Originally Posted By: rsmith5
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[ Image: http://www.nachi.org/bbsystem/usrimages/1/100_03041.JPG ]Originally Posted By: jlybolt
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What does the identification plate on the condensing unit call out for max. /min. breaker size?
Originally Posted By: rsmith5
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20amp
Originally Posted By: lkage
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| rsmith5 wrote: |
| Hi Folks,
I have a couple questions about these service panel pics. The top 240/20 amp breaker is feeding the AC disconnect with 12 gauge wire... Is this right? any help would be appreciated. |
What is the minimum circuit ampacity from the label?
If it is 20 amps or less 12 guage solid copper wire would be the minimum size wire required.
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"I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei
Originally Posted By: jmurphy1
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I’m certainly no expert but I thought 10 gauge wire and a 30 amp breaker was used with both a dryer and an a/c.
Originally Posted By: jlybolt
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I dont have great eye site, but it seams there are some hot spots on the wiring. Rust within the box usually means moisture is getting in it and if continues should be investigated. Just on this, I believe I would recommend a professional licensed electrician further evaluate the system.
Originally Posted By: lkage
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| jmurphy1 wrote: |
| I'm certainly no expert but I thought 10 gauge wire and a 30 amp breaker was used with both a dryer and an a/c. |
This was explained on this board at least once before and I pulled this explanation for future reference:
| Quote: |
| A/C condensers contain a hermetically sealed compressor motor as well as a fan to circulate air across the coils. The rules for protection to motor circuits are different than for circuits with simple resistive loads. When a motor first starts , it draws a much higher amount of current than it does after it is running. The high "inrush" current can exceed the rating of a breaker or fuse sized to protect the wire. The inrush current lasts typically only about 6 electrical cycles, or 1/10th of a second - less time than it would take to damage the wire or its insulation. However, if the overcurrent device is sized to protect the wire against overloads, the device might trip, and the machine would not be able to start.
Motor circuits get around this problem by dividing the two separate functions of an overcurrent protection device. "Overloads" are currents that can damage a circuit if allowed to continue for a sufficient time, whereas "short circuits" and "ground faults" are high currents that can cause immediate damage. Large motors and air conditioners separate these overcurrent functions. The breaker or fuse ahead of the air conditioner only protects against short circuits and ground faults. Overload protection is built into the compressor itself. The wire to a condensing unit must be large enough to allow the equipment to start. The device is therefore NOT sized to protect the wire against overloads. It is not uncommon to see a 50 Amp breaker on a #10 wire. The wire is protected against overloading by a separate thermal protection inside the compressor. How do we know what the motor requires for wire size and proper fuse/breaker protection? It's all on the mfg. label attached to the appliance. If the label calls for fuses, there MUST be a fuse in the disconnecting means, not a circuit breaker. If the label calls for a "HACR" type breaker (Heating, Air Conditioning and Refrigeration), then that is the type of breaker that must be used. If the label simply states "maximum sized over current protection" then any form of overcurrent protection may be used. The HACR designation is not always visible on a circuit breaker once it is installed inside a panel or disconnect. Note in the image taken from a Lennox A/C data plate: MIN. CKT. AMPACITY - 17.7. MAX. FUSE - 25 UL (CSA is a Canadian standard. We use UL in the U. S.) MAX. HACR TYPE CKT. BKR. - 25 UL MAX. CKT BKR. UL - Not allowed in U. S. All this means is the MINIMUM wire size required is #12 (solid copper); the MAXIMUM rating of a fuse (if a fuse is used) must be 25 amps and the MAXIMUM rating of a circuit breaker (if used) must be 25 amps AND the breaker must be a HACR type. I have seen many times where the electrician installs a 30 amp fuse or breaker instead of a 25 but the data plate clearly states MAX. 25, and 25?s ARE available. 30 amps would be truly over fusing in this case. |
I hope this helps.
--
"I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei
Originally Posted By: jmurphy1
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Interesting. I had central a/c installed in a house last summer. The home had never had central a/c.
I wish I had had this info a year ago. Thanks! 
Originally Posted By: lkage
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Glad I could help.
–
“I have never met a man so ignorant that I couldn’t learn something from him.”
Galileo Galilei
Originally Posted By: rsmith5
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Once again this membership proves to be worth every penny and a dime more! I will be revisiting this AC unit to get the full information again.Thank you lkage!
Ralph
Originally Posted By: lkage
This post was automatically imported from our archived forum.
| rsmith5 wrote: |
|  Once again this membership proves to be worth every penny and a dime more! Ralph |
For me, it has worked both ways and that's what it's all about...help and get help.
BTW, Ralph, you need a "dot" after the 3 w's of your homepage on your profile page.
--
"I have never met a man so ignorant that I couldn't learn something from him."
Galileo Galilei
Originally Posted By: jpope
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| rsmith5 wrote: |
| The junction of the 12 gauge to the 14 gauge. . . |
Are you referring to a splice? Splices within the panel are allowed. 12 to 14 or 14 to 12 is okay so long as you maintain the minimums required for the ampacity of the circuit (as was explained, A/C condensers allow a mismatched conductor/breaker size).
| rsmith5 wrote: |
| [also this wire is piggy backed on a 20amp breaker] |
Lost me there. What do you mean by "piggy backed?"
| rsmith5 wrote: |
| a 240/30amp breaker is feeding the kitchen stove. |
The 240v 30a breaker should be wired with 10 gauge. Electric ranges don't typically have their own OCPD's.
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Jeff Pope
JPI Home Inspection Service
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