3 Phase Air Conditioner Schematic

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frizbeedog

frizbeedog

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Oregon
I brought home the diagrams from the one of the units I connected today, just to study.

240V 3 phase air conditioner.

Here is a note I found on the drawing:

Note:

Three phase motor factory supplied in this equipment protected under primary single-phase conditions.
Click to expand...

I think I know what this means but enlighten me please. Codes references and other applications of this method would be appreciated.


....and everyone have a good weekend. You deserve it. :smile:
 
Not really a code issue. It basically means if the poco has a problem and looses a phase the comp. should shut down and not try to restart until is has all three phases back. At least that is what I understand it to be as I deal with pump motors that have this protection built in.
 
480sparky said:
Looks to me like it has single-phasing (or phase loss) protection.
Click to expand...

OK. I thought I knew what it meant.

Only two legs (if I am permitted to use the term legs :wink: ) go through the relay contacts. The third goes directly to the compressor, no taps from that to anything else.

If I can find the schematic online, I'll try to post it.
 
frizbeedog said:
Only two legs (if I am permitted to use the term legs :wink: ) go through the relay contacts. The third goes directly to the compressor, no taps from that to anything else.
Click to expand...
That is very common with equipment. There is no reason to open and close all 3 "legs" to control the compressor.
 
A phase loss relay is becoming more and more standard on RTU's and AHU's. It's wired in the control circuit, and is another one of the ba-jillion things that can now keep an RTU from running. If you ever puzzle on all the safeties and interlocks that the control circuit runs through before it gets to the compressor contactor coil, you'll be amazed. It can make these things a special treat to work on. There used to be a time when phase loss/phase reversal relays were only used on things where life was at stake, like elevators. The last 15 years or so, they're becoming more standard just for simple equipment protection. Makes sense, since the typical SSAC type phase loss relay is only around 100 bucks. Once upon a time, when phase loss/phase reversal relays were big mercury tilt switches, they could be near 1000 bucks.
 
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