Min/Max rating on HVAC unit

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TOOL_5150

TOOL_5150

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I have an A/C unit that I will be working on soon, and it has a min rating of 30/30 HACR or fuse and a max rating of 40/40 HACR or fuse type. I have #10's running to the unit. Now, the question, Why do A/C's and the like have min and max ratings? Why not just one?

~Matt
 
It goes along with section 430.52, that is, states the minimum for start-up current to start the motor but yet allows for a current trip range that still offers branch-circuit short-circuit and ground-fault protection. Remember that motors have overload protection devices that sense overloads.
 
I have never seen a minimum and maximum rating for the OCPD. I would expect to see a minimum circuit ampacity rating and a maximum OCPD rating. You use the first to size the conductors and the second to size the OCPD.
 
I agree with Don. Take another look and see if it does not say Minimum Circuit Ampacity _______ and Maximum Fuse or HVAC Rated Breaker_______.
 
Might look like this one...31 minimum circuit ampacity and a 50 amp maximum fuse or circuit breaker

simmons_img3.gif
 
cowboyjwc said:
I've seen the min/max lables. In the case stated the electrician will usually just throw in a 35 amp fuse.
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Yep, thats what I always did. Now that I look into it though am I correct that, say if your min ampacity rating was 20 and your max fuse was 30 it means that it is legal to run the circuit in #12NM and put it on a 2P30, correct?
 
Mr.Sparkle said:
Yep, thats what I always did. Now that I look into it though am I correct that, say if your min ampacity rating was 20 and your max fuse was 30 it means that it is legal to run the circuit in #12NM and put it on a 2P30, correct?
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You could use #14 AWG and 30 amp fuse. In your example,


Here is another example.
AC & Refrigeration Equipement Nameplate Rating.jpg
 
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They have nameplates because they have already done the math. The Minimum is probably at 175% and the Max is 225%. That is where they get the Min and Max for the circuit breaker or fuse. The conductor minimum ampacity size is at 125% for the conductor/ampacity sizing.
 
Paul,
Have you actually seen a nameplate with a minimum and maximum OCPD shown? As I said before I have never seen that information on a nameplate. All of the ones that I have looked at have a minimum circuit ampacity and maximum OCPD.
 
sorry I forgot......look at 440.22 and 440.32 and you will see how they came up with the nameplate markings for the most part. Also those sections tell you how to size the OCPD and Conductors in the event no nameplate is available.
 
don_resqcapt19 said:
Paul,
Have you actually seen a nameplate with a minimum and maximum OCPD shown? As I said before I have never seen that information on a nameplate. All of the ones that I have looked at have a minimum circuit ampacity and maximum OCPD.
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No Don...I have not but felt it was important to show HOW they actually do it and so on. No you are correct however, I really only see Minimum Ampacity and Maximum OCPD....

but if the electrician had to do it in the field....and no nameplate they should know how to do it without a nameplate....agreed?
 
radiopet said:
...but if the electrician had to do it in the field....and no nameplate they should know how to do it without a nameplate....agreed?
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That would be a neat bar trick, or maybe it would win you that round in a game of Trivial Pursuit. Otherwise, equipment has the necessary information on it already.
 
mdshunk said:
That would be a neat bar trick, or maybe it would win you that round in a game of Trivial Pursuit. Otherwise, equipment has the necessary information on it already.
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sorry marc...I just happen to think electricians should know how to do it without the nameplate....not much of a bar trick really...now drink beer through your nose...now you have my attention.
 
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