New Zealand
Sorry about the confusion, guys!, should have known that one, at the very least! [Linked Image]
It really depends upon the load current of the unit to be installed and of course, the
type of supply available, as a few light commercial installations over here, only have a 100A single phase supply.
Given the choice, 3 Phase wins hands down, because of smaller cable sizes and the compressors run a lot quieter.
With regard to sizing the Circuit Breaker,
you must take into account, the Start-Up current, which can be anywhere from 7-10times FLA.
But new technology over here, means that, Soft-starter units are normally fitted to Air con units, to prevent the A/C, effecting things like computers, upon start-up.


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