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#134636 - 11/23/02 08:11 PM Air Con/HVAC systems
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: 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?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#134637 - 11/24/02 04:59 AM Re: Air Con/HVAC systems
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
I am often confused about proper OCPD sizing

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#134638 - 11/24/02 08:44 AM Re: Air Con/HVAC systems
golf junkie Offline
Member

Registered: 04/22/01
Posts: 511
Loc: 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

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#134639 - 11/24/02 07:13 PM Re: Air Con/HVAC systems
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: 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.

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#134640 - 11/25/02 10:53 PM Re: Air Con/HVAC systems
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
BJ, what do these Dots, indicate?.
Only after I find out this, can I give you a
real sort of answer?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#134641 - 11/26/02 07:54 AM Re: Air Con/HVAC systems
CTwireman Offline
Member

Registered: 02/07/02
Posts: 839
Loc: 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."
_________________________
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#134642 - 11/26/02 11:24 AM Re: Air Con/HVAC systems
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: 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."

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#134643 - 11/26/02 10:03 PM Re: Air Con/HVAC systems
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Sorry about the confusion, guys!, should have known that one, at the very least!
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.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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