Thread: a/c compressor max Amp rating

Hello, I have a question. If the lable plate on the ac compressor states max amp 30, is it acceptible to install a 40 amp breaker in the breaker panel? The builder says its okay to do so. Anyone have any thoughts on this. Thanks, BigCid

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Breakers trip at about a 30 percent draw over the rated breaker. If it is already 10 amp over some serious damage could come to the unit No it is not alright. They don't list max breakers just to have a number on there. It is to protect the unit and system. Tell the builder politely to get a clue and do what is right.

Originally Posted by Alan Miles

If the lable plate on the ac compressor states max amp 30,

Alan,

Ask the builder to explain to you what "maximum" means, as related to something they should understand.

Start with something simple like: What is the maximum amount of liquid you can put into a one gallon jug?

Then proceed to something more complicated, such as: What is the maximum you can build your building to if restricted to a 35 foot maximum height?

Then ask him to read the label and explain what it means when it says "max amp 30".

See if he gets it.

This is one of the most common electrical defects here in GA. New homes or existing. There was only one time I that I can recall that the breaker did not meet the minimum size requirement on the AC nameplate.

Originally Posted by Hank Spinnler

This is one of the most common electrical defects here in GA. New homes or existing. There was only one time I that I can recall that the breaker did not meet the minimum size requirement on the AC nameplate.

Typically, there is no "minimum size" for the breaker.

There is, however, a "minimum size" for the conductors.

Originally Posted by Jerry Peck

Typically, there is no "minimum size" for the breaker.

There is, however, a "minimum size" for the conductors.

With out thinking to hard I cannot remember the last time I did not see a minimum and maximum breaker listed on an AC unit. Evryone That I ever recall (maybe) have listed min and max. Min being the smallest rating to operate the unit

This is typically what I see.

John,

That's what I usually see too:

Minimum circuit ampacity

Maximum fuse or HACR breaker ampacity

I do recall, vaguely, having seen one or two which did state a minimum breaker size ... I think ... but cannot swear to it ...

Alan, your original question was a simple question. Now, we are discussing minimum ampacity rating vs. minmum circuit breaker rating on an AC unit. I looked back at photos of nameplates my most recent inspections and could not find any minimum circuit breaker rating listed, just minimum ampacity. I delved a little further onto a couple websites and found some interesting information to help in our understanding:

July-August 1999: Air Conditioning & Heat Pump Equipment

A/C Electrical [Archive] - DoItYourself.com Community Forums

The IAEI article as a .pdf for anyone who want a reference copy for thier PDA/Tablet/PC:

Hi Michael. I was not able to open it. There was an error on the pages. Can anyone else see it?

Originally Posted by Hank Spinnler

Hi Michael. I was not able to open it. There was an error on the pages. Can anyone else see it?

I had no problem downloading it with Firefox.

I would like to correct what Istated above. Most of the newer units I inspect have a max and min breaker listed. The older units have max breaker and min circuit amps.

Opens for me in the Foxit .pdf reader from within IE 8 Beta.

Here's an example from an inspection a few weeks ago that listed the Minimum Fuse or Circuit Breaker size in addition to the other information.

It acceptable by NEC IF. At the unit if there is a fusible disconnect in the rating range per the nameplate .If there is only a disconnect at the unit it a violation.

Richard, care to post references and explanation about what "it" is that you are talking about?

Richard,

I'm with Jim, I have no idea what you are saying is right, wrong, allowed or not allowed in your post.

The label Hank posted shows the following *requirements*:
- *MINIMUM* circuit ampacity is required to be at least 19 amps
- *MAXIMUM* overcurrent protection allowed is 30 amps
- *MINIMUM* overcurrent protection size is 35 amps

That label Hank posted also shows the following *allowances*:
- *ANY* circuit ampacity over 19 amps is allowed
- *ANY* overcurrent protection size between, and including, 25 amps to 30 amps is allowed

over current device is fuse or breaker or both.. so when I see both , and the lower rated breaker or fuse is the maximum allowed.. I accept that .the AC is protected..
It's easy to miss because some fused disconnects have fuses behind a plastic panel that is screwed shut. I have found out you can't just look at them and tell.

Originally Posted by Richard Pultar

It's easy to miss because some fused disconnects have fuses behind a plastic panel that is screwed shut. I have found out you can't just look at them and tell.

Hopefully we are all taking those plastic covers off to look inside.

Also, most of those have no fuses, they are simply "disconnects", *not* "fused disconnects".

Richard, I think I understand... maybe.
Are you cautioning to make sure there is both a disconnect AND an over current protection device as called for on the unit name plate, not just a disconnect switch?

To clarify my understanding of the code, there must be a disconnect switch at the unit but the properly sized over current device can be either at the unit as part of the required disconnect or in the main panel.

exactly

Originally Posted by Jim Luttrall

Richard, I think I understand... maybe.
Are you cautioning to make sure there is both a disconnect AND an over current protection device as called for on the unit name plate, not just a disconnect switch?

To clarify my understanding of the code, there must be a disconnect switch at the unit but the properly sized over current device can be either at the unit as part of the required disconnect or in the main panel.

Originally Posted by Richard Pultar

exactly

Richard,

"exactly" to which?

While both of Jim's statements are correct, the first statement is only correct as far as it goes, the latter statement is fully correct.